Abstract
A large number of neuroimaging studies have shown that information about object category can be decoded from regions of the ventral visual pathway. One question is how this information might be functionally exploited in the brain. In an attempt to help answer this question, some studies have adopted a neural distance-to-bound approach, and shown that distance to a classifier decision boundary through neural activation space can be used to predict reaction times (RT) on animacy categorization tasks. However, these experiments have not controlled for possible visual confounds, such as shape, in their stimulus design. In the present study we sought to determine whether, when animacy and shape properties are orthogonal, neural distance in low- and high-level visual cortex would predict categorization RTs, and whether a combination of animacy and shape distance might predict RTs when categories crisscrossed the two stimulus dimensions, and so were not linearly separable. In line with previous results, we found that RTs correlated with neural distance, but only for animate stimuli, with similar, though weaker, asymmetric effects for the shape and crisscrossing tasks. Taken together, these results suggest there is potential to expand the neural distance-to-bound approach to other divisions beyond animacy and object category.
Highlights
Using multivariate pattern analysis (MVPA) several neuroimaging studies have investigated object category-selectivity in regions of the ventral visual pathway[1]
In the present study we sought to determine whether neural distance would predict observer reaction times (RT) when stimuli are balanced along orthogonal object category and shape dimensions
As cross-decoding was used to both investigate whether category information can be discriminated by image properties and to isolate category-specific information in the ventral pathway[5,6,31], our results cannot be explained by the sorts of image properties captured by GIST2–4
Summary
Using multivariate pattern analysis (MVPA) several neuroimaging studies have investigated object category-selectivity in regions of the ventral visual pathway[1]. Based on the predictions of classic psychophysics[12,13], if the neural activation space reflects the representation that determines observe categorization response, RTs should negatively correlate with distance from the decision boundary[14]. Recent studies have used NDBA to predict observer RTs for animacy categorization tasks based on neural distances measured with human fMRI and MEG15–18.
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