| Abstract No.: | A-D1159 |
| Country: | Canada |
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| Title: | PROGRAMMING REPEATED REACHES TO REMEMBERED VISUAL TARGETS. |
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| Authors/Affiliations: | 1 Aidan A. Thompson*; 3 Rohit Sharma; 2 Denise Y.P. Henriques;
1 Centre for Vision Research & School of Kinesiology and Health Science, York University; 2 Centre for Vision Research, School of Kinesiology and Health Science & Department of Psychology, York University; 3 Department of Psychology, York University, Toronto, ON, Canada
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| Content: | Objectives: Previous research has shown that pointing targets are stored and updated in an eye-fixed reference frame (e.g., Henriques et al., 1998). In the current experiment we investigated spatial updating across repeated reaches following intervening eye movements. We tested whether the target’s location is converted from an eye-fixed to an arm-fixed frame just once and then used to program repeated reaches to that same location, or whether the location of the remembered target relative to the eye is updated from an eye- to an arm-fixed frame for each movement.
Materials and Methods: Subjects fixated targets displayed briefly on a touch screen within arms’ reach. They then looked to a peripheral fixation position, and reached to touch the remembered location of the previously displayed target. After completing the first reach, subjects looked to a peripheral location on the opposite side of the target’s location and again reached to touch the location of the same remembered target. Fixation points were either 5 or 10 degrees of visual angle to either side of one of three possible target locations, and all reaches were performed in complete darkness with no visual stimuli of any kind. Eye movements were measured with a head-mounted infrared pupil tracker, and the head was fixed with a bite-bar.
Results: We compared endpoint errors of the second reach with those errors of the first when the eyes moved between the two reaching movements. If these errors are the same, despite the intervening eye movement, it would suggest that people relied on information from the previous movement (such as afferent and/or efferent signals, or an arm-related representation of the target) to program the second movement. If the reach endpoint errors differ it would suggest that the location of the target is updated relative to the new position of the eye and newly converted to an arm-fixed reference frame each time a reach is made. Our results indicate that the pattern of errors during the second reach movement was significantly different from that of the first, with reach endpoint errors typically varying as a function of concurrent gaze direction.
Conclusion: These pointing responses suggest that when programming repeated movements to the same location, the brain refers to an updated eye-fixed target representation to program each movement. Our next step is to determine at what point this spatial updating occurs by requiring intervening saccades at different temporal phases of movement planning and execution.
Acknowledgments: CIHR Training Grant in Vision Health Research (to AAT), and CFI & NSERC (to DYPH). |
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