A fronto-posterior network involved in visual dimension changes

Objects characterized by a unique visual feature may pop out of their envir onment. When participants have to search for such "odd-one-out" targets, de tection is facilitated when targets are consistently defined within the sam e feature dimension (e.g., color) compared with when the target dimension i s uncertain (e.g., color or motion). Further, with dimensional uncertainty, there is a cost when a given target is defined in a different dimension to the preceding target, relative to when the critical dimension remains the same. Behavioral evidence suggests that a target dimension change involves a shift of attention to the new dimension. The present fMRI study revealed increased activation in the left frontopolar cortex, as well as in posterio r visual areas of the dorsal and ventral streams, specific to changes in th e target dimension. In contrast, activation in the striate cortex was decre ased. This pattern suggests control of cross-dimensional attention shifts b y the frontopolar cortex, modulating visual cortical processing by increase d activation in higher-tier visual areas and suppression of activation in l ower-tier areas.