Loss of associability by a compound stimulus comprising excitatory and inhibitory elements

In each of two experiments rats learned a discrimination between a stimulus (A) that signaled shock and a compound stimulus (AB) that signaled no shock. In Experiment 1 it was found that the AB compound acquired excitatory strength only slowly when, in a second phase of training, it was made to signal the occurrence of shock. In Experiment 2 the acquisition of inhibitory strength by the compound was similarly found to be retarded. This second experiment also replicated the results of Experiment 1. The relevance of these results to current theories of latent inhibition and attention is discussed.     

Control of responding by the elements of a compound discriminative stimulus and by the elements as individual discriminative stimuli

In the first of two studies, the responding of four albino rats was differentially reinforced in the presence of noise and light together and then tested in the presence of the noise and the light separately during extinction. The light exercised substantially more control of responding than did the noise. In the second study the responding of a similar group of four rats was differentially reinforced in the presence of the noise and the light separately. Control of responding by the light developed more rapidly than control by the noise. Results suggest that levels of control by stimuli after differential reinforcement with respect to the stimuli together can be predicted by the rates of development of control during differential reinforcement with respect to the stimuli separately.     

Verbal self-reports about matching to sample: effects of the number of elements in a compound sample stimulus.

Adults' self-reports about their choices in a delayed matching-to-sample task were studied as a function of the number of elements (one, two, or three) in a compound sample stimulus. Signal-detection analyses were used to examine control of self-reports by the number of sample elements, by the speed and accuracy of choices reported about, and by several events contingent on self-reports. On each matching-to-sample trial, a sample element appeared as one of two comparison stimuli. Choice of the matching element, if made within 500 ms of the onset of the comparison stimuli, produced points worth money or chances in a drawing for money, depending on the subject. After each choice, subjects pressed either a "yes" or "no" button to answer a computer-generated query about whether the choice met the point contingency. The number of sample elements in the matching-to-sample task varied across trials, and events contingent on self-reports varied across experimental conditions. In Experiment 1, the conditions were defined by different combinations of feedback messages and point consequences contingent on self-reports, but self-reports were systematically influenced only by the sample-stimulus manipulation. Self-report errors increased with the number of sample elements. False alarms (inaccurate reports of success) were far more common than misses (inaccurate reports of failure), and false alarms were especially likely after choices that were correct but too slow to meet the point contingency. Sensitivity (A') of self-reports decreases as the number of sample elements increased. In addition, self-reports were more sensitive to choice accuracy than to choice speed. All subjects showed a pronounced bias (B'H) for reporting successful responses, although the bias was reduced as the number of sample elements increased and successful choices became less frequent. Experiment 2 demonstrated that the failure of point contingencies to influence self-reports in the first experiment was not due to a general ineffectiveness of the point consequences. Rates of inaccurate self-reports decreased when they resulted in point losses and increased when they resulted in point gains.     

Assessments of changes in the effective salience of stimulus elements as a result of stimulus preexposure

Rats received exposure to 3 flavor compounds, AX and BX, presented in alternation, and CX, presented on a separate block of trials. The hypothesis that this treatment would leave B effectively more salient than C was tested in 3 ways. Experiment 1 showed that the unconditioned response evoked by B was stronger than that evoked by C. Experiment 2 showed that B was more effective than C when used as a reinforcer in a sensory preconditioning procedure. Experiment 3 showed that B was learned about more readily than C as a conditioned stimulus in flavor aversion conditioning. Alternating preexposure to 2 similar stimuli may protect their distinctive features from the loss of salience normally produced by nonreinforced exposure to a stimulus.     

Evidence of interaction between deprivation effects and stimulus control

Discriminative responding in pigeons was studied under multiple variable-interval extinction and variable-ratio extinction schedules, as deprivation was varied. Generally, the greater the accuracy of discrimination that developed during training, the smaller the effect of deprivation upon subsequent performance. This was true both in terms of changes in response rates, and in the relationship between response rates during food reinforcement and extinction. When discrimination was inaccurate, increases in deprivation resulted in disproportionate increases in responding during extinction, as compared to increases during food reinforcement components of the schedule. The results suggest that as stimulus control (accuracy) of responding increases, discriminative performance becomes less and less susceptible to influence by deprivation.     

Response summation to a compound stimulus in a context of choice

Key pecks by two groups of pigeons were reinforced on concurrent schedules. For group Ē, pecks were reinforced during either a visual or an auditory stimulus; for group E, an additional, extinction component was available, during which both visual and auditory stimuli were absent. After training, both groups were given a compound test to measure preference among four stimuli, the three used in training plus a compound of the visual and auditory stimulus. Group E showed preference for the compound, emitting more pecks and spending more time in this stimulus than in other stimuli. Group Ē showed no preference between the compound and visual stimulus, nor between the auditory stimulus and the absence of both stimuli, but preferred the former pair over the latter pair of stimuli.     

Evidence for inhibitory associations between the unique elements of two compound flavours

In each of two experiments, rats were pre-exposed to two flavoured solutions, saline-lemon and sucrose-lemon. For group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution in a block, before any trials with the other. An associative theory suggests that the alternating, but not the blocked, schedule would establish an inhibitory association between sucrose and saline. To provide a retardation test of this inhibition, some animals in each group were then given a single pairing of saline and sucrose, experienced sodium depletion, and were finally tested for their consumption of sucrose. Sodium depletion increased consumption of sucrose more in group BLK than in group ALT. In groups given no saline-sucrose pairing, sodium depletion had only a small effect on sucrose consumption, which was the same in both groups. After multiple pairings of saline and sucrose, sodium depletion had an equally large effect on sucrose consumption in both ALT and BLK groups. These results imply that alternating pre-exposure to two compound solutions does establish an inhibitory association between their unique elements, and thus provide support for an associative theory of perceptual learning.     

Deepened extinction from compound stimulus presentation

Three experiments with rats and 2 with pigeons explored the effect of presenting 2 extinguished excitatory stimuli in compound. Four learning situations were used: Pavlovian magazine approach, Pavlovian fear conditioning, and instrumental discriminative instrumental learning in rats, as well as Pavlovian sign tracking in pigeons. All 5 experiments confirmed D. Reberg's (1972) observation that even after extinction of the individual stimuli, presenting them in compound evoked substantial responding. Moreover, nonreinforcement of that compound deepened extinction of an element more substantially than did additional presentation of that element alone. Such compound exposure reduced spontaneous recovery, reduced reinstatement, and slowed subsequent reconditioning. The primary determinant seemed to be the enhanced associative strength rather than the enhanced conditioned responding that occurred during the nonreinforced compound.     

Sample stimulus control shaping and restricted stimulus control in capuchin monkeys: a methodological note

This paper reports use of sample stimulus control shaping procedures to teach arbitrary matching-to-sample to 2 capuchin monkeys (Cebus apella). The procedures started with identity matching-to-sample. During shaping, stimulus features of the sample were altered gradually, rendering samples and comparisons increasingly physically dissimilar. The objective was to transform identity matching into arbitrary matching (i.e., matching not based on common physical features of the sample and comparison stimuli). Experiment 1 used a two-comparison procedure. The shaping procedure was ultimately effective, but occasional high error rates at certain program steps inspired a follow-up study. Experiment 2 used the same basic approach, but with a three-comparison matching task. During shaping, the monkey performed accurately until the final steps of the program. Subsequent experimentation tested the hypothesis that the decrease in accuracy was due to restricted stimulus control by sample stimulus features that had not yet been changed in the shaping program. Results were consistent with this hypothesis, thus suggesting a new approach that may transform the sample stimulus control shaping procedure from a sometimes useful laboratory tool to a more general approach to teaching the first instance of arbitrary matching performances to participants who show protracted difficulties in learning such performances.     

Misconvergence to the stimulus plane causes apparent displacement of the stimulus elements seen monocularly1

Abstract: When one binocularly views a group of vertical lines through a ring, the outermost line segments (one on each side) seen within the ring are seen monocularly while the segments of the same lines outside the ring are seen binocularly. The monocular segments appear to be displaced outward with respect to the center of the ring and with respect to the corresponding binocular segments outside the ring. Three experiments examined the extent and direction of this illusory displacement as a function of viewing distance, fixation disparity created by varying the angles of the two arms of a haploscope, and fixation disparity created by a stereoscope and different Nonius stimuli. The results of the experiments confirmed the hypothesis that the apparent displacement is due to misconvergence in accordance with Wells‐Hering's laws of visual direction.     

Fixed-interval stimulus control

Chlorpromazine was studied for its effects on responding under a second-order schedule in which food was presented following a sequence of 20 one-minute fixed-interval components. A brief visual stimulus occurred at the completion of each fixed interval including the one that terminated with food presentation. Chlorpromazine showed rate-dependent effects in that it increased low rates in the early components of the second-order schedule and, to a lesser extent, decreased high rates in the later components. Chlorpromazine also increased rates in the early quarters within the 1-min fixed-internal components and to a smaller extent decreased rates in the final quarter. The alteration in the patterns of responding within 1-min fixed-interval components terminating in a brief stimulus presentation was substantially less than that which occurred throughout the succession of 1-min fixed-interval components terminating in food presentation, thus suggesting that the presentation of the brief stimulus exerted more control over responding within components than did food presentation over the sequence of components. This result and others suggest that studies using drugs may be useful in elucidating the factors controlling patterns of responding in second-order schedules.     

On the development of stimulus control

Pigeons were trained to peck one key when presented with white noise at any of five intensities lower than a reference intensity, and to peck another key when presented with white noise at any of five intensities greater than the reference intensity. The shape of the stimulus control curves (proportion of responses to one key versus stimulus intensity) changed from a horizontal line at the beginning of training to the sigmoid form of typical psychometric functions at the end of training. The development of stimulus control is described in terms of a model based on the theory of signal recognition and a concept of attention.     

The interaction between stimulus and reinforcer control on remembering.

In a symbolic matching-to-sample task, 6 pigeons obtained food by pecking a red side key when the brighter of two white lights had been presented on the center key and by pecking a green side key when the dimmer of two white lights had been presented on the center key. Across Part 1 and Parts 6 to 10, the delay between sample-stimulus presentation and the availability of the choice keys was varied between 0 s and 25 s. Across Parts 1 to 5, the delay between the emission of a correct choice and the delivery of a reinforcer was varied between 0 s and 30 s. Although increasing both types of delay decreased stimulus discriminability, lengthening the stimulus-choice delay produced a greater decrement in choice accuracy than did lengthening the choice-reinforcer delay. Additionally, the relative reinforcer rate for correct choice was varied across both types of delay. The sensitivity of behavior to the distribution of reinforcers decreased as discriminability decreased under both procedures. These data are consistent with the view, based on the generalized matching law, that sample stimuli and reinforcers interact in their control over remembering.     

Transfer of configural learning between the components of a preexposed stimulus compound: implications for elemental and configural models of learning

In 2 experiments, rats received preexposure to 2 compound contexts: AB and CD for the congruent group and AC and BD for the incongruent group. Subsequently, all rats received a configural discrimination in which separate placement in contexts A or B indicated that presentations of stimulus X would be followed by food and presentations of Y would not, and separate placement in contexts C and D indicated that Y would be followed by food and X would not. In both experiments, rats in the congruent group acquired the conditional discrimination more rapidly than those in the incongruent group. These results are inconsistent with conventional associative accounts of either stimulus preexposure effects or configural learning and instead provide support for a connectionist account.     

Levels of stimulus control: a functional approach

This paper surveys some illustrative experiments on categorization of visual stimuli by animals other than human. The results suggest a classification of categorical powers in five steps from simple discrimination to rote and open-ended categorization, to concepts and the use of abstract relations. Nonhuman animals evidently readily categorize up to the fourth level as here defined, which is the level of concepts. With difficulty, they can sometimes be induced to rise even to the level of abstract relations. It is at the level of abstract relations that a large gap opens up between human categorizations and categorization by other animals.     

Effects of discrimination training on responding during a compound conditioned stimulus.

Four experiments examined responding in the presence of a triple-element compound ABC after discrimination training in which 2 compounds, AB and BC, signaled the delivery of food and 1 element alone, B, signaled the absence of food. In Experiments 1 and 2, using rats, responding during ABC was more vigorous than in a control group for which A and C but not B had been individually paired with food. This finding was replicated in Experiment 3, which used pigeons, and in Experiment 4, where all 3 stimuli of the control condition were individually paired with food. The results are more consistent with a configural than with an elemental theory of learning.     

Eliminating selective stimulus control: a comparison of two procedures for teaching mentally retarded children to respond to compound stimuli

Selective stimulus control occurs when behavior fails to come under control of all characteristics of a compound stimulus after discrimination training. Two different assessment procedures, one used in prior research and the other incorporating incorrect stimuli (S - 's) which differed minimally from the correct stimulus (S+), were used to detect stimulus control deficits characteristic of selective stimulus control. The efficacy of two training procedures in eliminating selective stimulus control observed with three trainable mentally retarded children was evaluated in Experiment 1. A training procedure using S - 's that were minimally different from the S+ was designed to reduce the probability that stimulus discriminations could be based on stimulus characteristics other than experimenter-specified characteristics defining the S+. This procedure proved more effective in preventing and eliminating selective stimulus control as measured by both assessment procedures than an alternate discrimination training procedure that failed to impact the more stringent measures of selective stimulus control. Experiment 2 indicated that these improvements in stimulus control were not a function of varying degrees of difficulty between stimulus sets or of a prior history of discrimination training with the less effective training procedure. The need for better assessment procedures to detect selective stimulus control and suggestions for further improvements in discrimination training procedures are discussed.     

The Stroop effect at 80: The competition between stimulus control and cognitive control

For more than 80 years, researchers have examined the interference between automatic processing of stimuli, such as the meaning of color words, on performance of a controlled‐processing task such as naming the color in which words are printed. The Stroop effect and its many variations provide an ideal test platform for examining the competition between stimulus control and cognitive control of attention, as reflected in behavior. The two experiments reported here show that rhesus monkeys, like human adults, show interference from incongruous stimulus conditions in a number‐Stroop task, and that the monkeys may be particularly susceptible to influence from response strength and less able, relative to human adults, of using executive attention to minimize this interference.