Research on perceptual learning shows that the way stimuli are presented leads to different outcomes. The intermixed/blocked (I/B) effect is one of these outcomes, and different mechanisms have been proposed to explain it. In human research, it seems that comparison between stimuli is important, and the placement of a distractor between the pre-exposed stimuli interferes with the effect. Results from animal research are usually interpreted in different terms because the type of procedure normally used in animal perceptual learning does not favour comparison. In our experiments, we explore the possibility that a distractor placed between the to-be-discriminated stimuli may interfere with the perceptual learning process in rats. In Experiment 1, two flavoured solutions are presented in an I/B fashion, with a short time lapse between them to favour comparison, showing the typical I/B effect. In Experiment 2, we introduced a distractor in between the solutions, abolishing this effect. Experiment 3 further replicates this by comparing two intermixed groups with or without distractor. The results replicate the findings from human research, suggesting that comparison also plays an important role in animal perceptual learning.

Pavlovian conditioning procedures result in dramatic individual differences in the topography of learnt behaviors in rats: When the temporary insertion of a lever into an operant chamber is paired with food pellets, some rats (known as sign-trackers) predominantly interact with the lever, while others (known as goal-trackers) predominantly approach the food well. Two experiments examined the sensitivity of these two behaviors to changing reinforcement contingencies in groups of male and female rats exhibiting the different phenotypes (i.e., sign-trackers and goal-trackers). In both phenotypes, behavior oriented to the food well was more sensitive to contingency changes (e.g., a reversal in which of two levers was reinforced) than was lever-oriented behavior. That is, the nature of the two behaviors differed independently of the rats in which they were manifest. These results indicate that the behavioral phenotypes reflect the parallel operation of a stimulus–stimulus associative process that gives rise to food-well activity and a stimulus–response process that gives rise to lever-oriented activity, rather than the operation of a single process (e.g., stimulus–stimulus) that generates both behaviors.

Associative treatments of how Pavlovian conditioning affects conditioned behavior are rudimentary: A simple ordinal mapping is held to exist between the strength of an association (V) between a conditioned stimulus (CS) and an unconditioned stimulus (US;i.e., VCS-US) and conditioned behavior in a given experimental preparation. The inadequacy of this simplification is highlighted by recent studies that have taken multiple measures of conditioned behavior: Different measures of conditioned behavior provide the basis for drawing opposite conclusions about VCS-US across individual animals. Here, we develop a simple model involving reciprocal associations between the CS and US (VCS-US and VUS-CS) that simulates these qualitative individual differences in conditioned behavior. The new model, HeiDI (How excitation and inhibition Determine Ideo-motion), enables a broad range of phenomena to be accommodated, which are either beyond the scope of extant models or require them to appeal to additional (learning) processes. It also provides an impetus for new lines of inquiry and generates novel predictions. c 1 c 1 6. Brimer, C.J. (1970). Inhibition and disinhibition of an operant response as a function of the amount and type of prior training.

AbstractAssociative treatments of how Pavlovian conditioning affects conditioned behavior are rudimentary: A simple ordinal mapping is held to exist between the strength of an association (V) between a conditioned stimulus (CS) and an unconditioned stimulus (US; i.e., VCS-US) and conditioned behavior in a given experimental preparation. The inadequacy of this simplification is highlighted by recent studies that have taken multiple measures of conditioned behavior: Different measures of conditioned behavior provide the basis for drawing opposite conclusions about VCS-US. Here, we develop a simple model involving reciprocal associations between the CS and US (VCS-US and VUS-CS) that simulates these qualitative individual differences in conditioned behavior. The new model, HeiDI (How excitation and inhibition Determine Ideo-motion), enables a broad range of phenomena to be accommodated, which are either beyond the scope of extant models or require them to appeal to additional (learning) processes. It also provides an impetus for new lines of inquiry and generates novel predictions.

Please cite this article as: Recio SA, Iliescu AF, de Brugada I, The amount of exposure determines generalization in animal perceptual learning using short inter-stimulus intervals, Behavioural Processes (2019),

The model elaborated here adapts the influential pooled error term, first described by Allan R. Wagner and his colleague Robert A. Rescorla, to govern the formation of reciprocal associations between any pair of stimuli that are presented on a given trial. In the context of Pavlovian conditioning, these stimuli include various conditioned and unconditioned stimuli. This elaboration enables the model to deal with cue competition phenomena, including the relative validity effect, and evidence implicating separate error terms and attentional processes in association formation. The model also includes a performance rule, which provides a natural basis for (individual) variation in the strength and nature of conditioned behaviors that are observed in Pavlovian conditioning procedures. The new model thereby begins to address theoretical and empirical issues that were apparent when the Rescorla-Wagner model was first described, together with research inspired by the model over ensuing 50 years.

Pavlovian conditioning procedures produce marked individual differences in the form of conditioned behavior. For example, when rats are given conditioning trials in which the temporary insertion of a lever into an operant chamber (the conditioned stimulus, CS) is paired with the delivery of food (the unconditioned stimulus, US), they exhibit knowledge of the leverfood relationship in different ways. For some rats (known as sign-trackers) interactions with the lever dominate, while for others (goal-trackers) approaching the food well dominates. A formal model of Pavlovian conditioning (HeiDI) attributes such individual differences in behavior to variations in the perceived salience of the CS and US. An application of the model in which the perceived salience of the CS declines (i.e., adapts) across its duration, predicts changes in these individual differences within the presentation of the CS: The sign-tracking bias is predicted to decline and goal-tracking bias is predicted to increase across the presentation of a lever. The accuracy of these predictions was confirmed though analysis of archival data from female and male rats.

The role of the brain systems modulating attentional processes is discussed.