Visual sensitivity shifts with perceived eye position.

Spatial attention can be defined as the selection of a location for privileged stimulus processing. Most oculomotor structures, such as the superior colliculus or the FEFs, play an additional role in visuospatial attention. Indeed, electrical stimulation of these structures can cause changes in visual sensitivity that are location specific. We have proposed that the recently discovered ocular proprioceptive area in the human postcentral gyrus (S1(EYE)) may have a similar function. This suggestion was based on the observation that a reduction of excitability in this area with TMS causes not only a shift in perceived eye position but also lateralized changes in visual sensitivity. Here we investigated whether these shifts in perceived gaze position and visual sensitivity are spatially congruent. After continuous theta burst stimulation over S1(EYE), participants underestimated own eye rotation, so that saccades from a lateral eye rotation undershoot a central sound (Experiment 1). They discriminated letters faster if they were presented nearer the orbit midline (Experiment 2) and spent less time looking at locations nearer the orbit midline when searching for a nonexistent target in a letter array (Experiment 3). This suggests that visual sensitivity increased nearer the orbit midline, in the same direction as the shift in perceived eye position. This spatial congruence argues for a functional coupling between the cortical eye position signal in the somatosensory cortex and visuospatial attention.