Variation of temporal order reveals deficits in categorisation of facial expressions in patients afflicted with depression

Introduction: It is well established that depressive disorders are associated with abnormalities in the processing of affective information. However, type of stimuli, perceptual complexity and cognitive demand are important factors in evaluating these findings. In particular, processing mechanisms of perceptual boundaries in ecologically valid face stimuli are largely unknown in depression.Methods: In the current study, intensity-ordered frame sequences provided a dynamic visualisation of happy or sad facial expressions fading from or to neutral expressions. Patients (n=20) with major depression (MD) disorder and controls (n=20) indicated their perceptual boundaries between neutral and emotional face depending on direction and emotion. The averaged time of the perceptual boundary entered a groupxcondition ANOVA and regression analysis.Results: MD group did not systematically shift perceptual boundaries in the dynamic emotional faces but yielded altered statistics in information processing. The Gaussian distribution of boundary judgements was disturbed in depression, increasing goodness-of-fit errors in disappearing emotions. Goodness-of-fit correlated with depression symptom score (Beck Depression Inventory-II (BDI-II)) in the MD group during the disappearing sad (r(18)=46, p=0.04) and happy (r(18)=51, p=0.02) conditions.Conclusion: We evaluated detection of appearing and disappearing emotions in dynamic faces. A deviant distribution of categorisation responses emerged in the MD group, which was not emotion-specific. Such a perceptional uncertainty can impede individuals' functioning in interpersonal interaction.