ABSENCE OF SNAPSHOT MEMORY OF THE TARGET VIEW INTERFERES WITH PLACE NAVIGATION LEARNING BY RATS IN THE WATER MAZE

Contribution of visual and nonvisual mechanisms to spatial behavior of rats in the Morris water maze was studied with a computerized infrare d tracking system, which switched off the room lights when the subject entered the inner circular area of the pool with an escape platform. Naive rats trained under light-dark conditions (L-D) found the escape platform more slowly than rats trained in permanent light (L). After g roup members were swapped, the L-pretrained rats found under L-D condi tions the same target faster and eventually approached latencies attai ned during L navigation. Performance of L-D-trained rats deteriorated in permanent darkness (D) but improved with continued D training. Thus L-D navigation improves gradually by procedural learning (extrapolati on of the start-target azimuth into the zero-visibility zone) but rema ins impaired by lack of immediate visual feedback rather than by absen ce of the snapshot memory of the target view.