Cerebral Cortex April 2007;17:760--765
doi:10.1093/cercor/bhk029
Advance Access publication May 12, 2006
Similar Frontal and Distinct Posterior
Cortical Regions Mediate Visual and
Auditory Perceptual Awareness
Johan Eriksson1, Anne Larsson2,3, Katrine Riklund Åhlström3,4
and Lars Nyberg3,4,5
Department of Psychology and 2Department of Radiation
Science, Radiation Physics, Umeå University, S-901 87 Umeå,
Sweden, 3Umeå Centre for Functional Brain Imaging (UFBI),
Umeå, Sweden, 4Department of Radiation Sciences, Diagnostic
Radiology and 5Department of Integrative Medical Biology,
Physiology Section, Umeå University, S-901 87 Umeå, Sweden
1
Activity in ventral visual cortex is a consistent neural correlate of
visual consciousness. However, activity in this area seems insufficient to produce awareness without additional involvement of
frontoparietal regions. To test the generality of the frontoparietal
response, neural correlates of auditory awareness were investigated in a paradigm that previously has revealed frontoparietal
activity during conscious visual perception. A within-experiment
comparison showed that frontal regions were related to both visual
and auditory awareness, whereas parietal activity was correlated
with visual awareness and superior temporal activity with auditory
awareness. These results indicate that frontal regions interact with
specific posterior regions to produce awareness in different
sensory modalities.
tested the generality of frontoparietal activity by examining
conscious perception in the visual and auditory modalities with
a fMRI paradigm that previously has revealed frontoparietal
activity during visual conscious perception (Portas and others
2000; Eriksson and others 2004). This paradigm makes it
possible to isolate transient brain activity related to conscious
awareness (Fig. 1a). We found that similar frontal regions were
related to conscious perception in both the visual and auditory
domains. By contrast, posterior brain activity was domain
selective with occipitotemporal and parietal activation for visual
stimuli and superior temporal activation for auditory stimuli.
Keywords: auditory awareness, fMRI, parietal cortex, prefrontal cortex,
visual awareness
Experiment 1
Introduction
Participants
Sixteen neurologically healthy subjects participated in the study, 24--37
years old (8 women). All participants were right handed by self-report,
had normal or corrected to normal vision, and no hearing impairments.
Participants gave their informed consent, and the study was approved by
the ethics committee at the University Hospital of Northern Sweden.
Consciousness is a central concept in the history of psychology
(Leahey 2000) but has only more recently become a topic of
study in the neurosciences. How the brain implements consciousness has been labeled ‘‘the deepest of biological mysteries’’ (Kandel and others 2000). Searching for the neural
correlates of consciousness, defined as neuronal events that give
rise to a specific aspect of a conscious percept, has been
proposed as a framework for consciousness (Crick and Koch
2003). Several previous studies have found that activity in
regions in ventral visual cortex is correlated with visual
conscious perception (Sheinberg and Logothetis 1997; Tong
and others 1998; Grill-Spector and others 2000). However, such
activity has been suggested to be necessary but not sufficient
for conscious visual experience in the sense that additional
contribution from parietal and prefrontal loci is required
(Rees and others 2002). This suggestion is supported by the
functional magnetic resonance imaging (fMRI) studies that
show transient changes in frontoparietal brain activity related
to visual conscious experience (Kleinschmidt and others 1998;
Lumer and others 1998; Portas and others 2000; Eriksson and
others 2004), as well as other studies that have implicated
frontoparietal regions with conscious awareness (McIntosh and
others 1999; Beck and others 2001; Dehaene and others 2001;
Kjaer and others 2001; Ehrsson and others 2004). Moreover,
frontoparietal activity has consistently been observed in relation
to visual attention (Kanwisher and Wojciulik 2000) and visual
working memory (Baddeley 2003), and similarities in frontoparietal activity for awareness, attention, and working memory
have been noted (Lumer and others 1998).
Most previous studies on conscious perception have involved
visual stimuli (Rees and others 2002). In the present study, we
Ó The Author 2006. Published by Oxford University Press. All rights reserved.
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Methods
Stimulus Material
The stimuli consisted of sounds of objects (animals) rather than tones
because this is more perceptually and conceptually comparable with
visual object recognition (Bregman 1990). The stimulus consisted of 24
animal sounds deemed commonly known, such as pig, dog, lion, etc. A
background noise (consisting of a conglomerate of all animal sounds
used) was custom made for each animal sound. Specifically, the noise
was made louder on some sections and quieter on others. This was to
make melodic and pitch clues less pronounced and thereby making the
different animal sounds more comparable in terms of recognizability.
The animal sounds were made either 1 3 4 or 2 3 4 s long to match the
timing of the noise reduction steps (4 s, see Procedures) and were
looped during playback to create a continuous sound image. The choice
between 1 3 4 and 2 3 4 s was based on whether the animal had
a characteristically repetitive sound or not. For example, a cricket would
get 1 3 4 s, whereas the howling of a wolf would get 2 3 4 s.
Procedure
Each animal sound remained constant throughout the trial with a loop of
4.0 or 8.0 s (see Stimulus Material) and a stimulus onset asynchrony of
60.0 s. The participants were required to fixate on a black crosshair
centered on a white screen throughout the experiment. Every 4.0 s, the
noise level was reduced one step (one step is –120, where 0 is no
reduction and –10 000 is complete silence, see E-Prime manual,
Psychology Software Tools, Inc. [Pittsburgh, PA], for further detail) until
the subject pressed a button with their left hand, thereby indicating
animal identification. This motor response was accompanied by a change
in background screen color from white to green. After identification, the
subject was required to continue attending to the animal sound during
the remainder of the trial (sustained perception).
During the period of sustained perception, a second change of
background color, from green to white, prompted the subject to press
Figure 1. (a) In both the auditory and visual paradigm, perception is made difficult by having noise in the stimulus presentation. This creates a delay in target identification (for
Experiment 2 M (mean) = 14.9 s, standard deviation [SD] = 6.4 s for sounds; M = 11.0 s, SD = 10.3 s for pictures) and dissociates the stimulus parameters from identification and
onset of a specific conscious content. For each trial, the participant presses a button when he/she identified the target object. To separate brain activity related to this motor
response from activity specific for identification, a second button press is made some time later during the same trial. This creates a unique blood oxygen level--dependent activation
profile for the motor response (M), identification (I), and also the continuous sustained perception (SP) following identification, allowing an analytical separation of each effect within
trials. (b) In Experiment 1, only auditory stimuli were used (supplementary wav-file online), and in Experiment 2, both auditory and visual stimuli were used. This example visual
stimulus depicts a small bird in green lines ‘‘hidden’’ among distractor lines (noise).
the button once again. This subsequent motor response served as
control for any brain activation in the first response that was due to the
response itself and not to perceptual identification because it also
consisted of seeing a color change and performing the same motor act
(Fig. 1a). This second response occurred 8.0--12.0 s after identification.
Following the second response, the stimulus presentation continued for
12.0 s. The described procedure with 1 target identification, 2 motor
responses, and an unbroken period of sustained perception enables
a comparison of the 3 conditions and identification of brain activity
specifically associated with each effect.
If identification did not occur within 28 s, the sound and trial were
terminated because there would not be enough time left of the
remaining trial to reliably separate each effect of interest. Although
each stimulus was constructed with the aim of an identification time of
8--28 s, no lower boundary was set. This was based on the argument that
if a larger proportion of the identifications occurred after 8 s, occasional
early responses would still provide useful information as in a jittered
design (Donaldson and Buckner 2001) and not be confounded by
stimulus onset.
The participants were asked to identify each animal as fast as possible.
To avoid false-positive responses, trials with only noise and no animal
sound were intermixed with the other trials, and the participants were
explicitly told not to respond unless they could identify the animal.
Despite these precautions, one false positive occurred which, combined
with low task performance, lead to the exclusion of the (male)
participant from the statistical analysis. After magnetic resonance
(MR) scanning, a debriefing was performed with each participant,
making sure that they had heard the correct animal in each trial. All trials
were deemed successful.
MR Procedures
Data collection was made on a 1.5-T Philips Intera scanner (Philips
Medical Systems, The Netherlands). Functional T2*-weighted images
were obtained with a single-shot gradient echo planar imaging sequence
used for blood oxygen level--dependent imaging. The sequence had the
following parameters: echo time 50 ms, repetition time 3000 ms (33
slices acquired), flip angle 90°, field of view 22 3 22 cm, 64 3 64 matrix,
and 4.4-mm slice thickness. To eliminate signals arising from progressive
saturation, 5 dummy scans were performed prior to the image
acquisition. The stimuli were presented through MR-compatible headphones (Silent Scan SS-3000 Audio System, Avotech, Stuart FL), and the
color background and crosshair were projected on a semitransparent
screen, which the participants viewed through a tilted mirror attached
to the head coil. Presentation and reaction time data were handled by
a PC running E-Prime 1.1 (Psychology Software Tools, Inc.,). Before the
functional imaging, high-resolution T1- and T2-weighted structural
images were acquired.
Data Analysis
The data were analyzed with statistical parametric mapping (SPM2)
(Wellcome Department of Cognitive Neurology, London, UK) on Matlab
6.5.1 (Mathworks Inc., Sherborn, MA). All images were corrected for
slice timing, realigned to the first image volume in the series, normalized
to standard anatomical space defined by the Montreal Neurological
Institute (MNI) atlas (SPM2), and smoothed using an 8.0-mm full width
half maximum Gaussian filter kernel. The effects of interest were
modeled using 3 regressors: identification, sustained perception, and
sensorimotor integration (Fig. 1a). Because onset for the regressors
varied in every trial depending on the participants’ identification time,
each regressor parameter was based on reaction time data for that
specific trial. All regressors were convolved with a hemodynamic
response function. Model estimations of main effects from each
individual were taken into a second level random-effects model to
account for interindividual variability. The statistical threshold was set to
P < 0.05 (familywise error—corrected for multiple comparisons).
Experiment 2
Participants
Twelve healthy volunteers (6 women) aged 20--42 years participated
(no one from Experiment 1 participated in Experiment 2). All
participants were right handed by self-report, had normal or corrected
to normal vision, and no hearing impairment. All gave informed consent,
and the study was approved by the ethics committee at the University
Hospital of Northern Sweden.
Stimulus Material
Twenty of the 24 sounds from Experiment 1 were reused for the
auditory condition. For the visual condition, 20 pictures developed for
an earlier experiment were used. These are fragmented pictures where
an object is made out of a subset of colored fragments and is therefore
difficult to identify. However, once the object is identified, there is no
ambiguity in the picture and sustained perception can occur (Fig. 1b; for
further detail, see Eriksson and others 2004).
Procedure
Each trial was randomly selected without replacement from 1 of 2 lists,
consisting of auditory and visual trials, respectively. The procedure for
auditory trials was similar as in Experiment 1 except that trial duration
was interactive (i.e., no fixed stimulus onset asynchrony). The visual
trials proceeded as follows: The picture was projected on the semitransparent screen and remained unchanged throughout the trial. When
identification occurred, the participant pressed a button and continued
looking at the identified object. As a consequence of the button press,
a short beep appeared in the headphones. After 8.0--12.0 s, the beep
reappeared prompting a second button press. Following the second
response, the stimulus presentation continued for 12.0 s. All trials
(auditory and visual) were separated by a 9.0-s presentation of
a crosshair on a gray background.
MR Procedures and Data Analysis
The MR procedures for Experiment 2 were the same as in Experiment 1.
Data analysis was similar to Experiment 1 except that 6 regressors were
Cerebral Cortex April 2007, V 17 N 4 761
used to model the effects of interest (3 for auditory and 3 for visual
trials). One participant did not show the expected activation pattern for
sensorimotor integration and was therefore excluded from the group
analysis. The statistical threshold was set to P < 0.01 corrected for false
discovery rate (Genovese and others 2002). This more liberal threshold
compared with Experiment 1 was chosen because of the power
difference between the 2 experiments (14 vs. 10 degrees of freedom).
The random-effects conjunction analysis was implemented in in-house
software on the relevant main effects contrasts (testing the conjunction
null hypothesis, Nichols and others 2005).
Data Extraction for Selected Regions
Regions of interest (Fig. 3) were defined from the random-effects
analysis, where the superior temporal region was selected as the
regional peak voxel for auditory identification, the parietal region as
the regional peak voxel for visual identification, and the anterior
cingulate and dorsolateral (DL) prefrontal regions as regional peak
voxels for the conjunction analysis on identification. Data (effect size)
were extracted using the Marsbar software (Brett and others 2002) from
a spherical region with a radius of 6 mm.
Figure 2. Identification of sounds in Experiment 1 activated right superior temporal
cortex (MNI x, y, z = 64, –24, 4), bilateral prefrontal cortex (–42, 20, –6; 52, 30, 18),
ACC (6, 34, 38), and cerebellum (–28, –66, –30). All activations are significant at P <
0.05 corrected for whole-brain volume. Right hemisphere activations are illustrated as
volume clouds (Van Essen and others 2001; left in figure), and left hemisphere
activations are overlaid on single-subject T1-weighted images (right).
Results
Sensorimotor Processes
In Experiment 1, the motor responses activated primary motor
cortex (x, y, z = 30, –20, 64, z-score = 7.29) and color-related
regions in the fusiform gyrus (26, –74, –14, z-score = 6.88; –20,
–68, –10, z-score = 6.50). This result was replicated in Experiment
2 for auditory stimuli (motor cortex: 48, –14, 62, z-score = 5.77;
fusiform gyrus: –16, –54, –16, z-score = 5.71). For visual stimuli,
sensorimotor activity was observed in primary motor cortex
(28, –26, 58, z-score = 6.10) and auditory cortex (–52, –32, 14,
z-score = 5.33). These results confirm that the analytic strategy
of separating effects of interest within trials was successful.
Conscious Awareness
In Experiment 1, identification of target sounds activated lateral
prefrontal cortex (PFC), anterior cingulate cortex (ACC),
superior temporal cortex, and cerebellum (Fig. 2 and Table 1).
However, in contrast to previous research on visual awareness
(Portas and others 2000; Eriksson and others 2004), no parietal
activity increase was observed. To consider possible parietal
activity at a lower statistical threshold, we reexamined the
results at a threshold of P < 0.001 uncorrected for multiple comparisons. At this more liberal threshold, some parietal activity
was seen (x, y, z = –6, –74, 40; –30, –58, 42), but frontotemporal
activity continued to be the most salient response.
In Experiment 2, a similar pattern of results was observed as
in Experiment 1. Identification of sounds activated lateral PFC,
ACC, superior temporal cortex, and cerebellum. Again, no
parietal activity increase was found (Fig. 3), and this was true
even at a threshold of P < 0.001 uncorrected. In contrast,
identification of visual stimuli did activate regions in the parietal
cortex. In addition, increased activity was observed in inferior
occipitotemporal cortex, lateral PFC, and ACC (Fig. 3 and Table 2).
The results of Experiment 2 showed overlapping frontal
activity for visual and auditory perception. To formally characterize similarities in activation patterns associated with awareness in different sensory modalities, a conjunction analysis was
performed. This analysis revealed exclusively frontal (lateral
PFC and ACC) activity across modalities, mainly in the right
hemisphere (Fig. 3). These results suggest that activity in the
same frontal regions is related to awareness regardless of
sensory modality.
762 Visual and Auditory Perceptual Awareness
d
Eriksson and others
Table 1
Brain regions related to identification and sustained perception for Experiment 1
Brain region
Identification
DLPFC
ST
VLPFC
ACC
Cerebellum
Sustained perception
Parietal
Premotor
Cerebellum
LPFC
x
y
z
z-score
BA
52
64
ÿ42
6
ÿ28
30
ÿ24
20
34
ÿ66
18
4
ÿ6
38
ÿ30
5.46
5.43
5.40
5.40
5.32
45/46
22
47
32
—
52
ÿ44
40
44
ÿ38
16
38
ÿ38
32
34
36
ÿ48
ÿ46
ÿ48
ÿ76
ÿ42
ÿ62
18
10
ÿ68
ÿ50
ÿ72
36
50
36
36
22
56
42
58
46
ÿ44
ÿ30
ÿ26
20
ÿ6
6.19
5.48
5.44
5.42
5.21
5.64
5.27
5.50
5.26
5.21
5.40
5.22
40
40
39/19
40/7
40/19
6
6/8
—
—
—
46
47
Note: P \ 0.05 familywise error corrected, only clusters larger or equal to 5 voxels are reported.
x, y, z, MNI coordinates; BA, Brodmann area; ST, superior temporal cortex; VLPFC, ventrolateral
prefrontal cortex; LPFC, lateral prefrontal cortex.
Sustained Perception
For both visual and auditory stimuli, sustained perception
activated extensive brain networks (Supplementary Table 1
online; Table 1 for results from Experiment 1). Critically, in both
modalities, the networks included frontal and parietal regions,
and a conjunction analysis revealed overlapping frontal and
parietal activity during visual and auditory sustained perception
(Table 3).
Control Analysis of Experiment 1 and 2
A difference between the auditory and visual stimuli is that in
the auditory version, the stimuli change in a systematic way,
whereas the visual stimuli remain unchanged throughout each
trial. To control for possible confounding effects from this on
the results of Experiment 1 and 2, we reanalyzed both data sets
with the addition of a fourth (for Experiment 1, seventh for
Experiment 2) regressor modeling the noise levels parametrically (assuming linearity among levels). This analysis revealed
activity in auditory cortex related to noise level for both
Figure 3. Lateral view (top right) of left and right hemispheres with auditory (red) and visual (green) activations from Experiment 2 (P < 0.01 corrected for false discovery rate).
Blue regions designate results from the conjunction analysis across modalities. Diagrams show group mean effect size in selected regions. The left part of the figure shows
activations projected on flat maps (Van Essen and others 2001). The within-experiment comparison showed that ACC (A) and lateral PFC (B) were similarly activated for both
auditory and visual awareness, whereas parietal (C) and occipitotemporal regions were exclusively activated for visual awareness and superior temporal cortex (D) exclusively for
auditory awareness. (Center coordinates for (A): –2, 26, 44; (B): 48, 44, 14; (C): 22, –66, 54; (D): 66, –22, –10). Letter indexing designates the same regions in flat maps, lateral
views, and diagrams.
experiments. Importantly, the activation pattern for all previous
contrasts remained unchanged, although statistical power was
reduced (Supplementary Fig. 1).
Discussion
A consistent finding in neuroimaging research on visual
awareness is that activity in both visual sensory regions and
frontoparietal regions is correlated with the subjective experience of seeing a particular percept (Rees and others 2002).
Frontoparietal activity correlates with awareness of a number of
different visual stimuli (words, Kjaer and others 2001; motion,
Williams and others 2003; objects, Portas and others 2000) and
may thus reflect general stimulus-independent cognitive processes. The aim of Experiment 1 was to test the apparent
generality of frontoparietal regions in relation to perceptual
awareness by using auditory stimuli in a paradigm that previously has revealed frontoparietal activity during visual conscious perception (Portas and others 2000; Eriksson and others
2004). Whereas both auditory sensory regions and frontal
regions were activated for auditory awareness, only weak
parietal activity was found. This result was replicated in
Experiment 2 where visual and auditory awareness were
directly compared. In this experiment, parietal activity correlated exclusively with visual awareness.
Parietal cortex is reciprocally connected with visual areas,
and activity in secondary visual cortex during visual perceptual
rivalry has been found to correlate with parietal and prefrontal
activity (Lumer and Rees 1999). These previous observations
converge with the present findings of frontoparietal activity
during visual awareness, and they provide support for neural
theories that visual awareness depends on interactions between
visual cortex and PFC (Crick and Koch 1995). Our finding that
frontal and temporal regions showed increased activity during
auditory perceptual awareness extends this theory by suggesting that auditory awareness depends on frontotemporal interactions. In support of this interpretation, auditory object
identification has been associated with a region in temporal
cortex (Binder and others 2004), and anatomical connections
between PFC and auditory association areas have been demonstrated (Romanski and others 1999).
Our experiments on auditory and visual awareness thus
suggest that frontal regions interact with posterior regions in
a modality-specific manner to create perceptual awareness in
different sensory modalities. Several frontal regions were
identified here in relation to perceptual awareness. Ventrolateral PFC activation may be related to making decisions about
sensory stimuli (Bar and others 2001; Binder and others 2004).
ACC has been associated with conflict monitoring (Dehaene
and others 2003), and interactions among ACC and regions in
lateral PFC have been related to the ability to decide whether
a response is correct (Gehring and Knight 2000). A region in
right DLPFC was also engaged. This prefrontal region has
consistently been observed in previous studies of conscious
Cerebral Cortex April 2007, V 17 N 4 763
Table 2
Brain regions related to identification in Experiment 2
Brain region
x
Auditory object identification
ST
66
ÿ66
DLPFC
48
48
VLPFC
ÿ32
ÿ42
MPFC
ÿ2
ÿ4
ÿ14
ÿ6
MTL
30
Visual object identification
Occipital
ÿ34
ÿ40
ÿ14
30
VLPFC
34
ÿ38
IT
48
Parietal
22
ÿ16
DLPFC
46
MTL
ÿ36
MPFC
ÿ2
Conjunction
VLPFC
ÿ42
34
ACC
ÿ2
10
DLPFC
48
62
y
z
z-score
BA
ÿ22
ÿ40
20
20
16
24
10
26
36
24
18
ÿ10
0
28
10
ÿ14
ÿ4
62
46
22
30
ÿ24
5.65
4.93
5.30
5.20
5.23
4.81
5.00
4.91
4.71
4.08
4.84
21
21
9/44
45
47/38
47
6
8
32
32
38
ÿ98
ÿ74
ÿ96
ÿ72
32
20
ÿ52
ÿ66
ÿ68
8
ÿ32
26
8
ÿ14
ÿ14
36
ÿ14
ÿ10
ÿ14
54
58
26
ÿ26
44
5.36
4.73
4.73
4.36
4.89
4.25
4.81
4.57
4.13
4.57
3.95
3.76
18/19
18/19
17/18
39/19
47
47
37
7
7
44
36/20
6/8
24
30
26
32
44
22
ÿ8
ÿ10
44
26
14
14
3.97
3.65
3.76
3.31
3.70
3.39
47
47
32
32
45
44/45
Note: P \ 0.01 false discovery rate corrected (P \ 0.001 uncorrected for conjunction), only
clusters larger or equal to 5 voxels are reported. MPFC, medial prefrontal cortex; MTL, medial
temporal lobe; IT, inferior temporal cortex. Other abbreviations as in Table 1.
Table 3
Conjunction analysis of auditory and visual sustained perception
Brain region
x
y
z
z-score
BA
LPFC
40
ÿ38
42
ÿ44
8
58
14
28
ÿ58
ÿ62
0
56
44
32
64
4.70
4.65
4.59
4.35
4.12
46/47/10
8/9/46
8/9/46
39/40
7/40
Parietal
Note: Subset of regions activated according to conjunction analysis of auditory and visual
sustained perception (for full report, see Supplementary Table 2). P \ 0.001 uncorrected.
Abbreviations as in Table 1.
perception (Rees and others 2002; Naghavi and Nyberg 2005),
and it is also consistent with the model by Frith and Dolan
(1996) that advocate a principal role for PFC in establishing
conscious states. Frith and Dolan suggested that posterior
regions define the specific content of consciousness, whereas
frontal regions are needed to become aware of this content.
DLPFC has also been linked to a variety of cognitive functions,
such as attention (Kanwisher and Wojciulik 2000), working
memory (Baddeley 2003), and cognitive control (Miller and
Cohen 2001). Furthermore, DLPFC and also ACC are important
regions in a recent version of global workspace theory
(Dehaene and Naccache 2001). In relation to this theory,
Dehaene and Naccache notice several empirical findings that
connects the mentioned cognitive functions with consciousness 1) that attention may be a requirement for conscious
awareness, 2) that consciousness seems to require durable and
764 Visual and Auditory Perceptual Awareness
d
Eriksson and others
explicit information maintenance (implicating working memory), and 3) that some functions seem impossible without
consciousness, for example, intentional behavior and novel
combinations of operations. These latter functions are related
to cognitive control because they tend to involve some form of
conflict resolution. The exact relation between attention,
working memory, cognitive control, and consciousness is not
yet clear, but recent theories suggest that they may share
underlying information-processing mechanisms (Courtney
2004; Maia and Cleeremans 2005; Naghavi and Nyberg 2005),
thus explaining the common activation of PFC across functions.
Our results further indicated that once modality-specific
frontoposterior interactions had defined a percept, an amodal
brain system contributed to actively holding this percept in
mind. That is, for both visual and auditory stimuli, a network
including frontoparietal regions was activated during sustained
perception. Conceivably, representation maintenance during
sustained perception involves working memory processes and/
or selective attentional enhancement due to the relative
difficulty of the perceptual task. In previous studies, working
memory and also selective attention have been found to engage
a similar frontoparietal network for many different kinds of
stimuli (Cabeza and Nyberg 2000), and a recent fMRI study
found considerable overlap in frontal and parietal activity for
visual and auditory working memory (Crottas-Herbette and
others 2004). Critically, the fMRI protocol allowed us to isolate
transient brain activity related to perceptual awareness from
brain activity during sustained perception, which made possible
the demonstration that parietal cortex was differentially involved in auditory and visual awareness and commonly involved
in auditory and visual sustained perception.
In conclusion, this study demonstrates that the role of
frontoparietal regions in perceptual awareness may not be as
general as previously thought. Instead, common frontal regions
seem to interact with specific posterior regions to produce
awareness in different sensory modalities.
Supplementary Material
Supplementary material
oxfordjournals.org/.
can
be
found
at:
http://www.cercor.
Notes
This research was supported by an infrastructure fMRI grant from
Umeå University to LN and Roland Johansson. We thank the staff at the
MR centre, University Hospital of Northern Sweden, for assisting us
during MR imaging. Conflict of Interest: None declared.
Address correspondence to Johan Eriksson, Department of Psychology, Umeå University, S-901 87 Umeå, Sweden. Email: johan.eriksson@
psy.umu.se.
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