EFFECTS OF DIFFERENTIAL LIGHTING ON DELAYED-RESPONSE IN CAPUCHIN AND SQUIRREL MONKEYS

Abstract

Six naive capuchin monkeys (Cebus appella) and six naive squirrel monkeys (Saimiri sciureus) were tested on an 8 second indirect delayed-response task in a modified Wisconsin General Test Apparatus (WGTA). Six experimental conditions were used to vary the lighting conditions during the 8 second delay between the termination of the 5 second cue light behind a door panel and the raising of a 2-way mirror screen which allowed the subject to respond to one of the two panels. These six conditions were altered by timers which controlled a small light located in the top of the test cage. The six experimental conditions were (1) light in test cage remained on for the entire 8 seconds; (2) light went off immediately following the termination of the cue light and remained off for the entire 8 seconds at which time the light came on simultaneously with the raising of the 2-way mirror screen; (3) light on for 4 seconds and then off for 4 seconds; (4) light off for 4 seconds then on for 4 seconds; (5) light on for 2 seconds, off for 4 seconds and on for 2 seconds; and, (6) light off for 2 seconds, on for 4 seconds and off for 2 seconds. A randomized 6 x 6 Latin Square was used to assign subject and condition per day. Testing was conducted six days per week which allowed each condition to be presented to each subject every week. The 6 x 6 Latin Square was then repeated five times for a total test period of 30 weeks or 180 days. The 30 weeks were divided into 3 blocks of 10 weeks each. The results were analyzed with the Sequential State Theory (SST) which was developed by King and Fobes and is a two-stage theory of learning. The two stages are defined as attention which is followed by an associative stage of bias free learning. The results indicated that, to the contrary of some recent research, proactive inhibition was a significant source of error under all conditions and for both species. There were no significant species differences as a function of the different lighting condition during the period of delay. The Sequential State Theory hypothesizes a triphasic model for the acquisition of a complex learning task. When the learning task is sufficiently difficult there are three clearly identifiable curves in the acquisition of learning. First, the animal exhibits error tendencies such as position perseveration. This tendency is followed by an increase in random responding. Finally, detect responses emerge which are manifested by attending to the relevant dimensions of the stimulus object. The data for both the capuchin monkeys and squirrel monkeys supported this model of learning with the response curves emerging in the predicted manner.