Prolonged exposure to a stimulus biases perception of a subsequent stimulus away from the adapting stimulus (Clifford & Rhodes, 2005). These aftereffects have been observed with a wide variety of stimuli, including facial identity (Rhodes & Jeffery, 2006) and emotional facial expression (e.g., Webster et al., 2004). In the current experiment, we used this paradigm to examine the effect of anxiety on the perception of emotional expression. Photographs of a male and a female model from the Karolinska Directed Emotional Faces set (KDEF; Lundqvist et al. 1998) were selected and a series of morphs created by interpolating a fear exemplar with a neutral exemplar for each model. A pilot study established a range of morphed expressions falling on either side of the fear/neutral boundary, and these were then used in the main study. There were 16 adaptation blocks in the experiment proper, and each block began with an adapting phase in which participants viewed (and categorized) 35 presentations of one endpoint from the morph continuum. This was immediately followed by a test phase, during which participants viewed and categorized 33 images of the same model (8 dummy trials, 5 top-up trials and 20 test trials – 10 from either side of the categorical boundary). We predicted that all test trials would be perceived as having an emotional expression opposite to that of the adapting stimulus (e.g., adaptation to fear would produce ‘neutral’ classifications for the test stimuli that were originally on the ‘fear’ side of the boundary). EEG was recorded using a NeuroScan NuAmps system, and stimulus presentation was controlled using E-Prime. An analysis of the behavioural classification data revealed that adaptation to fear created a shift in the classification of morphs towards ‘neutral’ and adaptation to neutral created a shift towards ‘fear’. This shift was equivalent in high and low anxiety. An analysis of the ERP data, however, revealed a more pronounced late positive potential in the high, but not the low, anxiety group following adaptation to neutral compared to fear, and this effect was particularly enhanced for male than female expressions
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