Abstract
Hemispatial neglect is a common outcome of stroke that is characterized by the inability to orient toward, and attend to stimuli in contralesional space. It is established that hemispatial neglect has a perceptual component, however, the presence and severity of motor impairments is controversial. Establishing the nature of space use and spatial biases during visually guided actions amongst healthy individuals is critical to understanding the presence of visuomotor deficits in patients with neglect. Accordingly, three experiments were conducted to investigate the effect of object spatial location on patterns of grasping. Experiment 1 required right-handed participants to reach and grasp for blocks in order to construct 3D models. The blocks were scattered on a tabletop divided into equal size quadrants: left near, left far, right near, and right far. Identical sets of building blocks were available in each quadrant. Space use was dynamic, with participants initially grasping blocks from right near space and tending to “neglect” left far space until the final stages of the task. Experiment 2 repeated the protocol with left-handed participants. Remarkably, left-handed participants displayed a similar pattern of space use to right-handed participants. In Experiment 3 eye movements were examined to investigate whether “neglect” for grasping in left far reachable space had its origins in attentional biases. It was found that patterns of eye movements mirrored patterns of reach-to-grasp movements. We conclude that there are spatial biases during visually guided grasping, specifically, a tendency to neglect left far reachable space, and that this “neglect” is attentional in origin. The results raise the possibility that visuomotor impairments reported among patients with right hemisphere lesions when working in contralesional space may result in part from this inherent tendency to “neglect” left far space irrespective of the presence of unilateral visuospatial neglect.
Highlights
Successful action and interaction with the environment are dependent on correctly perceiving the space around us as well as the objects within that space
The results demonstrated that space use for grasping varied according to hemispace and spatial proximity to the participant
If the pattern of grasping observed in Experiment 1 was a consequence of handedness, it was expected that left-handed participants would display the reverse behavior; that is, participants would choose to grasp from left hemispace first, and would “neglect” right rather than left far space
Summary
Successful action and interaction with the environment are dependent on correctly perceiving the space around us as well as the objects within that space. We interact with objects which are further away by moving to the target, changing posture, or using a tool to bring the object within working space. Space is typically behaviorally differentiated into peripersonal and extrapersonal space. Peripersonal space is commonly defined as the space immediately surrounding the body in which hand and arm actions on objects can be performed most effectively [1]. Extrapersonal space refers to the space beyond peripersonal space [2]. Interactions with an object in extrapersonal space would require a person to physically move toward the object, or the object would need to be moved toward the person. Impairments of spatial perception can have a devastating effect on our functional independence and quality of life
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