Corrugator muscle responses are associated with individual differences in positivity-negativity bias

Abstract

Corrugator supercilii muscle activity is considered an objective measure of valence because it increases in response to negatively valenced facial expressions (angry) and decreases to positive expressions (happy). The authors sought to determine if corrugator activity could be used as an objective measure of positivity-negativity bias. The authors recorded corrugator responses as participants rated angry, happy, and surprised faces as "positive" or "negative." The critical measure of bias was the percentage of positive versus negative ratings assigned to surprised faces by each participant. Reaction times for surprise expressions were longer than for happy and angry expressions, consistent with their ambiguous valence. Participants who tended to rate surprised faces as negative showed increased corrugator activity to surprised faces, whereas those who tended to rate surprise as positive showed decreased activity. Critically, corrugator responses reflected the participants' bias (i.e., their tendency to rate surprise as positive or negative). These data show that surprised faces constitute a useful tool for assessing individual differences in positivity-negativity bias, and that corrugator activity can objectively reflect this bias.

Figure 1

A depiction of the experimental design. Angry, happy, and surprised faces were presented for either 17, 50, or 1,000 ms. The task for each face was to decide whether the expression was positive or negative. The second fixation appeared in red. Reprinted with permission from MacArthur Network.

Figure 2

Individual differences in rating valence of surprised expressions. (A) Angry faces are rated consistently negative, happy faces are consistently positive, and surprised ratings vary from negative to positive, revealing individual differences in how people interpret the valence of these expressions. (B) There was a significant positive correlation between percentage “negative” responses to surprised expressions from Time 1 to Time 2 (1 year later).

Figure 3

Individual difference in corrugator supercilii activity in response to surprised facial expressions, as compared to those with clear valence. In the S_neg group, surprised expressions elicit significantly greater standardized corrugator activity than happy expressions that is not significantly different from angry expressions. For the S_pos group, surprised expressions elicit activity that is significantly lower than angry expressions that is not significantly different from happy expressions.

Figure 4

Corrugator supercilii activity reflects an individual’s bias more than their valence judgment on a given trial. (A) Time-course activity for participants who tend to rate surprise as negative reveals no difference in activity for trials in which they rate surprise as positive, as compared to trials in which they rate surprise as negative. (B) Time-course activity for participants who tend to rate surprise as positive reveals no difference in activity for trials in which they rate surprise as negative, as compared to trials in which they rate surprise as positive.

Figure 5

Electrodermal activity to surprised facial expressions, as compared to those with clear valence. There was no significant difference in standardized electrodermal activity for angry and happy expressions, though surprised expressions elicited greater activity than expressions of clear valence.