Abstract
In a typical visual Event Related Potential (ERP) study, the stimulus is presented centrally on the screen. Normally an ERP response will be measured provided that the participant directs their gaze towards the stimulus. The aim of this study was to assess how the N400 component of an ERP was affected when the stimulus was presented in the foveal, parafoveal or peripheral vision of the participant’s visual field. Utilizing stimuli that have previously produced an N400 response to action incongruities, the same stimuli sequences were presented at 0°, 4°, 8° and 12° of visual angle from a fixation location. In addition to the EEG data, eye tracking data were recorded to act as a fixation control method and to allow for eye artifact detection. The results show a significant N400 effect in the right parieto-temporal electrodes within the 0° visual angle condition. For the other conditions, the N400 effect was reduced (4°) or not present (8° and 12°). Our results suggest that the disappearance of the N400 effect with eccentricity is due to the fixation distance to the stimulus. However, variables like attentional allocation could have also had an impact on the results. This study highlights the importance of presenting a stimulus within the foveal vision of the participant in order to maximize ERP effects related to higher order cognitive processes.
Highlights
When visual gaze remains relatively still, known as a fixation, the spatial resolution of the human visual field changes as a function of the distance from the center of the fixation point [1]
One for each of eccentricity condition, showed the effect that the fixation distance to the stimuli had on the N400 component of the Event Related Potential (ERP)
In the right parietotemporal region of the scalp, the results indicated a congruency by time interaction in the repeated measures analysis of variance (ANOVA), F(3.51, 59.77) = 2.838, p = 0.038
Summary
When visual gaze remains relatively still, known as a fixation, the spatial resolution of the human visual field changes as a function of the distance from the center of the fixation point [1]. Researchers often divide the visual field into three areas: foveal, parafoveal and peripheral. Foveal vision is the area with the highest visual acuity, extending approximately 2° around the fixation point. In the parafoveal area the visual acuity decreases. It extends between 2° and 5° around the fixation point. The peripheral vision extends from 5° around the fixation point until the edge of the field of view. In this area, visual acuity decreases abruptly [2,3]. Parafoveal and peripheral vision play a role when planning eye movements and PLOS ONE | DOI:10.1371/journal.pone.0134339. Parafoveal and peripheral vision play a role when planning eye movements and PLOS ONE | DOI:10.1371/journal.pone.0134339 July 29, 2015
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