Eye movement related brain responses to emotional scenes during free viewing

Mona Moisala,Jari Torniainen,Jaana Simola,Markus Kivikangas,Christina M. Krause

doi:10.3389/fnsys.2013.00041

Abstract

Emotional stimuli are preferentially processed over neutral stimuli. Previous studies, however, disagree on whether emotional stimuli capture attention preattentively or whether the processing advantage is dependent on allocation of attention. The present study investigated attention and emotion processes by measuring brain responses related to eye movement events while 11 participants viewed images selected from the International Affective Picture System (IAPS). Brain responses to emotional stimuli were compared between serial and parallel presentation. An “emotional” set included one image with high positive or negative valence among neutral images. A “neutral” set comprised four neutral images. The participants were asked to indicate which picture—if any—was emotional and to rate that picture on valence and arousal. In the serial condition, the event-related potentials (ERPs) were time-locked to the stimulus onset. In the parallel condition, the ERPs were time-locked to the first eye entry on an image. The eye movement results showed facilitated processing of emotional, especially unpleasant information. The EEG results in both presentation conditions showed that the LPP (“late positive potential”) amplitudes at 400–500 ms were enlarged for the unpleasant and pleasant pictures as compared to neutral pictures. Moreover, the unpleasant scenes elicited stronger responses than pleasant scenes. The ERP results did not support parafoveal emotional processing, although the eye movement results suggested faster attention capture by emotional stimuli. Our findings, thus, suggested that emotional processing depends on overt attentional resources engaged in the processing of emotional content. The results also indicate that brain responses to emotional images can be analyzed time-locked to eye movement events, although the response amplitudes were larger during serial presentation.

Highlights

Real world scene viewing is an active process during which viewers select regions of scenes that will be processed in detail by prioritizing highly salient and unexpected stimuli at the expense of other stimuli and ongoing neural activity
In order to control for the possibility that the emotional LPPresponses in the parallel condition were affected by earlier differences between the emotional conditions during or after the offset of the saccadic eye movement, we analyzed the event-related potentials (ERPs) amplitudes between −50 and 50 ms around the first target entry
Most likely due to differences in saccade durations, there is some jitter in the latencies of the Lambda responses resulting in longer responses than the ones typically observed in studies using the co-registration of eye movements and EEG

Summary

Introduction

Real world scene viewing is an active process during which viewers select regions of scenes that will be processed in detail by prioritizing highly salient and unexpected stimuli at the expense of other stimuli and ongoing neural activity. Visual search studies propose that emotional detectors work preattentively by directing attention automatically toward threat without conscious effortful processing These studies have shown that potentially threatening stimuli are found efficiently among neutral distractors (Öhman et al., 2001; Blanchette, 2006; Fox et al, 2007). A decrease in the amplitudes of the ssVEPs and in target detection rates have been observed when the primary attentional task (detecting coherent motion of dots) is superimposed over pictures of emotional scenes as compared to neutral scenes (Hindi Attar et al, 2010) Taken together, these studies support the view that affective processing can occur without allocation of attentional resources, and that emotional processing precedes semantic processing (i.e., the affective primacy hypothesis)

Objectives

Methods

Results

Conclusion