Behaviorally Relevant Abstract Object Identity Representation in the Human Parietal Cortex

Abstract

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.

Feature-coding transitions to conjunction-coding with progression through human visual cortex

“…In addition, this study provided the first explicit investigation of feature-coding in human cortex, revealing significant selectivity for features over conjunctions across posterior occipital regions binding. That is, our observation of object-specific coding in parietal cortex -elicited while participants discriminated between highly similar visual objects -suggests that the dorsal pathway constructs content-rich, hierarchical representations containing abstract information that is critical for object identification, in parallel with the ventral stream (54,55).…”

Goal-Directed Visual Processing Differentially Impacts Human Ventral and Dorsal Visual Representations

“…3). V1 was chosen for early visual areas because it was the first cortical stage of visual information processing, pFs was chosen for ventral regions due to its role in visual shape processing and detection (Grill-Spector et al, 2000;Williams et al, 2007), and superior IPS was chosen for dorsal regions due to its ability to represent a variety of visual features (Xu and Jeong, 2015;Bettencourt and Xu, 2016;Jeong and Xu, 2016). In the MDS plots, while the categories from the two tasks appeared to be spread out to a similar extent in V1 and pFs in all three experiments, the spread was much greater for the shape than the color task in superior IPS in Experiments 1 and 2.…”

“…However, both monkey and human studies over the last two decades have reported robust representations of a variety of "what" information in the dorsal pathway (Sereno and Maunsell, 1998;Sawamura et al, 2005;Janssen et al, 2008;Konen and Kastner, 2008;Liu et al, 2011;Christophel et al, 2012;Hou and Liu, 2012;Ester et al, 2015;Xu and Jeong, 2015;Bettencourt and Xu, 2016;Bracci et al, 2016;Freud et al, 2016;Jeong and Xu, 2016). These findings challenge the two-pathway view and argue for a convergence between the two pathways.…”

Extracting Object Identity: Ventral or Dorsal Visual Stream?

“…The former was measured as the correlation between response patterns to each identity pair in each region, and the latter as the reaction time to detect one identity among distractors of another identity (such that the greater the similarity, the slower the reaction time). A correlation between the neural and behavioral representations was again found solely in IPS [Jeong and Xu (2016), their Fig. 4D].…”

“…The hypothesis that two functionally independent streams process visual information has been challenged and revisited (Milner and Goodale, 2008), and we still do not know with confidence whether category and identity information are present exclusively in one visual stream and not in the other. In a recent article in The Journal of Neuroscience, Jeong and Xu (2016) raised further questions about the two-streams hypothesis by reporting that abstract identity information for complex stimuli is represented in the dorsal stream.…”