RATS PERFORM BETTER ON SPATIAL THAN BRIGHTNESS DELAYED MATCHING-TO-SAMPLE WATER-ESCAPE DUE TO AN UNLEARNED BIAS TO USE SPATIAL CUES

Rats readily acquire water-escape spatial delayed matching-to-sample ( DMTS) tasks and show excellent performance with retention intervals as long as 120 m(17). They also acquire the task more readily with a fi- min retention interval (RI) than with a 1-min RI (16). To determine if these observations are unique to spatial DMTS, or are also true of no nspatial water-escape DMTS, 75-day-old rats were compared on acquisiti on and subsequent retention of spatial and brightness DMTS. A larger p roportion of the rats tested on the spatial problem were able to acqui re the task, made fewer acquisition errors, and demonstrated better re tention when tested at RIs of 1, 5, 15, 30, 60. and 120 min than did t he rats tested on the brightness problem. Acquisition RI did not affec t the rate of acquisition on either task. Examination of perseveration errors, the occurrence of intrusions, and position-congruent performa nce (escape platform in the same physical location on both runs of a t rial) revealed that the choices of brightness-trained rats were often more influenced by spatial than brightness cues, suggesting that rats have an unlearned bias to use spatial cues in water-escape DMTS tasks. Copyright (C) 1996 Elsevier Science Inc.