FRAMES AND SPATIAL MEMORY OPERATIONS: AREA LIP AND SACCADE
J.T.Baker*; R.L.White; L.H.Snyder
Parietal area LIP is thought to maintain a stable map of the visual world by combining retinal and extraretinal signals whenever gaze shifts. To test whether LIP combines these signals according to task demands, we trained monkeys to memorize spatial locations in two different reference frames: either fixed in the world or fixed to gaze. Each trial consisted of an initial reference frame instruction (world- or gaze-fixed), a peripheral flash, a memory-period gaze shift, and finally a saccade to the memorized location in the instructed reference frame. Memory-period gaze shifts occurred either abruptly (visually-guided saccade) or gradually (smooth pursuit eye movement or whole-body rotation). Critically, retinotopic memories must be adjusted for gaze shifts on world-fixed trials only. Several observations supported a link between LIP and the animals' spatial memory. During the memory period after the gaze shift, LIP reflected the position of the remembered target, adjusting for gaze shifts only on world-fixed trials. Also, neuronal precision reflected behavioral precision: both LIP and memory-guided saccade endpoints showed (a) more variability under world- vs gaze-fixed conditions following gradual gaze shifts and (b) equal variability for the two reference frames following abrupt gaze shifts. However, LIP reflected only ~75% of the gaze change after gradual shifts (world-fixed), despite accurate performance on these trials. These observations suggest that LIP processes spatial signals to guide action. However, the incomplete adjustment after gradual gaze shifts suggests that processing in LIP may effect a partial transformation that is completed by downstream structures.
Supported by: NIH, McDonnell Found
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Citation: J.T.Baker, R.L.White, L.H.Snyder. REFERENCE FRAMES AND SPATIAL MEMORY OPERATIONS: AREA LIP AND SACCADE BEHAVIOR Program No. 57.16. 2002 Abstract Viewer/Itinerary Planner. Washington, DC: Society for Neuroscience, 2002. CD-ROM.