Abstract
According to the normalization framework the neural response to multiple stimuli is normalized by the response of surrounding neurons. Here we attempt to assess the contribution of object-category selectivity - a fundamental feature of high-level visual cortex – to the normalized response to simultaneously-presented multiple categories. Taken together the normalization model and the spatial proximity of category-selective areas, we predicted that the representation of multiple categories would be influenced by the selectivity to all of its components. Particularly, we hypothesized that the relative contribution of each category would be correlated with the selectivity to each of the categories, but in an opposing manner. In an fMRI study, participants were presented with a compound stimulus made of two components: face+body or face+object as well as with isolated face, body and object stimuli. We used a linear model to estimate the relative contribution of each component to the representation of the compound stimulus. Results show that the response to the compound stimuli in face, body and object-selective areas is a weighted mean of the response to each of the isolated components, consistent with a normalization model. The response to the compound stimulus was dominated by the preferred category, but was also influenced by the non-preferred category. A searchlight analysis further shows that the contribution of each isolated component to the compound stimulus was positively correlated to the voxel’s selectivity to that component and negatively correlated to the selectivity to the other component in category selective cortex but not in early visual cortex. The same pattern was observed for the face-body and for face-object compound stimuli. We conclude that spatial proximity among category-selective areas together with a normalization mechanism enables a representation of a compound stimulus that preserves the information of each of its categories while maintaining the neural response within the dynamic range.