Perceiving the whole individual person

A method called fMRI-adaptation has been used to show a neural population that is activated by whole individuals rather than just faces or bodies. The fMRI-A effect depends on the adaptation or attenuation of the BOLD signal because of the repetition of a specific stimulus in a neural population that is sensitive to that particular stimulus.

So far fMRI-A has been used to characterize the representations underlying neural responses to a number of visual stimulus classes including faces, headless bodies, objects, scenes, as well as more generally to the binding of objects and background scenes and to the coding of objects presented in peripersonal space.

 

Schmalzl, Zopf, and Williams have recently published a paper (see citation below) in which they use fMRI-A to investigate the neural populations that show selective adaptation to the visual presentation of whole individuals, as opposed to just isolated faces or bodies.

In the fusiform gyrus and extrastriate regions, they found areas of specific adaptation effects for same faces, same bodies, either same faces or same bodies, same whole individuals, whole individuals whether same or different (individual category classification).

While the existence of voxels that show significant adaptation only when both the same face and the same body are presented points into the direction of response selectivity for whole individuals, it cannot be taken as evidence for it. The adaptation effect for whole individuals could be merely additive, namely a sum of face and body specific responses. That is, it could simply reflect the fact that some voxels contain a mixture of face and body selective neurons whose individual category specific response is not strong enough to yield significant adaptation, but whose combined response is. We therefore took our analysis one step further and defined a superadditive contrast for the SFSB (same face same body) condition. Specifically, we defined a new independent contrast that allowed us to investigate whether for some voxels showing significant SFSB adaptation, this adaptation was actually larger than the sum of the adaptation shown for all other conditions.

 

Here is their abstract:

Our ability to recognize other people’s faces and bodies is crucial for our social interactions. Previous neuroimaging studies have repeatedly demonstrated the existence of brain areas that selectively respond to visually presented faces and bodies. In daily life, however, we see “whole” people and not just isolated faces and bodies, and the question remains of how information from these two categories of stimuli is integrated at a neural level. Are faces and bodies merely processed independently, or are there neural populations that actually code for whole individuals? In the current study we addressed this question using a functional magnetic resonance imaging adaptation paradigm involving the sequential presentation of visual stimuli depicting whole individuals. It is known that adaptation effects for a component of a stimulus only occur in neural populations that are sensitive to that particular component. The design of our experiment allowed us to measure adaptation effects occurring when either just the face, just the body, or both the face and the body of an individual were repeated. Crucially, we found novel evidence for the existence of neural populations in fusiform as well as extrastriate regions that showed selective adaptation for whole individuals, which could not be merely explained by the sum of adaptation for face and body respectively. The functional specificity of these neural populations is likely to support fast and accurate recognition and integration of information conveyed by both faces and bodies. Hence, they can be assumed to play an important role for identity as well as emotion recognition in everyday life.

 

 

ResearchBlogging.org

Schmalzl, L., Zopf, R., & Williams, M. (2012). From Head to Toe: Evidence for Selective Brain Activation Reflecting Visual Perception of Whole Individuals Frontiers in Human Neuroscience, 6 DOI: 10.3389/fnhum.2012.00108

Leave a Reply

Your email address will not be published. Required fields are marked *