fMR-adaptation reveals separate processing regions for the perception of form and texture in the human ventral stream.

We recently demonstrated that attending to the form of objects and attending to their surface properties activated anatomically distinct regions of occipito-temporal cortex (Cant and Goodale, Cereb Cortex 17:713-731, 2007). Specifically, attending to form activated the lateral occipital area (LO), whereas attending to texture activated the collateral sulcus (CoS). Although these regions showed preferential activation to one particular stimulus dimension (e.g. texture in CoS), they also showed activation to other, non-preferred stimulus dimensions (e.g. form in CoS). This raises the question as to whether the activation associated with attention to form in CoS, for example, represents the actual processing of object form or instead represents the obligatory processing of object texture that occurred when people attended to form. To investigate this, we conducted an fMR-adaptation experiment which allowed us to examine the response properties of regions specialized for processing form, texture, and colour when participants were not explicitly attending to a particular stimulus dimension. Participants passively viewed blocks where only one dimension varied and blocks where no dimensions varied, while fixating a cross in the centre of the display. Area LO was most sensitive to variations in form, whereas the CoS was most sensitive to variations in texture. As in our previous study, no regions were found that were most sensitive to variations in colour, but unlike the results from that study, medial regions of the ventral stream along the fusiform gyrus and CoS showed some selectivity to colour. Taken together, these results replicate the findings from our previous study and provide additional evidence for the existence of separate processing pathways for form and surface properties (particularly texture) in the ventral stream.