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.

Parietal Mechanisms for Transsaccadic Spatial Frequency Perception: An fMRI Study

Posterior parietal cortex (PPC), specifically right supramarginal gyrus, is involved in transsaccadic memory of object orientation for both perception and action. Here, we investigated whether PPC is involved in transsaccadic memory of other features, namely spatial frequency. We employed a functional magnetic resonance imaging paradigm where participants briefly viewed a grating stimulus with a specific spatial frequency that later reappeared with the same or different frequency, after a saccade or continuous fixation. Post-saccadic frequency modulation activated a region in the right hemisphere spanning medial PPC (ventral precuneus) and posterior cingulate cortex. Importantly, the site of peak precuneus activation showed saccade-specific feature modulation (compared to fixation) and task-specific saccade modulation (compared to a saccade localizer task). Psychophysiological interaction analysis revealed functional connectivity between this precuneus site and the precentral gyrus (M1), lingual gyrus (V1/V2), and medial occipitotemporal sulcus. This differed from the transsaccadic orientation network, perhaps because spatial frequency signaled changes in object identity. Overall, this experiment supports a general role for PPC in transsaccadic vision, but suggests that different networks are employed for specific features.