[Sequential learning and memory-related structure formation].
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Association Learning↗
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Discrimination of duration ratios.
Trained pigeons to make discriminations on the basis of the ratio of two stimulus durations. A red light of one duration was followed by a green light of a different duration, with 900 red-green pairs intermixed over trials. A choice followed the red-green pair; a response to a green side key was reinforced if the red-green ratio was less than a criterion ratio, and a response to a red side key was reinforced if the ratio exceeded the criterion. Reinforcement depended on whether red or green was longer under the basic condition; in other conditions, however, reinforcement depended on whether one duration was two or four times longer than the other. Sensitivity was similar across conditions, for the basic shorter-longer rule, and for the more complex rule of one duration as two or four times the other. Most choices were made on the basis of the ratio relation between the two durations and according to Weber's law. These results extend the findings of Dreyfus, Fetterman, Smith, and Stubbs (1988), and provide a new methodology for psychophysical scaling with animals.
Animals↗
Implicit learning in patients with probable Alzheimer's disease.
The purpose of the present study was to determine whether patients with probable Alzheimer's disease (AD) were capable of implicit procedural learning. AD patients and elderly control subjects were given a serial visual reaction time task with an embedded repeating sequence. The AD patients responded more slowly than the controls, but many nonetheless showed learning of the repeating sequence. Patients who failed to learn the sequence were similar in age and overall severity of dementia to those who learned, but they scored lower on some tasks of nonverbal reasoning.
Aged↗
The method of constant stimuli is inefficient.
Simpson (1988) has argued that the method of constant stimuli is as efficient as adaptive methods of threshold estimation, and has supported this claim with simulations. We show that Simpson's simulations are not a reasonable model of the experimental process, and that more plausible simulations confirm that adaptive methods are much more efficient than the method of constant stimuli.
Attention↗
Learning disabilities as a probable consequence of using chloride-deficient infant formula.
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Child↗
The role of contingency in classical conditioning.
The assumption that classical conditioning depends on a contingent relation between the conditioned stimulus (CS) and the unconditioned stimulus (US), which was proposed some decades ago as an alternative to the traditional contiguity assumption, still is widely accepted as an empirical generalization, if no longer as a theoretical postulate. The first support for the contingency assumption was provided by experiments in which occasional CS-US pairings produced no response to the CS in random training--i.e., training in which the probability of the US was the same in the presence and absence of the CS. Those early experiments, the results of which too often are taken at face value, are reconsidered along with various later experiments that show conditioning, both of the CS and its context, in random training. The evidence suggests that CS-US contingency is neither necessary nor sufficient for conditioning and that the concept has long outlived any usefulness it may once have had in the analysis of conditioning.
Animals↗
A table of d' for M-alternative odd-man-out forced-choice procedures.
There is a class of multiple-alternative forced-choice psychophysical procedures in which the subject is required to identify which one of a number of stimuli differs from the remaining stimuli, without having to consider the direction or sign of the difference. A table giving values of the discrimination index d' as a function of the proportion of correct responses in such odd-man-out procedures was generated by numerical simulation. The table covers experiments with 3 to 32 alternative stimuli.
Attention↗
[Dependence of search activities on the probability of random execution of instrumental reaction].
The increase in rat search activity was found to develop in early stages of the learning when probability of random performance of instrumental reaction to light was equal to 0.25. This phenomenon was not depended on duration of conditioned signal and/or/of intersignal period at the invariable probability. The probability of random performance of instrumental reaction is suggested to determine search activity and to be able to influence leaning rate.
Animals↗
Choice with uncertain outcomes: conditioned reinforcement effects.
Pigeons responded on concurrent chains with equal initial- and terminal-link durations. In all conditions, the terminal links of one chain ended reliably in reinforcement; the terminal links on the alternative chain ended in either food or blackout. In Experiment 1, the terminal-link stimuli were correlated with (signaled) the outcome, and the durations of the initial and terminal links were varied across conditions. Preference did not vary systematically across conditions. In Experiment 2, terminal-link durations were varied under different stimulus conditions. The initial links were variable-interval 80-s schedules. Preference for the reliable alternative was generally higher in unsignaled than in signaled conditions. Preference increased with terminal-link durations only in the unsignaled conditions. There were no consistent differences between conditions with and without a common signal for reinforcement on the two chains. In the first series of conditions in Experiment 3, a single response was required in the initial links, and the stimulus conditions during 50-s terminal links were varied. Preference for the reliable outcome approached 1.0 in unsignaled conditions and was considerably lower (below .50 for 3 of 5 subjects) in signaled conditions. In a final series of signaled conditions with relatively long terminal links, preference varied with duration of the initial links. The results extend previous findings and are discussed in terms of the delay reduction signaled by terminal-link stimuli.
Animals↗
Dissociation of theories of choice by temporal spacing of choice opportunities.
Rats were trained on a discrete-trial version of a concurrent variable-interval (VI) variable-ratio (VR) schedule in which the relative reinforcement rates were varied across conditions. Subjects with the shorter intertrial interval (ITI) had a significant bias toward the VR alternative, as predicted by optimality theory, and were also more likely to choose the VI alternative with longer times since responses to the VI alternative, as predicted by momentary-maximizing theory. Subjects with the longer ITI failed to show either of these effects. Approximation to the matching law was greater with the longer ITI. Thus, matching is not derivative of the processes postulated by optimality or momentary-maximizing theory but instead is in competition with those processes.
Animals↗
Rule abstraction, item memory, and chunking in rat serial-pattern tracking.
Two studies used a stimulus tracking paradigm to test whether rats are sensitive to the rule-based formal properties of structured serial patterns. Hooded rats tracked 16-element patterns of flashing lights by pressing levers under an array of 6 indicator lights. In Experiment 1, rats tracked a pattern similar to one previously used with human subjects and yielded remarkably similar results. More errors and response omissions occurred at boundaries of structural "chunks" than within chunks, and errors often reflected anticipation of the next chunk or extrapolation of the preceding chunk. In Experiment 2, temporal "phrasing" cues encouraged different groups to encode a pattern as a series of either "runs" or "trills." Differential placement of pauses induced rats to encode different rule-based representations of the pattern. Results indicate that under appropriate conditions rats may encode a representation of formal structure when they learn organized response patterns.
Animals↗
Base-rate effects in category learning: a comparison of parallel network and memory storage-retrieval models.
Exemplar-memory and adaptive network models were compared in application to category learning data, with special attention to base rate effects on learning and transfer performance. Subjects classified symptom charts of hypothetical patients into disease categories, with informative feedback on learning trials and with the feedback either given or withheld on test trials that followed each fourth of the learning series. The network model proved notably accurate and uniformly superior to the exemplar model in accounting for the detailed course of learning; both the parallel, interactive aspect of the network model and its particular learning algorithm contribute to this superiority. During learning, subjects' performance reflected both category base rates and feature (symptom) probabilities in a nearly optimal manner, a result predicted by both models, though more accurately by the network model. However, under some test conditions, the data showed substantial base-rate neglect, in agreement with Gluck and Bower (1988b).
Adult↗
Suboptimal choice in a percentage-reinforcement procedure: effects of signal condition and terminal-link length.
Pigeons' choice between reliable (100%) and unreliable (50%) reinforcement was studied using a concurrent-chains procedure. Initial links were fixed-ratio 1 schedules, and terminal links were equal fixed-time schedules. The duration of the terminal links was varied across conditions. The terminal link on the reliable side always ended in food; the terminal link on the unreliable side ended with food 50% of the time and otherwise with blackout. Different stimuli present during the 50% terminal links signaled food or blackout outcomes under signaled conditions but were uncorrelated with outcomes under unsignaled conditions. In signaled conditions, most pigeons displayed a nearly exclusive preference for the 100% alternative when terminal links were short (5 or 10 s), but with terminal links of 30 s or longer, preference for the 100% alternative was sharply reduced (often to below .5). In unsignaled conditions, most pigeons showed extreme preference for the 100% alternative with either short (5 s) or longer (30 s) terminal links. Thus, pigeons' choice between reliable and unreliable reinforcement is influenced by both the signal conditions on the unreliable alternative and the duration of the terminal-link delay. With a long delay and signaled outcomes, many pigeons display a suboptimal tendency to choose the unreliable side.
Animals↗
Hierarchical structures: chunking by food type facilitates spatial memory.
Three experiments assessed the ability of male Sprague-Dawley rats to organize the spatial locations of different food types in a hierarchical manner to maximize the efficiency of working memory. Independent groups were exposed, on a 12-arm radial maze, to baiting arrangements varying in the stability of the pattern and type of food used as bait. Training rats with stable, differentiable baiting arrangements produced increased accuracy in choice performance, hierarchically ordered patterns of choice selection, slower growth of proactive interference when trials were massed, and the learning of the geometrical relations among food types independent of other extramaze cues. Such findings are strong evidence of the rat's ability to encode and use local cues for navigation, based on properties of the reinforcer. The application of a chunking strategy may provide for more efficient use of working memory by facilitating information storage, recall, or resetting mechanisms.
Animals↗
Deficits in visual learning produced by posterior temporal lesions in cats.
Eight cats with lesions in the posterior temporal (PT) cortex, seven cats with lesions in the basolateral amygdala (BLA), and eight intact controls were observed on eight tests of visual discrimination learning and of spontaneous responses to salient visual stimuli. The effects of the two lesions were somewhat dissociable. The PT lesions were accompanied by a severe deficit in pattern discrimination learning but no loss in visual tracking or orientation to the silhouette of a threatening cat. The BLA lesions produced a milder and less consistent loss in pattern discrimination but serious defects in tracking and reponse to the cat silhouette. Both operated groups performed well on the visual cliff. The deficit from PT lesions appeared independent of damage to the geniculocortical system. The parallel of symptoms from PT lesions in cats and inferotemporal lesions in monkeys is discussed.
Amygdala↗
Expectancy and visual-spatial attention: effects on perceptual quality.
When we expect important stimuli at a particular spatial location, how does our perceptual sensitivity change over space? Subjects were cued to expect a target stimulus at one location and then required to perform one of the following tasks at that and three other locations: luminance detection, brightness discrimination, orientation discrimination, or form discrimination. The analysis of subjects' performance according to signal detection theory revealed changes in both sensitivity and bias for each of these tasks. Sensitivity was maximally enhanced at the location where a target stimulus was expected and generally decreased with distance from that location. Factors that influenced the gradient of sensitivity were (a) the type of task performed and (b) the spatial distribution of the stimuli. Sensitivity fell off more steeply over distance for orientation and form discrimination than for luminance detection and brightness discrimination. In addition, it fell off more steeply when stimuli were near each other than when they were farther apart.
Attention↗
Integrating information from separable psychological dimensions.
This article examines decision processes in the perception and categorization of stimuli composed of the separable psychological dimensions, orientation and size. The randomization technique (Ashby & Gott, 1988) of general recognition theory, which allows accurate estimation of a subject's decision boundary in a categorization task, is used in 4 experiments. Even though the stimulus components are clearly separable, it was found that Ss were not constrained to use separable response strategies, nor were they constrained to attend to distance to the prototypes. Instead, they used decision rules that were nearly optimal, even if this required information integration or for the Ss to attend to higher level category properties such as component correlation.
Adult↗
The Kamin blocking effect, incidental learning and psychoticism.
The Kamin blocking effect consists in impaired learning of an association between a conditioned stimulus (CS2) and an unconditioned stimulus (UCS) if CS2 is presented simultaneously with a different CS (CS1) already associated with the UCS. It is well established with animal but not human subjects. In the two experiments presented here, the effect was clearly demonstrated with UCS = a computer-presented yellow square, CS1 = a blue square and CS2 = a noise (Expt 1) or two smaller white squares (Expt 2). The Kamin effect has, by some theorists, been attributed to switching of attention away from CS2, which conveys only redundant information. If so, the size of the effect should co-vary with indices of selective attention commonly used with human subjects. As predicted, the blocking effect was found to be smaller in subjects who displayed a high degree of incidental learning in either of two tasks in which intentional vs. incidental learning corresponded to (1) words vs. word position, or (2) a target initial word letter vs. non-target initial letters. We report elsewhere that the blocking effect is absent in acute schizophrenics. In the present experiments, however, there was no systematic relation between any of four measures of psychoticism, or intelligence, and either the blocking effect or incidental learning.
Adult↗