Abstract
Each time we make an eye movement the retinal image shifts, yet we typically perceive the external world as stable. Predictive remapping mechanisms contribute to this visual stability by anticipating the future position of the eye, either by shifting visual receptive fields in direction of the saccade ("retinotopic" remapping) or by shifting attentional pointers in the direction opposite to the saccade ("spatiotopic" remapping) immediately prior to the eye movement. Here we used focal transcranial magnetic stimulation (TMS) to test for the first time the role of the human posterior parietal cortex (PPC) in retinotopic and spatiotopic predictive visual remapping. In an initial experiment (modified from Hunt & Cavanagh, 2011), 20 participants judged the orientation of a target in one of two vertically aligned locations in the left visual field. Targets flashed briefly and were followed by a mask at the same location as the target or at the other location. In separate runs participants either maintained fixation or performed a vertical saccade. We observed a reliable predictive remapping effect (both retinotopic and spatiotopic) for saccade trials only, for target-mask displays flashed in the 100 ms prior to saccade onset. To investigate the role of the human PPC in predictive remapping, we implemented a second experiment in which online, high-frequency repetitive TMS (rTMS) pulses were delivered 150 ms before saccade onset, either to the right superior parietal lobule (SPL) or the primary somatosensory cortex (S1; control). We chose the SPL as the experimental site based on its high spatial selectivity. Results from nine participants again revealed a significant predictive remapping effect, but no reliable influence of stimulation of the SPL relative to the S1 control site. Future experiments will involve more participants and stimulation of the inferior parietal sulcus, which some studies have also implicated in predictive remapping processes.
Meeting abstract presented at VSS 2016