V. D. Chamizo

Blocking in the Spatial Domain

An initial series of experiments with rats in a swimming pool established that they could find a hidden platform the location of which was defined in terms of 3 or 4 landmarks and that, when trained with all 4, any subset of 3 (or even, after a sufficient number of swimming trials, 2) landmarks was sufficient to produce accurate performance. When only one landmark was present during testing, however, performance fell to chance. Two additional experiments demonstrated a significant blocking effect: If rats were first trained to locate the platform with 3 landmarks, they did not learn to use a 4th landmark added to their initial set of 3.

Acquisition of knowledge about spatial location: assessing the generality of the mechanism of learning.

A selection of studies in the last 20 years is reviewed. These studies show basic Pavlovian phenomena in the spatial domain (like blocking, overshadowing, latent inhibition, and perceptual learning) with nonhuman subjects, specifically with rats, both in the radial maze and in the circular pool. The generality of these phenomena with respect to other species and to other spatial preparations is also discussed. The conclusion is that the mechanism responsible for the acquisition of knowledge about spatial location seems to be associative in nature.

Overshadowing in the spatial domain

In Experiments 1 and 2, rats were trained in a Morris water maze to locate a hidden platform, the location of which in the circular pool was defined by four visual landmarks (A, B, C, and D), spaced at equal intervals around the edge of the pool. Control animals were trained with these four visual landmarks only. But for animals in the overshadowing groups, an auditory component, X, was added to Landmark D. Test trials, given at the end of training, consisted of placing the rat in the pool with no platform present and recording the time rats spent in the platform quadrant. In Experiment 1, the overshadowing group spent less time in the platform quadrant than controls when tested with D, but the two groups performed equally well on test trials that did not use D. We conclude that the auditory Component X overshadowed the visual Landmark D. In Experiment 2, we obtained evidence of reciprocal overshadowing, of D by X and of X by D. The results of Experiment 3 suggested that an appeal to generalization decrement might not be sufficient to explain these overshadowing effects.

Latent learning and latent inhibition in maze discriminations

Rats were trained on an elevated maze where the rewarded alternative was defined either in terms of intra-maze or in terms of extra-maze cues. Pre-exposure to these cues produced a small latent or perceptual learning effect, i.e. facilitated subsequent learning of both problems, by comparison with animals pre-exposed to the maze with no cues present. Experiment 2 examined whether the effect of pre-exposure on intra-maze discrimination learning varied with the nature of the intra-maze cues. When positive and negative arms were further differentiated by painting the walls white and black, a marginal perceptual learning effect was turned into significant latent inhibition, i.e. a retardation of subsequent learning. Pre-exposure thus reliably facilitated extra-maze discrimnation learning, and its beneficial effects on intra-maze discrimination could be reversed by reducing the overlap between the intra-maze cues. Perceptual learning may therefore depend on requiring animals to discriminate between stimuli containing many common elements.

Human overshadowing in a virtual pool: Simple guidance is a good competitor against locale learning☆

Abstract In four experiments a new virtual preparation for humans of the Morris water task (VMWT) was used. Psychology students were trained to locate a platform (either visible or invisible) in the presence of four landmarks (A, B, C, D), spaced at equal intervals around the edge of the pool. At the end of training one test trial was given in the presence of one or several landmarks, without the platform, and the time the students spent in the platform quadrant was registered. Experiment 1 used an invisible platform. It was designed to see how much the students had learned either of the whole set of four landmarks or of some subset of it when searching for the platform on test. When tested with four or two landmarks (either relatively near or far from the platform), the students’ performance was equivalent and significantly better than that obtained with one landmark only (either relatively near or far from the platform). In Experiment 2, for Group Experimental, the platform was visible, while for Group Control, it was invisible. On the test trial, a clear overshadowing effect was found: the Overshadowing group spent significantly less time in the platform quadrant than the Control group. A third group, Group Experimental-Slow, was subsequently added to eliminate an alternative explanation of spatial overshadowing in terms of differential experience with the landmarks during training. Finally, Experiments 3 and 4 were conducted to control for generalization decrement. The data are discussed within the growing body of evidence that suggests that the general laws of learning apply to many species, both in the spatial and temporal domains.

Sex Differences in the Strategies Used by Rats to Solve a Navigation Task

Rats were trained in a triangular-shaped pool to find a hidden platform, whose location was defined in terms of two sources of information, a landmark outside the pool and a particular corner of the pool. Subsequent test trials without the platform pitted these two sources of information against one another. This test revealed a clear sex difference. Females spent more time in an area of the pool that corresponded to the landmark, whereas males spent more time in the distinctive corner of the pool even though further tests revealed that both sexes had learned about the two sources of information by presenting cues individually. The results agree with the claim that males and females use different types of information in spatial navigation.

Competition between landmarks in spatial learning: the role of proximity to the goal

In two experiments, rats were trained to find a hidden platform in a Morris pool in the presence of two landmarks. Landmark B was present on all training trials, on half the trials accompanied by landmark A, on the remainder by landmark C. For rats in Group Bn, B was near the location of the platform; for those in Group Bf, B was far from the platform. Group Bn performed better than Group Bf on test trials to B alone, but significantly worse on test trials to a new configuration formed by A and C. Thus, the spatial proximity of B to the platform affected not only how well it could be used to locate the platform, but also its ability to prevent learning about other landmarks.

Perceptual learning in maze discriminations

In Experiment 1, rats were trained on a discrimination between rubber- and sandpaper-covered arms of a maze after one group had been pre-exposed to these intra-maze cues. Pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made easier by adding further discriminative stimuli, when it now significantly retarded learning. In Experiment 2, rats were trained on an extra-maze spatial discrimination, again after one group, but not another, had been pre-exposed to the extra-maze landmarks. Here too, pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made substantially easier by arranging that the two arms between which rats had to choose were always separated by 135°. The results of both experiments can be explained by supposing that perceptual learning depends on the presence of features common to S+ and S-.

Latent inhibition and perceptual learning in a swimming-pool navigation task.

In each of 3 experiments, rats were preexposed to the 4 distinct landmarks surrounding a circular pool before being trained to find a submerged platform located in a fixed position in the pool. When preexposure was to pairs of adjacent landmarks, it consistently retarded subsequent learning (a latent inhibition effect). When preexposure was to 1 landmark at a time, then, provided the 4 landmarks all contained a salient feature in common, preexposure facilitated subsequent learning (a perceptual learning effect). The results provide little support for the notion of a cognitive map and are quite consistent with an associative analysis.

Inhibitory associations between neutral stimuli: A comparative approach

In Experiments 1A, 1B, and 1C, nonhuman subjects, rats, received long alternated exposures to two compound flavors, AX and BX, that shared one flavor in common, X. Following this, conditioning of an aversion to A was sufficient to establish B as a conditioned inhibitor of the aversive unconditioned stimulus, passing both summation and retardation tests. Two additional experiments (Experiments 2 and 3) expanded the generality of these results to humans, using similar designs but an auditory discrimination learning task. A set of notes sequentially presented served as cues and fictitious composers served as outcomes. Both summation and retardation effects were found (Experiments 2 and 3, respectively). Experiment 4 then sought to clarify the mechanism underlying these effects. The results are discussed within several theoretical frameworks, most centrally the McLaren, Kaye, and Mackintosh (1989) theory of perceptual learning.