Is the number of trials a primary determinant of conditioned responding?

Abstract

Acquisition of conditioned responding is thought to be determined by the number of pairings of a conditioned stimulus (CS) and an unconditioned stimulus (US). However, it is possible that acquisition is primarily determined not by the number of trials but rather by quantities that often correlate with the number of trials, such as cumulative intertrial interval (ITI) and the number of sessions. Four experiments examined whether the number of trials has an effect on acquisition of conditioned responding, once cumulative ITI and number of sessions are equated. Results of the experiments with rats and mice favor the hypothesis that over an eightfold range, variation in number of CS-US pairings has little effect. It is suggested that learning curves might more accurately be plotted across cumulative ITI or number of sessions, and not across number of trials. Results pose a challenge to trial-centered accounts of conditioning, as demonstrated by simulations of the Rescorla-Wagner model, a simplified version of Wagner's standard operating procedure model (SOP), and Stout & Miller's sometimes competing retrieval model (SOCR). A time-centered account, rate estimation theory (RET), predicts the main finding but has trouble with other aspects of the learning process more easily accommodated by trial-centered models.

Acquisition of conditioned responding in a multiple schedule depends on the reinforcement's temporal contingency with each stimulus

“…More recent accounts use the average cycle time between reinforcer deliveries (denoted by C) and describe acquisition in terms of the C/T ratio (Balsam et al 2006). Across these studies, only cumulative CS and ITI time, as well as CS-US contingency, are required to predict acquisition speed (Gottlieb 2008). These results are consistent with Rate Expectancy Theory (RET) (Gallistel and Gibbon 2000), which eschews associations and argues that conditioned responding reflects knowledge of temporal rates and conditional probabilities.…”

Pavlovian conditioning and cumulative reinforcement rate.

“…This matching was achieved by providing three times as many reinforcements to the long (60 s) 100% CS as to the short (20 s) 33% CS, while keeping the number of trials of each equal. Because the long CS had three times as many reinforced trials as the short CS, this may have increased the rate of conditioning to the long CS which could have mitigated any difference in conditioning that would otherwise favor the short CS (see Gottlieb, 2008). Experiment 2 addressed this confound by equating CSs for the number of reinforced trials per session; it thus allowed CSs to differ threefold in the number of presentations per session.…”

The dual role of the context in postpeak performance decrements resulting from extended training

“…All groups were trained using relatively massed trials, which result in higher context conditioning and facilitate the stimulus-like (i.e., competitive) function of the context (Urcelay & Miller, 2010). To equate the number of sessions and to preclude alternative explanations based on differing retention intervals between training and testing or different numbers of sessions (see Gottlieb, 2008, for a discussion), all subjects received five sessions of reinforced training. However, the different groups received different numbers of trials in each session (see Table 1).…”