Visual phosphene perception modulated by subthreshold crossmodal sensory stimulation

Abstract

Crossmodal sensory interactions serve to integrate behaviorally relevant sensory stimuli. In this study, we investigated the effect of modulating crossmodal interactions between visual and somatosensory stimuli that in isolation do not reach perceptual awareness. When a subthreshold somatosensory stimulus was delivered within close spatiotemporal congruency to the expected site of perception of a phosphene, a subthreshold transcranial magnetic stimulation pulse delivered to the occipital cortex evoked a visual percept. The results suggest that under subthreshold conditions of visual and somatosensory stimulation, crossmodal interactions presented in a spatially and temporally specific manner can sum up to become behaviorally significant. These interactions may reflect an underlying anatomical connectivity and become further enhanced by attention modulation mechanisms.

Figure 1.

Test conditions used in the experiment in conjunction to TMS delivered to the occipital cortex. PES was delivered in conjunction with occipital TMS at varying ISIs (40, 60, 80, and 100 ms) to either the right or left hand and with the hands in the uncrossed or crossed position.

Figure 2.

Rate of phosphene detection for each condition (left and right hand in the crossed and uncrossed position) and for each ISI tested. The largest crossmodal enhancement effect was apparent after subthreshold stimulation of the right hand at an ISI of 60 ms and with the hands in the uncrossed position. Error bars represent SEM.