USC Brain Project: Hippocampus and Navigation Group

The TAM-WG Model: Affordance-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-


Theoretical background:

Gibson (1966) observed that the pattern of optic flow contains valuable information that can be used to guide navigation through the environment without prior recognition of objects. In this way, Gibson made clear that there was a great deal of information which could be "picked up" for use by an animal even without the invocation of object recognition. We thus adopt Gibson's term affordances for parameters for motor interactions signaled by sensory cues without the necessary intervention of object recognition. Unlike Gibson, however, we view this "pick up" not as "direct" but rather as involving neural mechanisms, at least some of which are embedded in the parietal cortex.

We relate the taxon to the notion of affordances for movement. Just as a rat may have basic taxes for approaching food or avoiding a bright light, so does it have a wider repertoire of affordances for possible actions associated with its immediate sensing of its environment. In this sense, affordances would then include: for a dark hole - hide; for visual sighting of a corridor - go straight ahead; for sensed branches in a maze or the sight of the end of the corridor - turn; for food as sensed generically - eat; etc.

For more information on affordances or on the taxon systems, please refer to the papers listed in the Hippocampus and Navigation Group homepage.

Representing affordances for movement ...

TAM employs coarse coding in a linear array of cells, in this way affordances are coded as bumps of activity for turns from -180 to +180 degrees.

When in the dais of the 8-arm radial maze, for example, the rat is able to sense eight different visible arms and consequently, eight different affordances (since a rat's visual field covers approximately 320 degrees, we assume it is able to visually sense the turning affordance given by the arm behind it).

When the rat is the junction of the T-maze, 4 affordances are available: 90 and 180 degrees - left and right.

After turning right, but when still in the junction of the T-maze, 4 affordances are available: straight ahead, 90 degrees left, and 180 degrees - left and right.

After turning left, but when still in the junction of the T-maze, 4 affordances are available: straight ahead, 90 degrees right, and 180 degrees - left and right.

When in the middle of a corridor, 3 affordances are available: straight ahead and 180 degrees left and right.

Finally, when the rat reaches the end of an arm, only the affordances to turn backwards are available: 180 degrees left and right.

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University of Southern California Brain Simulation Lab
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Author: Alex Guazzelli <aguazzel@rana.usc.edu>