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Impairments in action and perception after right intraparietal damage
Jared Medina1, Steven A Jax2, H Branch Coslett3
1Department of Psychological and Brain Sciences, University of Delaware, United States.
Abstract:
We examined visually-guided reaching and perception in an individual who underwent resection of a small tumor in right intraparietal sulcus (pIPS). In the first experiment, she reached to targets presented on a touch screen. Vision was occluded from reach onset on half of the trials, whereas on the other half she had vision during the entire reach. For visually-guided reaching, she demonstrated significantly more reach errors for targets left of fixation versus right of fixation. However, there were no hemispatial differences when reaching without vision. Furthermore, her performance was consistent for reaches with either hand, providing evidence that pIPS encodes location based on an eye-centered reference frame. Second, previous studies reported that optic ataxics are more accurate when reaching to remembered versus visible target locations. We repeated the first experiment, adding a five second delay between stimulus presentation and reach initiation. In contrast to prior reports, she was less accurate in delayed versus immediate reaching. Finally, we examined whether a small pIPS resection would disrupt visuospatial processing in a simple perceptual task. We presented two small circles in succession in either the same location or offset at varying distances, and asked whether the two circles were presented in the same or different position. She was significantly more impaired left of fixation compared to right of fixation, providing evidence for a perceptual deficit after a dorsal stream lesion.
Insights
A small tumor resection in the right intraparietal sulcus (pIPS) impaired visually-guided reaching and spatial perception, particularly for stimuli on the left. This suggests the pIPS is crucial for encoding spatial information in an eye-centered frame.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Visuospatial Processing
Background:
- The intraparietal sulcus (IPS) plays a critical role in sensorimotor transformations and visuospatial cognition.
- Previous research on optic ataxia suggests preserved accuracy in reaching to remembered targets.
Purpose of the Study:
- To investigate the impact of a small right intraparietal sulcus (pIPS) tumor resection on visually-guided reaching and perception.
- To determine if the pIPS utilizes an eye-centered reference frame for spatial encoding.
- To examine the effect of delayed versus immediate target presentation on reaching accuracy.
Main Methods:
- A patient with a resected right pIPS tumor performed visually-guided reaching tasks with and without vision, and with immediate or delayed target presentation.
- A simple perceptual task assessed visuospatial processing by presenting successive visual stimuli.
- Reaching errors and perceptual accuracy were analyzed for hemispatial differences and effects of visual guidance and delay.
Main Results:
- The patient exhibited increased reaching errors for left-sided targets when vision was available, but no hemispatial difference when vision was occluded, supporting an eye-centered reference frame.
- Contrary to previous findings, the patient was less accurate in delayed reaching compared to immediate reaching.
- A significant deficit in visuospatial perception was observed for stimuli presented to the left of fixation, indicating a perceptual impairment after dorsal stream lesion.
Conclusions:
- Resection in the right pIPS leads to deficits in visually-guided reaching and visuospatial perception, particularly affecting the left hemifield.
- The findings suggest the pIPS is essential for maintaining accurate spatial representations in an eye-centered coordinate system.
- The study highlights the role of the dorsal stream in both online motor control and spatial perception.
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