Medial occipital cortex participates in a cortical network for transsaccadic feature discrimination: an fMRI paradigm

To date, the cortical correlates for human transsaccadic vision have been probed for single object features such as orientation (associated with parietal repetition suppression) and spatial frequency (associated with occipital repetition enhancement). Here, we used functional magnetic resonance imaging to distinguish cortical modulations associated with transsaccadic perception of multiple object features. Participants (n=21) viewed a 2D object and then, after sustained fixation or a saccade, judged whether the shape or orientation of the re-presented object had changed. Since feature change was randomized, participants had to remember both features across saccades to perform the task. A whole-brain voxelwise contrast (Saccade > Fixation; n=17) uncovered areas that might be specialized for transsaccadic memory, updating and/or perception, including medial occipital, dorsomedial posterior parietal, and dorsal frontal cortex. Searching within these regions, we then employed a feature contrast (Orientation vs. Shape change). This contrast revealed feature-specific modulations (consistent with shape change enhancement) in left medial occipital cortex. The peak site (left cuneus) showed contralateral functional connectivity with early visual cortex (lingual gyrus), object-processing areas (occipitotemporal cortex) and saccade / motor areas in parietal cortex. These observations show that medial occipital cortex participates in a cortical network involved in transsaccadic feature perception. Together with the previous literature, this suggests separate mechanisms for transsaccadic perception of intrinsic object features (spatial frequency, shape) versus object location and orientation.

Chances and challenges for an active visual search perspective

Using fixations as the fundamental unit of visual search is an appealing gear change in a paradigm that has long dominated attention research. To truly inform theories of search, however, additional challenges must be faced, including (1) an empirically motivated definition of fixation in the presence of fixational saccades and (2) the biases and limitations of transsaccadic perception and memory.