Objective: To study in Parkinson’s disease (PD) the dependence of saccadic and perceptual reaction times (SRT and PRT) upon the temporal asynchrony (TA) between central fixation point offset and peripheral target onset.

Background: Previously, we found that healthy subjects report SRT and PRT with the same time-change dependence upon TA. We also found that subjects misperceived small overlapping TAs as gaps. We hypothesized that the mechanism which temporally couples action and perception is a prominence map located in the superior colliculus (SC). In this map, the perception of a target would be delayed by the presence of competitive stimuli, causing the misperception of briefly overlapping stimuli as separated in time. In PD, the SC is abnormally inhibited by increased basal ganglia output, which might affect the coupling of action and perception and cause the misperception.

Methods: Fifteen PD patients and twelve normal volunteers performed a gap/overlap paradigm. Subjects made saccades to targets with different TA and reported whether they perceived the stimuli as separated by a gap or overlapped in time. SRT, PRT and perceptual transition thresholds were analyzed as functions of TA.

Results: SRT and PRT in PD did not show the same time-change dependence upon TA as controls. The effect of the SRT dependence upon TA (longest minus shortest reaction time) was smaller than in controls. In contrast, PD showed longer PRTs than normal, but had a close to normal time-change dependence upon TA. SRT and PRT in PD were still correlated, but did not show the same 1:1 dependence as in controls. Moreover, in PD longer overlapping TAs were misperceived as gaps (<200ms in PD vs. <100ms in controls).

Conclusions: In PD, SRT and PRT are dependent upon TA, but they do not change as in controls. Thus, in PD temporal coupling of action and perception is abnormal. The increased basal ganglia inhibition of SC in PD might interfere with the mechanism of coupling, causing SRT and PRT to change differently in response to the TA. The same dysfunction might be also responsible of the misperception of longer overlaps as gaps. The observed action/perception decoupling and misperception in PD could affect functions that require fine action-perception coordination, such as dual-task and attention performances, visual sampling, reading, and locomotion.

Preliminary data from a smaller sample were presented at the meeting of the Society for Neuroscience 2015.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/impaired-temporal-coupling-of-action-and-perception-in-parkinsons-disease/