Abstract

The ability of people with Parkinson’s (PwP) to discriminate upright and inverted facial expressions
is evaluated using a temporal two-interval forced-choice paradigm. Stimuli are black and white images of neutral, happy, angry, disgusted, fearful, sad and surprised expressions. Inverted stimuli are the two expressions that participants are most and least sensitive to. A range of intensities of expressions (0–100%) are created by morphing between neutral and expressive images. The
neutral image (0%) is presented in one interval and the expressive image (varies –100%) in the other. Observers indicate the interval that contained the image that was most expressive. For all upright expressions and all participants, performance increases from chance to 100% correct as intensity of expression increases. Fitted functions describing performance of happy and disgust are
shifted to the left of others. This suggests that PwP are most sensitive to expressions of happiness and disgust. PwP and control participants show a small reduction in sensitivity for the expression they are most sensitive to when it is inverted (Face Inversion Effect). For PwP there is a considerable Face Inversion Effect for the expression they are least sensitive to. This suggests
that configural face processing is disrupted in Parkinson’s disease.