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.     

Role of the CS-US interval in the US preexposure effect

Theory and research suggest that long delay taste-aversion conditioning should be less affected by proximal US preexposure than short-delay conditioning. The present research tested this hypothesis by administering illness-inducing LiCl shortly before a saccharin-LiCl pairing in which the postsaccharin LiCl was administered either immediately or 20 min. after access to saccharin. The results suggest that US preexposure has a more deleterious effect on conditioning when the illness-inducing US is delayed in conditioning than when it is immediate. These results are to be expected on the basis of classical conditioning principles and question theory and research that suggest more deleterious effects of US preexposure with shorter intervals between the preexposed and conditioning US.     

Rapid acquisition of discrete-trial lever-press avoidance: effects of signal-shock interval

Acquisition of discrete-trial lever-press avoidance learning was studied in three experiments. Experiment I compared a new training procedure, which produces rates of lever-press avoidance learning comparable to those obtained in shuttle boxes, with a “conventional”, less efficient training procedure. A factorial design was used to compare continuous versus intermittent shock and a long-variable versus a short-fixed signal-shock interval. Learning was best in the groups trained with the long and variable interval and poorest in those trained with the short and fixed interval. Type of shock had no effect. Experiment II separated the effects of duration from those of variability of the signal-shock interval. Fixed and variable intervals of 10 and 60 sec were tested and duration was the only significant factor. Experiment III addressed the effect of the differential opportunity to avoid provided by long signal-shock intervals by varying this interval from 10 to 60 sec in 10-sec steps. Only the 10-sec group showed slow acquisition relative to the others. Analysis of avoidance response latencies showed that the distributions for all groups were positively skewed and that skewness increased with increasing duration of the signal-shock interval. At intervals longer than 20 sec, the animals made progressively less use of their increased opportunity to respond. The data do not support the opportunity-to-respond interpretation of the effects of duration of signal-shock interval and suggest that some type of inhibitory process may block lever-press avoidance learning at intervals as short as 10 sec. The significance of these findings for species-specific defense reaction and preparedness theories was emphasized.     

Dual effects of response blocking following avoidance learning

It was shown that either enhanced or decreased avoidance responding by rats could be produced by the same response blocking procedure occurring after avoidance training. The particular result produced depended on (1) the duration of the blocking trial and (2) when during the retention interval the blocking trial occurred. Results were interpreted in terms of a memory reactivation explanation and implications for the therapeutic uses of extinction were discussed.     

The effects of physostigmine during the acquisition of avoidance behaviour as a function of the intersession interval

Rats were trained and tested on an avoidance task in a shuttle box. The change in the performance of the control rats over two sessions was found to be a U-shaped function of the interval between the sessions. The change in performance of rats injected with physostigmine prior to the second session was also found to be a U-shaped function of the intersession interval, although the drug was shown to impair avoidance behaviour. These results are consistent with those of Hamburg (1967) and of Biederman (1970), and support the general contention that cholinergic mechanisms in the brain are involved in the control of avoidance and escape behaviour in the rat. They do not, however, necessarily support the hypothesis advanced by Deutsch (1969, 1971) to describe a biochemical basis of learning and memory, especially if it is used to explain the effects of cholinesterase inhibitors on avoidance behaviour in the shurtlebox.     

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.