Eye-hand coordination: memory-guided grasping in a cluttered environment
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Date
2019-06-27
Authors
Abbas, Hana H
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Abstract
We often reach for remembered objects, such as when picking up a coffee cup from behind our laptop. In cases like this, we rely on visuospatial memory, encoded by the perceptual mechanisms of the ventral visual stream, to guide our actions, rather than on the real-time control of action by the dorsal visual stream (Milner & Goodale, 1995). Further, our motor plans must often accommodate for the messy spaces within which we act, avoiding irrelevant objects in our way. Little research has examined obstacle avoidance during memory-guided grasping, though it is likely obstacles perceived by the ventral stream as more salient will produce exacerbated avoidance maneuvers. This study examined how the availability of visual feedback altered eye-hand coordination in an obstacle avoidance paradigm. Eye and hand movements were monitored as subjects had to reach through a pair of obstacles in order to grasp a 3-D target object, under full visual feedback (visually-guided), immediately in the absence of visual feedback (memory-guided no-delay), or after a 2-s delay in the absence of visual feedback (memory-guided delay). Positions and widths of obstacles were manipulated, though their inner edges remained a constant distance apart. We expected the memory-guided delay group to exhibit exaggerated avoidance strategies due to a reliance on the perceptual mechanisms of the ventral steam. Results revealed successful obstacle avoidance and grasps of the target object in all groups, however different avoidance strategies emerged depending on the availability of visual feedback. The visually-guided and memory-guided no-delay groups used real-time visual information to alter the paths of the index finger and wrist and adjust final index finger positions on the target object, to account for positioned obstacles. Still, the no-delay group showed wider index finger paths and a failure to adjust final fixations, resulting from the inability to use visual information for the online control of action. Unexpectedly, the memory-guided delay group employed a rather moderate strategy for avoiding obstacles, in that positioned obstacles less often prompted alterations in the mechanics of the reach. In conclusion, obstacle avoidance when reaching to remembered objects adopts a more moderate, rather than exaggerative, strategy.
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Keywords
Vision, Grasping, Obstacle avoidance, Visuomotor control, Eye-hand coordination, Delayed reaching