Brief communicationFace-related ERPs are modulated by point of gaze
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, , 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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2018, CortexCitation Excerpt :In addition, studies that investigated the neural response to facial features typically compared features to whole faces centered on the nasion or nose. However, given the evidence that featural fixation within a face modulates N170 responses (de Lissa et al., 2014; Itier & Preston, 2018; McPartland et al., 2010; Neath & Itier, 2015; Neath-Tavares & Itier, 2016; Nemrodov et al., 2014), the comparison of isolated features to faces should be made when fixation location is controlled. Therefore, the current study compared the N170 response to the same facial features presented in isolation and within the context of a face, using a gaze-contingent procedure.
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2017, Brain and CognitionCitation Excerpt :Event-related potentials (ERPs) have been widely used to examine brain activity in response to others’ eye gaze in healthy subjects. The N170, which occurs in response to gaze perception, has been examined in the occipito-temporal region (Carrick, Thompson, Epling, & Puce, 2007; Conty, N’Diaye, Tijus, & George, 2007; McPartland, Cheung, Perszyk, & Mayes, 2010; Nomi, Frances, Nguyen, Bastidas, & Troup, 2013). Several studies reported that the N170 amplitude was greater in response to images of the eye region alone, compared with full face images.
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2017, Biological PsychologyCitation Excerpt :This location for the P300 was chosen as it overlaps with regions described in prior literature on dynamic faces (Carrick et al., 2007; Conty et al., 2007). P100 and N170 electrodes were selected based on prior research (Cheung, Rutherford, Mayes, & McPartland, 2010; McPartland, Cheung, Perszyk, & Mayes, 2010) and maximal observed amplitude of the P100, N170, and P300. As our stimuli exhibit subtle visual change, i.e., only mouth or eyes opening instead of an image appearing, we did not see the large amplitude P100 and P300 s commonly associated with face perception studies.
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2014, NeuroImageCitation Excerpt :However, recent studies have reported changes in N170 amplitude as a function of fixation location on the face. Fixation on the nasion and mouth yielded larger N170 amplitudes than fixation on the nose in one study (McPartland et al., 2010), although eye-tracking was not employed to ensure participants were indeed fixating at these fixation locations during face presentation. Another study using a gaze contingent paradigm with eye tracking reported largest N170 response for fixation on the nasion when faces were presented upright and for fixation on the mouth when faces were presented inverted (Zerouali et al., 2013).