Abstract
The purpose of the study was to compare event-related potentials (ERPs) to different transitions between emotional and neutral facial expressions. The stimuli contained a single transition between two different images of the same face, giving a strong impression of changing expression though apparent motion whilst eliminating change in irrelevant stimulus variables such as image contrast or identity. Stimuli were calibrated for intensity, valence and perceived emotion category and only trials where the target emotion was correctly identified were included. In the first experiment, a magnification change (zoom) was a control condition. Transitions from neutral to angry expressions produced a more negative N1 with longer peak latency, and more positive P2 than did an increase in magnification. Critically, response to neutral following angry, relative to neutral following magnified, showed a generally more negative ERP with a delayed N1 peak and reduced P2 amplitude. In the second experiment, comparison of neutral-happy and neutral-frightened transitions showed significantly different ERPs to emotional expression change. Responses to the reversed direction of a transition (happy-neutral and frightened-neutral) were much reduced. Unlike the comparison of angry-neutral with magnified-neutral, there were minimal differences in the responses to neutral following happy and neutral following frightened. The results demonstrate in a young adult sample the directionality of responses to facial expression dynamics, and suggest a separation of neural mechanisms for detecting expression changes and magnification changes.
Highlights
Facial expressions change: they are intrinsically dynamic
The study addressed the directionality of the event-related potentials (ERPs) response in transitions from emotional to neutral versus neutral to emotional facial expressions
The present data suggested that the direction of change from emotional to neutral or neutral to emotional expressions can influence the ERP signal and this is true for a range of emotions and is qualitatively and quantitatively different to the response to a non-emotional change in magnification of faces
Summary
Facial expressions change: they are intrinsically dynamic. All facial expressions arise from preceding expressions, and an emotional expression will often arise from a neutral facial expression and at some point return to an emotionally neutral expression, so what is needed initially is an understanding of the transitions from neutral to emotional and from emotional to neutral. Regarding the neural basis for processing dynamic facial expressions, Haxby, Hoffman and Gobbini [6] proposed that, after initial visual perception of faces in the inferior occipital gyri. ERPs to changes in facial expression (occipital face area: OFA), the fusiform face area (FFA) mediates the perception of relatively unchanging aspects of faces such as identity and gender, whereas the superior temporal sulcus (STS) mediates the perception of changeable aspects such as facial expression and gaze. If initial structural face encoding and later emotion encoding are embedded in anatomically segregated systems [6, 11], investigating changes to emotional expression should tap into the system that processes changeable aspects of faces in the STS as compared to the perception of early face signals in the OFA and stable face attributes in the FFA
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