Fixation to features and neural processing of facial expressions in a gender discrimination task

Abstract

Early face encoding, as reflected by the N170 ERP component, is sensitive to fixation to the eyes. Whether this sensitivity varies with facial expressions of emotion and can also be seen on other ERP components such as P1 and EPN, was investigated. Using eye-tracking to manipulate fixation on facial features, we found the N170 to be the only eye-sensitive component and this was true for fearful, happy and neutral faces. A different effect of fixation to features was seen for the earlier P1 that likely reflected general sensitivity to face position. An early effect of emotion (~120 ms) for happy faces was seen at occipital sites and was sustained until ~350 ms post-stimulus. For fearful faces, an early effect was seen around 80 ms followed by a later effect appearing at ~150 ms until ~300 ms at lateral posterior sites. Results suggests that in this emotion-irrelevant gender discrimination task, processing of fearful and happy expressions occurred early and largely independently of the eye-sensitivity indexed by the N170. Processing of the two emotions involved different underlying brain networks active at different times.

Neural processing of fearful and happy facial expressions during emotion-relevant and emotion-irrelevant tasks: A fixation-to-feature approach

“…A face stimulus was then presented offset so as to put the desired feature in fovea, at the location of the fixation cross. We expected to replicate the findings of Neath and Itier (2015) regarding low-level stimulus position effects on the P1, as well as the larger N170 amplitude for fixation to the eyes compared to the nose and mouth (see also de Lissa et al, 2014;Nemrodov, Anderson, Preston, & Itier, 2014). We also hoped to reproduce their distinct spatio-temporal pattern of fear and happiness effects.…”

“…Some studies have suggested that the EPN reflects the neural activity related to the processing of the emotion that is superimposed onto the normal processing of the face. This superimposed activity would sometimes start around the N170 and be responsible for the emotional effects reported for the N170 (Leppänen et al, 2008;Rellecke et al, 2011;Schupp et al, 2004), although it seems largest after the N170 peak and around the visual P2 (see Neath & Itier, 2015, for a recent example). In other words, the emotion effect on the N170 would actually reflect superimposed EPN activity (Rellecke et al, 2011;Rellecke, Sommer, & Schacht, 2012;Schacht & Sommer, 2009).…”

“…Using an eye-tracker and a gaze-contingent procedure to ensure fixation on specific facial features of fearful, happy, and neutral expressions, Neath and Itier (2015) recently reported different spatio-temporal emotion effects for happy and fearful faces. Smaller amplitudes for happy than neutral faces were seen mainly at occipital sites, starting on the P1 and most pronounced around 120ms, followed by a sustained effect until 350ms post-stimulus onset.…”

“…The present study-The Neath and Itier (2015) study employed a gender discrimination task, which was emotion-irrelevant. However, the diagnostic feature hypothesis suggests that different features might be used depending on task demands ( (Schyns, Jentzsch, Johnson, Schweinberger, & Gosselin, 2003;Schyns et al, 2007Schyns et al, , 2009;Smith & Merlusca, 2014).…”

“…In the present study, fearful, happy and neutral faces were presented with fixation to the left eye, right eye, nose and mouth using the same gaze-contingent design as Neath and Itier (2015). That is, the stimulus was presented only when an eye-tracker detected that the fixation cross was fixated for a certain amount of time.…”