Abstract
Both human occipito-temporal and parietal cortices exhibit strong attentional effects as well as robust object representations. To understand how attention may interact with object representations, here we examined fMRI response patterns in topographic and functionally defined regions in occipito-temporal and parietal cortices to images of eight object categories under different attentional tasks. Participants viewed a sequential presentation of 10 exemplars of each object category, with each exemplar paired with a color, and performed a one-back repetition detection on either the objects or the colors. Using SVM classifiers, we examined the effect of attentional modulations 1) by comparing object classification when participants attended to object to that when they attended to color, and 2) by classifying the same objects across the two attentional tasks. In Experiment 1 colored dots were superimposed on uncolored objects. In both occipito-temporal and parietal regions object classification accuracy was higher when participants attended to objects than colors. Thus diverting attention away from the objects degraded object responses. A significant classification of the attentional tasks was also observed in these regions. This could reflect the degradation of object responses in the color task and/or a difference between the representations for the two attentional tasks. In Experiment 2 color appeared directly on the objects. None of the occipito-temporal and parietal regions examined showed a difference in object classification across the two attentional tasks, indicating automatic processing of all the features of an attended stimulus in an object-based manner. Interestingly, significant classification of the two attentional tasks was still observed in parietal but not in occipito-temporal regions. A representational similarity analysis further confirmed the results of the two experiments, showing that orthogonal representations for objects and attentional tasks can co-exist in parietal regions, but attentional effects only appear through modulations of object representations in occipito-temporal regions.
Meeting abstract presented at VSS 2016