Neural Responses in Parietal and Occipital Areas in Response to Visual Events Are Modulated by Prior Multisensory Stimuli

Hamish Innes-Brown,David P. Crewther,Ayla Barutchu,Suliann Ben Hamed

doi:10.1371/journal.pone.0084331

Abstract

The effect of multi-modal vs uni-modal prior stimuli on the subsequent processing of a simple flash stimulus was studied in the context of the audio-visual ‘flash-beep’ illusion, in which the number of flashes a person sees is influenced by accompanying beep stimuli. EEG recordings were made while combinations of simple visual and audio-visual stimuli were presented. The experiments found that the electric field strength related to a flash stimulus was stronger when it was preceded by a multi-modal flash/beep stimulus, compared to when it was preceded by another uni-modal flash stimulus. This difference was found to be significant in two distinct timeframes – an early timeframe, from 130–160 ms, and a late timeframe, from 300–320 ms. Source localisation analysis found that the increased activity in the early interval was localised to an area centred on the inferior and superior parietal lobes, whereas the later increase was associated with stronger activity in an area centred on primary and secondary visual cortex, in the occipital lobe. The results suggest that processing of a visual stimulus can be affected by the presence of an immediately prior multisensory event. Relatively long-lasting interactions generated by the initial auditory and visual stimuli altered the processing of a subsequent visual stimulus.

Highlights

When a brief flash stimulus is accompanied by two brief sounds, the single flash is sometimes perceived as two discrete flashes
Neural correlates of the fusion illusion, measured using functional magnetic resonance imaging [9,10] and event-related potentials (ERPs) [6], are correspondingly reduced in the same areas
The experiment found that the electric field strength related to a flash stimulus was stronger when it was preceded by a multi-modal flash/beep stimulus, compared to when it was preceded by another uni-modal flash stimulus

Summary

Introduction

When a brief flash stimulus is accompanied by two brief sounds, the single flash is sometimes perceived as two discrete flashes This phenomenon has been termed the ‘fission’ illusion [1]. Several neuro-imaging studies [5,6,7,8] have shown that the perception of the fission illusion is correlated with increased activity in the primary visual cortex. These studies generally support the hypothesis that the illusion results from the integration of auditory and visual information, rather than the possible introduction of response biases. Disruption of the right angular gyrus in parietal cortex by trans-cranial magnetic stimulation (TMS) reduces susceptibility to the illusion [12]

Results

Discussion

Conclusion