2.2. Materials
2.2.1. Facial expression recognition task
In this computer-based task faces displaying five of the basic emotions (anger, disgust, fear, happy, and sad) or neutral expressions were used. The faces were taken from the Ekman and Friesen Pictures of Affect Series (Ekman and Friesen, 1976) and were morphed so that each picture contained part of the emotional prototype and part of the neutral expressions. By varying the portions of each of these parts faces with varying intensity of emotional expression were created. Faces used in this study contained 10%, 30%, 50%, 70%, or 90% of the full emotional expression. This design was used to access more subtle difficulties in our participants. Each emotion was displayed 20 times, that is each of the five intensities occurred four times within each emotion. In addition 10 neutral faces were displayed, giving a total of 110 stimuli presentations. In each trial a face was displayed for 500 ms. This was followed by a blank screen until the response occurred, which triggered the start of the next trial. Participants were informed about the five emotions and the neutral expressions they had to recognise. They were also informed about the different intensities used. Responses were given on a response pad with labels indicating which of the six keys represented which of the six emotions. The task was programmed using eprime (Schneider et al., 2002) and began with a practise block to familiarise participants to the task. During this block 18 faces were presented in a fixed order. The participant could then self-initiate the start of the experimental block which contained 110 randomised trials. Only data from the experimental block was used for data analysis. Recognition accuracy and reaction time (RT) were recorded. Only correct trials were considered for the reaction time analysis. In addition, we measured the neutral misinterpretation bias (the percentage of neutral expressions misclassified as an emotion).