| Abstract No.: | A-D1154 |
| Country: | Canada |
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| Title: | THE EFFECT OF GAZE DIRECTION ON REACHING TO PROPRIOCEPTIVE TARGETS |
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| Authors/Affiliations: | 1 Stephanie A. H. Jones*; 1 Christopher Hideg; 1 Denise Y. P. Henriques;
1 York University, Toronto, ON, Canada
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| Content: | Objective: Previous behavioural and neurophysiology research has shown that visual reach targets are stored and updated in a gaze centered frame of reference. However, it is not known whether the remembered locations of non-visual targets are also represented in the same frame. The purpose of the present study was to examine how the CNS stores and updates information about the location of proprioceptive reach targets. Materials and methods: We measured proprioceptive sense of hand position by having participants point to the location of their unseen left hand (the proprioceptive target) using their right index finger. To specify the locations of the proprioceptive target, participants gripped the handle of a robot-manipulandum with their left hand, and moved it along a robot-generated groove to one of three target sites (in front of the right eye, 10o to its left, or 10o to its right). Participants began with their left hand at a common illuminated origin, so that they saw the location of their hand at the beginning of each trial, and were asked to touch this location prior to continuing. A touch screen recorded the location of the right index finger during reaching. Participants completed 3 conditions: (1) Proprioceptive guided reaching condition: From the origin location, participants moved their left hand to one of the target sites. Once the left hand reached this location, a fixation (red) LED appeared in front of them at one of four horizontal locations: 15o or 5o left or right of the midline. While maintaining gaze toward the fixation site, participants reached to the unseen location of their left hand. (2) Proprioceptive memory guided reaching condition: The procedure was similar to the proprioceptive guided condition except that participants reached to the remembered location of their unseen left-target hand. That is, prior to reaching to the location of their left hand, they were asked to return the robot arm to the origin position. As such, the reach was completed using the proprioceptive memory of the location of their left hand. (3) Visual memory guided reaching condition: participants reached to the remembered location of a briefly flashed visual target while fixating on one of the 4 fixation LEDs. Visual targets were white LEDs located at the same three spots that the proprioceptive targets had been. In this condition, the left hand was not used. Results: We found that pointing errors to both current and remembered proprioceptive targets systematically varied with the degree of gaze eccentricity relative to the target, much like errors do for visually remembered targets. Overall, when fixating to the right, participants overestimated the location of their hand to the left and when fixating to the left, participants overestimated the location of their hand to the right. This effect was greater in the proprioceptive memory guided reaching condition than in the proprioceptive guided or visual memory guided pointing conditions. Conclusion: Our results suggest that the CNS may be encoding and updating the location of proprioceptive targets in an eye fixed frame or relative |
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