Processing dynamic facial affect in frequent cannabis-users: evidence of deficits in the speed of identifying emotional expressions.

Background: While heavy cannabis-users seem to show various cognitive impairments, it remains unclear whether they also experience significant deficits in affective functioning. Evidence of such deficits may contribute to our understanding of the interpersonal difficulties in cannabis-users, and the link between cannabis-use and psychological disorders (Moore et al., 2007).

Method: Emotion recognition performance of heavy cannabis-users and non-using controls was compared. A measure of emotion recognition was used in which participants identified facial expressions as they changed from neutral (open-mouth) to gradually more intense expressions of sadness, neutral, anger or happiness (open or closed mouth). Reaction times and accuracy were recorded as the facial expressions changed. Participants also completed measures of 'theory of mind,' depression and impulsivity.

Results: Cannabis-users were significantly slower than controls at identifying all three emotional expressions. There was no difference between groups in identifying facial expressions changing from open-mouth neutral expressions to closed-mouth neutral expressions suggesting that differences in emotion recognition were not due to a general slowing of reaction times. Cannabis-users were also significantly more liberal in their response criterion for recognising sadness.

Conclusion: Heavy cannabis-use may be associated with affect recognition deficits. In particular, a greater intensity of emotion expression was required before identification of positive and negative emotions. This was found using stimuli which simulated dynamic changes in emotion expression, and in turn, suggests that cannabis-users may experience generalised problems in decoding basic emotions during social interactions. The implications of these findings are discussed for vulnerability to psychological and interpersonal difficulties in cannabis-users.