Facial expression processing is not affected by Parkinson’s disease itself, but by age related factors

Abstract

Although the degree of facial movement decrease in patients with Parkinson’s disease (PD), the question whether facial expression processing may be impaired in PD so far has yielded equivocal results. Recent studies have focused on testing expression processing in recognition tasks with static images, not with dynamic conditions. Both conversational, emotional and dynamic facial expressions in three groups were tested. PD patients (n = 20), age- and education-matched healthy controls (n = 20), and young adult healthy controls (n = 20) were recruited. This setup allows us to address both effects of PD and age-related differences. We employed a multi-dimensional rating task for all groups in which 12 rating dimensions were used to assess evaluative processing of 27 expression videos from 6 different actors. We found that ratings overall were consistent across groups with several rating dimensions having a strong correlation with the expressions’ motion energy content as measured by optic flow analysis. Most importantly, we found that the PD group did not differ in any rating dimension from the older healthy control group, indicating highly similar evaluation processing. Both older groups, however, showed significant differences for several rating scales in comparison with the younger control group. Older participants rated negative expressions compared to the younger participants as more positive, but also as less natural, persuasive, empathic, and sincere. We interpret these in the context of positivity effect and in-group processing advantages. Overall, our findings do not support processing deficits due to PD, but rather point to age-related differences in facial expression processing.