Biases in the perception and affective valence of neutral facial expressions induced by the immediate perceptual history

We report a new perceptual distortion of neutral facial expressions induced by the immediate dynamic perceptual history. In Experiment 1, participants evaluated the facial expression on the last frame of videoclips showing morphs from a happy or angry expression to neutral, and consistently judged these as slightly angry in the happy-to-neutral condition, and as slightly happy in the angry-to-neutral condition. To exclude the possibility of a cognitive response strategy, in Experiments 2 and 3 the sequences were used in an affective priming paradigm as task-irrelevant distractors, with positive or negative words superimposed on the last frame as targets. Participants made speeded evaluations of word valence. In Experiment 2, neutral-to-intense sequences produced clear affective congruence effects. In Experiment 3, intense-to-neutral sequences again produced affective congruence effects, but in opposite direction. This suggests that the perceptual biases found in Experiment 1 were not due to a cognitive response strategy but reflected a genuine change in the observer's judgement. We speculate that the bias in perceptual report reflected the influence of top-down emotional anticipation processes.