Abstract
In this work, we investigate the effect of Parkinson’s disease (PD), and common corresponding therapies on vision-based perception of motion, a critical perceptual ability required for performing a wide range of activities of daily livings. While PD has been recognized as mainly a motor disorder, sensory manifestation of PD can also play a major role in the resulting disability. In this paper, for the first time, the effect of disease duration and common therapies on vision-based perception of displacement were investigated. The study is conducted in a movement-independent manner, to reject the shadowing effects and isolate the targeted perceptual disorder to the maximum possible extent. Data was collected using a computerized graphical tool on 37 PD patients [6 early-stage de novo, 25 mid-stage using levodopa therapy, six later-stage using deep brain stimulation (DBS)] and 15 control participants. Besides the absolute measurement of perception through a psychometric analysis on two tested position reference magnitudes, we also investigated the linearity in perception using Weber’s fraction. The results showed that individuals with PD displayed significant perceptual impairments compared to controls, though early-stage patients were not impaired. Mid-stage patients displayed impairments at the greater of the two tested reference magnitudes, while late-stage patients were impaired at both reference magnitudes. Levodopa and DBS use did not cause statistically significant differences in absolute displacement perception. The findings suggest abnormal visual processing in PD increasing with disease development, perhaps contributing to sensory-based impairments of PD such as bradykinesia, visuospatial deficits, and abnormal object recognition.
Highlights
Movement abnormalities have clinically defined Parkinson’s disease (PD) since its 19th century definition, the motor system is not necessarily the sole root of abnormalities (Jankovic, 2008)
Part A When comparing all PD patients with the control participants, there were no perceptual abnormalities seen at the smaller standard stimulus for those with Parkinson’s disease OFF their respective primary therapies (p-value = 0.595; average Difference Threshold (DL) for PD patients OFF therapy: 1.69 ± 0.48; average DL for control participants: 1.60 ± 0.58) and ON their respective therapies [p-value = 0.566; average DL for PD patients ON therapy: 1.50 ± 0.47) (Figure 2A)]
These perceptual impairments arise without related movements, suggesting that the observed abnormality is intrinsic to the processing of visual information, and not dysfunctions occurring in sensorimotor integration or with the motor system
Summary
Movement abnormalities have clinically defined Parkinson’s disease (PD) since its 19th century definition, the motor system is not necessarily the sole root of abnormalities (Jankovic, 2008). As exemplified with force computing and reproduction that is accurate in simple tasks, but slowed and variable during complex tasks, aspects of the abnormal motor functionality of PD can be rooted in neural dysfunction (Stelmach et al, 1989; Lafargue et al, 2008). Movement abnormalities in PD are not necessarily due to abnormal motor function alone. Due to movement generation being heavily used as a measure of the response in most clinical studies on PD it is not possible to decipher if abnormalities arise through the perceptual, motor, or sensorimotor integration deficits
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