1
2
Can generic expertise explain
special processing for faces?
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3 Elinor McKone , Nancy Kanwisher and Bradley C. Duchaine
4 1School of Psychology, Australian National University, ACT 0200, Australia
5 2Department of Brain and Cognitive Sciences and McGovern Institute for Brain Research, Massachusetts Institute of
6 Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA
7 3Institute of Cognitive Neuroscience, University College London, 17 Queen Square, London WC1N 3AR, UK
8 Corresponding author: McKone, E. ([email protected]).
9 Does face recognition involve face-specific cognitive and 59 how experience affects object recognition; understanding
10 neural processes (‘domain specificity’) or do faces only 60 these effects is important but orthogonal to the
11 seem special because people have had more experience of 61 hypothesis, except where putatively face-specific
12 individuating them than they have of individuating 62 properties are tested. Also note the explicit [5] or implicit
13 members of other homogeneous object categories (‘the 63 [6] assumption of the hypothesis that expertise leading to
14 expertise hypothesis’)? Here, we summarize new data that 64 special face-like processing can occur at any age; it is not,
15 test these hypotheses by assessing whether classic face- 65 for example, limited to experience obtained in childhood or
16 selective effects – holistic processing, recognition 66 infancy.
17 impairments in prosopagnosia and fusiform face area 67 The crucial prediction of the expertise hypothesis is
18 activation – remain face selective in comparison with 68 that, in the rare circumstances where someone has trained
19 objects of expertise. We argue that evidence strongly 69 to become a perceptual expert in another domain (e.g. a
20 supports domain specificity rather than the expertise 70 dog-show judge), then faces should no longer be unique.
21 hypothesis. We conclude that the crucial social function of 71 Instead, the hallmarks that usually differentiate face
22 face recognition does not reflect merely a general practice 72 processing from object processing should also emerge for
23 phenomenon and that it might be supported by evolved 73 objects of expertise.
24 mechanisms (visual or nonvisual) and/or a sensitive period
74 Faces versus objects of expertise: holistic processing
25 in infancy.
75 In evaluating this prediction, first we consider behavioural
26 Introduction
76 studies of holistic processing (see Glossary). In novices, it
27 How are faces recognized? In particular, are the cognitive 77 is accepted that face and object processing dissociate in
28 and neural processes that are used for identifying faces 78 several classic paradigms, illustrated in Figure 1. Early
29 the same as or different from those that are used to 79 research indicated that the inversion effect is much more
30 recognize other objects? Evidence has shown that they can 80 severe for faces than for other object classes, even when
31 be different, with faces processed in a more holistic or 81 the tasks are matched and require within-class
32 configural fashion than objects [1–3] and preferentially 82 discrimination [7]. This difference was attributed to
33 activating the cortical region known as the fusiform face 83 upright faces being processed holistically, and inverted
34 area (FFA) [4]. Recently, debate has centred on whether 84 faces and objects (in both orientations) being processed in
35 face processing is always different from object processing 85 a parts-based fashion. The disproportionate inversion
36 in these respects (referred to as ‘domain specificity’) or 86 effect does not demonstrate this directly. Direct
37 whether visual processing of faces only seems to be special 87 demonstration was subsequently provided by two
38 because people have greater expertise in individuating 88 paradigms. In the part–whole effect [2], memory for a face
39 faces than in performing within-class discrimination of 89 part is much more accurate when that part is presented to
40 other object classes (‘the expertise hypothesis’). The 90 subjects in the whole face than when it is presented alone;
41 primary aim of this Opinion article is to summarize key 91 in the composite effect [3], aligning two half faces of
42 new evidence from multiple approaches – behavioural 92 different individuals increases reaction times (or decreases
43 studies, neuropsychology, brain imaging and monkey 93 accuracy) for tasks that require perception of either half
44 single-unit recording – that we argue strongly favours face 94 independently, compared with an unaligned condition. For
45 specificity over expertise.
95 upright faces, these effects are strong; for inverted faces,
96 they are absent; and for objects, in novices, they are weak
46 What is the expertise hypothesis?
47 The expertise hypothesis [5] attributes putatively face- 97 (part–whole) or absent (composite) (Figure 1).
48 specific processing to form-general mechanisms that can 98 Are these classic hallmarks of face processing found for
49 potentially apply to all objects; these mechanisms are 99 objects of expertise? Figure 1 illustrates results from all
50 restricted to faces in most people only because the typical100 available studies. We argue that the results favour face
51 human adult is highly practised at identifying individual 101 specificity. Objects of expertise are processed in the same
52 faces (e.g. Mary versus Jane) but is poor at discriminating102 way as objects in novices and not in the same way as faces.
53 members of other object classes (e.g. two Labrador dogs).103 One exception to this general rule is presented by
54 Importantly, the hypothesis is a specific proposal about104 Diamond and Carey [5], who found that dog experts
55 the cause of ‘special’ processing for faces (holistic105 looking at their breed of expertise showed as large an
56 processing and a face-specific, distinct neural substrate); it106 inversion effect as they did for faces. This highly cited
57 is not merely a statement of the uncontroversial fact that107 finding has had an extensive influence on the field.
58 experience influences perception. Nor is it a theory about108 However, in the 20 years since its publication, no
1
1 replication of the finding has appeared in the literature.
2 Instead, Figure 1 shows that inversion effects increase
3 only slightly with expertise for a wide range of object
4 classes and expert types. In a recent study [1], we used the
5 original Diamond and Carey procedure – dog experts of 20
6 years’ experience looking at side-on photographs of their
7 breed of expertise – and failed to replicate the original
8 result. Instead, we found no difference between experts
9 and novices for the dog inversion effect. (We suspect the
10 original finding could have been due to experts being
11 familiar, before the experiment, with the dogs tested,
12 which would provide an artificial boost to memory in the
13 upright orientation.)
14 More direct measures of holistic processing confirm
15 face-like holistic processing does not occur for objects of
16 expertise. Figure 1 shows that the small part–whole effect
17 for objects is no stronger among experts than among
18 novices, and experts do not show a composite effect for
19 objects, including dog experts who are looking at their
20 breed of expertise. The ‘part in original whole’ versus ‘part
21 in feature-spacing-altered whole’ version of the part–whole
22 paradigm also shows no greater sensitivity to spacing
23 changes among experts than among novices (see Ref. [1]
24 for a review). Furthermore, we have argued elsewhere
25 [1,8] that a non-standard task that is claimed to show
26 holistic processing by experts [9] merely measures the
27 inability to ignore competing response cues from
28 notionally irrelevant information (as in the Stroop effect),
29 rather than integration of parts into a whole at a
30 perceptual level.
31 In summary, substantial evidence indicates that face32 like holistic processing does not emerge for objects of
33 expertise. These results are contrary to the core prediction
34 of the expertise hypothesis.
65 standard resolution had conflated faces and bodies.
66 Furthermore, in monkeys, a recent study using the
67 ultimate high-resolution method – single-unit recording
68 within a face-selective patch in monkey cortex – found
69 that 97% of visually responsive neurons in this region
70 were strongly face selective (Figure 2).
71 The expertise hypothesis predicts that the FFA should
72 be more strongly engaged by objects of expertise than by
73 control objects. Eight studies have tested this prediction.
74 Three report small but significant increases in responses
75 to objects of expertise compared with control objects in the
76 FFA [15,16] or a larger region centred around the FFA
77 [17], two report nonsignificant trends in this direction
78 [18,19] and three report no effect [10,20,21]. Controversy
79 has surrounded the implications of these findings. We
80 argue that the weakness and unreliability of the effects is
81 problematic for the expertise hypothesis. The account we
82 favour is that the effects do not reflect a special role for
83 the FFA in processing objects of expertise but rather an
84 overall increased attentional engagement for these
85 stimuli. For example, car fanatics pay more attention to
86 car stimuli than to other objects, thus elevating neural
87 responses to objects of expertise (which produce a small
88 response in the FFA even in nonexperts; see earlier in this
89 section). Five studies have provided data bearing on the
90 prediction of the attentional explanation that expertise
91 effects for objects should be at least as large in other
92 cortical regions as in the FFA. All five report larger effects
93 of expertise outside the FFA than within it. This includes
94 locations throughout the fusiform [18], parahippocampal
95 cortex (see Figure 6 in Ref. [15]) and the lateral occipital
96 complex, a cortical region near the FFA that is involved in
97 processing object shape, in the three studies that have
98 included localizers for this region [19–21]. Consistent with
99 an attentional explanation is the finding that correlations
35 Faces versus objects of expertise: neural substrates
100 between the FFA response to objects of expertise and
36 The second question is whether identification of faces and
101 behaviourally measured expertise have been shown in
37 objects of expertise engage common or distinct neural
102 location-discrimination tasks but not in identity38 substrates.
103 discrimination tasks [10,15], contrary to predictions of the
39 In neuropsychological lesion studies, face recognition
104 expertise hypothesis. Overall, the data provide no
40 can be damaged independently of object-of-expertise
105 evidence for the special relationship between expertise
41 recognition, and vice versa (Box 1). We argue that this
106 and the FFA predicted by the expertise hypothesis.
42 unequivocally supports face specificity.
107 Instead, fMRI studies are more consistent with the
43 Turning to brain imaging (fMRI) studies, the site of
108 alternative hypothesis that experts pay more attention to
44 primary interest is the FFA, for several reasons. (i) In
109 their objects of expertise, with corresponding increases in
45 novices, the FFA responds at least twice as strongly to
110 the response of multiple extrastriate regions.
46 faces as to other object classes [4,10]. (ii) Its location is
111 Finally, we consider the single-unit recording approach
47 consistent with the critical lesion site for loss of face112 in monkeys. In this case, there are no direct tests of the
48 recognition ability. (iii) It reflects two of the classic
113 expertise hypothesis, in terms of studies that directly
49 behavioural markers of face processing – greater
114 contrast responses for faces versus objects of expertise.
50 sensitivity to differences between individual upright faces
115 The most relevant data come from tests of bodies and
51 than differences between inverted faces [11], and holistic
116 hands, stimuli for which monkeys have had the same
52 processing [12] – which suggests it is a locus of face117 opportunity, and perhaps more motivation [22], to develop
53 specific processing, measured behaviourally. Other face118 expertise as they have for faces. Neurons in the monkey
54 selective regions (the occipital face area and the superior
119 middle face patch [23] do not respond to these stimuli
55 temporal sulcus) are not detectable in all subjects and
120 (Figure 2). The point that monkeys, and humans, do not
56 seem to perform different functions [13]. Although the
121 develop expertise in recognizing conspecifics (members of
57 FFA responds selectively to faces, it does produce an
122 their own species) based on these stimuli is an important
58 above-baseline response to nonface objects in novices
123 argument in favour of domain specificity, to which we
59 [4,10]. This might arise in part because limits in the
124 return later.
60 spatial resolution of fMRI can conflate adjacent functional
125 To summarize, we argue that there is clear evidence of
61 regions (each voxel sums activity over hundreds of
126 different neural substrates for faces and objects of
62 thousands to millions of neurons). Recent scans at high
127 expertise based on neuropsychological cases, and
63 resolution have indicated distinct regions selective for
128 consistent evidence from fMRI and single-unit recording.
64 faces and for bodies [14], whereas earlier results at
2
1 In the three studies that reported small expertise effects 64 body parts. Neural substrates supporting body and hand
2 in the FFA, evidence suggests that these effects arise from 65 recognition also differ from those supporting face
3 attentional confounds.
66 recognition [4,14,23,36,37].
67 Fourth, a genetic component is implicated in some cases
4 But isn’t there other evidence for the expertise hypothesis?
68 of developmental prosopagnosia – that is, it seems to run
5 We now briefly describe, and discard, two other arguments
69 in families [38].
6 that are sometimes made to support the expertise
7 hypothesis. The first concerns development of face 70 Explanatory theories
8 recognition in children. Early evidence claimed that 71 So, what is the origin of special processing for faces?
9 children needed ten years of experience of faces to develop 72 Clearly, it is not generic expertise: if it were, then objects
10 the hallmarks of adult holistic processing (see Ref. [24]). 73 of expertise should be processed in the same way as faces,
11 This was taken as strong support for the expertise 74 and they are not. Instead, some variant of face specificity
12 hypothesis [5] (although, logically, late emergence could 75 is implicated, given evidence that the adult visual system
13 reflect maturational processes). However, this early 76 contains specific mechanisms that are tuned to faces as a
14 evidence was rapidly refuted. All the classic holistic effects 77 structural form.
15 of faces have now been demonstrated in children as young 78 We suggest two general possibilities, which differ in
16 as four years, including the inversion effect [24], the 79 whether they include an innate representation of face
17 composite effect [25], the part–whole effect [26] and 80 structure. Within an ‘experience-expectant innate
18 sensitivity to exact spacing between facial features [27]. 81 template’ theory, we propose that four components would
19 There is even evidence that these effects can be 82 be necessary to explain the major extant findings. First,
20 quantitatively mature in early childhood [26,28]. Seven- 83 an innate template would code the basic structure of a face
21 month-old babies also show holistic-processing effects [29]. 84 (e.g. this might take the form of eye blobs above nose blob
22 Thus, developmental results do not provide support for the 85 above mouth blob, as in the Morton and Johnson
23 expertise hypothesis. (The early emergence of holistic face 86 CONSPEC theory [39]). Second, the template must
24 processing also disposes of the idea that experts might 87 provide the developmental impetus not just for good face
25 show face-like processing for objects if they were ‘more’ 88 recognition [39] but also for the emergence of holistic
26 expert: if babies and young children show clear effects for 89 processing and the grouping of face-selective neurons seen
27 faces, then surely the ten or more years of experience 90 as the FFA in adults. Third, the activation of the template
28 should be sufficient for significant effects to emerge.)
91 must rely on appropriate input during a sensitive period
29 Second, some have argued in favour of the expertise 92 in early infancy, without which it would no longer
30 hypothesis because face recognition is sensitive to 93 function. Fourth, following a typical infancy, the coding of
31 experience. For example, holistic processing is affected by 94 face structure must remain general enough to enable
32 race of the face [30] and by training with other-race 95 holistic processing to be applied to initially
33 individuals [31], and FFA activation is sensitive to race 96 nonexperienced subtypes of faces after practice (e.g. other34 [32]. However, such findings are not evidence that 97 race faces), but must be permanently tuned to the upright
35 learning has taken place within a generic expertise 98 orientation of faces; this is supported by evidence that
36 system. The effects are consistent with tuning within face- 99 adults cannot learn holistic processing for inverted faces
37 specific mechanisms.
100 (Figure 3). This theory proposes that a face template has
101 developed through evolutionary processes, reflecting the
38 Other important facts about face recognition
102 extreme social importance of faces. At the same time, the
39 Several other facts about face recognition will be
103 visual system has maintained an independent and more
40 important for the development of a detailed domain104 flexible generic system suitable for recognizing any type of
41 specific theory.
105 object (including objects that are recent in evolutionary
42 First, exposure to faces in early infancy is essential to
106 timescales). This theory is consistent with the results we
43 develop holistic processing. People born with dense
107 have reviewed. We also know of no results inconsistent
44 bilateral cataracts blocking all pattern vision input who
108 with it.
45 have them removed at 2–6 months of age show no
109 A second variant is that domain specificity for faces is
46 composite effect at 9–23 years, despite substantial post110 due entirely to biased exposure to faces in early infancy
47 cataract exposure to faces [33]. Revealingly, deficits arise
111 that arises from some factor other than an innate face
48 with deprivation to the right but not the left hemisphere
112 template. This ‘infant experience plus other factor’ theory
49 [34].
113 would explain the evidence that holistic processing is
50 Second, six-month-olds can discriminate individual
114 restricted to (upright) faces in adults by arguing that faces
51 monkey faces but nine-month-olds, like adults, have lost
115 are the only homogeneous stimuli for which individual52 this ability [35]. This loss of an initial ability with
116 level discrimination is practised during the sensitive
53 nonexperienced face types, rather than just improved
117 period; importantly, the mechanisms supporting this
54 ability for experienced types, is similar to the loss of initial
118 expertise in the infant brain would be necessarily different
55 ability seen in language for discriminating nonexperienced
119 from those supporting general object expertise in the adult
56 phonemes.
120 brain. This theory can explain many of the other findings
57 Third, all typically developing humans choose to
121 reviewed earlier in this article. For example, heritability of
58 individuate conspecifics based on the face, rather than
122 developmental prosopagnosia could arise if there is a
59 some other body part. Despite extensive opportunity to
123 genetic abnormality in the ‘other factor’, rather than in a
60 develop expertise with, for example, hands or body shape,
124 face template. We have no clear idea what the other factor
61 adults fail to do so, remaining poor at identifying these
125 might be, but possibilities include: faces being presented
62 stimuli compared with faces – the classic observation is
126 close enough to infants so they are in focus more often
63 that bank robbers cover their faces rather than cover other
127 than other stimuli; preference for stimuli that have more
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12 Concluding remarks
13 Resolution of the debate about whether faces are ‘special’ 84
85
14 is of substantial theoretical importance. In psychology, 86
15 researchers need to know why faces have special status in 87
16 regard to crucial social interactions (e.g. parent–infant 88
17 attachment). There could be no role for critical early 89
90
18 infancy effects [33,42] or an evolved representation of face 91
19 structure [39] if face recognition reflected merely a generic 92
20 practice phenomenon. Similarly, researchers who are 93
94
21 attempting to understand the computational principles of 95
22 face recognition need to know whether models, 96
23 particularly of the holistic aspect of face recognition, must 97
24 be general enough to be applicable to any structural form 98
99
25 or whether they can be limited to the (presumably100
101
26 simpler) case of the structural form of faces.
27 In this article, we have argued that a clear resolution of102
103
28 the debate is implied by the data. Converging evidence104
29 from four approaches shows that cognitive and neural105
30 mechanisms engaged in face perception are distinct from106
31 those engaged in object perception, including objects of107
108
32 expertise.
109
33 We have proposed two variants of a domain-specificity 110
34 theory. To discriminate between these, we suggest future111
112
35 research
should
concentrate
on
developmental 113
36 prosopagnosia and typical infancy. In developmental114
37 prosopagnosia, understanding patterns of face versus115
38 ‘other factor’ problems in the disorder should cast light on116
117
39 whether there is an innate face representation. Patterns of118
40 inheritance and genes are also of great interest. With119
41 respect to typical infancy, an innate face template predicts120
42 that an infant monkey preferentially exposed to, for121
122
43 example, dogs or inverted faces would fail to learn holistic123
44 processing for those stimuli and could still develop holistic124
45 processing only for upright faces. By contrast, if early125
126
46 experience alone is the key factor, it should be possible for127
47 infants to learn holistic processing for nonface objects.128
129
48 Questions for future research are outlined in Box 2.
130
49 Acknowledgements
50 Supported by grants ARC DP0450636 (E.M.), EY13455 (N.K.) and ESRC RES-061-131
51 23-0040 (B.C.D.). We thank Romina Palermo for part–whole stimuli in Figure 1 132
52 and Chris Baker, Lucia Garrido, Gillian Rhodes, Rachel Robbins and Doris Tsao133
134
53 for comments on the manuscript.
135
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Sergent, J. and Signoret, J.L. (1992) Varieties of
functional deficits in prosopagnosia. Cereb. Cortex 2, 375–388
52
Assal, G. et al. (1984) Nonrecognition of familiar
animals by a farmer: zooagnosia or prosopagnosia for animals.
Rev. Neurol. (Paris) 140, 580–584
53
Moscovitch, M. et al. (1997) What is special about
face recognition? Nineteen experiments on a person with visual
object agnosia and dyslexia but normal face recognition. J.Cogn.
Neurosci. 9, 555–604
54
McNeil, J.E. and Warrington, E.K. (1993)
Prosopagnosia: a face-specific disorder. Q. J. Exp. Psychol. 46A, 1–
10
55
Duchaine, B.C. et al. (2004) Normal greeble learning
in a severe case of developmental prosopagnosia. Neuron 43, 469–
473
65 Glossary
66 Holistic or configural processing: empirical evidence in standard behavioural paradigms (Figure 1) indicates that faces are recognized using a different style of
67 computation from objects. The difference is not precisely understood, but it is established that, in comparison to objects, processing for faces involves (i) a stronger
68 and mandatory perceptual integration across the whole (in one theory, the mechanism does not decompose faces into smaller parts [2]) and (ii) a more precise
69 representation of the ‘second-order’ deviations from the basic (‘first-order’) shape, including precise spatial-relational information (e.g. distance from corner of left
70 eye to tip of nose) and precise feature shape [11]. This computational style is referred to as holistic or configural processing (terminology differs among researchers),
71 notwithstanding the use of these same terms to refer to something less stringent in other areas of vision science (e.g. the general processing of global structure that
72 occurs in context and gestalt effects) and cognitive psychology (e.g. field dependence).
73 Inversion effect: performance decrement for upside-down stimuli compared with upright stimuli.
74 Level of expertise: novices might have general familiarity with an object class, in its usual upright orientation, but are poor at telling members of an object class apart
75 (e.g. 20 upright Labrador dogs will all look much the same to a novice). Experts have good within-class discrimination for an object class. Most studies test real-world
76 experts (e.g. dog-show judges [5]) who have 5–30 years of experience. Some studies use 8–10 hours of laboratory training with greebles, a class of novel animal-like
77 objects [6].
78 Prosopagnosia: a severe deficit in recognizing faces following brain injury (acquired) or through failure to develop the required mechanisms (developmental). In pure
79 cases, most probably arising from localized lesions or localized developmental irregularities, the disorder manifests without object-recognition deficits.
5
1 Box 1. Neuropsychological evidence of independent neural substrates for faces and objects of expertise
2 It is generally agreed that prosopagnosia without object agnosia and object agnosia without prosopagnosia can occur, even when tasks are
3 matched to require within-class discrimination for both faces and objects (see Ref. [36]). With respect to the expertise hypothesis, the question
4 is whether the face–object dissociation still holds when the objects are objects of expertise. The expertise hypothesis predicts that ability to
5 recognize objects of expertise should always track ability to recognize faces (e.g. if one is damaged, both should be damaged), whereas the
6 face-specificity view predicts that objects of expertise should track other objects and dissociate from faces.
7 The evidence supports the face-specific view. Some individuals who have prosopagnosia show relatively pure face deficits but excellent
8 recognition of objects of expertise. For example, following an aneurysm, RM had extremely poor face recognition but retained his expertise
9 with cars, recognizing far more makes, models and years than controls recognized [51]. Figure I shows results from two similar cases. The
10 converse pattern has also been reported; that is, normal face recognition but impaired recognition of former objects of expertise. Cases include
11 MX, a farmer who could recognize faces but who could no longer recognize his cows [52], and CK, who retained perfect face recognition but
12 lost interest in his toy-soldier collection, which numbered in the thousands [53]. No cases have been reported in which recognition of faces and
13 objects of expertise have both been impaired while recognition of nonexpert objects is unimpaired, or vice versa.
14
(a)
Recognition memory
Picture-name learning
Percentage correct
100
80
60
40
20
0
Faces
Sheep
Prosopagnosic WJ
Naming
famous
faces
(b)
Matching
novel
faces
Faces
Sheep
Sheep-experienced controls
CMFT
Name
verification Naming
Percentage correct
100
80
60
40
20
0
Faces
Edward
Greebles
Six controls
15
16
17 Figure I. Two cases showing that people who have prosopagnosia can become experts with other objects. (a) Acquired prosopagnosic WJ retired following vascular
18 episodes and acquired a flock of sheep. Two years later, his recognition of individual sheep was as good as similarly sheep-experienced controls, despite extremely
19 poor human face recognition [54]. (b) Developmental prosopagnosic Edward demonstrated severe face-recognition problems on three tasks [naming famous faces,
20 matching novel faces and the Cambridge Face Memory Test (CFMT), which assesses memory for novel faces across changes in view], despite a lifetime of exposure
21 to faces. However, in a training study, Edward learned to identify individual greebles at the same rate as controls, in terms of accuracy and reaction time; scores
22 shown are accuracy in the last two blocks of training [55]. Both cases are consistent with independent neural substrates for face recognition and expertise with other
23 objects.
TRENDS in Cognitive Sciences
24 Box 2. Questions for future research
25 • What are the patterns of deficit in developmental prosopagnosia (e.g. severity of disorder; face detection versus identity versus expression
26
problems) and how do these relate to neural and genetic abnormalities?
27 • Do infant animals that have been brought up with atypical stimulus exposure patterns – for example, inverted rather than upright faces, or
28
non-conspecifics – develop holistic processing for those stimuli? (Ethically, these studies cannot be conducted in humans because of the
29
possibility of interference with normal development of upright face processing.)
30 • In developmental prosopagnosia, is there a common deficit in a nonface factor that might normally draw newborns’ attention to faces (e.g.
31
attention to mother’s voice)?
32 • What are the computational or coding advantages of closely packing face cells into a common cortical location?
33 • How face-like does a stimulus have to be to activate face-specific cognitive and neural mechanisms?
34 • What processes of neural development produce the adult FFA?
35 • Do the different face-selective regions differ from each other functionally and are any of these regions homologous across humans and
36
monkeys?
37 • Computationally and neurally, what might a face ’template’ look like and how would it perform holistic processing?
38
6
1
(a) Inversion effect
Upright–inverted difference
Recognition memory
%
*
*
*
10
*
NS
15
75
*
50
*
NS
NS
0
Simultaneous
matching
(vi) Dogs
Face–print
classification
(vii) Finger%
prints
*
10
Objects - experts
5
5
NS
(b) Part–whole effect
10
*
25
5
0
0
NS
Sequential matching
d’
1.5
(viii) Cars
d’
(ix) Birds
1.5
*
NS
1.0
NS NS
0.5
NS
0
% (v) Cars
NS
NS
10
Faces
(iii) Handwriting
(ii) Dogs
*
20
%
Objects - novices
(i) Dogs
Sequential matching
RT
(ms) (iv) Greebles
1.0
*
0.5
*
0.0
0
NS
0.0
All panels show whole–part difference in recognition memory
Learn: Jim
%
Test:
Which is Jim's...
20
face (whole)
10
(ii) Dog
faces
(i) Cars
(iii) Biological
cells
(iv) Greebles (v) Greebles (vi) Greebles
d’
1
*
NS
*
*
NS
0
NS
NS
NS
*
*
eyes (part)
NS
NS
*
NS
NS
0
(c) Composite effect
Name one half...
Unaligned–aligned difference
(for accuracy; reverse for RT)
Unaligned
% (i) Dogs
6
*
4
2
0
–2
NS
NS
(ii) Inverted
dogs and
faces
Aligned
RT
(ms) % (iv) Greebles
150 6
% (iii) Greebles
6
RT
(ms)
150
RT
(ms) (v) Greebles
150
100
4
100
100
2
50
2
50
50
0
0
0
0
0
4
–2
NS
–50 –2
–50
–50
TRENDS in Cognitive Sciences
2
3
4
5 Figure 1. No holistic processing for objects of expertise. (a) Inversion effects [7] for homogeneous objects increase little with expertise and do not become face-like,
6 even in a recent direct replication (see (ii) and (vi); data taken from Ref. [1]) of the classic Diamond and Carey experiment using dogs (see (i); data taken from Ref. [5]).
7 (Instead, in most studies, experts improve relative to novices for both upright and inverted stimuli, which suggests expertise in part-based processing.) Data taken
8 from Ref. [43] in (iii), Ref. [44] in (iv), Ref. [16] in (v), Ref. [45] in (vii) and Ref. [15] in (viii) and (ix). (b) The part–whole effect [2] does not increase with expertise and
9 does not become face-like; unlike inversion, this task assesses holistic processing directly. Data taken from Ref. [46] in (i)–(iii), from Ref. [6] in (iv), from Ref. [47] in (v)
10 and from Ref. [48] in (vi). (c) In another direct test of holistic processing, the composite effect [3] is not found for objects of expertise, in contrast to strong effects for
11 upright faces. The two double-panel plots in (iii) and (iv) show cases where both accuracy (%) and reaction time (RT) were reported. Data taken from Ref. [1] in (i) and
12 (ii), from Ref. [47] in (iii) and (iv), and from Ref. [6] in (v). Some studies measured signal-detection discriminability (d’). Abbreviations: *, p < 0.05; NS, p > 0.05.
13 Statistical symbols within bars refer to comparison to zero; symbols above bars refer to comparison between conditions; missing bars or statistics indicate
14 information not tested or not reported in the original study.
15
7
Mean response
0.5
0.4
0.3
0.2
0.1
0.0
Monkey 1
0 .5
0.4
0.3
0.2
0.1
0.0
–0.2
Monkey 2
Faces Bodies Fruits Gadgets Hands Scram
1
2
3 Figure 2. Responses from cells in the macaque middle face patch, located using fMRI by a standard faces-versus-objects localizer task, as used in humans. Averaged
4 responses from all visually responsive cells in two laboratory-raised monkeys (monkey 1, 182 cells; monkey 2, 138 cells) to 96 images of human faces, human bodies,
5 fruits, gadgets, human hands and scrambled patterns (16 images per category). All cells were highly responsive to faces; averaged responses to other categories
6 were extremely weak, including bodies and hands with which the monkeys had as much experience as faces. Figure adapted, with permission, from Ref. [23].
7
Inverted
–135
–90
–45
0
45
90
135
180
Upright
9
8
7
6
5
4
3
2
1
–180
Rated strength of face percept
(a) Difficult-to-see Mooney face (hundreds of trials)
Orientation (°) away from upright
(b) Learning identical twins (thousands of trials)
Aligned
Unaligned
Composite test:
Name one half...
Ruth
Liz
Training (eight hours):
Each learned in
seven views
Ruth
...
Unaligned
Percentage correct
Aligned
Liz
80
NS
*
70
60
50
Upright
Inverted
8
9
10 Figure 3. No learning of holistic processing for inverted faces. Both methods illustrated isolate the holistic contribution to face recognition by minimizing the
11 usefulness of information from single local features. (a) For this difficult-to-see high-contrast ‘Mooney’ face, approximately 80% of people perceive the face upright
12 (hint: young attractive female, lit from top right) but not inverted. If the inverted face is not seen within the first few trials, our observation is that it is never seen at all.
13 The plot shows rated strength of the face percept for different orientations averaged over 580 trials [49]. Reproduced, with permission, from Ref. [49]. (b) After eight
14 hours of training to distinguish identical twins (2200 trials), subjects who learned the twins inverted showed no aligned–unaligned composite effect, despite a
15 composite effect in control subjects who learned the twins upright. Instead, inverted subjects identified the twins by differences in the way they had combed their
16 eyebrows [50]. Adapted, with permission, from Ref. [50].
17
8