The effects of the facial expression of emotions on time perception in patients with Parkinson's disease

Objective: In the present study, we investigate the magnitude of temporal distortions caused by the presentation of facial expression of emotions in PD patients and controls. Background: Several studies have demonstrated an interaction between time perception and affective dimensions in healthy participants, and many of them showed that time distortions are caused at the view of facial emotional expressions. Previous studies have demonstrated temporal judgment impairment in Parkinson’s disease (PD) patients. No previous studies have investigated the distortion caused on time perception by facial expression of emotion in PD patients. Methods: Twenty-five older adults with PD and 17 healthy older adults took part in the present study. PD patients were also divided into two sub-groups, with (PD-MCI) and without mild cognitive impairment (PD-non-MCI), according to their score at a neuropsychological evaluation. Stimuli used in the time bisection task were black-and-white pictures of male and female with the facial expression of anger or shame, or a neutral expression. Two standard durations were used: 400 ms (short standard) and 1600 ms (long standard). Participants were required to judge if the duration presented was closer to the short standard or to the long standard. Results: PD-MCI were less accurate than PD-non-MCI and controls in the way that PD-MCI perceived temporal intervals as shorter than the presented interval. Moreover, PD-MCI patients judged longer temporal intervals as shorter and short intervals as longer than the presented durations. When the stimuli showed the facial expression of anger, temporal intervals were over-estimated whereas when the stimuli showed the facial expression of shame, temporal intervals were under-estimated. Moreover, significant differences were found between emotional stimuli (anger and shame facial expressions) and neutral stimuli only at 400 ms in PD-MCI patients. Conclusions: Effect of facial emotional stimuli on time perception is evident in all participants. Also, PD-MCI patients were less accurate than PD-non-MCI and controls: PD-MCI patients underestimated long and over-estimated short temporal intervals more than PD-non-MCI patients.