Cognition 110 (2009) 412–431
Contents lists available at ScienceDirect
Cognition
journal homepage: www.elsevier.com/locate/COGNIT
Beyond perceptual symbols: A call for representational pluralism
Guy Dove *
Department of Philosophy and Department of Psychological and Brain Sciences, 313B Humanities Building,
University of Louisville, College of Arts and Sciences, Louisville, KY 40292, United States
a r t i c l e
i n f o
Article history:
Received 14 August 2007
Revised 12 November 2008
Accepted 17 November 2008
Keywords:
Concepts
Representation
Perceptual symbol systems
Imagery
Empiricism
a b s t r a c t
Recent evidence from cognitive neuroscience suggests that certain cognitive processes
employ perceptual representations. Inspired by this evidence, a few researchers have proposed that cognition is inherently perceptual. They have developed an innovative theoretical approach that rests on the notion of perceptual simulation and marshaled several
general arguments supporting the centrality of perceptual representations to concepts.
In this article, I identify a number of weaknesses in these arguments and defend a multiple
semantic code approach that posits both perceptual and non-perceptual representations.
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
Cognitive scientists have traditionally assumed that our
concepts are couched in amodal (i.e. non-perceptual) representations. On the standard view, perception and cognition are distinct mental activities that are served by
different representational systems. This orthodoxy has
been challenged by an ever increasing body of research
that implicates the use of perceptual representations in
cognitive tasks (Barsalou, 1999; Kosslyn, 1994). There have
been three major types of response to this evidence: one
that generalizes from this evidence and proposes that concepts are generally couched in perceptual or motor representations (Barsalou, 1999; Damasio, 1989; Glenberg,
* Tel.: +1 502 852 1450.
E-mail address: [email protected]
0010-0277/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.cognition.2008.11.016
1997; Prinz, 2002),1 a second that explains away this evidence and reaffirms the orthodox view that concepts are
couched solely in amodal representations (Caramazza, Hillis,
Rapp, & Romani, 1990; Pylyshyn, 1973; Pylyshyn, 1981), and
a third that interprets this evidence cautiously and posits
both amodal and modal conceptual representations (Goldstone & Barsalou, 1998).2
1
This characterization of perceptually based approaches is qualified
because there seems to be some variability in the degree to which
proponents of perceptual symbols are committed to their universality.
Prinz (2002) explicitly holds that all conceptual representations are
perceptual or motor representations. Damasio (1989) does not offer a
complete theory of conception so it is difficult to judge where he stands on
this issue. Glenberg (1997) speaks of concepts as being embodied and
grounded in perception and action, but it is not absolutely clear that this
excludes the possibility of amodal symbols. Although Barsalou (1999)
proposes that cognition is ‘‘inherently perceptual,” he explicitly acknowledges the possibility that some conceptual representations are amodal
(Barsalou, Simmons, Barbey, & Wilson, 2003; Goldstone & Barsalou, 1998).
In personal communication on this issue, Barsalou argues that his
conception of perceptual symbol systems is inconsistent with the universality thesis because it assigns a central role to introspection, and
introspection, as he views it, is not perceptual.
2
Goldstone and Barsalou do not explicitly embrace representational
pluralism but, rather, acknowledge it as a possibility.
G. Dove / Cognition 110 (2009) 412–431
While the sympathies of many active researchers lie
with the more ecumenical view, the other views have received more attention in the literature. Defenses of ecumenicalism have tended to be rare and limited in scope – often
invoking little more than a methodologically based agnosticism. In this article, I offer a broad defense of the view that
there are diverse semantic codes, some of which are indigenous to perceptual systems and some of which are not.
This defense unfolds in three stages: first, I show that the
empirical evidence for perceptually based conception is
fundamentally circumscribed. For the most part, it involves
concrete or highly imageable concepts. The available evidence involving abstract concepts is limited in scope and
incomplete. Second, I argue that the general arguments offered in support of perceptual symbols are much stronger
with respect to concrete or highly imageable concepts than
with respect to abstract concepts. In other words, they are
more compelling with respect to just the sort of concepts
for which perceptually based theories have always seemed
well suited and not with respect to the sort of concepts for
which they have always seemed ill-suited. Third, I offer a
variety of empirical and theoretical reasons to think that
some abstract concepts employ amodal representations.
My core thesis is that our concepts contain both modal
and amodal representations. I make no other claims concerning their realization. In other words, I remain neutral with regard to other important issues concerning representational
format and cognitive architecture. While my position is consistent with the existence of a language – or languages – of
thought (Fodor, 1975), it is also consistent with views that
posit amodal representations that are not language-like in
any important sense. Amodal symbols could be, for instance,
highly distributed representations in a neural network. I
emphasize this neutrality because my argument is aimed
squarely at the question of modal-specificity.
More is at stake than just the nature of the vehicles of
thought. If representational pluralism is true, this should
inform how we investigate and understand the human
conceptual system. On a practical level, it offers a potential
explanation for the specificity of cognitive deficits found in
many lesion patients and children with developmental disorders. On a broader level, representational pluralism implies the existence of a cognitive heterogeneity and
flexibility that is not implied by the other views. The general point that representational systems have distinct computational properties is a familiar one (Marr, 1982; Pani,
1996). My proposal is that the human conceptual system
is characterized by a representational division of labor in
which modal and amodal representations handle different
aspects of our concepts. Although many of our concepts
may be grounded in perception, the existence of amodal
codes provides a partial explanation of how we are able
to acquire semantic content that goes beyond perceptual
experience. This capacity to go beyond experience may reflect a fundamental design feature of human minds.3
3
This capacity does not appear to be unique to humans. For example,
evidence discussed in Section 6 of this essay suggests that some animals
employ amodal symbols when they approximate quantities. The distinction
between animal and human cognition with respect to amodal representations is thus likely to be a matter of degree.
413
2. The empirical evidence for perceptual symbols
2.1. A circumscribed body of evidence
The orthodox separation of conception and perception is threatened by an ever increasing body of evidence that perceptual symbols are important for
certain cognitive activities. For instance, behavioral
and brain imaging studies suggest that mental imagery
(Farah, 2000; Kosslyn, 1994) and motor imagery (Grèzes & Decety, 2001; Jeannerod, 1995; Kan, Barsalou,
Solomon, Minor, & Thompson-Schill, 2003) depend on
sensory and motor representations, respectively. Perceptual representations have also been implicated in
several aspects of memory (Glenberg, 1997; Martin,
2001).
A number of recent behavioral experiments lend further support to the notion that perceptual representations
are central to some cognitive tasks. For instance, Pecher,
Zeelenberg, and Barsalou (2003) found a modality-switching cost in a non-imagistic property verification task. Participants verified verbally expressed facts involving one
perceptual modality (such as the fact that leaves rustle)
more rapidly after verifying a fact involving the same perceptual modality (such as the fact that blenders make
noise) than after verifying a fact involving a different perceptual modality (such as the fact that cranberries are
tart). More recently, van Dantzig, Pecher, Zeelenberg, and
Barsalou (2008) found a similar modality-switching cost
between a perceptual detection task and a property verification task. In a related vein, Stanfield and Zwaan
(2001) asked participants to affirm whether or not pictures depicted the actions described in previously presented sentences. The actions had either a vertical or
horizontal orientation (such as driving a nail into a floor
or into a wall). Participants responded more quickly to
the pictures that had the same orientation as the action
described. Stanfield and Zwaan hypothesize that subjects
generate a perceptual image of the action described in
the sentence and then use this image to carry out the
affirmation task.
The proposal that some of our concepts are couched in
perceptual codes also fits well with neuropsychological
evidence showing that damage to sensory or motor areas
can contribute to the loss of category-specific knowledge.
Neurospychological case studies have shown that there
are some patients who perform well on naming tasks
involving artifacts but poorly on naming tasks involving
living things and that there are other patients who exhibit
the reverse pattern (Farah & McClelland, 1991; Warrington
& Shallice, 1984). A common explanation of this double
dissociation is that these categories are represented by different perceptual features (Warrington & McCarthy, 1987;
Warrington & Shallice, 1984). Further support is provided
by the fact that lesions can lead to the loss of multiple categories that share perceptual properties (Simmons &
Barsalou, 2003). For instance, Adolphs, Damasio, Tranel,
Cooper, and Damasio (2000) found that damage to the
somatosensory cortex was correlated with deficits in the
visual recognition of facial expressions. They propose that
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G. Dove / Cognition 110 (2009) 412–431
the simulation of producing facial expressions is involved
in the recognition of facial expressions in others.4
Some recent neuroimaging data support the perceptually based interpretation of the lesion data. Martin, Wiggs,
Ungerleider, and Haxby (1996), for example, found robust
activation in visual areas with categories that appear to
rely heavily on visual information for identification. Using
a visual naming task and functional Magnetic Resonance
Imaging (fMRI), Chao and Martin (2000) found increased
activity in motor areas with highly manipulable objects
when compared to less manipulable objects. In another
fMRI study, Hauk, Johnsrude, and Pulvermüller (2004)
had participants read individual words that referred to actions involving leg, arm, and head movements. They found
that reading each type of action word produced increased
activation in the particular areas within the motor cortex
associated with performing the relevant movements.
In sum, a number of studies employing distinct experimental paradigms and techniques suggest that some conceptual tasks involve perceptual representations. Positing
such representations provides an economical and robust
explanation for a diverse set of observed phenomena,
including reaction times in behavioral studies, the functional character of some neuropathologies, and neural activation patterns in response to certain cognitive tasks. A
caveat is warranted, however, because perceptual symbols
are implicated in a circumscribed set of concepts. The relevant experiments involve concepts such as RUSTLING and
NAIL DRIVING which seem to lend themselves to perceptual representation. To be more precise, most of the concepts employed in these studies are highly imageable
(Paivio, 1971). This is important because the central point
of disagreement between perceptually based views of conception and representational pluralism concerns the prevalence of perceptual symbols.
Recently, investigators have gathered evidence that
implicates perceptual representations in some cognitive
tasks involving abstract concepts. Richardson, Spivey,
Barsalou, and McRae (2003), for instance, attempted to
ascertain whether or not comprehending abstract verbs
such as argue and respect automatically activates spatial
image schemas with a specific orientation (horizontal for
argue and vertical for respect). Participants listened to short
sentences while engaged in either a visual discrimination
task or a picture memory task. Reaction times suggest that
there was an interaction between the horizontal/vertical
orientation of the image schema and the horizontal/vertical orientation of the visual stimuli. In a similar vein, Glenberg and Kaschak (2003) found that reaction times
increased when response direction (a button press either
away/toward the body) and the implied direction of either
concrete action sentences (e.g. Andy gave you the pizza/You
gave Andy the pizza) or abstract transfer sentences (e.g. Liz
4
A word of caution is needed, though, because the correlation between
modality-specific damage and category-specific semantic deficits is not
universal. Category-specific semantic deficits are not always associated
with corresponding modality-specific perceptual impairments and, conversely, significant modality-specific perceptual impairments are not
always associated with category-specific semantic deficits (Caramazza &
Mahon, 2006).
told you a story/You told Liz a story) matched. They suggest
that this ‘‘action-sentence compatibility effect” is the result
of competition for resources by the motor planning associated with the action and the language processing associated with the sentence.
Casasanto and Boroditsky (2008) describe six psychophysical experiments involving judgments about distance
or duration using non-linguistic stimuli. Their findings
suggest that irrelevant spatial information often interferes
with judgments of duration, but the converse is not true.
Casasanto and Boroditsky infer from these studies that
temporal judgments rely on spatial representations. Casasanto (in press) provides a summary of evidence suggesting
that the dominant spatial metaphor in a participant’s first
language predicts performance on such non-linguistic
tasks and that this performance can be altered by training
a participant to use a different metaphor.
2.2. Interpreting the evidence
While the evidence for perceptual symbols is suggestive, it is important to recognize that it does not conclusively establish that conceptual representations are
perceptual. Indeed, the inference to perceptually based
cognition can be questioned on a number of grounds. For
one, the observed phenomena could be the result of perceptual processes merely correlating with conceptual processes served by amodal representations (Adams &
Campbell, 1999). In other words, perceptual representations could be a consequence of thinking rather the vehicles of thinking. Second, amodal systems exist that can
mimic the behavior of any perceptually based system
(Anderson, 1978; Pylyshyn, 1973). Although this flexibility
does not provide sufficient reason to posit amodal symbols
– indeed it can be seen as problematic – it remains a fact
that amodal representational systems can exhibit the
behaviors outlined above. If there are independent reasons
to posit amodal symbols, then they remain a live possibility. Third, amodal accounts are not monolithic. Indeed,
some types will exhibit the features cited in support of perceptual symbols (Machery, 2007). For instance, despite the
fact advocates of perceptual symbols often point to evidence of analogue representations as support for their approach, amodal symbol systems can also employ analogue
representations.
Although these epistemological and methodological
considerations should give us pause, they do not prevent
us from making a reasonable inference to the best explanation. Much of the evidence outlined above strongly suggests that highly imageable concepts involve perceptual
representations. The skeptical hypothesis that the observed perceptual activity is epiphenomenal fits poorly
with the lesion data and is undermined by some recent
studies. For example, Pulvermüller, Hauk, Nikulin, and
Ilmonlemi (2005) carried out a transcranial magnetic stimulation study in which they found that stimulation over
motor areas affects action word processing (see also Buccino et al., 2005).
The situation is different with respect to abstract concepts. Here the evidence is limited and incomplete.
Although it gives provisional support for the notion that
G. Dove / Cognition 110 (2009) 412–431
some abstract conceptual processing is handled by sensorimotor representations, it falls well short of establishing
that abstract concepts are generally couched in such representations. Our notion of RESPECT may involve a vertical
metaphor, but there is certainly more to this concept.
The significance of the data concerning judgment of duration is also far from clear. Although the findings are surprising and provide intriguing evidence of the influence
of cognitive metaphors on a non-linguistic task, a number
of questions remain. For one, the extant literature on temporal processing suggests that it involves the interaction of
multiple brain regions (Bhattacharjee, 2006). In addition,
the proposition that all temporal processing is based on
spatial metaphors seems unlikely because our ability to
think about events depends centrally on both spatial and
temporal information (Shipley, 2008). Indeed, the cited
experiments could be interpreted as involving spatial and
temporal judgments of individual events (a growing line,
a moving dot and – more controversially – the presence
of a line). Understood this way, Casasanto and Boroditsky’s
findings suggest that the spatial extent of an event can affect our judgment of its duration. This would certainly be
interesting and important, but it seems to have limited
empirical reach with respect to the issue of perceptually
based cognition. All in all, the available evidence suggests
that some of our concepts employ perceptual representations – particularly concrete or highly imageable concepts
– but fails to support the conclusion that perceptual symbols are the lingua franca of concepts.
415
In order to properly evaluate the claim that concepts are
perceptually based, we need to have an appreciation of the
nature of perceptual symbol systems. Here and throughout
the paper, I rely heavily on the work of Barsalou (1999);
Prinz (2002) and Prinz (2005) because I believe that they
have developed the most sophisticated and complete perceptually based approaches to concepts. This is not to say
that they speak with one voice. Indeed, meaningful differences exist between their respective views. Whenever
these differences are substantial and relevant to the topic
at hand, I will address their views separately.
The first question that arises is just what makes a mental representation perceptual or modal. Both Barsalou and
Prinz maintain that a representation is modal if it is part of
a specific sensory code: that is, if it is contained within a
neural system specifically designed through natural selection to detect internal or external objects or events.5 They
both extend this notion to include motor representations.
By these lights, a key feature of perceptual symbol systems
is that concepts are couched largely in sensorimotor representations. Prinz (2002) extends this idea and proposes that
all conceptual representations are indigenous to a sensory or
motor modality. He refers to this as the modal-specificity
hypothesis and claims that it can be thought of as a modern
version of Hume’s dictum, ‘‘All our ideas are nothing but
copies of our impressions” (Hume, 1748/1975, p. 686).
Barsalou thinks that Prinz’s hypothesis goes too far. In particular, he believes that some amodal representations are
needed to explain the functioning of introspection (personal
communication).
Both Barsalou and Prinz are committed to the idea that
perceptual symbols involve simulations of experience.6
Roughly put, they propose that our conceptualization of a
category consists of simulations of the experiences of perceiving exemplars of that category. Such simulations are
the result of a kind of neurophysiological reenactment
(Barsalou, 1999). Information concerning the neural activation patterns associated with the perception of an object
or event that have been captured and stored by conjunctive
neurons in neighboring association areas or convergence
zones (Damasio, 1989; Damasio & Damasio, 1994) are used
later, in the absence of perceptual input, to generate a partial
reactivation of the sensory representations.
These simulations are thought to have a number of
important properties that make them well suited to serve
as the vehicles for cognition (Barsalou, 1999; Barsalou,
2003a; Barsalou, 2003b; Barsalou, Solomon, & Wu, 1999).
First, simulations need not be conscious. In other words,
they may contain unconscious perceptual representations.
This property removes some of the traditional objections to
imagistic theories based on the unreliability or vagueness
of introspection. Second, simulations will often be schematic in the sense they contain only some of the perceptual representations involved in the experience being
simulated. For instance, a simulation in the visual modality
of the concept CAT might involve shape representations
but not color representations. Third, they will typically be
multi-modal in the sense that they involve the reactivation
of perceptual representations in several sensorimotor
modalities. Finally, these simulations will generally be context-sensitive. In other words, they will be tailor-made in
some sense for each circumstance. For instance, the simulation of CAT might re-enact the perception of a running
cat on one occasion and the perception of a meowing cat
on another.
Part of the appeal of perceptual symbol systems is
that they hold the promise of providing a revisionist
explanation of important aspects of the human conceptual system. For instance, a benefit of perceptual symbols is that they can account for the demonstrated
flexibility of cognition (Barclay, Bransford, Franks,
McCarrell, & Nitsch, 1974; Barsalou, 1982). Because concepts are not associated with individual simulations but
are instead variable constructions which occur temporarily within working memory (Prinz, 2002), simulations
will vary relative to the task demands of a given context
5
Aydede (1999) argues that this definition of a perceptual symbol casts
its net too widely because arbitrary and abstract representations could be
located within sensory systems. This is an excellent point, but I am not
going to belabor it because my arguments for amodal representations
succeed even if we adopt this liberal definition of a perceptual symbol.
6
I am using Barsalou’s terminology here because it seems both more
intuitive and general than Prinz’s. Prinz employs the notion of a ‘‘proxytype,” a technical term of his own invention that is more intimately tied to
details of his specific position. It does not do terrible violence to the notion
of a proxytype to say that it involves simulation.
3. Perceptual symbol systems
3.1. Simulation and conception
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G. Dove / Cognition 110 (2009) 412–431
and will typically involve only a small subset of the
information stored in memory. Another intriguing aspect
of a perceptual symbol system approach is that it provides a novel means of distinguishing types from tokens.
Barsalou (1999) and Barsalou (2003) suggests that the
conceptual system should be understood in terms of
both simulators and simulations. A simulator is a distributed system spanning association and perceptual areas
that generates simulations. To possess a concept such
as DOG is to have a skill or ability to generate appropriate perceptual representations of dogs in a given situation. Any particular simulation will contain a subset of
the modal representations contained within the simulator. Categorization can in turn be explained in terms
of the degree of fit between actual perception and simulation. The productivity of concepts can also be explained
through
the
interaction
of
simulators.
Simulators can be combined in a combinatorial fashion
to produce complex perceptual simulations (Barsalou,
1999; Barsalou & Prinz, 1997).
Concepts support a number of cognitive functions.
They help explain our ability to appropriately categorize
objects and to draw inferences about category members.
More generally, they play fundamental roles in language,
memory, and thought. Barsalou and Prinz provide three
general arguments for their claim that cognition is handled by a perceptual symbol system: one that straightforwardly appeals to recent empirical results, a second that
extols to the general advantages of perceptual symbols,
and a third that attacks the empirical basis for amodal
symbols. I have already shown that the first argument is
insufficient; in subsequent sections, I critically assess the
other two.
3.2. The problem of non-perceptual memory processes
Supporters of perceptual symbol systems recognize that
the ability to partially re-enact perceptual experiences cannot fully explain our ability to generalize and abstract
away from particular exemplars. They typically propose
that long-term memory integration processes underlie
our ability to create appropriate simulations (Barsalou,
2003a). This move offloads significant aspects of conceptualization into non-perceptual association areas of the
brain. It also raises a significant problem: because category
knowledge across modalities must be integrated to produce adequate simulations, it seems likely that convergence zones will contain amodal symbols.
Both Barsalou and Prinz are aware of this problem and
adopt deflationary strategies to defuse it. Although the details differ, both argue that the conceptual role played by
long-term memory processes is somehow constrained enough to not require conceptual representations. For instance, after Barsalou et al. (2003, p. 87) concede that
‘‘. . .conjunctive neurons in convergence zones constitute
a somewhat amodal mechanism for capturing and reenacting modality-specific states,” they go on to argue that
the role of this mechanism is simply to enable the activation of appropriate perceptual symbols that then support
conceptual processing. They also contend that alternative
explanations of this capacity are available that do not re-
quire amodal symbols.7 Prinz (2002) argues that long-term
memory networks form various types of links between perceptual representations in various different codes. Although
he admits that these links can be more than bare associations – he proposes, for instance, that some are transformational and others are situational – he claims that they are
insufficiently rich to count as conceptual representations.
In the end, both Barsalou and Prinz seek to preserve their
commitment to perceptual symbols by limiting the scope
of influence of any possible representations within relevant
long-term memory systems.
Whether or not these deflationary arguments can be
sustained remains an open question. Their fate will ultimately be decided by further empirical work. It is important to recognize, however, that there is a place in the
very conception of a perceptual symbol system where
amodal symbols might be effective. The functional argument for amodal symbols has always rested in large part
on their capacity to encode, integrate, and transfer information obtained from different modalities. If association
areas contained amodal symbols, this would provide an
economical explanation of how coordinated multi-modal
perceptual simulations were possible.
4. The argument from methodological parsimony
Proponents of perceptual symbols often argue that considerations of methodological parsimony favor their position (Barsalou, 1999; Prinz, 2002). Their reasoning is
roughly that adopting perceptual symbols frees us from
having to posit a separate class of amodal representations.
According to Occam’s razor, less is more when it comes to
theoretical posits. A theory that only posits perceptual representations should therefore be preferred over one that
posits both perceptual and amodal representations.
Three factors undermine the argument from methodological parsimony. The first is that it rests on a partial
accounting. While perceptual symbol theories are clearly
more parsimonious than pluralistic theories with regard
to the representations that they posit, this does not mean
that they are more parsimonious overall. An assumption
shared by all of the theories under consideration is that
two things are constitutive of concepts: representations
and mental operations involving those representations. A
consequence of this is that we need to assess the relative
complexity of the mental operations associated with a
hypothesized perceptual symbol system in order to adjudicate the issue of its overall parsimony. There are reasons,
however, to suspect that the mental operations needed
for an adequate perceptual symbol system will be appreciably complex. As mentioned above, perceptual simulators need to be more than systems for replaying recorded
information. Barsalou (1999) proposes that simulators employ introspection and Barsalou et al. (2003) propose that
they employ processes of abstraction, generalization, and
evaluation. Given that the extent and complexity of the
7
On more than one occasion, Barsalou has suggested that simulators
might contain ‘‘supramodal” representations. I am not convinced that it is
possible to make a principled distinction between supramodal and amodal
representations.
G. Dove / Cognition 110 (2009) 412–431
mental operations needed to explain these processes remains in question, we are not yet in a position to judge
the overall complexity the perceptual symbol approach.
The second difficulty with the argument from methodological parsimony is that parsimony considerations are
defeasible. It is not difficult to come up with examples
from the history of psychology and neuroscience where
analogous reasoning would have lead researchers astray.
For example, at the time of its inception, the reflex arc theory of memory was parsimonious in the sense outlined
above (Finger, 1994). Unfortunately, the theory turned
out to be incompatible with a host of behavioral and neuropsychological evidence (Lashley, 1950).
None of this is to suggest that parsimony considerations
are irrelevant; it is just that they cannot be viewed in isolation. The central question within any scientific debate is
ultimately which theoretical explanation enjoys the greatest empirical support. Parsimony may factor into this
judgement, but so should other considerations such as
the degree to which each theory fits with the available evidence, the testable predictions that each theory makes, the
background assumptions behind each theory, and so on.
Parsimony considerations come into play primarily when
other things are equal. The third problem with the argument from parsimony is that other things are not likely
to be equal. As I will argue in subsequent sections, empirical evidence and theoretical considerations support the
notion that abstract concepts are handled at least in part
by amodal representations.
417
which we identify dogs and the natural kind itself. The notion of nominal content is important for two reasons. The
first is that it provides an explanation of how we are able
to use our concepts to carry out actions such as tracking
and categorizing objects. The second is that the ability to
carry out these actions helps explain how our concepts
are able to represent real contents. In terms of our example, the ability to recognize dog appearances helps us track
real dogs.
Prinz’s idea is that nominal contents associated with
perceptual symbols make them well suited for bearing real
contents. His argument for this turns on two claims. The
first is that mental states represent entities and properties
because they stand in certain nomic relations to them.
Prinz, in other words, adopts an information-based approach to meaning. On this approach, mental representations have intentional content because, under certain
conditions (to be specified by the particular semantic theory), they causally co-vary with their contents.8 The second
is that perceptual symbols can secure these nomic relations
in a way that amodal symbols cannot because they are already causally connected to the referents. Prinz (2005, p.
684) explains that, ‘‘The mechanisms that allow us to identify objects and interact with them also, thereby, establish
reliably causal relations with those objects.” The fact that
perceptual representations are already causally engaged
with the intentional objects of our concepts presumably
helps us enter into appropriate causal relations with them.
5.1. A reformulation of the abstract ideas objection
5. The argument from intentionality
A central issue for any theory of concepts is how mental
states come to represent things or events in the world.
Both Barsalou and Prinz argue that, because of their dual
role as vehicles for perception and conception, perceptual
symbols are better situated for bearing content than amodal symbols. Comparing the relative merits of amodal and
perceptual symbols, Barsalou writes (1999, p. 597; emphasis in the original),
Where perceptual symbols do have an advantage [over
amodal symbols] is in the ability of their content to play
a heuristic role in establishing reference. Although perceptual content is rarely definitive for intentionality, it
may provide a major source of constraint and assistance
in determining what a symbol is about.
A perceptual symbol consists of a neurophysiological
re-enactment of a collection of perceptual representations.
It can be thought of as having perceptual content because
there are certain states of affairs in the world that would be
likely to elicit these representations under normal conditions. Barsalou’s suggestion is that this perceptual content
can facilitate the possession of intentional content.
Following Locke (1690/1979), Prinz (2002) claims that
perceptual simulations bear two distinct kinds of content:
nominal (or cognitive) content and real content. To put it
roughly, his position is that perceptual symbols refer both
to the appearances of objects and their essences. By these
lights, our concept DOG refers both to the properties by
The argument from intentionality has weak and strong
versions that need to be kept distinct. The weak version is
that a system containing some perceptual representations
is better situated to solve the problem of intentionality
than one that contains no perceptual symbols. Both Barsalou and Prinz point out that a system containing only amodal symbols struggles to explain how individual symbols
come to be associated with things and events in the world
(see also Glenberg & Robertson, 2000). This weak form of
the argument does not threaten representational pluralism
because a representational pluralist can concede that perceptual symbols are well suited for bearing certain contents while maintaining that they are poorly suited for
bearing others. Both Barsalou and Prinz also make statements that express a strong version of the argument from
intentionality. This form of the argument from intentionality holds that perceptual symbols are better situated to
represent most concepts (including abstract concepts).
The strong form of the argument from intentionality is
the one needed to exclude representational pluralism. In
order to defeat it, I need to show that there is some class
of concepts for which perceptual symbols have no clear
8
It is possible to criticize Prinz for his appeal to information-based
semantics (e.g. DeMoss, 2004). I do not have the space to assess this
semantic approach here, but it is worth pointing out that it allows both
Prinz and Barsalou to avoid many of the traditional problems associated
with imagistic theories of concepts. Adopting a different approach might
very well require significant changes to the overall conception of perceptual symbol systems.
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G. Dove / Cognition 110 (2009) 412–431
heuristic advantage with respect to their intentionality. I
contend that abstract concepts are just such a class. This
claim builds on a traditional objection to perceptual representations. As many have noted, perceptual representations seem ill-suited for representing abstract concepts.
Some of the most obvious candidates are logical concepts
such as NEGATION, OR, and TRUTH. Other commonly cited
exemplars are theoretical concepts about unobservable
entities such as ELECTRON and mathematical concepts
such as NUMBER. Perhaps the largest category includes social concepts such as JUSTICE, DEMOCRACY, or MORALITY.
Within philosophy, critics of perceptually based approaches to cognition have traditionally argued that perceptual symbols cannot possibly represent abstract
concepts. This is too strong. The hypothesis that abstract
concepts are represented by perceptual symbols may be
empirically implausible, but it is not impossible. Indeed, I
take it that Barsalou (1999) has shown that a perceptual
symbol system can exhibit many of the necessary conditions for representing concepts (abstract or otherwise),
including productivity, implementing a type/token distinction, supporting inferences, and the ability to represent
propositions.
Below, I defend a weaker assessment of the problem
posed by abstract concepts that is nevertheless sufficient
to undermine the strong version of the argument from
intentionality. My claim is that proponents of perceptual
symbols have failed to show that modal-specificity confers
any special benefit on perceptual symbols as vehicles for
abstract concepts. For the sake of expedience, I focus on a
particular abstract concept, DEMOCRACY. I have chosen
this example because it seems fairly pedestrian, and any
problems associated with it are likely to be the rule rather
than the exception. Because Prinz and Barsalou offer distinct approaches to abstract concepts, I discuss each
separately.
5.2. Prinz on abstract concepts
Supporters of perceptual symbols typically argue that
they can, at least in principle, account for abstract concepts. In keeping with this, Prinz (2002, p. 148) argues that,
‘‘. . . the failure to see how certain properties can be perceptually represented is almost always a failure of the imagination.” In order to support this claim, he identifies several
possible means by which perceptual symbols might handle
abstract ideas: including mental operations, sign tracking,
metaphorical projection, and labeling. In order to undermine the argument from intentionality therefore, I need
to demonstrate that none of these strategies manifests a
heuristic advantage for perceptual symbols.
5.2.1. Mental operations
The modal-specificity hypothesis applies to mental representations but not to mental operations. Therefore, a
possible strategy for handling problematic cases is to claim
that they involve the latter rather than the former. Advocates of perceptual symbols have adopted this strategy
with a number of abstract concepts. For instance, Barsalou
(1999) explicates our everyday notion of TRUTH in terms
of a matching operation that compares our expectations
to our perceptual experiences. On this view, in other
words, our everyday notion of TRUTH involves a recognized correspondence between our beliefs and our perceptions. Information that has been stored in long-term
memory is used to generate perceptual simulations for
sentences. These simulations are then compared to the
perceptual representations produced by our experience of
and interaction with the world. A sentence is judged to
be true when there is a sufficient match between the perceptual simulation associated with it and our actual perceptual experience. Prinz (2002) similarly explicates
NEGATION as an inversion of the matching function.
According to his view, the thought that rocks are not animals will be judged to be true if there is a failed mapping
between our experience and the perceptual simulations
associated with the thought that rocks are not animals.
As a defense of modal-specificity, the key idea is that the
thought associated with a sentence and the thought associated with a negation of that sentence are purported to
contain the same conceptual constituents. These thoughts
are distinguished by the mental operations carried out on
these constituents.
These proposals have generated a great deal of controversy. A number of intertwined criticisms are common.
One is that they conflate truth with perceptual similarity
(Mitchell & Clement, 1999). Another is that they leave
something out because TRUTH is more than matched
expectations (Adams & Campbell, 1999). Recall that perceptual symbol theorists typically appeal to perceptual
matching in their account of categorization. But categorizing something as a dog is not the same as thinking that it is
true that it is a dog. A third criticism is that these proposals
are simply too verificationist. It seems possible to accept a
statement as true without having a clear set of perceptually based expectations for that statement.
Both Barsalou (1999) and Prinz (2002) offer responses
to these criticisms. Rather than wade more deeply into
these turbulent waters, though, I am going to acknowledge
the controversies and move on to the question of applying
this strategy to DEMOCRACY. This seems reasonable because the subject of truth is a contentious topic within
both philosophy and psychology. Requiring that a general
theory of conceptual representation solve this problem
seems to be setting the bar too high. Given the long history
of disagreement on this topic, there are also just too many
positions and nuances to consider. In addition, logical concepts seem to be a special and circumscribed class of abstract concepts. For this reason, it seems possible and
perhaps even reasonable to bracket off our concerns about
this class of concepts.
Even if we assume that logical concepts can be treated
as mental operations, there is no reason to think that the
mental operation strategy will be able to capture the full
content of DEMOCRACY – a concept that likely involves a
number of social concepts, such as GOVERNMENT, CONSENSUS, ELECTION, etc. that are neither straightforwardly
perceptual nor fully explainable in terms of internal mental dynamics. This is not to say that mental operations may
not be important to some aspects of DEMOCRACY. Certainly, representing this concept may involve a number
of logical operators. In addition, it is conceivable that
G. Dove / Cognition 110 (2009) 412–431
aspects of the decision making involved in voting can
be partially explained in terms of mental operations.
Nevertheless, it remains the case that significant aspects
of the concept of democracy cannot be captured by mental
operations.
5.2.2. Sign tracking
The basic idea behind Prinz’s second strategy is that
perceptual representations of contingently correlated perceptual features can be used as a symbol for an abstract
category. Applying this strategy to DEMOCRACY, one might
propose that it is represented on a given occasion by a
schematic perceptual simulation of people carrying out
one or some of the actions associated with democracy
(placing ballots in a box, punching out chads, pulling levers
in a booth, penciling-in bubbles on a scantron sheet, dipping fingers in ink, and so on).
A challenge faced by this proposal is that there are
many actions and events associated with democracy. This
seems to imply that a complex set of simulations may be
needed. How complex though? Do we need to simulate
the counting of the ballots, the official declaration of a winner, the transfer of power, the functioning of government,
the rule of law, and so on? Any proposal that we simulate a
large subset of the relevant events faces a number of difficulties. At some point, considerations of cognitive economy may come into play because the perceptual symbol
representing the concept cannot completely tax our cognitive resources. Processing load is only one consideration,
though. A further problem with positing complex simulations is that the more complex a simulation associated
with an abstract concept is, the more difficult it is to envision how it could productively combine with other concepts. It even seems doubtful that people actually have a
rich enough knowledge of the functioning of democracies
to create a sufficiently complex symbol. Furthermore, we
seem able to think about DEMOCRACY in situations where
we have incomplete knowledge. For example, I can wonder
about whether or not Moldova is a democracy without
knowing many of the details concerning how elections
are held, power is transferred, etc. Given my palpable lack
of knowledge about Moldova, any simulations of these
events (even highly schematic ones) would likely contain
many inaccurate details. Despite this deficit with regard
to my simulation abilities, I am able to draw general inferences about what would be the case if Moldova is in fact a
democracy.
Given these considerations, it seems reasonable to propose that the relevant schematic simulations should only
encompass the perceptual features associated with a circumscribed subset of the activities associated with democracy. These features are also likely to be idiosyncratic
because there are many physical ways to hold an election.
Does this sort of perceptual symbol enjoy a clear advantage
over an arbitrary amodal one? It does not for the simple
reason that the perceptual properties it contains are not
a reliable means of tracking democracies. The argument
from intentionality turns on the idea that perceptual properties give us a leg up with regard to entering into the
appropriate nomic relationships between the symbol and
its referent. This strategy seems to work with a concept
419
like DOG because one can track dogs by their appearances.
The problem with an abstract concept such as DEMOCRACY is that the correlation between the perceptual features likely to be contained within a perceptual symbol
for this concept and the presence of its referent is loose
at best. The problem is not just that there are hard cases
or even that false positives are likely; instead, it is that little direct connection exists between these perceptual features and what makes a government a democracy.
Recently, Prinz (2005) has suggested that an appeal to
internal perceptual states, particularly ones associated
with emotions, might be employed to help with abstract
concepts. Applying this strategy to the issue at hand,
one might try to enrich the perceptual simulation of the
act of voting by including certain internal somatic perceptions. If we assume that different emotions can be broadly
distinguished by somatic state (Prinz, 2004), we should be
able to associate the act of voting with a certain type of
emotion. Unfortunately, there is little reason to think that
it will provide any help. The trouble is that genuine acts
of voting are not distinguished from false ones by the
emotion experienced by the voters at the time of voting.
Fear, for instance, can be associated with both freely chosen and coerced votes. The only way an appeal to emotions can help is if one is allowed to include the
conceptual content of the emotion (such as the fear that
one will be punished by the government for voting the
wrong way). This will not work as an attempt to provide
a perceptual symbol for the concept DEMOCRACY, though,
because the relevant conceptual content of an emotion is
itself likely to contain abstract concepts (such as
GOVERNMENT).
The main problem with the sign tracking strategy is
that a perceptual symbol of democracy is likely to be a
poor democracy-detector. If it is a poor democracy-detector, however, there is little reason to suppose that it has
an advantage over an amodal symbol with regard to representing DEMOCRACY. Because perceptual properties generally fail to distinguish true from false instances of
democracy, perceptual symbols appear to be at a disadvantage when it comes to entering into the appropriate nomic
relations needed for possession of the concept.
5.2.3. Metaphorical projection
Prinz’s third strategy for addressing the abstract ideas
objection, metaphorical projection, emerges from work in
cognitive linguistics. Several cognitive linguists have proposed that metaphor plays a fundamental role in our conceptual system (Lakoff, 1987; Lakoff & Johnson, 1980). To
give an example, Lakoff and Johnson (1980) claim that
our understanding of the concept ARGUMENT is shaped
by the metaphor of ARGUMENT IS WAR. This metaphor appears to explain aspects of our linguistic behavior, such as
the fact that we use words associated with war to describe
arguments. For example, one defends a position in an argument while attempting to attack, demolish, and shoot down
the claims of one’s interlocutor.
There are a number of reasons to be skeptical of the attempt to infer metaphoric representation from this sort of
linguistic evidence. For one, it is not clear that linguistic
patterns such as those outlined above directly reflect
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G. Dove / Cognition 110 (2009) 412–431
conceptual structure. Indeed, alternative explanations of
metaphors that do not require positing metaphoric representations are available (Murphy, 1997). Another problem
is that the proposed metaphoric projections seem developmentally implausible (Murphy, 1996). It seems unlikely
that an understanding of the complexities of war is required to understand the nature of arguments. Furthermore, evidence suggests that children’s understanding of
metaphor remains quite poor before the ages of 8–10
(Winner, Rosenstiel, & Gardner, 1976).
Applying the metaphor strategy to DEMOCRACY would
most likely involve two steps. The first would be to decompose this concept into a set of sub-concepts such as FREEDOM and CONTROL. The second would be to offer an
explanation of these sub-concepts in terms of a perceptual
metaphor. FREEDOM might, for instance, be interpreted as
a metaphorical extension of an absence of physical restraint. For this two stage strategy to work as a defense
of the modal-specificity hypothesis, it must be the case
that all of the content of FREEDOM can be captured by
the application of a perceptually based metaphor. There
is an inherent difficulty faced by the attempt to capture
conceptual content in terms of metaphor, however: while
a metaphor enables us to highlight the similarities between two concepts, it cannot capture the important differences. Arguments, after all, are not really wars.
Freedom is both more and less than a lack of physical restraint. Recognizing the appropriate connections between
a perceptual experience and what it is being metaphorically extended to cover seems to require a prior understanding of the concept. Without such an understanding,
it is difficult to see how one can arrive at a correct interpretation of a metaphor.
5.2.4. The labeling strategy
The labeling strategy co-opts a common strategy for
handling abstract content by means of amodal symbols.
On this strategy, a concept such as DEMOCRACY is understood in terms of a complex network of inferentially related concepts such as GOVERNMENT, ELECTION,
CONSENSUS, FREEDOM, and RULE OF LAW. The labeling
strategy reconstitutes this strategy within a perceptual
symbol system. The general idea is that abstract concepts
can be captured in terms of networks of verbal labels
rather than networks of inferentially related amodal symbols. DEMOCRACY would then be represented by means
of a lexical network connecting the English word democracy to the English words government, election, consensus,
rule of law, etc.9
With the labeling strategy, language becomes a virtual
amodal symbol system because external labels are abstract, non-analogical representations. Unlike other perceptual symbols, external labels are not simulations of
experience with the referent of the concept. They are only
modal in the sense that they are simulations of verbal
experience. In other words, the connection between the
modal-specificity of the symbol and its ability to refer
9
Burgess and Lund (1997) and Landauer and Dumais (1997) provide
examples of how the labeling strategy might be realized in a semantic
theory.
has been removed. Unfortunately, it is precisely this connection that is supposedly responsible for the advantage
of perceptual symbols over amodal ones. Adopting the
labeling strategy therefore abandons the argument from
intentionality precisely when it seems most needed.
Little appears to be gained by adopting the label strategy other than the preservation of the nomological possibility of a perceptual symbol approach. Something
appears to be lost, however, because special challenges
face the label strategy. For instance, it is not clear how to
handle something as basic as semantic ambiguity or polysemy. In a system employing amodal representations, the
same external label can be associated with separate internal labels, which in turn bear distinct contents. This technique is not available if our concepts are tied to the
external label itself. One might propose that ambiguity occurs when distinct networks are associated with the same
label, but this just raises the question of how we individuate and track these networks.
To get an idea of the nature of the problem of posed by
polysemy, consider the external label value. When used as
a noun, this label can express a number of different meanings including, but not limited to, a fair return in an exchange of goods, services, or money; monetary worth;
relative worth; an intrinsically desirable or worthwhile
principle or quality; an assigned numerical quantity; the
relative duration of a musical note; and the relative luminosity of a color. The current proposal would distinguish
the different meanings of such external labels by networks
containing associations with different external labels. This
only shifts the problem, though, since many of these labels
will also be polysemous. Moreover, these networks are
associated with each other because they are associated
with the same label. What makes them separate networks
as opposed to just a single network? What enables us to
track these networks? Similar issues arise with synonymy.
The supporter of perceptually based conception needs to
show how two terms with distinct networks of associations can be synonymous. Similarity alone is unlikely to
be a sufficient condition. For example, the networks associated with the labels buy and sell are likely to be very similar because every instance of buying is also an instance of
selling.
The difficulty posed by polysemy and synonymy is part
of a more general problem faced by the labeling strategy.
Any theory of lexical concepts must be able to distinguish
associations that have to with conceptual content and
those that do not. Amodal approaches typically handle this
problem by associating external labels with internal symbols that are part of a semantic representation system.
External labels, though, have any number of associations
that have nothing to do with semantic content. For example, external labels have phonological associations that
manifest themselves in speech errors. If the labeling strategy is to be considered a viable alternative to amodal approaches, it needs to provide at least an outline of how to
distinguish between those associations that are relevant
to a particular concept expressed by an external label
and those that are not. Appealing to a vague notion of simulation competence does little more than rename the
problem.
G. Dove / Cognition 110 (2009) 412–431
My point is not that amodal symbols provide an easy
solution to the difficult problems of psychosemantics. Instead, I am appealing to the fact that internal amodal representations seem to make these difficult problems more
tractable than they would be otherwise. Prinz claims that
perceptual symbols are better suited to representing our
concepts than amodal symbols. The burden of proof thus
falls on him to show that external labels can handle fundamental semantic phenomena such as polysemy and synonymy more effectively than amodal symbols. No such
demonstration has been supplied.
5.3. Barsalou on abstract concepts
Barsalou offers a single general strategy for representing abstract categories (Barsalou, 1999). This strategy has
two stages: first, one identifies the conceptual content of
the abstract concept under consideration. Second, one creates a perceptually based representation of this content by
applying three core mechanisms: framing, selectivity, and
introspective symbols. Barsalou maintains that once we
have the right content, it is possible to represent that content ‘‘directly” through perceptual reenactment.
According to Barsalou (2003b), amodal theorists have
insufficiently considered the conceptual content of abstract concepts. Despite the widespread recognition of
the existence of situation effects on cognitive performance, the situational nature of our concepts has been
overlooked by the mainstream because researchers have
generally assumed that details concerning background
situations have been lost in the process of abstraction.
The standard view is that conceptual representations capture relatively invariant properties of category members.
In contrast to this view, Barsalou proposes that extensive
information about background situations is preserved in
the process of abstraction and is stored in long-term
memory. Within a particular context, this situational
information can become active and influence cognitive
processing.
The notion that our concepts are embedded within
knowledge of background situations is supported by evidence from feature generation experiments. In a preliminary study, Barsalou and Wiemer-Hastings (2005) asked
participants to generate typical properties for three abstract concepts (TRUTH, FREEDOM, and INVENTION), three
concrete concepts (BIRD, CAR, and SOFA) and three intermediate concepts (COOKING, FARMING, and CARPETING).
Barsalou and Wiemar-Hastings coded these responses into
various property types, such as taxonomic, entity, setting/
event, and introspective properties. They make much of
two findings: the finding that participants generated situational properties with both concrete and abstract concepts and the finding that participants tended to
generate more event and introspective properties with abstract concepts. In a more fully realized experiment
employing similar methodology, Wiemar-Hastings and
Xu (2005) found support for quantitative and qualitative
differences between abstract and concrete concepts. Their
participants tended to produce fewer entity properties,
more introspective properties, and more relational properties with abstract concepts than with concrete concepts.
421
Wiemar-Hastings and Xu propose that abstract and concrete concepts are generally associated with different aspects of situations: abstract concepts tend to focus on
introspective and social aspects of situations while concrete concepts tend to focus on physical entities and
actions.
Even if it is true that all concepts are situated, this alone
does not establish that they are represented by perceptual
symbols. One could reasonably argue that amodal symbols
are well suited for representing the objects and events that
make up situations. Barsalou and his colleagues make the
further argument that perceptual symbols are in a better
position than amodal symbols to account for situation effects. They claim that, if perceptual simulation underlies
conception, this imposes a de facto constraint on our concepts because simulations are likely to involve relevant
settings, actions, and events. Yeh and Barsalou explain
(2006, p. 352):
If a perceptual experience takes the form of a situation,
and if a conceptual representation simulates perceptual
experience, then the form of a conceptual representation should take the form of a perceived situation.
When people construct a simulation to represent a category, they should tend to envision it in a relevant perceptual simulation, not in isolation. When people
conceptualize chair, for example, they should attempt
to simulate not only a chair but a more complete perceptual simulation, including not only a chair but a
more complete perceptual situation, including surrounding space and any relevant agents, objects and
events.
According to this approach, people represent a category of simulating perceptual experiences of it members. These simulations are likely to include features
of background situations because objects are typically
not perceived in isolation but, rather, within a context.
Barsalou proposes that information about the typical
background situations of category exemplars is stored
in long-term memory during category learning and
becomes
active
when
a
concept
is
being
processed.
Barsalou’s counter-argument to the traditional abstract
ideas objection is essentially an inductive one. He provides
a recipe for representing abstract concepts and proposes
that one can derive an empirically promising account of
an abstract concept using this recipe. He writes (1999,
pp. 600–601).
First, identify an event sequence that frames the
abstract concept. Second, categorize the multimodal
symbols that represent not only the physical events in
the sequence but also the introspective and proprioceptive events. Third, identify the focal elements of the
simulation that constitutes the core representation of
the abstract concept of the event background. Finally,
repeat the above processes for any other event
sequences that may be relevant to representing the
concept (abstract concepts often refer to multiple
events, such as marriage referring to a ceremony, interpersonal relations, domestic activities, etc.).
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G. Dove / Cognition 110 (2009) 412–431
Barsalou challenges his critics to attempt the same with
any proposed counterexamples. I am going to take up that
challenge and apply his recipe to the concept DEMOCRACY.
A reasonable initial hypothesis concerning an event sequence that frames the concept DEMOCRACY is that of voting in an election. With respect to this event sequence, a
context-specific perceptual simulation should include not
only some of the relevant physical actions but also the
introspective states of individuals carrying out those actions. Certain elements of the simulation (such as those aspects of voting that are associated with the process being
free and fair) should be selected as more central than other
aspects of the event sequence. Since democracy involves
more than elections, a the DEMOCRACY simulator should
also be able to simulate event sequences associated with
the counting of votes, the orderly transfer of power, the
rule of law, etc. Just how many relevant events need to
be included remains an open question.
Introspective events play an important role in Barsalou’s approach. They help distinguish concepts that do
not seem initially to be perceptually distinct. For instance,
from the perspective of a third-person observer, there is
little perceptual difference between signing and forging a
check (Anderson, 2005). The first-person experience of
these two events, though, is presumably different. A perceptual simulation that involves introspective events
would thus be able, at least in principle, to disambiguate
these concepts. Introspective events could also play a similar role in distinguishing freely chosen votes from coerced
ones.
I do not dispute that introspective events can serve such
a functional role. Instead, I contend that the appeal to
introspection fails to provide compelling support for the
existence of perceptual symbols. Barsalou himself denies
that introspection is perceptual and from this concludes
that at least some conceptual representations are not perceptual (personal communication). This appears to make
him a representational pluralist on some level. Interestingly, Barsalou (1999) and Barsalou (2008a) maintains that
introspective events are more central to abstract concepts
than concrete ones. His solution to the problem of abstract
concepts thus involves, at least in part, an appeal to amodal
symbols.
Within cognitive science, there are two basic approaches to introspection: one that treats it as a form of
higher-order thought and another that treats it as a form
of higher-order perception (Güzeldere, 1999). It is thus
possible to view introspection as perceptual. This move,
however, is not enough to exclude amodal symbols. The
problem is that the question of what is being perceived
arises. What does the ‘‘mind’s eye” see? Consider an act
of voting. Whether or not it is freely chosen or coerced depends on a complex set of emotions, beliefs, and cognitive
operations. The relevant introspective events, therefore, require access to complex judgments. If these judgments involve amodal symbols, however, the appeal to
introspection provides little help as a defense of perceptual
symbols. In order for introspection to help as a defense of
perceptual symbols, it should be the case that the introspected appraisals themselves contain only perceptual
representations. The most straightforward means of
accomplishing this would be to suggest that what is introspected is a perceptual simulation associated with forming
the judgment. This will not work though because the relevant judgment itself is likely to contain abstract concepts.
If so, then further introspective events, perhaps ones that
also contain abstract concepts, will need to be simulated.
This raises the specter of a problematic regress of multiply
embedded perceptual simulations. In the end, the appeal
to introspection leads to something of a dilemma for the
proponent of perceptual symbol systems: either one accepts that introspection involves amodal symbols or one
places unwieldy and implausible constraints on theories
of introspection.
The other important finding from property generation
studies is that abstract concepts often involve social properties. This is certainly the case with an inherently social
concept such as DEMOCRACY. Applying Barsalou’s strategy
to this concept leads to the proposal that it is represented
by situated perceptual simulations of the event sequences
such as voting that are associated with democracies. A significant problem emerges with respect to the perceptual
simulations of such social events. What makes a particular
event sequence an instance of voting is not its sensorimotor details but rather a series of institutional and relational
properties. Voting is a performative act that depends crucially on external social factors. Carrying out an appropriate action in the wrong social context achieves nothing.
Indeed, the difficult task of deciding whether an election
was free and fair can often turn on factors that are external
to individual perceptual experiences (such as whether or
not there was ballot stuffing, whether or not the voting
machines functioned properly, or whether or not the
counting process was interrupted by an act of the judiciary
branch of government).
Barsalou’s proposal that our concepts, including abstract ones, are fundamentally situated is intriguing and
has the potential to transform the field. Manifestly, it warrants further empirical investigation. In the end, though, it
is not enough to secure the argument from intentionality.
Many abstract concepts focus on introspective and social
properties. It is far from clear, though, that these properties can be adequately represented using perceptual
symbols.
5.4. Intentionality and the problem of abstract concepts
A common complaint about perceptually based approaches to conception is that they are poorly suited for
representing abstract concepts. In defense of perceptual
symbols, supporters have endeavored to show that perceptual symbol systems have, in principle, the conceptual resources to deal with abstract concepts. To this end, they
have identified a number of possible strategies. The very
difficulty of this exercise, however, undercuts the argument from intentionality. While there are manifold reasons to believe that perceptual symbols are particularly
well suited to represent many concepts – particularly
those associated with perceptually identifiable categories
– advocates of perceptual symbols have yet to provide
compelling reasons to believe that they are similarly well
equipped to handle abstract concepts.
G. Dove / Cognition 110 (2009) 412–431
The fact that perceptual symbols do not seem to be well
suited to representing abstract concepts does not completely rule out an appeal to intentionality. After all, it
could be the case that amodal symbols are substantially
worse off than perceptual symbols when it comes to representing abstract content. There are four reasons why this
negative defense of perceptual symbols is not promising:
first, the burden of proof falls on defenders of perceptual
symbols who appeal to intentionality to demonstrate that
perceptual symbols are better suited to representing abstract concepts. They need to show that there is a clear
way in which the modal-specificity of perceptual symbols
confers an advantage on them with respect to representing
abstract concepts. So far, they have not succeeded in this
endeavor. Second, amodal symbols have proved to be flexible and robust. As supporters of perceptual symbols often
point out, they are posited by most current accounts of
concepts. Although it is true that too little attention has
been paid to the empirical investigation of abstract concepts, the fact remains that there are number of well established theoretical options for providing an amodal account
of abstract concepts (definitions, exemplars, prototypes,
theories, and massively distributed representations to
name a few). An advantage of representational pluralism
is that it enables one to appeal to any one of these types.
Third, it is possible to turn the tables on the advocate of
perceptual symbol systems. Several of the proposed strategies would be strengthened by the presence of amodal
symbols. For instance, positing internal amodal symbols
would enable us to avoid many of the problems associated
with the external label strategy. Fourth, a split-decision between modal and amodal approaches (one in which both
are found to be equally deficient with respect to abstract
concepts) would be enough to block the argument from
intentionality.
This section should not be seen as providing a conclusive argument that abstract concepts are handled by amodal symbols. Amodal symbols may be better positioned to
handle abstract concepts, but this does not establish that
our conceptual system actually employs them. Reverse
engineering in the biological and psychological sciences
is a tricky business. The proper conclusion to draw is that
general considerations about intentionality do not resolve
the empirical issue of how abstract concepts are represented. Any advantage that perceptual symbols might enjoy over amodal symbols with regard to intentionality
appears to evaporate with respect to abstract concepts. Because of this, the argument from intentionality cannot be
used to decide between a perceptually based approach to
concepts and a pluralistic one.
6. Positive evidence for amodal symbols: the case of
number approximation
6.1. Barsalou’s criticism of the evidence for amodal symbols
The most straightforward justification for amodal symbols is that they are theoretically expedient. Almost no one
disagrees that amodal systems have a number of desirable
qualities. Barsalou himself concedes (1999, p. 579):
423
Amodal systems have many powerful and important
properties that any fully functional conceptual system
must exhibit. These include the ability represent types
and tokens, to produce categorical inferences, to combine symbols productively, to represent propositions,
and to represent abstract concepts.
In other words, researchers have favored amodal symbol systems because in general they appear to have design-specs that seem suited to fulfill the desiderata for
theories of concepts. After conceding that amodal symbols
seem well suited for supporting a conceptual system,
Barsalou (1999) goes on to lament that, ‘‘. . .there is little
direct empirical evidence that amodal symbols exist” (see
also Barsalou, 2008b; Barsalou et al., 2003). As he sees it,
researchers have failed to adequately address the issue of
whether or not conceptual representations are perceptually based, and the predominance of amodal symbol systems is the result of theoretical considerations and
preconceptions concerning the limitations of modal systems rather than an assessment of a substantial body of
evidence.
An immediate problem with Barsalou’s charge is that
evidence in cognitive science is rarely direct. Barsalou himself follows this charge with the introduction of indirect
evidence supporting perceptual symbols. The requirement
of directness is therefore dubious and should be removed.
The real question is whether or not there is any empirical
support for the existence of amodal symbols. The answer
to this question is that researchers in the cognitive sciences
have, in fact, gathered a great deal of evidence for amodal
symbols. We can see this clearly through an example: research on number approximation.10
6.2. Number approximation
Several different species have been examined for their
ability to make numerical judgments, including dolphins,
pigeons, raccoons, rats, and monkeys (for general summaries of this literature see Flombaum, 2002; Gallistel, 1990;
Hauser, 2000). Sensitivity to numerical properties has been
measured in the wild and in the lab using a number of different research paradigms. In many experiments, researchers have been careful to distinguish between sensitivity to
the relative cardinality of sets from sensitivity to other scalar physical attributes of the stimuli. One reason to think
that a form of numerical competence is involved is the ease
with which animals can transfer numerosity between
modalities (Hauser & Spelke, 2004). A striking example of
this is that rats trained to respond to numerical sequences
in one modality are able to generalize to novel sequences
involving stimuli in other modalities or, even, two modalities (Meck & Church, 1983). A common feature of this research is that number discrimination varies with the ratio
of the two numerosities in accordance with Weber’s law:
that is, in order to obtain the same level of performance
with larger numerical quantities that is obtained with
smaller quantities, the difference between the compared
10
After developing this example, I discovered that Machery (2007) also
appeals to it. I take this convergence as evidence of its aptness.
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G. Dove / Cognition 110 (2009) 412–431
quantities must be greater. In other words, there is typically a numerical distance effect.
Behavioral research on adult humans suggests a similar
capacity. In a common experimental paradigm, adults are
given brief presentations of stimuli containing large cardinalities in order to prevent them from using explicit verbal
counting. Another paradigm involves responses (such as
sequential button presses) at rates that exclude the possibility of vocal or subvocal counting. These studies indicate
that adults are able to represent approximate cardinality
despite not having access to verbal representations. Their
judgments are at above chance and vary in accuracy in proportion to size of the compared sets (Cordes, Gelman, &
Gallistel, 2002; Hauser & Spelke, 2004). As was the case
with the animal studies, there are several reasons to believe that amodal representations underlie this capacity.
One indication is that similar performance has been found
using various types of stimuli presented in various different modalities (Whalen, Gallistel, & Gelman, 1999). Another is that adults are just as successful when
comparing sets across modalities as they are within a
modality (Barth, Kanwisher, & Spelke, 2003; Barth et al.,
2005).
A body of research indicates that pre-verbal infants
have a similar capacity for number approximation. Several
studies have shown that infants as young as 6 months have
the ability to distinguish sets involving 8 vs. 16 or, even, 16
vs. 32 elements when other continuous variables such as
element size and total filled area are controlled for (Lipton
& Spelke, 2003; Xu, Spelke, & Goddard, 2005). It appears
that this ability requires large ratios at first, but becomes
more precise over development (Lipton & Spelke, 2003;
Xu, 2003; Xu & Arriaga, 2007).11 As was true with the adult
studies, these abilities have been shown in experiments
involving different modalities.
A body of evidence from neuropsychology and cognitive
neuroscience provides further support for a number
approximation system. Lesion studies establish a double
dissociation between number processing and semantic
processing. In general, cases in which there is preserved
linguistic and semantic processing but deficient number
processing involve damage to one of several areas of the
parietal cortex (Dehaene, Piazza, Pinel, & Cohen, 2003).
Piazza and Dehaene (2004) argue that previous research
indicates that one area of the parietal cortex in particular,
the HIPS (horizontal segment of the intraparietal sulcus), is
the best candidate for a domain-specific numerical estimation system. Some of their reasons for this claim are the
following: the HIPS is more active during estimation tasks
than those involving accurate computation; activation in
11
There is an ongoing controversy concerning infant number perception
that centers on small number (1, 2, or 3) discrimination. A great deal of
interest was generated by early studies which seemed to indicate that
infants were able to discriminate small numbers (Starkey & Cooper, 1980;
Strauss & Curtis, 1981). This research, though, failed to account for potential
confounds between number and other continuous variables. More recent
studies which have controlled for these factors have found no evidence of
small number discrimination (Clearfield & Mix, 2001; Feigenson, Carey, &
Spelke, 2002,). Interestingly, small number discrimination has been shown
in monkey studies that control for these factors (e.g. Brannon & Terrace,
2000).
the HIPS correlates with numerical distance between compared sets; the HIPS shows higher activation when processing numbers than when processing other continuous
categories such as colors or letters; and stimuli presented
in different modalities can activate the HIPS in number-related tasks. While it is too soon to definitively identify the
HIPS or any other part of the parietal cortex as where number approximation is localized, the results of the imaging
studies are suggestive and fit well with the behavioral results described above.
The existence of amodal symbols for approximate quantities is thus buttressed by a diverse, multi-disciplinary,
and convergent body of research using various research
measurements and methodologies. Pace Barsalou, there is
at least one area of cognition where extensive research
supports amodal symbols.
Two responses to this argument are possible. The first is
that alternative explanations may be available. We should
not rush to conclude that the representations employed in
number approximation are amodal because one could explain this cognitive ability without appealing to extrasensory representations. This response can be cashed out in
one of two ways. One possibility is that number approximation is handled by mapping operations between representations in different modalities (Prinz, 2002). The
evidence outlined above, however, suggests that we are
able to estimate number both within and across modalities. Given this, number estimation cannot be fully explained in terms of a mapping operation between
modalities. Another weakness of this proposal is that it
does not specify the mechanism by which the mapping is
carried out. This is problematic because an effective means
of carrying out such a mapping is to have an amodal symbol system tracking approximate numerosity (Meck &
Church, 1983). A second possibility is that number approximation is handled by perceptual representations within a
single modality. In other words, input from different
modalities could be translated into a representational format indigenous to a particular sensory modality. The trouble with this response is that it actually makes the case for
amodal symbols rather than speaks against them. Recall
that modal-specificity is defined with regard to input. Representations contained within a mechanism that has been
shaped by natural selection to handle inputs from multiple
modalities are amodal by definition.12
The second plausible response to the literature on number approximation is a deflationary one. The evidence only
shows that amodal symbols are used in a single cognitive
domain. Perhaps, concepts generally contain perceptual
symbols, and number approximation is just an exception
to the rule (Machery, 2007). This deflationary move faces
three main challenges: First, it sets foot on a slippery slope
because the difference between it and representational
12
In order to make this defense of perceptual symbols work, one would
need to provide a new, non-circular definition of a perceptual symbol. Not
only would this be suspiciously ad hoc, but it would require making an
already fairly broad definition of a perceptual symbol even broader. Given
the well known existence of top-down influences on perception, there is a
real danger of making every cognitive representation a perceptual one as
matter of definition (Aydede, 1999).
G. Dove / Cognition 110 (2009) 412–431
pluralism is at best a matter of degree. Second, the extant
data provides no clear reason to prefer this deflationary
proposal over representational pluralism since the positive
evidence for perceptual symbols is itself limited in scope.
Given the limited evidence, why should we think that most
concepts are couched in perceptual representations? Third,
there are other cognitive domains that seem to involve
amodal representations. For example, psycholinguists have
long argued that many linguistic representations are amodal. If other domains involve amodal representations, then
we should be open to the possibility of amodal semantic
representations.
While neither of the counter-argument strategies is
particularly effective, two intriguing speculations emerge
from the discussion. The first is that amodal codes may
be a fairly common solution to the problem of information
integration within cognitive systems that receive input
from diverse sources. This proposal is in keeping with the
ever increasing evidence of cross-modal effects (Shimojo
& Shams, 2001). The second is that modality might be, in
the end, a degree property. Some codes may be more closely tied to a particular modality than others. Although I
do not have the space to defend either of these hypotheses
here, both are worth exploring and fit naturally with representational pluralism.
In the end, the literature on number approximation
shows that Barsalou’s assertion that there is little evidence
for amodal symbols is far too strong. A question remains,
though, with regard to the frequency of amodal symbols.
In the next section, I outline a body of evidence that suggests that amodal symbols play a more widespread role
in our concepts.
7. Imageability and the need for representational
pluralism
Part of the appeal of a deflationary interpretation of the
data on number approximation may lie in the fact that it
enables one to avoid pluralism. Admittedly, there are prima facie reasons to be skeptical of pluralistic solutions to
scientific questions. Compromise may be an effective way
to govern, but it is generally not a good research strategy,
and scotch-verdicts are rare in science.13 Furthermore, pluralistic theories tend to be overly flexible and difficult to falsify. Given these inherent drawbacks, pluralism should only
be adopted when there strong reasons to do so. In this section, I will argue that the literature on imageability effects
provides such reasons.
A theme that has emerged in this essay is that there
appears to be a qualitative difference between abstract
and concrete concepts. While some tantalizing evidence
implicates perceptual representations in the latter, proponents of perceptual symbols have failed to provide
compelling reasons to think that they are involved in
the former. There is also positive evidence with regard
13
They are not, however, unheard of. A classic example comes from vision
science: two theories of color vision, the trichromatic and the opponentprocess theories, proposed different basic mechanisms. It turned out that
distinct components of the retina realize each of these mechanisms.
425
to at least one cognitive domain, number approximation,
that some abstract concepts are handled by amodal representations. I propose that the empirical literature on
imageability provides evidence of a further, more general
neurophysiological dichotomy between abstract and
concrete concepts. Converging evidence from cognitive
science, neuropsychology and cognitive neuroscience
supports the conclusion that abstract and perceptually
derived concepts are handled by different representations and mechanisms.14
Imageability effects have been found in multiple disciplines by different investigators using different research
methodologies and measures. Typically, imageability is defined as the ease with which a word gives rise to a sensorymotor mental image (Paivio, 1971).15 Highly reliable
imageability ratings on number scales have been gathered
for linguistic concepts by number of researchers (Bird,
Franklin, & Howard, 2001; Paivio, Yuille, & Madigan, 1968;
Toglia & Battig, 1978). Much of the original research on
imageability was behavioral and demonstrated a processing
advantage for highly imageable concepts in a number of cognitive tasks.16 For instance, lexical access has been shown to
be quicker for highly imageable words than for abstract ones
(Coltheart, Patterson, & Marshall, 1980). Highly imageable
words are also recalled more quickly in memory tasks than
abstract words (Paivio, 1971; Paivio, 1987; Wattenmaker &
Shoben, 1987). A similar advantage is also found in word
comprehension tasks (Schwanenflugel, Harnishfeger, &
Stowe, 1988).
Two major accounts of imageability effects dominate
the literature on imageability: the context-availability theory and the dual code theory. The core idea behind the context-availability theory is that highly imageable words
have greater contextual information stored in semantic
memory networks. Imageability effects are explained by
the facilitation of processing associated with increased
activation in these networks. The reason that participants
respond more quickly in a lexical decision task to a word
such as ‘‘fingertip” than to one such as ‘‘idea” is that the
former has more semantic associations than the latter.
According to the so-called dual code theory (Paivio,
1987), two semantic systems exist, one supported by linguistic representations and the other supported by percep-
14
The imageability literature admittedly implicates different cortical
areas than those implicated by the research on number sense. Clearly, this
is compatible with representational pluralism.
15
Strictly speaking, imageability is a property of lexical concepts rather
than words. However, a convention exists among researchers to refer to
words as having high or low imageability. For the sake of convenience, I
follow this convention in this essay.
16
Some researchers compare concrete and abstract words. Imageability is
a broader concept than concreteness because in addition to including the
perceptual images of concrete objects it includes sensory images of bodily
states and motor images. It is generally recognized that imageability
supports more robust generalizations than concreteness.
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G. Dove / Cognition 110 (2009) 412–431
tual representations.17 Words with low imageability are
associated primarily with verbal representations while
highly imageable words are associated with both linguistic
representations and perceptual ones. Imageability effects
are then explained in terms of the greater availability of perceptually encoded information.
The debate between the context-availability and the dual
code theories has proven to be difficult to settle through
behavioral studies because supporters of each theory can
point to some behavioral evidence. For example, supporters
of the context-availability theory can point to studies that
show imageability effects can be nullified when a rich supporting context is provided (Schwanenflugel & Shoben,
1983; Schwanenflugel et al., 1988). Supporters of the dual
code theory can point to divided visual field studies that show
a concreteness advantage for words presented to the right
hemisphere (Day, 1979; Deloche, Seron, Scius, & Segui,
1987). A further problem is that these theories are not mutually exclusive. The dual code theory, for instance, is compatible
with the existence of context-availability effects. Such effects
are only threatening to the dual code theory if all imageability
effects are reducible to the context-availability effect. This sort
of universal negative claim, however, is difficult to establish.
Recently, investigators have increasingly turned to neuropsychology and cognitive neuroscience in order to resolve this debate. In general, evidence from these fields
supports the notion that there are distinct neural processes
associated with context-availability and imageability effects. Below, I focus on the evidence for the latter because
this evidence is more directly relevant to the issue of representational pluralism.
Within neuropsychology, it has long been observed that
some patients exhibit a processing impairment for verbs,
but not for nouns, and other patients exhibit the reverse
pattern. Researching this noun–verb dissociation is complicated by the fact that nouns and verbs tend to have different semantic properties (Druks, 2002). A number of
studies, for instance, use only names of concrete things
for nouns and actions for verbs. In response to this potential confound, some researchers have examined the degree
to which imageability is a factor in the performance of
aphasic patients. For instance, Bird, Howard, and Franklin
(2003) examined three ‘‘verb-impaired” patients. They
found that when imageability is taken into account, the
purported verb-impairment disappears. Based on this finding, they propose that there are no true verb-selective deficits.18 More recent evidence suggests that many, but not all,
17
Paivio (1986) proposes that the linguistic representations used to
encode semantic content are perceptual (i.e. they are auditory, visual, or
motor representations). I part company with Paivio on this point and
instead propose that the relevant linguistic representations are likely to be
amodal. Paivio’s commitment to perceptual representations is problematic
because there are independent reasons to posit amodal linguistic representations. For example, some aphasia patients exhibit deficits with regard
to meaning related tasks such as providing definitions or object naming
without exhibiting a corresponding deficit with respect to word form
related tasks such as repetition or reading aloud (Caplan, 1987).
18
Bird et al. (2003) also examined three ‘‘verb spared” patients. They did
not find a reverse imageability effect per se but found evidence that these
patients have difficulties with concepts defined in terms of certain sensory
features. This is compatible with the idea that highly imageable concepts
involve collections of sensorimotor representations.
verb deficits are reducible to imageability differences. To
give an example that is consistent with other studies, Crepaldi et al. (2006) examined 16 verb-impaired patients and
found that 14 did not show a verb-impairment after imageability was controlled for (see also Berndt, Haendiges, Burton, & Mitchum, 2002; Luzzatti et al., 2002). The reverse
dissociation, with preserved abilities for abstract words
but a deficit for high imageable words, is attested but less
common. For instance, Marshall, Pring, Chiat, and Robson
(1996) describe a nonfluent patient, RG, who uses a
disproportionate amount of abstract nouns in natural
speech, exhibits better comprehension of abstract nouns
than concrete nouns and performs poorly on object naming
tasks. In a follow up paper, Marshall, Chiat, Robson, and
Pring (1996) provide evidence that RG has similar difficulties with verbs that are distinguished by perceptual features.
In general, the neuropsychological literature suggests that
patients can be selectively impaired for concepts of high or
low imageability, although the latter seems more common
than the former.
A number of electrophysiological experiments employing event-related potentials (ERPs) support a neuroanatomical distinction between concepts of high and low
imageability. Often these experiments involve the elicitation of a specific electrophysiological component known
as the N400 (a negatively directed waveform that tends
to peak at 400 ms after the onset of the stimulus). This
component has been shown to be sensitive to both contextual and semantic manipulations and is likely to be associated with several neurally distinct generators (Key, Dove, &
Maguire, 2005). Several studies have found imageability
effects on the N400 (Kounios & Holcomb, 1994; West &
Holcomb, 2000). Nittono, Suehiro, and Hori (2002), for
example, found that low imageable words elicited a smaller and more left-laterialized N400 than high ones in a
reading task. In an effort to evaluate the claims of the context-availability and the dual code theories, Holcomb,
Kounios, Anderson, and West (1999) created a task that involved a manipulation of both context and concreteness.
ERP recordings were time-locked to sentence final words
in a word-by-word reading task in which participants
made semantic congruency judgments (e.g. Armed robbery
implies that the thief used a weapon vs. Armed robbery implies that the thief used a rose). The researchers found that
sentence final concrete words generated a larger and more
anterior N400 in both neutral and semantically anomalous
sentential contexts. Although it is difficult to precisely
localize the neural generators from electrical potentials recorded at the scalp, the fact that concrete and abstract
words elicited distinct topographic patterns suggests that
they are caused by activity in different populations of
neurons.
Some critics have proposed that this evidence has limited implications with regard to concreteness effects because of the use of a sentential context rather than a
single word presentation. Further studies, though, have
found context-independent topographic effects associated
with imageability in single word presentations (Kellenbach, Wijers, Hovis, Mulder, & Mulder, 2002; Swaab, Baynes, & Knight, 2002). For example, Kellenbach and
colleagues visually presented three subclasses of nouns
G. Dove / Cognition 110 (2009) 412–431
and verbs (abstract, high visual, and high visual and motor)
in the context of a recognition memory task. They found
that grammatical class and imageability were associated
with robust but distinct electrophysiological effects. In
sum, various ERP studies employing diverse tasks support
the notion that different cognitive systems are associated
with the semantic processing of high and low imageable
words.
The evidence from functional brain imaging studies is
somewhat variable, with different studies finding that different patterns of activation are associated with the
semantic processing of high and low imageable concepts.
This may in part be due to the number of different tasks
used. These include, but are not limited to, lexical decision,
imageability judgment, mental imagery, memory encoding, semantic judgment and sentence verification. Despite
the variability in the findings, the idea that neural activity
is modulated by imageability is generally supported. A
number of studies find that abstract words elicit greater
activation in superior regions of the left temporal lobe
(Binder, Westbury, McKiernan, Possing, & Medler, 2005;
Giesbrecht, Gamblin, & Swaab, 2004; Kiehl et al., 1999;
Mellet, Tzourio, Denis, & Mazoyer, 1998; Noppeney & Price,
2004; Perani et al., 1999; Sabsevitz, Medler, Seidenberg, &
Binder, 2005; Wise et al., 2000) and inferior regions of the
left prefrontal cortex (Binder et al., 2005; Fiebach & Friederici, 2003; Giesbrecht et al., 2004; Jessen et al., 2000; Kiehl
et al., 1999; Noppeney & Price, 2004; Perani et al., 1999;
Sabsevitz et al., 2005). When researchers look for areas of
increased activity in response to high imageable words
when compared to low imageable ones, the pattern is less
clear. Whereas some studies find no areas of increased
activation (Grossman et al., 2002; Kiehl et al., 1999;
Noppeney & Price, 2004; Perani et al., 1999; Tyler, Russell,
Fadili, & Moss, 2001), others find increased activation in
right hemisphere areas (Binder et al., 2005; Jessen et al.,
2000; Mellet et al., 1998; Sabsevitz et al., 2005). The fact
that there is a more distinct pattern of increased activation
elicited by low imageable words than by high imageable
words fits with the neuropsychological observation that
patients are more likely to have a selective deficit for low
imageable concepts than for high imageable concepts.
Although I do not have the space to adequately address
the complexities of the imaging data in this essay, two recent experiments are particularly suggestive and worth
discussing. Responding to the inconsistencies in the literature, Sabsevitz and colleagues (2005) attempted to control
for some of the possible confounds. Their fMRI study incorporated a larger sample (28 adults) than previous studies
and a task (judgment of semantic similarity) that is more
likely to elicit deep semantic processing than a more
superficial task such as lexical decision. Participants were
visually presented with three words (e.g. cheetah, wolf,
and tiger) in the form of a triangle. The task was to decide
which of the two bottom words was most semantically
similar to the top word. In this task, abstract nouns elicited
greater activation in the left superior temporal and left
inferior frontal cortex than concrete nouns, while concrete
nouns elicited greater activation in a bilateral network of
association areas than abstract nouns. Given that the left
superior temporal and left inferior frontal cortex have been
427
associated with language processing in previous studies
(Bookheimer, 2002), these results fit well with the dual
code theory.
In an effort to test the context-availability and dual
code theories, Giesbrecht et al. (2004) manipulated both
imageability and semantic priming (a measure of the influence of context) in an event-related fMRI study. Participants were presented with prime word followed by a
target word. The words were either semantically related
(bread and butter) or unrelated (wheat and slipper). In addition, half of the pairs consisted of two high imageable
words and half of the pairs consisted of two low imageable
words. Both of these manipulations modulated activity in
anatomically distinct areas of the left hemisphere. This
study thus provides further support for the notion that
context effects are distinct from imageability effects.
Current evidence from cognitive neuroscience does not
give us an unequivocal picture of how the lexical properties of high and low imageable words are represented in
the brain. Many questions remain, and further research is
needed to resolve conflicting results, disentangle possible
confounds, and adjudicate outstanding theoretical issues.
Despite the somewhat inchoate state of the field, however,
the general hypothesis that distinct brain systems process
high and low imageable concepts is supported by a diverse
collection of behavioral, clinical, electrophysiological, and
functional imaging studies.
The functional distinction between concepts of high and
low imageability implied by this body of evidence creates a
serious problem for supporters of perceptual symbols because the strongest empirical evidence for their position
involves highly imageable concepts. Research on imageability undermines their project because, if there are distinct cognitive mechanisms for processing high and low
imageable concepts, then we cannot infer that one system
uses perceptual representations from evidence that the
other system uses them.
Recently, Barsalou, Santos, Simmons, and Wilson (2008)
offer a variant of the dual code theory. They propose that
the imageability literature supports the existence of two
modal-specific systems of knowledge representation: one
employing linguistic representations and the other
employing situated simulations. They refer to this as the
LASS (language and situated simulation) theory of conceptual processing. There is a temporal dimension to this theory. Although conceptual processing involves a continuous
interaction between these two systems, the more superficial linguistic processing tends to predominate early on
and the deeper processing associated with the simulation
system tends to predominate later. The key difference between this version of the dual code theory and a pluralistic
one is its commitment to the modal-specificity of linguistic
representations. Barsalou et al. (2008) are very clear on this
point:
According to this approach, there is no underlying
system of amodal symbols that correspond to language
– there are only linguistic forms (i.e. words). The
intriguing proposition is that statistical distributions
of linguistic forms represent knowledge. For example,
the representation of bird is not an amodal symbols
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G. Dove / Cognition 110 (2009) 412–431
but is instead the distribution of words that co-occur
with ‘‘bird” in natural language.
This amounts to a partial adoption of Prinz’s labeling
strategy because some semantic processing involves associations between perceptual representations of external labels. The novel aspect of this theory is that linguistic
representations are only involved in superficial processing.
They act as pointers to potentially relevant perceptual simulations that then perform the heavy lifting of conceptual
processing.
The appeal to language forms has a number of problems.
First, there are a number of independent reasons to think
that the some of the representations of language forms
themselves are amodal. Psycholinguists have implicated
amodal representations at many levels of linguistic analysis, including phonology, morphology and syntax. For
example, amodal phonological representations are often
posited to explain the fact that phonological generalizations
hold with respect to both speech production and comprehension. While it is possible that all of the relevant information is encoded redundantly in both motor and auditory
codes, the existence of amodal representations provides a
parsimonious explanation of how auditory and motor information is integrated. Similar considerations apply to morphology. Furthermore, morphology involves properties
such as agreement that do not seem tied to any particular
perceptual modality. Syntax correspondingly employs abstract grammatical categories and constructions that apply
equally to language production and comprehension. The
case for amodal language representations is further bolstered by evidence that natural sign languages exhibit similar structure to natural spoken languages at all of these
levels of analysis (Poizner, Klima, and Bellugi, 1987). Brain
imaging research also finds increased activation in speech
processing areas when profoundly deaf individuals view
signs (Petito et al., 2000). For the appeal to language forms
to work as a defense of perceptual symbols, one must show
that the phonological, morphological, and syntactic generalizations at the heart of psycholinguistics can be captured
in an empirically plausible way by a system employing only
modal representations. Whether this can be achieved remains to be seen. Without this demonstration, though, LASS
accomplishes little more than exchanging one controversial
modal-specificity hypothesis for another.
A further problem with the appeal to language forms is
that it faces the same challenges with respect to polysemy and synonymy that Prinz’s labeling strategy faces.
As we saw earlier, excluding an independent level of
semantic representations has clear costs. Additionally, a
robust body of ERP literature suggests that distinct syntactic and semantic processing begins almost immediately
after a word stimulus is presented in the context of a sentence. While semantic incongruency is associated with
the N400 (a negative deflection in the brainwave that
peaks at around 400 ms), grammatical violations are associated with both the ELAN (an early left anterior negativity that typically occurs between 100 ms and 300 ms),
and the P600 (a positive shift that tends to be largest at
600 ms; Friederici, 2002). Finally, several lines of evidence
within cognitive neuroscience suggest that phonological,
syntactic and semantic processes are handled by distinct
portions of the left inferior frontal gyrus or IFG
(Bookheimer, 2002).
There is a clear affinity between the pluralistic explanation of imageability effects that I favor and the LASS explanation. Both explanations hold that perceptual simulations
play an important role in highly imageable concepts and
linguistic representations play an important role in abstract concepts. Where the two approaches differ is with
respect to how they view linguistic representations. On
the LASS view, linguistic representations are purely modal
and there is no independent level semantic representation.
Neither of these claims is well supported by the extant
psycholinguistic or cognitive neuroscience evidence.
8. Conclusion
A revolution is occurring in cognitive science. Researchers are beginning to recognize that the orthodox distinction between perception and conception is no longer
tenable. Part of the reason for this revolution is an emerging body of evidence that suggests that some semantic
information is perceptually encoded. A question that remains is whether or not any semantic information is encoded by amodal representations. In this essay, I have
defended a form of representational pluralism that posits
perceptual and amodal semantic codes. This defense has
negative and positive aspects. On the negative side, I have
argued that the empirical evidence cited in support of perceptual symbols is fundamentally circumscribed. It is compelling with respect to concrete or highly imageable
concepts but has limited reach with respect to abstract
concepts. I have also argued that the general arguments offered in support of perceptual symbols are unconvincing.
Neither the argument from parsimony nor the argument
from intentionality provides compelling support for the
view that our concepts are generally grounded in perception. On the positive side, I have argued that theoretical
considerations and a growing body of empirical evidence
suggest that amodal symbols are used to represent aspects
of abstract concepts. Research on number approximation
and imageability strongly suggest that amodal symbols
play an important role in some of our concepts.
Acknowledgements
I have benefited greatly from discussions with Murat
Aydede, Cara Cashon, Julia Chariker, Mandy Maguire, John
Pani, and Jesse Prinz. A section of this paper was presented
at the 33rd annual meeting of the Society for Philosophy
and Psychology, Toronto, 2007, and I am grateful for the
questions and suggestions provided by participants. I also
thank Larry Barsalou, Arthur Glenberg, and an anonymous
reviewer for their helpful comments on previous versions
of this paper.
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