Elsevier

Neuropsychologia

Volume 48, Issue 12, October 2010, Pages 3657-3660
Neuropsychologia

Brief communication
Face-related ERPs are modulated by point of gaze

https://doi.org/10.1016/j.neuropsychologia.2010.07.020Get rights and content

Abstract

This study examined the influence of gaze fixation on face-sensitive ERPs. A fixation crosshair presented prior to face onset directed visual attention to upper, central, or lower face regions while ERPs were recorded. This manipulation modulated a face-sensitive component (N170) but not an early sensory component (P1). Upper and lower face fixations elicited enhanced N170 amplitude and longer N170 latency. Results expand upon extant hemodynamic research by demonstrating early effects at basic stages of face processing. These findings distinguish attention to facial features in context from attention to isolated features, and they inform electrophysiological studies of face processing in clinical populations.

Introduction

Human face perception is a vital social function subserved by specialized brain mechanisms. Event-related potential (ERP) studies reveal a face-sensitive negative component peaking approximately 170 ms after viewing a face (N170; Bentin, Allison, Puce, Perez, & McCarthy, 1996). Relative to other visual stimuli, the N170 elicited by faces tends to be larger in amplitude and shorter in latency. Because of its short latency, sensitivity to perturbations in face configuration (e.g., face inversion), and relative insensitivity to higher order features (e.g., identity and emotion), the N170 is hypothesized to mark structural encoding, an early stage of face perception (Eimer, 2000). Isolated face parts also evoke an N170, with eyes eliciting the greatest amplitude, followed by whole faces and then noses and mouths (Bentin et al., 1996). This differential responsiveness to the eyes and an accelerated developmental maturation of the N170 elicited by eyes (Taylor, Edmonds, McCarthy, & Allison, 2001) has spurred speculation that the component may reflect activity in brain regions specifically subserving eye detection. With respect to N170 latency, intact faces evoke the shortest latencies, followed by eyes then noses and mouths (Bentin et al., 1996).

Though previous ERP research has examined N170 response to isolated facial features, attention to facial features within the context of an intact face remains unexplored via electrophysiological methods. Functional magnetic resonance imaging research (fMRI) indicates that manipulating attention to the eyes and mouths modulates hemodynamic activity in face-related areas, such as the fusiform gyrus (FG), with attention to these regions most strongly activating the FG in typical adults (Morris, Pelphrey, & McCarthy, 2007). These findings bear relevance to understanding face-related ERPs, as source estimation and co-recording of ERP and fMRI suggest neural generators of the N170 in FG (Itier and Taylor, 2004, Rossion et al., 2003, Sadeh et al., 2010, Shibata et al., 2002).

The current study extends extant neuroimaging work by using electrophysiological methods to investigate the influence of point of gaze on face-related brain activity. This approach expands upon current understanding by (a) extricating the influence of differential attention to eyes versus mouths, (b) examining attention to faces in a more natural presentation, i.e., without a superimposed fixation crosshair, and (c) applying the temporal resolution of ERP to specifically examine modulation at the earliest stages of face perception. ERPs were recorded as typical adults viewed neutral faces without a fixation crosshair and with a variable fixation crosshair directing attention to the upper, central, or lower face. We hypothesized that visual fixations to the eyes would elicit N170 with enhanced amplitude and shorter latency relative to other fixation positions. Though previous research has not consistently revealed face-selective effects at an earlier sensory component, the P1, we explored this ERP component to determine whether gaze manipulation effects might be exerted through low-level visuoperceptual mechanisms. We did not predict P1 modulation by point of gaze.

Section snippets

Methods

Participants included 28 typically developing adults enrolled in an ongoing ERP study in the Developmental Electrophysiology Laboratory at the Yale Child Study Center (http://childstudycenter.yale.edu/del). Participants were screened by self-report for current or historical brain injury or disease and for normal or corrected-to-normal visual acuity. Thirteen participants’ data were excluded from analysis for: equipment failure (n = 1), visual impairment (n = 1), excessive EEG artifact (n = 11). The

Neural response to faces

To confirm the presence of a face-selective N170, faces and houses were compared across viewing conditions using univariate repeated measures ANOVA with condition (face/house) and hemisphere (left/right) as within-subjects factors. For amplitude, N170 to faces but not houses was reflected in a main effect of condition [F(1,14) = 31.11, p < .01, ηpartial2=.69, observed power = .99], indicating larger amplitude to faces across hemispheres. Faces also elicited an N170 with shorter latency in the right

Discussion

The present study examined electrophysiological brain response to faces while manipulating point of gaze. Prior hemodynamic work has shown increased activity in face-related brain regions associated with viewing of the internal features of the face; research has not yet addressed whether directing attention to eyes versus mouths differentially modulates activity, whether modulation is contingent upon superimposition of a crosshair on a face, or whether modulation occurs at early stages of face

Acknowledgements

This work was supported by the Anna Freud Centre-University College London-Yale Child Study Center program (CC), the Gustavus and Louise Pfeiffer Research Foundation (LCM), NIMH R03 MH079908 (JM), NIMH K23MH086785 (JM), a NARSAD Young Investigator Award (JM), and CTSA Grant Number UL1 RR024139 (JM, LCM) from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH), and NIH roadmap for Medical Research (USA). Its contents are solely the

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