Approach of visual stimuli modulates spatial expectations for subsequent somatosensory stimuli.

To examine how the approach of visual stimuli toward the body influences expectations regarding subsequent somatosensory stimuli, we recorded event-related brain potentials (ERPs; nose reference) during a simple reaction time to somatosensory stimuli task. Twelve participants were asked to place their arms on a desk, and three LEDs were placed between their arms at equal intervals. Electrical stimuli were presented to the left (or right) wrist at a high probability (80%) or to the opposite wrist at a low probability (20%). Each trial was composed of three visual stimuli followed by one electrical stimulus. In Experiment 1, the right, center, and left (or left, center, and right) LEDs were turned on sequentially toward the wrist to which the high probability somatosensory stimuli was presented (congruent condition), or the center LED were presented three times (neutral condition). Experiment 2 was composed of the congruent condition and the inverse of the congruent condition (incongruent condition). In both experiments, the reaction times to low probability stimuli were longer than those to high probability stimuli. Moreover, the low probability stimuli elicited a larger P3 amplitude than the high probability stimuli. In addition, the P3 amplitude was higher under the visual approach condition (i.e., the congruent condition in each experiment) than under the control condition (i.e., the neutral and incongruent conditions). Furthermore, no effect on the CNV amplitude before the somatosensory stimuli was found. These results suggest that visual stimuli directed toward the body induce an automatic spatial expectation for subsequent somatosensory stimuli.