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Cibu Thomas, Dwight Kravitz, Chris Baker; Position in space defines the structure of object representations throughout the ventral visual pathway. Journal of Vision 2011;11(11):875. doi: 10.1167/11.11.875.
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© ARVO (1962-2015); The Authors (2016-present)
In both monkey and human, there is stronger activation for stimuli presented in the contralateral visual field. This bias extends from low-level to high-level regions along the ventral visual pathway and contributes to the position dependence of object recognition. However, the impact of the contralateral bias on the structure of object representations along the ventral visual pathway remains unclear. Here, we used fMRI to localize cortical regions-of-interest (ROIs), selective for faces, bodies, objects and scenes. Next, in an ungrouped event-related experiment, participants were presented with 7 exemplars from each of 7 categories (bodies, cars, chairs, faces, fans, flowers and houses), 7 degrees of visual angle to the left or right of fixation. We then extracted the response to each of the 98 exemplars from each ROI and used multi-voxel pattern analyses to: 1) decode category in particular ROIs and visual fields, and 2) examine the structure of exemplar representations as a function of both visual field and ROI in the two hemispheres. Consistent with prior reports, we found better decoding of category in the contra- than ipsilateral field across all the ROIs. To examine the structure of representations we extracted the pattern of between-exemplar correlations for each combination of visual field and ROI. We then correlated these patterns with each other and found that visual field was the primary determinant of the structure of representations, with high correlations across ROIs within- but not between-fields. Thus, the correlation between regions in the same hemisphere with different selectivity (faces/houses) was greater than the correlation between regions in different hemispheres with the same selectivity. This suggests that high-level visual object representations are common across ROIs, but differ across retinotopic positions. These findings lead to the prediction that agnosias resulting from unilateral lesions should be more severe in the contralateral field.
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