The CS-US interval function in rabbit nictitating membrane response conditioning: Single vs multiple trials per conditioning session

The effect of varying trials per day conditions on the CS-US interval or interstimulus interval (ISI) function in rabbit nictitating membrane response conditioning was studied in two experiments. Experiment 1 showed that a 1250-msec ISI was more effective than a 250-msec ISI when there was 1 trial/day. Experiment 2 showed that as the number of trials per day decreased from 20 to 1, the superiority of the 250-msec ISI group over the 1250-msec ISI group declined, with a reversal at 1 trial/day. Results are interpreted in terms of the role of a hypothesized CS-elicited short-duration orienting response in CR performance.     

Time course of cardiac conditioned responses in restrained rats as a function of the trace CS-US interval

Two experiments aimed at understanding the temporal characteristics of trace-conditioned heart-rate responses to a 0.5-s tone (conditioned stimulus [CS]) in restrained rats. A CS paired with a tail-shock (unconditioned stimulus [US]) elicited lasting bradycardiac responses. The magnitude and extinction rate of conditioned responses (CR) were independent of the CS-US interval (interstimulus interval [ISI], 3 s to 20 s). Unreinforced test trials were analyzed for CR topography. Responding was delayed in groups with longer ISIs, but CR latencies, peak and decay times were not proportional to the ISI. Response peaks tended to cluster either about 6 s after CS onset, or about 10 s with a slow decay, depending on the ISI. The authors postulated 2 components of auditory stimulus traces involved in cardiac conditioning, maximally active 6 s and 10 s respectively after CS onset. The topography of the CR could be constrained to combinations of associative strength and instantaneous activity of these 2 components.     

The influence of CS-US interval on several different indices of learning in appetitive conditioning

Four experiments examined the effects of varying the conditioned stimulus-unconditioned stimulus (CS-US) interval (and US density) on learning in an appetitive magazine approach task with rats. Learning was assessed with conditioned response (CR) measures, as well as measures of sensory-specific stimulus-outcome associations (Pavlovian-instrumental transfer, potentiated feeding, and US devaluation). The results from these studies indicate that there exists an inverse relation between CS-US interval and magazine approach CRs, but that sensory-specific stimulus-outcome associations are established over a wide range of relatively long, but not short, CS-US intervals. These data suggest that simple CR measures provide different information about what is learned than measures of the specific stimulus-outcome association, and that time is a more critical variable for the former than latter component of learning.     

Conditioning,attention, and the CS-US interval

A revised version of the Rescorla-Wagner (1972) mathematical model is presented. A metatheoretical assumption of an attentional process, the added revision, is conceived as an independent α-salience growth factor determining both rate of association and performance. Conditioned stimulus-unconditioned stimulus (CS-US) correlation, and CS-US interval (two primary conditioning parameters) are incorporated in the mathematical model as α-salience growth rate and as α-salience and association asymptote factors, respectively. In this manner, the long-standing issue of necessary and sufficient factors in classical conditioning is resolved. An empirical assessment of the model’s parameters has been included.