N1 enhancement in synesthesia during visual and audio–visual perception in semantic cross-modal conflict situations: an ERP study

Christopher Sinke,Hinderk M Emrich,Stefan Bleich,Daniel Wiswede,Janina Neufeld,Thomas F Münte,Gregor R Szycik

doi:10.3389/fnhum.2014.00021

Abstract

Synesthesia entails a special kind of sensory perception, where stimulation in one sensory modality leads to an internally generated perceptual experience of another, not stimulated sensory modality. This phenomenon can be viewed as an abnormal multisensory integration process as here the synesthetic percept is aberrantly fused with the stimulated modality. Indeed, recent synesthesia research has focused on multimodal processing even outside of the specific synesthesia-inducing context and has revealed changed multimodal integration, thus suggesting perceptual alterations at a global level. Here, we focused on audio–visual processing in synesthesia using a semantic classification task in combination with visually or auditory–visually presented animated and in animated objects in an audio–visual congruent and incongruent manner. Fourteen subjects with auditory-visual and/or grapheme-color synesthesia and 14 control subjects participated in the experiment. During presentation of the stimuli, event-related potentials were recorded from 32 electrodes. The analysis of reaction times and error rates revealed no group differences with best performance for audio-visually congruent stimulation indicating the well-known multimodal facilitation effect. We found enhanced amplitude of the N1 component over occipital electrode sites for synesthetes compared to controls. The differences occurred irrespective of the experimental condition and therefore suggest a global influence on early sensory processing in synesthetes.

Highlights

Synesthesia describes a specific kind of perception in which a particular stimulus in one sensory modality (“inducer”) induces a concurrent perception in another sensory modality
Synesthesia entails a special kind of sensory perception, where stimulation in one sensory modality leads to an internally generated perceptual experience of another, not stimulated sensory modality.This phenomenon can be viewed as an abnormal multisensory integration process as here the synesthetic percept is aberrantly fused with the stimulated modality
ERP RESULTS In the overall ANOVA comparing factors synesthesia, stimulation, laterality, and electrodes for the peak analysis (N1 component) we found a significant effect of synesthesia (F1,24 = 5.4, p = 0.03) and a significant effect of electrodes (F3,72 = 32.4, p = 0.00) comparing signal from frontal (F3 and F4) vs. central (C3 and C4) vs. parietal (P3 and P4) vs. occipital (O1 and O2) electrodes

Summary

Introduction

Synesthesia describes a specific kind of perception in which a particular stimulus in one sensory modality (“inducer”) induces a concurrent perception in another sensory modality. Recent research suggests synesthesia to be an extreme form of multisensory processing within a continuous spectrum of normal perceptual processes involving multiple senses (Bien et al, 2012) Following this point of view it is not surprising that synesthetes show differences in multisensory processing restricted to the inducerconcurrent sensory modalities (Brang et al, 2012; Neufeld et al, 2012c; Sinke et al, 2012b) and that these differences are similar for both grapheme-color and audio–visual synesthetes (Neufeld et al, 2012c; Sinke et al, 2012b) indicating common sensory effects for different synesthesia phenotypes. Up to now research on multimodal processing in synesthesia beyond typical inducer-concurrent perception is scarce

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