Abstract
Each of 48 rabbits received 1 adaptation, 8 acquisition, and 1 extinction session in a heart-rate (HR) classical discrimination conditioning experiment using 2 tone CSs and a shock UCS. The experiment was a 2 * 3 factorial design with delay vs. a 5-sec trace CS procedure as 1 dimension and interstimulus intervals (ISIs) of 7, 14, and 21 sec. as the other. Major findings were that (1) level of conditioning (CR +) and discrimination (CR + minus CR-) varied inversely with ISI, (2) better discrimination was observed under the delay than under the trace procedure, and (3) magnitude of HR conditioning and discrimination revealed an inverted U shaped function over acquisition sessions.
