Differential Acquisition of An Instrumental Response in Albino and Hooded Rats

Abstract

The present experiment investigated hooded-albino strain differences in acqu~s~tion of an instrumental task (bar pressing) with two levels of sucrose reinforcement (8% 3and 32% by weight in water). The Hooded Group contained 12 Long-Evans female rats and the Albino Group 12 Sprague-Dawley female rats. All Ss were experimentally naive and approximately the same age (140 ro 160 days). One week prior to the start of the experiment Ss were placed on a 23-hr. food deprivation schedule. Eight liquid reinforcement boxes, previously described (Marx & Pieper, 1962), were used for bar-press (BP) training. Operant BP rate was observed in all Ss during 10-min. sessions over the first three days. Equating for differences in operant rate, we randomly assigned Ss of each strain to either a 32% or 8% sucrose reinforcement group. The next three days consisted of magazine training with the bar removed. Each minute during the 10-min. session, E manually operated the magazine, thus delivering a total of 10 .lo-ml. reinforcements of the appropriate concentration to each S. Following this, BP training using a continuous reinforcement schedule was instituted for 18 days. The albino strain demonsrrated the higher over-all BP rate irrespective of reinforcement concentration. Analysis of vzriance of the daily BP totals indicated the main effects of Srrain and Trials to be reliable (F = 10.37, p < .01, df = 1/20; F = 7.05, p < .01, df = 17/320), as was the interaction of Strain by Trials (F = 2.56, p < .01, df = 17/320). Neither the main effect of Concentration nor any of its interactions was statistically reliable (F < 1.00 in all cases). The BP plot for the albinos was curvilinear, FIG. 1. Mean number of bar presses m 50