Abstract

According to the studies of simul aneous measurment of heart rate and conditioned nictitating memberane response, the asymtotic level of heart rate conditioning could be attained only in 10-20 ·trials of the first session, whereas conditioned nictitating membrane response did not appear, yet. And recent studies have demonstrated that only 10-30 trials are enough to reach the asymtotic level of conditioning in one trial per day NMR paradigm. This number of trials are within the range of early portion of first session that does not show conditioned response in massive trials per session paradigms. So, the purpose of this study is to investigate the roles of initial trials of NMR with two experimental groups and one control group. Experimental group I received one CS A (tone)-US sessions in phase I and five CS A+CS B (Iight)-US sessions in phase II. Experimental group II received five CS A-US sessions in phase I and five CS A+CS B-US sessions in phase II. Control group received only five CS A+CS B-US sessions. Then, two test sessions, each of which contains 40 CS A and 40 CS B presentations without US, were followed to compare the levels of blocking among three groups and to find the evidence of learning in initial trials. Results showed that significant differnces of mean CR rate to CS B existed between control group and experimental groups I and II. It means there was an associative learning at the first session in experimental group I in spite of no CR performance. But it also means the learning was incomplete compared with the results of experimental group II. Resulis of the experments were explained in terms of performance factor and pre paratory and consummatory conditioning.