Background/objective: Some of the behavioral disorders associated with Parkinson's disease (PD), such as the reduced magnitude of actions (hypometria) may be related to an impairment in cognitive disengagement. A reduced ability to disengage attention from previous sensory stimuli will alter perception with a reduced range of estimated stimulus magnitudes (contraction to the mean). To test this disengagement hypothesis, participants with PD were tested to learn whether they had abnormal sensory perception with overestimation of the relative magnitude of weaker tactile stimuli and underestimation of the relative magnitude of stronger tactile stimuli in relation to a reference stimulus.
Design/method: The participants were 12 people with PD and 12 healthy adults. Test stimuli were applied to the palm using Semmes-Weinstein monofilaments (SWM) of 6 magnitudes, 3 greater and 3 less than a standard stimulus. In each trial, after being stimulated with the reference (standard) stimulus, a test monofilament was applied, and the participant was asked to provide a numerical estimate of the magnitude of the second stimulus relative to the standard.
Results: Compared to the control group, participants with PD overestimated the magnitudes of the tactile stimuli below the standard stimulus and underestimated the magnitudes of stimuli above the standard stimulus.
Conclusions: These results demonstrate that people with PD likely have a reduced ability to estimate the relative magnitudes of tactile sensory stimuli. Whereas deafferentation would alter perception in one direction, the impairment of these participants with PD may result from a disorder of disengagement, and disorders of disengagement are often due to frontal-executive dysfunction.
Keywords: Attentional grasp; Frontal-executive dysfunction; Parkinson’s disease; Perceptual grasp; Sensory perception.