Contralateral Biases in Category-selective Areas Are Stronger in the Left Hemisphere than the Right Hemisphere

Contralateral bias is a well-known feature of early visual cortex, but how it varies across higher-level, category-selective visual cortex and how much that bias differs between preferred and nonpreferred is unclear. Here, we examined 12 category-selective regions across 4 experiments using peripherally presented faces, bodies, houses, and scenes, to measure the difference in contralateral bias between preferred and nonpreferred stimuli. The results showed a substantial range of contralateral biases across the category-selective regions, similar to prior studies using category-selective stimuli [Silson, E. H., Groen, I. I., & Baker, C. I. Direct comparison of contralateral bias and face/scene selectivity in human occipitotemporal cortex. Brain Structure and Function, 227, 1405-1421, 2022; Gomez, J., Natu, V., Jeska, B., Barnett, M., & Grill-Spector, K. Development differentially sculpts receptive fields across early and high-level human visual cortex. Nature Communications, 9, 788, 2018; Silson, E. H., Groen, I. I. A., Kravitz, D. J., & Baker, C. I. Evaluating the correspondence between face-, scene-, and object-selectivity and retinotopic organization within lateral occipitotemporal cortex. Journal of Vision, 16, 14, 2016; Kay, K. N., Weiner, K. S., & Grill-Spector, K. Attention reduces spatial uncertainty in human ventral temporal cortex. Current Biology, 25, 595-600, 2015; Silson, E. H., Chan, A. W.-Y., Reynolds, R. C., Kravitz, D. J., & Baker, C. I. A retinotopic basis for the division of high-level scene processing between lateral and ventral human occipitotemporal cortex. Journal of Neuroscience, 35, 11921-11935, 2015]. These contralateral biases were stronger in the left hemisphere regions than right, an asymmetry that was unchanged even when participants performed an attentionally demanding task. Thus, corresponding pairs of category-selective regions (e.g., left fusiform face area [lFFA] and right FFA [rFFA]) do not appear to be mirror images of each other; instead, the right hemisphere regions engage in greater integration of information from the two hemifields. The rFFA and right fusiform body area-both located on the right lateral fusiform gyrus-consistently had the weakest contralateral biases. That this asymmetry was most pronounced in the fusiform gyrus may account for why a unilateral lesion to the rFFA but not the lFFA can produce prosopagnosia. Together, our findings demonstrate that category-selective areas show pronounced differences in the extent of their contralateral biases and that a consistent asymmetry in the strength of the contralateral biases exists between the two hemispheres.