| Abstract No.: | B-D2135 |
| Country: | Canada |
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| Title: | THE EFFECT OF GAZE SHIFT ON VISUOSPATIAL MEMORY OF THE RELATIVE LOCATIONS OF OBJECTS |
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| Authors/Affiliations: | 1 David C Cappadocia*; 1 Denise YP Henriques;
1 York University, Toronto, ON, Canada
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| Content: | Objectives: Each time the eyes move, the brain must update its internal representation of objects in the environment. When this updating occurs, how does the brain compute the changing relative locations of remembered objects in visual memory? Does the brain update using a reference frame with respect to gaze (egocentric), a reference frame independent of gaze (allocentric), or a combination of both?
Materials and Methods: We asked subjects to remember whether the location of a previously displayed bar was to the left or right of a second bar presented in the periphery. This is an ‘allocentric task’, as subjects judged the remembered location of one external object relative to another external object. All subjects were head-fixed and did this for three different gaze conditions. Gaze was monitored using an Eyelink infrared pupil tracker. In the gaze-fixed condition, subjects maintained their gaze either left or right of the two bars. In the gaze-shifted condition, subjects foveated on the first bar and then saccaded 5o, 10°, or 15o left or right before being presented with the second bar near the location of the first. This shift in gaze required the brain to remap the location of the first bar. For the gaze-adapted condition, subjects’ eye control was altered by a saccadic adaptation training session. While the eyes were in mid-flight (during saccadic suppression), the saccade target (a cross) would jump back 25% of the original distance, e.g., subjects were trained to perform an 11.25° saccade to a cross initially displaced 15°, so that they would unknowingly learn to make shorter saccades to these targets. Following adaptation, they performed a task similar to the gaze-shifted condition (10° or 15° saccades to the right only), except that the saccade between the bar and cross was also reduced (by again jumping the saccade target), so that the distance of actual saccade was around 25% smaller than the seen gaze target. For all three conditions, the location of the second bar was determined by an adaptive staircase that adjusted the distance between the locations of the first and second bar based on correct or incorrect responses.
Results: The thresholds for location judgements produced by the adaptive staircases were computed for all three conditions. When comparing the estimated distance of the bars from the gaze-fixed and gaze-shifted conditions, it was found that the intervening eye movement significantly affected the way people judged the distance between the bars when their eyes moved to the left of the bars, but not when the eyes moved to the right. When comparing the trials from the gaze-shifted condition with eye movements to the right to the gaze-adapted condition, no significant difference was found. We are currently testing the gaze-adapted condition on eye movements to the left.
Conclusion: Our results suggest that the relative locations of the two objects may be updated with respect to gaze at least following eye movements made to the left.
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