AN ATTEMPT TO OVERCOME THE PROBLEM OF MOTOR MEDIATION BY RATS IN THE DELAYED NONMATCHING-TO-POSITION TASK

This report describes the performance of rats in a delayed non matchin g-to-position task using an automated visual memory apparatus. A new t esting procedure has been used to restrict the problem of motor mediat ion. In this procedure the rat must first activate a sample stimulus ( either the right or left visual display panel). It has then to respond to one of three retractable levers that were extended throughout the retention delay before it can receive a reinforcer (reward pellet vs. nothing) for a response made to either one of the two visual stimulus display panels. A response on the levers was independent from a respon se on the stimulus display panels. These retractable levers were set i n a compartment that protruded 15 cm from the back wall below the disp lay panels, forming a platform which the rat needed to climb in order to reach the stimulus display panels. By requiring the rat to respond to one of these levers the rat could not linger by the correct display panel. Furthermore, as the rat could not anticipate the location of t he response lever which would permitted the trial to continue nor the duration of the retention delays before a lever press allow access to the choice stimuli, the rat could not position itself by the correct p anel during the retention delay. Rats were able to learn this task rea dily and perform above chance over delays of up to 16 sec, even though the task demands were likely to restrict any motor mediation strategi es.