Exploring Biological Motion Processing in Parkinson's Disease Using Temporal Dilation

Abstract

Biological motion (BM) perception is the compelling ability of the visual system to perceive complex animated movements effortlessly and promptly. A recent study has shown that BM can automatically lengthen perceived temporal duration independent of global configuration. The present study aimed mainly to investigate this temporal dilation effect of BM signals in Parkinson's disease (PD) patients. We used the temporal dilation effect as an implicit measure of visual processing of BM. In all, 32 PD patients (under off-therapy conditions) and 32 healthy controls (HCs) participated in our study. In each trial, an upright BM sequence and an inverted BM sequence were presented within an interval in the center of the screen. We tested both canonical and scrambled BM sequences; the scrambled ones were generated by disturbing the global configuration of the canonical ones but preserving exactly the same local motion components. Observers were required to make a verbal two-alternative forced choice response to indicate which interval (the first or the second) appeared longer. Statistical analyses were conducted on the points of subjective equality (PSEs). We found that the temporal dilation effect was significantly reduced for PD patients compared with HCs in both canonical and scrambled BM conditions. Moreover, no temporal dilation effects of scrambled BM were shown in both early- and late-stage PD patients, while the temporal dilation effect of canonical BM was relatively preserved in the early stages.

Fig 1. Task design.

Experiment 1 employed scrambled biological motion (BM) sequences. Either an upright or an inverted scrambled BM stimulus was presented for an interval, followed by an interstimulus interval (ISI) and then the other stimulus. Experiment 2 employed canonical BM sequences. The presentation order of the two stimuli was randomized across trials.

Fig 2. Psychometric functions in two conditions.

(A) Psychometric function in the scrambled biological condition: the X-axis shows the deviation in the durations of the two stimuli (upright minus inverted), ranging from -900 ms to +900 ms; the Y-axis shows the proportion of “long” responses to upright stimuli. The arrow with the dashed line indicates the PSE, and the arrows with solid lines indicate the DL. A negative PSE indicates a temporal dilation effect for upright stimuli. (B) Psychometric function in the canonical biological condition. The psychometric functions shown represent the means of these individual functions.

Fig 3. Estimated marginal means of points of subjective equality (PSEs) in experiments 1 and 2.

Effects of group [Parkinson’s disease (PD) patients vs. health controls (HCs)] and task [canonical vs. scrambled biological motion (BM) condition] on PSEs and their interactions.

Fig 4. Group scatter plot of the distribution of the temporal dilation effect at different Hoehn-Yahr stages of Parkinson’s disease (PD) patients.

Fig 5. Estimated marginal means of points of subjective equality (PSEs) for Parkinson’s disease (PD) patients in experiments 1 and 2.

Effects of subgroup [early-stage vs. late-stage PD] and task [canonical vs. scrambled biological motion (BM) condition] on PSEs and their interactions.

Fig 6. Decreases of the temporal dilation effect with disease stage increasing in canonical BM and scrambled BM conditions.

Deficits in the temporal dilation effect in the canonical BM condition correlated with Hoehn-Yahr stages; patients in stages 3–4 were most involved, while deficits in the scrambled BM condition happened much earlier, independent of disease severity. Error bars indicate standard error.