REFERENCE
FRAMES AND SPATIAL MEMORY OPERATIONS: A NEURAL NETWORK
MODEL
R.L.White*; J.T.Baker; L.H.Snyder
Neurons in the lateral intraparietal area (LIP) represent
remembered spatial locations in retinotopic coordinates. During a
gaze shift, the representation of a target fixed in the world
(world-fixed reference frame) must be updated, while the
representation of a target fixed relative to center of gaze
(gaze-fixed) must remain constant. We trained a three-layered
recurrent neural network to remember the location of visual targets
as world-fixed or gaze-fixed based on a contextual cue and compared
the network with neurophysiological data obtained from monkeys
performing the same task. The neural network was able to perform
reference frame dependent updating with either gaze position or gaze
velocity as input. When only position information was provided,
activity modulations by gaze position (gain fields) were observed in
the middle (hidden) layer. When both position and velocity were
provided, the network preferentially relied on velocity, and gain
fields were weak or absent. Thus, a simple recurrent network
architecture can compute and maintain spatial location in either of
two reference frames, even without positional information or gain
field mechanisms. Hidden layer nodes shared some features with
single neurons in LIP. Depending on the contextual cue, all neurons
and most hidden nodes appropriately compensated for or ignored a gaze
shift. Furthermore, both hidden nodes and neurons showed incomplete
compensation for gaze shifts on world-fixed trials, even when network
output and animal behavior were accurate. Activity in LIP, like the
hidden layer, may reflect a partial sensorimotor transformation that
is read out by downstream structures analogous to the output
layer.
Supported by: NIH; McDonnell and EJLB
Foundations
Download a PDF of the poster
Citation: R.L.White, J.T.Baker,
L.H.Snyder. REFERENCE FRAMES AND SPATIAL MEMORY OPERATIONS: A NEURAL
NETWORK MODEL Program No. 57.17. 2002 Abstract Viewer/Itinerary
Planner. Washington, DC: Society for Neuroscience, 2002. CD-ROM.