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.

Occipital Transcranial Magnetic Stimulation Has Opposing Effects on Visual and Auditory Stimulus Detection: Implications for Multisensory Interactions

“…Second, although acoustic startle responses may go along with changes in cortical excitability, they would not be expected to be limited to specific latencies coinciding with visual input given that they would likely generalize to other cortical areas. Third, a previous TMS study of tactile influences on TMS-induced phosphene perception showed that the likelihood of perceiving a visual phosphene (induced by subthreshold TMS) is greatest when the tactile pulse precedes occipital TMS by 60ms (Ramos-Estebanez et al, 2007), matching the peak-latency of increased visual cortex excitability we observed. Notably, their use of subthreshold tactile stimulation, which did not reach perceptual awareness, excluded startle responses as a basis for increased cortical excitability (namely, enhanced phosphene perception).…”

“…We show that occipital TMS has opposing effects on visual and auditory stimulus detection over identical time periods. In a follow-up experiment, we further demonstrate that external auditory stimuli enhance visual cortex excitability as measured by phosphene induction via TMS (Silvanto et al, 2006;Bestmann et al, 2007;Ramos-Estebanez et al, 2007).…”

“…After the above experimental session, all participants were asked whether they had perceived visual sensations other than the presented white disc during the experiment. TMS over the occipital pole can induce illusory visual percepts (called phosphenes) if applied at sufficiently high intensities (Meyer et al 1991;Cowey and Walsh, 2000), but often requires several perceptual training sessions (Kammer et al, 2005b;Ramos-Estebanez et al, 2007). None of participants reported having seen phosphenes or any other illusory visual sensations, except one.…”

“…To further address the issue of multisensory interactions in early visual areas, we tested for auditory-induced modulation of visual cortex excitability by using phosphene perception as a probe measure of cortical excitability, similar to previous studies (Silvanto et al, 2006;Bestmann et al, 2007;Ramos-Estebanez et al, 2007). We retested those subjects who perceived phosphenes and were available to take part in additional sessions (n ϭ 6) and one participant who initially did not perceive phosphenes but agreed to undergo additional training after which he also reliably perceived a phosphene (total n ϭ 7).…”

Seeing with Your Fingers: A Transcranial Magnetic Stimulation Investigation of Multimodal Sensory Perception

“…In their recent Journal of Neuroscience article, Ramos-Estebanez et al (2007) bridge this gap by taking a novel approach to early visuotactile interactions. The authors asked whether subthreshold sensory stimulation can sum across modalities to produce a reportable percept and, if so, what is the precise timing of the interaction.…”