Abstract:

Aggressive individuals show abnormality in recognizing angry expressions. Limited research has specifically examined the nature of the dysfunction in expression categorization in normal individuals with high-level aggression. The current study aimed to examine which hypothesis, the response bias or the perceptual sensitivity, could account for the abnormality in identifying angry faces in normal individuals with high-level aggression. By using the Chinese version of Buss- Perry Aggression Questionnaire (AQ-CV), 29 high-level aggressive individuals and 25 low-level aggressive individuals were chosen as participants from 846 undergraduates. Using FaceGen Modeller software, the prototype photographs of anger and fear were morphed to create a linear continuum of 11 facial images with 10% increment between each intermediate image. By employing a categorical perception paradigm, participants were told to complete a discrimination task and then an identification task. In the identification task, the shift points, indicating the emotional intensity where the participants' identification was 50%, and the response slopes, indicating how rapidly the changes have happened at the shift points in the anger to fear continuum, were measured. In the discrimination task, participants had to decide whether the second face of the pair was exactly the same as the first one and only accuracy was analyzed. We compared the differences of shift point and response slope on identifying morphed expressions and the accuracy on discriminating anger to fear images between individuals with high- and low-level aggression. In the identification task, the shift point and slope of the anger to fear continuum were analyzed with Independent-Sample T Test, which revealed a significant difference between the two groups on response slope, but not shift point. The slope of individuals with high-level aggression was significantly higher than that of the individuals with low-level aggression. By repeated measure ANOVA, it showed that comparing with low level aggressive individuals, the response time of high-level aggressive individuals was significantly faster when they identified the expression closest to anger prototype. In the discrimination task, we discovered that the peak points of discriminating accuracy in the two groups were differed, though insignificantly, with high-level aggressive individuals displaying a bias for perceptual categories of anger relative to low-level aggressive individuals. Further analysis on sub-dimension of AQ-CV indicated that individuals with high-level physical aggression, verbal aggression or hostility showed significantly more sensitivity to angry expression when compared with corresponding low-level aggressive individuals. In conclusion, the findings of the present study suggest that, compared with individuals with low-level aggression, individuals with high-level aggression (1) are more perceptually sensitive to the change of facial anger and fear, which supports the sensitivity perspective; (2) tend to exhibit a bias to perceive ambiguous expressions as angry, but this tendency was not statistically significant, which did not support the hostility attribution bias perspective.

Key words: expression processing, aggression, categorical perception, hostile attribution bias, sensitivity