How does Parkinson’s disease alter visual search?

Parkinson’s disease (PD) does not just affect the body’s movements; it also influences how we see the world. While symptoms such as tremors, muscle stiffness, and slowed motion are visible, the challenges with eye movements often go unnoticed. Individuals with Parkinson’s struggle to scan for visual information and process its meaning. This difficulty extends to visual working memory and spatial perception, suggesting that these issues might be linked to changes in cognitive abilities related to aging and not solely to motor disturbances. Interestingly, when people with Parkinson’s view complex, meaningful images, visual processing difficulties are less likely to occur than viewing meaningless shapes.

A study from Japan by leading author N. Takahashi investigated this further. They had individuals with PD and healthy controls view three types of images in a visual search task: operation, noun, and meaningless. During the task, they simultaneously recorded eye movements and brain activity. The authors recorded eye movements with Tobii Pro Spectrum eye tracker and used Tobii Pro Lab for the analysis. To quantify the visual exploration of the images, the authors have analyzed saccade and fixation metrics.

Concerning brain activity, the scientists looked at so-called Event-related potentials (ERPs), which are brain activity in response to specific stimuli or events (e.g., seeing a face). Specific ERPs can give insights into different stages in visual information processing. Recording ERPs concurrently with tracking eye movements during a visual search task enables scientists to identify the neural activity patterns associated with specific eye movement behaviors during visual processing.

The study showed that regardless of image type (meaningful or not), PD patients constantly showed smaller values for all eye tracker measurements than the control group. PD patients had fewer saccades when viewing operational and meaningless figures. This suggests that adding meaning to a visual stimulus can change the eye movement pattern, possibly by engaging brain circuits involved in different levels of visual cognitive processing. To this regard, ERP recording revealed that PD patients’ brains show excessive top-down processing during visual search. This is particularly evident while viewing meaningless or operational images. The study authors discuss that the brains of individuals with PD might be trying to find or create meaning when the images lack it.

In conclusion, the findings of this study contribute to our growing knowledge of visual processing in PD. The results suggest that disturbances in eye movements observed in individuals with PD may occur independently of motor symptoms and might vary according to the meaningfulness of the visual information.

Cited publication

Takahashi, N., Kawamura, M., Kobayashi, Y., & Hitosugi, M. (2024). Impaired eye movements in Parkinson’s disease and their relationship to top–down and bottom–up neural processing. Brain and Behavior, 14(2), e3404.