Processing multiple visual objects is limited by overlap in neural channels

Cohen, Konkle, Nakayama & Alvarez

The visual processing stream contains regions that selectively respond to different objects, and the representational geometry within each region can be measured by the similarity of responses across different items. Here we asked if interference between objects in a perceptual task is predicted by the representational geometry across different regions of the visual system.

Participants performed a visual search task with eight categories. We measured the time to find a target from one category among distractors from a different category, (e.g. one face among seven chairs), for all possible category pairings. These reaction times were used as an index of perceptual similarity, yielding an 8x8 behavioral similarity matrix. Six new participants underwent functional neuroimaging while viewing individual items from each category. We computed the correlation in responses for all category pairings, yielding an 8x8 neural similarity matrix for each region.

We found a significant correlation between behavioral and neural similarity in ventral-temporal (r=0.62), lateral-temporal (r=0.48), and dorsal-parietal cortex (r=0.28), but not early visual cortex (r=-0.07). To explore the spatial locus, each region was divided into ten ROIs based on overall voxel activity. The correlations in these sub-regions remained high throughout ventral-temporal and lateral-temporal cortex (rs>0.39; Ps<0.05).

This uniformity in the brain-behavior correlations across the ventral stream is surprising given the well-known differences in response selectivity, and suggests that different regions of this cortex may be emphasizing different aspects of a common perceptual feature space. Broadly, these results suggest that the representational geometry across high-level ventral visual cortex constrains object perception.

Cohen, M., Konkle, T., Nakayama, K., & Alvarez, G. A. (2014). Exploring the representational geometry of object representation in the ventral stream using brain-behavior correlations. Poster presented at the annual meeting of the Cognitive Neuroscience Society, April 5-8, Boston, MA.