Person:

Xu, Yaoda

Although human lesion data have indicated the importance of the parietal cortex in object-based representations, our understanding of parietal object grouping and selection mechanisms in normal observers remains largely incomplete. This study manipulated the grouping between shapes and found that fMRI response from the inferior intraparietal sulcus (IPS) was higher for the disconnected (ungrouped) than for the connected (grouped) shapes in a task in which observers simply watched the displays and performed a simple image motion jitter detection task. These results replicated similar findings from a previous study employing a different paradigm and showed that the inferior IPS plays an important role in tracking the grouping between visual elements during visual perception. Assuming that a lower response corresponds to a greater ease of representation, these results may explain why after parietal brain lesions grouped visual elements are easier to perceive than ungrouped ones.

The representation of object identity is fundamental to human vision. Using fMRI and multivoxel pattern analysis, here we report the representation of highly abstract object identity information in human parietal cortex. Specifically, in superior intraparietal sulcus (IPS), a region previously shown to track visual short-term memory capacity, we found object identity representations for famous faces varying freely in viewpoint, hairstyle, facial expression, and age; and for well known cars embedded in different scenes, and shown from different viewpoints and sizes. Critically, these parietal identity representations were behaviorally relevant as they closely tracked the perceived face-identity similarity obtained in a behavioral task. Meanwhile, the task-activated regions in prefrontal and parietal cortices (excluding superior IPS) did not exhibit such abstract object identity representations. Unlike previous studies, we also failed to observe identity representations in posterior ventral and lateral visual object-processing regions, likely due to the greater amount of identity abstraction demanded by our stimulus manipulation here. Our MRI slice coverage precluded us from examining identity representation in anterior temporal lobe, a likely region for the computing of identity information in the ventral region. Overall, we show that human parietal cortex, part of the dorsal visual processing pathway, is capable of holding abstract and complex visual representations that are behaviorally relevant. These results argue against a “content-poor” view of the role of parietal cortex in attention. Instead, the human parietal cortex seems to be “content rich” and capable of directly participating in goal-driven visual information representation in the brain.