"What?" and "where?" versus "what is where?": The impact of task on coding of object form and position in the lateral occipital complex

Abstract

Fast and accurate recognition of both the identities and positions of objects in visual space is critical to deciphering visual environments. Studies in both humans and nonhuman primates have demonstrated that neural populations in ventral temporal visual areas are jointly tuned to both the form and position of objects, allowing information about the identities of objects to be "tagged" with their positions. Because not all behaviors demand that the identities of objects be associated with position information with equal precision, however, the present study asked whether the spatial tuning of form-encoding populations in the human lateral occipital complex (LOC) is sculpted by task demands. Subjects were scanned using functional magnetic resonance imaging while viewing matches of the game Rock, Paper, Scissors played with exemplar pairs from those categories. Subjects first performed a repetition-detection task that depended on object form but not position; subsequently, subjects viewed the same stimuli while determining the position of each pair's "winner," a task that depended upon the conjunction of object form and position. Compared to data from the initial scan, multivoxel activity patterns evoked in the lateral occipital (LO) subdivision of LOC while subjects judged winners showed enhanced sensitivity to the relative positions of objects in pairs. Although superficially consistent with dynamic position tuning, this effect appears to be attributable to an accompanying task-dependent improvement in the sensitivity of LO populations to object form. The results thus suggest that the spatial tuning of form-encoding populations in LO does not depend upon the precision of spatial information demanded by a task.