Marius V. Peelen

The neural basis of visual body perception

The human body, like the human face, is a rich source of socially relevant information about other individuals. Evidence from studies of both humans and non-human primates points to focal regions of the higher-level visual cortex that are specialized for the visual perception of the body. These body-selective regions, which can be dissociated from regions involved in face perception, have been implicated in the perception of the self and the body schema, the perception of others emotions and the understanding of actions.

Patterns of fMRI Activity Dissociate Overlapping Functional Brain Areas that Respond to Biological Motion

Accurate perception of the actions and intentions of other people is essential for successful interactions in a social environment. Several cortical areas that support this process respond selectively in fMRI to static and dynamic displays of human bodies and faces. Here we apply pattern-analysis techniques to arrive at a new understanding of the neural response to biological motion. Functionally defined body-, face-, and motion-selective visual areas all responded significantly to point-light human motion. Strikingly, however, only body selectivity was correlated, on a voxel-by-voxel basis, with biological motion selectivity. We conclude that (1) biological motion, through the process of structure-from-motion, engages areas involved in the analysis of the static human form; (2) body-selective regions in posterior fusiform gyrus and posterior inferior temporal sulcus overlap with, but are distinct from, face- and motion-selective regions; (3) the interpretation of region-of-interest findings may be substantially altered when multiple patterns of selectivity are considered.

Neural mechanisms of rapid natural scene categorization in human visual cortex

The visual system has an extraordinary capability to extract categorical information from complex natural scenes. For example, subjects are able to rapidly detect the presence of object categories such as animals or vehicles in new scenes that are presented very briefly. This is even true when subjects do not pay attention to the scenes and simultaneously perform an unrelated attentionally demanding task, a stark contrast to the capacity limitations predicted by most theories of visual attention. Here we show a neural basis for rapid natural scene categorization in the visual cortex, using functional magnetic resonance imaging and an object categorization task in which subjects detected the presence of people or cars in briefly presented natural scenes. The multi-voxel pattern of neural activity in the object-selective cortex evoked by the natural scenes contained information about the presence of the target category, even when the scenes were task-irrelevant and presented outside the focus of spatial attention. These findings indicate that the rapid detection of categorical information in natural scenes is mediated by a category-specific biasing mechanism in object-selective cortex that operates in parallel across the visual field, and biases information processing in favour of objects belonging to the target object category.

The effect of viewpoint on body representation in the extrastriate body area

Functional neuroimaging has revealed several brain regions that are selective for the visual appearance of others, in particular the face. More recent evidence points to a lateral temporal region that responds to the visual appearance of the human body (extrastriate body area or EBA). We tested whether this region distinguishes between egocentric and allocentric views of the self and other people. EBA activity increased significantly for allocentric relative to egocentric views in the right hemisphere, but was not influenced by identity. Whole-brain analyses revealed several regions that were influenced by viewpoint or identity. Modulation of EBA activity by viewpoint was modest relative to modulation by stimulus class. We propose that the EBA plays a relatively early role in social vision.

Within-subject reproducibility of category- specific visual activation with functional MRI

We used functional magnetic resonance imaging (fMRI) to investigate within‐subject reproducibility of activation in higher level, category‐specific visual areas to validate the functional localization approach widely used for these areas. The brain areas investigated included the extrastriate body area (EBA), which responds selectively to human bodies, the fusiform face area (FFA) and the occipital face area (OFA), which respond selectively to faces, and the parahippocampal place area (PPA), which responds selectively to places and scenes. All six subjects showed significant bilateral activation in the four areas. Reproducibility was very high for all areas, both within a scanning session and between scanning sessions separated by 3 weeks. Within sessions, the mean distance between peak voxels of the same area localized by using different functional runs was 1.5 mm. The mean distance between peak voxels of areas localized in different sessions was 2.9 mm. Functional reproducibility, as expressed by the stability of T‐values across sessions, was high for both within‐session and between‐session comparisons. We conclude that within subjects, high‐level category‐specific visual areas can be localized robustly across scanning sessions. Hum Brain Mapp, 2005.

Emotional modulation of body-selective visual areas

Emotionally expressive faces have been shown to modulate activation in visual cortex, including face-selective regions in ventral temporal lobe. Here, we tested whether emotionally expressive bodies similarly modulate activation in body-selective regions. We show that dynamic displays of bodies with various emotional expressions vs neutral bodies, produce significant activation in two distinct body-selective visual areas, the extrastriate body area and the fusiform body area. Multi-voxel pattern analysis showed that the strength of this emotional modulation was related, on a voxel-by-voxel basis, to the degree of body selectivity, while there was no relation with the degree of selectivity for faces. Across subjects, amygdala responses to emotional bodies positively correlated with the modulation of body-selective areas. Together, these results suggest that emotional cues from body movements produce topographically selective influences on category-specific populations of neurons in visual cortex, and these increases may implicate discrete modulatory projections from the amygdala.

The role of the extrastriate body area in action perception

Abstract Numerous cortical regions respond to aspects of the human form and its actions. What is the contribution of the extrastriate body area (EBA) to this network? In particular, is the EBA involved in constructing a dynamic representation of observed actions? We scanned 16 participants with fMRI while they viewed two kinds of stimulus sequences. In the coherent condition, static frames from a movie of a single, intransitive whole-body action were presented in the correct order. In the incoherent condition, a series of frames from multiple actions (involving one actor) were presented. ROI analyses showed that the EBA, unlike area MTu200a+u200aand the posterior superior temporal sulcus, responded more to the incoherent than to the coherent conditions. Whole brain analyses revealed increased activation to the coherent sequences in parietal and frontal regions that have been implicated in the observation and control of movement. We suggest that the EBA response adapts when succeeding images depict relatively similar postures (coherent condition) compared to relatively different postures (incoherent condition). We propose that the EBA plays a unique role in the perception of action, by representing the static structure, rather than dynamic aspects, of the human form.

Differential development of selectivity for faces and bodies in the fusiform gyrus.

Viewing faces or bodies activates category-selective areas of visual cortex, including the fusiform face area (FFA), fusiform body area (FBA), and extrastriate body area (EBA). Here, using fMRI, we investigate the development of these areas, focusing on the right FFA and FBA. Despite the overlap of functionally defined FFA and FBA (54%-75% overlap), we found that these regions developed along different trajectories. With age (7-32 years old), the FFA gradually increased in size and selectivity, and was significantly larger and more face-selective in adults than children. By contrast, the size and selectivity of the FBA did not correlate with age, and were equivalent in children and adults. Whereas in adults the FFA and FBA were comparable in size, in children the FBA was on average 70% larger than the FFA. These findings suggest that, in children, the fusiform gyrus is predominantly selective for bodies, with commensurate face-selective responses apparent later in development. Moreover, differences in the development of the FFA and FBA indicate that overlapping functional brain areas, supported by the same anatomical structure, can develop along different trajectories.

Using multi-voxel pattern analysis of fMRI data to interpret overlapping functional activations

Norman et al. [1] recently reviewed the use of multi-voxelpattern analysis (MVPA) of fMRI data. They providedexamples that showed that patterns of activation acrossa set of voxels can contain far more information aboutmental states than the more typically used univariateapproach. Patterns of fMRI activation can be used todiscriminate cognitive states (sometimes called ‘mindreading’),torelatebrainactivitytobehaviourandtoclarifythe structure of neural representations. Here, we point outan additional use of MVPA: its ability to interpret over-lapping functional activations.A general issue that arises in fMRI studies concerns theinterpretation of overlapping activity from independentcontrasts. When a set of voxels is commonly activated bytwo (or more) contrasts of experimental conditions, twointerpretations are possible. In a common-coding interpre-tation,thesharedregionisthoughttocontainneuronsthatare engaged in a common computational process, which isshared by the two experimental conditions (but not therespective controls). For example, this interpretation hasbeen the favoured account for brain areas that are acti-vated by both observed and performed manual actions [2]and, in this case, has been taken as evidence for ‘mirrorneuron’ [3]systemsin thehuman brain. Alternatively,inafunctional-independence interpretation, two overlappingbut functionally independent neural populations arethought to be engaged within the common region.We have recently presented several examples offunctional independence in overlapping extrastriatecortical regions using MVPA [4,5]. For example, we foundhighly overlapping activations in response to motion andhuman bodies in lateral occipitotemporal cortex. Univari-ate analysis showed that most voxels in this region wereselective for both motion and bodies, which suggestsengagement of common neural mechanisms. By contrast,MVPA revealed that the patterns of activation in responseto bodies and motion were unrelated, which favours afunctional-independence account [5].Thus, in addition to ‘mind reading’, MVPA can assessthefunctionalsignificanceofoverlapbetweenfMRIactiva-tions. This issue is relevant for fMRI studies in all areas ofcognitive neuroscience because overlapping activationsanywhere in the brain cannot be assumed to reflect sharedneural processing. We expect that future experiments thatare designed for MVPA should help to support or rejectclaims about neural mechanisms that are shared acrossmultiple tasks or stimuli.

Selectivity for large nonmanipulable objects in scene-selective visual cortex does not require visual experience

The principles that determine the organization of object representations in ventral temporal cortex (VTC) remain elusive. Here, we focus on the parahippocampal place area (PPA), a region in medial VTC that has been shown to respond selectively to pictures of scenes. Recent studies further observed that this region also shows a preference for large nonmanipulable objects relative to other objects, which might reflect the suitability of large objects for navigation. The mechanisms underlying this selectivity remain poorly understood. We examined the extent to which PPA selectivity requires visual experience. Fourteen congenitally blind and matched sighted participants were tested on an auditory size judgment experiment involving large nonmanipulable objects, small objects (tools), and animals. Sighted participants additionally participated in a picture-viewing experiment. Replicating previous work, we found that the PPA responded selectively to large nonmanipulable objects, relative to tools and animals, in the sighted group viewing pictures. Importantly, this selectivity was also observed in the auditory experiment in both sighted and congenitally blind groups. In both groups, selectivity for large nonmanipulable objects was additionally observed in the retrosplenial complex (RSC) and the transverse occipital sulcus (TOS), regions previously implicated in scene perception and navigation. Finally, in both groups the PPA showed resting-state functional connectivity with TOS and RSC. These results provide new evidence that large object selectivity in PPA, and the intrinsic connectivity between PPA and other navigation-relevant regions, do not require visual experience. More generally, they show that the organization of object representations in VTC can develop, at least partly, without visual experience.