Subproblem learning: A misnomer

Among other things, K. J. Rust and T. S. Kendler (1987, Developmental Review, 7, 326–362) tested and disconfirmed the Tighes' independent subproblem learning hypothesis experimentally. The Tighes defended themselves by claiming that independent subproblem learning (ISPL) is a label, not a hypothesis and that our tests were invalid. In this reply we showed that ISPL is either an erroneous hypothesis or a misnomer because our tests were valid demonstrations that for young children the so-called “subproblems” are dependent rather than independent.     

Overtraining, extinction and shift learning in a concurrent discrimination in rats

Two experiments examined the influence of overtraining on the reversal of a concurrent discrimination. After rats are trained to criterion on two different discriminations in the same apparatus, the reversal of one of these proceeds more rapidly than when both are reversed. If the reversal is conducted after overtraining on the original discriminations, then the opposite pattern of results is observed. That is, learning about the reversal of both discriminations is more rapid than when only a single discrimination is reversed. Experiment 1 replicated this effect and suggested that it is not caused by differences in the rate of extinction during reversal learning. In order to test a cue-association account for these findings, Experiment 2 examined the effect of exchanging the negative stimuli of a concurrent discrimination. This manipulation had a disruptive influence on performance, but only when subjects were not overtrained on the original discrimination.     

Stimulus generalization, discrimination learning, and peak shift in horses.

Using horses, we investigated three aspects of the stimulus control of lever-pressing behavior: stimulus generalization, discrimination learning, and peak shift. Nine solid black circles, ranging in size from 0.5 in. to 4.5 in. (1.3 cm to 11.4 cm) served as stimuli. Each horse was shaped, using successive approximations, to press a rat lever with its lip in the presence of a positive stimulus, the 2.5-in. (6.4-cm) circle. Shaping proceeded quickly and was comparable to that of other laboratory organisms. After responding was maintained on a variable-interval 30-s schedule, stimulus generalization gradients were collected from 2 horses prior to discrimination training. During discrimination training, grain followed lever presses in the presence of a positive stimulus (a 2.5-in circle) and never followed lever presses in the presence of a negative stimulus (a 1.5-in. [3.8-cm] circle). Three horses met a criterion of zero responses to the negative stimulus in fewer than 15 sessions. Horses given stimulus generalization testing prior to discrimination training produced symmetrical gradients; horses given discrimination training prior to generalization testing produced asymmetrical gradients. The peak of these gradients shifted away from the negative stimulus. These results are consistent with discrimination, stimulus generalization, and peak-shift phenomena observed in other organisms.     

Effects of monochromatic rearing on spectral discrimination learning and the peak shift in chicks

Chicks were hatched and raised in white or monochromatic sodium (589 nm) light. They were trained on a 590 (+) vs. 580 (-) nm successive discrimination. The combined results of two experiments indicated that rearing illumination did not affect discrimination acquisition. All subjects given generalization tests after discrimination training exhibited peak shifts that were equivalent for the two rearing conditions. The peak shifts exhibited by the monochromatically reared subjects represent maximum responding to stimuli they had not previously seen. This result further confirms the notion that behavioral control by the spectral dimension in birds is organized independently of differential early experience on that dimension.     

A configural analysis for feature-negative discrimination learning.

In 4 experiments, rats were initially trained with an A+ AXo discrimination in which Stimulus A by itself signaled the delivery of food, A+, whereas the simultaneous presentation of A and X was followed by nothing, AXo. In each experiment X was then paired with food prior to a test phase in which A and X were again presented for a discrimination. The discrimination was of the form A+ AXo in Experiments 1 and 2, whereas it was of the form X+ AXo for Experiments 3 and 4. In all 4 experiments the test discrimination was acquired more rapidly than a control discrimination. The results are interpreted in terms of the original A+ AXo discrimination resulting in the growth of an association between a representation of the entire AX compound and the effects of nonreinforcement.     

Extradimensional shift learning in pigeons: Positive and negative transfer produced by prior discrimination training

Four groups of pigeons were trained on a free operant successive discrimination between line-stimuli differing in orientation. The groups differed according to their previous treatment. Two groups had received true discrimination (TD) training with stimuli differing in colour and two groups had received pseudo-discrimination (PD) training. For one pair of groups the line-stimulus that was to become the positive stimulus in the transfer stage of the experiment was superimposed on both colours and in these the subjects given PD training learned the orientation discrimination more readily than those given TD training. In the other pair of groups TD animals learned more readily than PD. These results require us to modify current theories of attentional factors in transfer.     

Optional shift,and discrimination learning with redundant relevant dimensions: Predictions of an attentional model

The Zeaman-House-Lovejoy (ZHL) model for discrimination learning involves interacting perceptual and response learning processes, with rate parameters ? and θ, respectively. This paper describes a number of predictions of the ZHL model for the optional shift paradigm. Kendler and Kendler showed that the proportion of subjects who learn an optional shift as a reversal increases with subject's age, and Campione and others have argued that this trend may reflect developmental variation in parameters like ? and θ. Our main result is a formula specifying the dependence of reversal probability on ? and θ for the ZHL model.     

Observing responses and discrimination learning

An operant response in the pigeon, whose performance results in exposure to the discriminative stimuli, is described and suggested as an experimental analogue for “observing.” Such an operant response is then used to explore the relationship between observing responses and discrimination learning in a variety of discrimination situations, of progressively increasing complexity. In general, the results support the contention that the development and maintainence of observing responses is closely related to the degree of differential behaviour manifested toward the discriminative stimuli. Certain modifications are suggested in the theoretical formulation underlying the concept of “observing responses.”