All animals are faced with the computationally intense task of continuously acquiring and analyzing sensory data from their environment. To ensure maximally useful data, animals appear to use a variety of motor strategies or behaviors to optimally position their sensory apparatus. In all higher animals, neural structures which process both sensory and motor information are likely to exist which can coordinate this exploratory behavior for the sake of sensory acquisition.
To study this feedback loop, we have chosen the weak electric fish, which use a unique electrically based means of exploring their environment [Bullock:86a], [Lissman:58a]. These nocturnal fish, found in the murky waters of the Congo and Amazon, have developed electrosensory systems to allow them to detect objects without relying on vision. In fact, in some species this electric sense appears to be their primary sensory modality.
This sensory system relies on an electric organ which generates a weak electric field surrounding the fish's body that in turn is detected by specialized electroreceptor cells in the fish's skin. The presence of animate or inanimate objects in the local environment causes distortions of this electric field, which are interpreted by the fish. The simplicity of the sensory signal, in addition to the distributed external representation of the detecting apparatus, makes the electric fish an excellent animal through which to study the involvement in sensory discrimination of the motor system in general, and body position in particular.
Simulations in two dimensions [Bacher:83a], [Heiligenberg:75a] and measurements with actual fish have shown that body position, especially the tail angle, significantly alter the fields near the fish's skin.
To study quantitatively how the fish's behavior affects the ``electric images'' of objects, we are developing three-dimensional computer simulations of the electric fields that the fish generate and detect. These simulations, when calibrated with the measured fields, should allow us to identify and focus on behaviors that are most relevant to the fish's sensory acquisition tasks, and to predict the electrical consequences of the behavior of the fish with higher spatial resolution than possible in the tank.
Being able to visualize the electric fields, in false color on a simulated fish's body as it swims, may provide a new level of understanding of how these curious animals sense and respond to their world. For this simulation, we have chosen the fish Gnathonemus petersii.