Trustworthiness and electrocortical processing of emotionally ambiguous faces in student police officers

Abstract

Perceptions of emotional facial expressions and trustworthiness of others guides behavior and has considerable implications for individuals who work in fields that require rapid decision making, such as law enforcement. This is particularly complicated for more ambiguous expressions, such as 'neutral' faces. We examined behavioral and electrocortical responses to facial expressions in 22 student police officers (18 males; 23.2 ± 3.63 years). Participants completed an emotional face appraisal task that involved viewing three expressions (fearful, neutral, happy) and were asked to identify the emotion and rate the trustworthiness of each face. The late positive potential (LPP), an event-related potential that tracks emotional intensity and/or salience of a stimulus, was measured during the task. Overall, participants rated neutral faces similarly to fearful faces and responded fastest to these expressions. Neutral faces also elicited a robust late LPP response that did not differ from LPP to fearful or happy faces, and there was substantial individual variation in trustworthiness ratings for neutral faces. Together, 'neutral' facial expressions elicited similar trustworthiness ratings to negatively-valenced stimuli. Brain and behavioral responses to neutral faces also varied across student officers; thus, encounters with ambiguous faces in the field may promote increased perceived threat in some officers, which may have real-world consequences (e.g., decision to shoot, risk of psychopathology).

Keywords: Emotion; Late positive potential; Police officers; Trustworthiness.

Figure 1.

Exemplar EFAT trial for a fearful facial expression. During the trustworthiness rating period, participants selected how trustworthy they perceived the face on a scale from 0–100 (0 = low trustworthiness, 100 = high trustworthiness). Of note, face stimuli shown are from a standardized database of 3-dimensional images of emotional facial expressions (Gur et al., 2002) and reprinted here with permission.

Figure 2.

Mean trustworthiness rating (a), accuracy (b), and reaction time (c) for each condition. During the emotion recognition period, participants selected the emotion that best represented the affect displayed by the face (fear, happy, neutral) for which accuracy and reaction time were recorded. Error bars represent standard error of the mean. *denotes significant p-value after correcting for multiple comparisons (Trustworthiness: p ≤ .02; Accuracy, Reaction Time: p ≤ .008).

Figure 3.

Late positive potential (LPP) grand-average waveforms for each condition in the emotional faces task (EFAT) (a), mean activity of early and late LPP (b), and head maps depicting the spatial distribution of voltage differences for each condition (c). Of note, the LPP response shown in panel (a) was pooled across four parieto-occipital electrodes, where LPP was shown to be maximal. In addition, positive amplitude is plotted downwards on the y-axis, for panel (a).