REFERENCE
FRAMES AND SPATIAL MEMORY OPERATIONS: AREA LIP AND SACCADE
BEHAVIOR
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
Download a PDF of the poster
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.