Stimulus properties of conspecific behavior

Two experiments identified the conditions in which the behavior of one bird acquired discriminative control of the behavior of a second bird. The schedule-controlled behaviors of the “stimulus” bird were differentially correlated with the components of a multiple schedule according to which the pecking of an “experimental” bird produced food. In Experiment 1, three pairs of pigeons acquired a successive discrimination and two reversals with the conspecific stimuli. Experiment 2 included a control condition in which no systematic relationship existed between the conspecific stimuli and the component schedules. While differential responding during the components of the multiple schedule was again found when the conspecific stimuli were available, differential responding did not occur in the control condition. Test conditions included in the experiments indicated that (a) the differential responding was not dependent on the discriminative properties of reinforcement, (b) the pecking of the stimulus and experimental birds was temporally interrelated, (c) the visual conspecific stimuli were critical to the maintenance of the discrimination, and (d) the observed stimulus control immediately generalized to an unfamiliar conspecific.     

Cross modal transfer of a conditional flexion response in dogs

Two experiments investigated cross modal transfer of a conditional flexion response. In the first experiment, two dogs with extensive experimental past histories transferred a discrimination based on the pattern of presentation of auditory stimuli to a comparable pattern of visual stimuli. A second experiment with a naive dog demonstrated that such stimulus patterning also occurred from visual to auditory modalities. Additional tests showed that transfer was based on the relationship between discriminative stimuli and that the negative stimulus in the second modality was actively inhibitory. The data were discussed with reference to general attentiveness and rudimentary concept learning.     

Exposure effects and associative learning

The contributions of initial stimulus affect and of associative learning to the effects of repeated stimulus exposures were examined in two experiments. Stimuli that were initially positive and stimuli that were initially negative were presented for different number of times, and subjects rated these stimuli afterward on a number of affective dimensions. In all cases, except when negative affect was associatively paired with every stimulus exposure, affective responses became increasingly more positive with increasing exposures. The results were taken to indicate that the exposure effect can overcome an initially negative stimulus affect when the conditions of the mere exposure hypothesis are satisfied. Initial stimulus affect and associative learning of affect were shown to be independent factors, the first influencing the intercept of the exposure function, the second its slope.     

Discrimination of word-like compound visual stimuli by monkeys

In Experiment I, two monkeys solved a successive visual discrimination in which the four positive stimuli were the visual arrays RIM, LID, RAD and LAM while the four negative stimuli were RID, LIM, RAM and LAD. In Experiment II the same monkeys first learned a discrimination where the positive stimuli were pairs of letters (e.g. OB and AK) while the negative stimulus was the letter I; in a subsequent generalization test with all four possible pairings of the stimulus elements that had been positive during training (i.e. with OB, AK, OK and AB) the monkeys responded more strongly to the pairs that had been present in initial training. These results were discussed in relation to the theoretical analysis of configurational cues in animal discrimination learning and to the mechanism underlying visual discrimination of words by people.     

Contextual conditional discriminations

Three experiments used a discriminated operant procedure to study conditional discrimination learning in rats. The first experiment showed that rats were capable of learning a biconditional discrimination in which two contexts served as conditional cues signalling the reinforcement contingencies associated with two discriminative stimuli. The discrimination was learned equally well when one discriminative stimulus signalled food, the other its absence, and when one stimulus signalled food, the other extinction plus mild footshock.

In Experiment 2 it was shown that prior training on such a conditional discrimination enhanced the subsequent context specificity of simple conditioning relative to control groups of animals for whom the prior training had not been conditional. Experiment 3 showed that a reversal of the significance of one pair of discriminative stimuli produced no spontaneous reversal in performance to a second, target, pair.

The pattern of results is best accounted for by an analysis of contextual conditional discrimination learning in terms of stimulus configurations and offers no support for the notion that rats may learn a general conditional rule or set.     

Exclusion performance and learning by exclusion in dogs

Responding by exclusion is a type of emergent repertoire in which an individual chooses an alternative by the apparent exclusion of other available alternatives. In this case it is possible to respond appropriately to an undefined stimulus (one that has not previously acquired discriminative functions) by excluding the defined alternatives. There is evidence of exclusion in humans and nonhuman animals, although learning as an outcome of exclusion does not always occur. This study aimed to investigate exclusion in visual simple discriminations and learning of new simple discriminations resulting from exclusion in four border collies. Subjects were trained to perform simple simultaneous discriminations between pairs of tridimensional objects, and were then tested for exclusion, novelty control and learning of new simple discriminations. All dogs successfully responded by exclusion, choosing an undefined stimulus displayed with an S‐. For three dogs, it was possible to conclude that these previously undefined stimuli acquired S+ functions, documenting learning of new simple discriminations. However, this required up to four exposures to exclusion trials with each pair of stimuli.     

Enhanced Latent Inhibition Following Compound Pre-exposure

The influence of non-reinforced exposure to compound stimuli on subsequent appetitive classical conditioning was examined in five experiments with rats as the subjects. Non-reinforced exposure to a visual stimulus retarded subsequent acquisition of conditioned responding relative to a non-pre-exposed condition (latent inhibition). If the target stimulus was pre-exposed in compound with a second (non-target) stimulus, then latent inhibition was abolished. Exposure to the non-target stimulus prior to compound exposure had varying effects on subsequent conditioning to the target: 40 exposures to the non-target stimulus resulted in latent inhibition to the target stimulus that was comparable in magnitude to that observed when the target stimulus was exposed in isolation; 120 exposures to the non-target stimulus enhanced latent inhibition to the target stimulus.     

Classical conditioning of autonomic fear responses is independent of contingency awareness

The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an "easy" discrimination, and another was exposed to a "difficult" CS+ and CS-. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies. The role of contingency awareness in classical conditioning experiments using human subjects is currently under debate. This study took a novel approach to manipulating contingency awareness in a differential Pavlovian conditioning paradigm. Complex sine wave gratings were used as visual conditional stimuli (CS). By manipulating the fundamental spatial frequency of the displays, we were able to construct pairs of stimuli that varied in discriminability. One group of subjects was given an "easy" discrimination, and another was exposed to a "difficult" CS+ and CS-. A 3rd group was exposed to a stimulus that was paired with the unconditional stimulus (UCS) 50% of the time and served as a control. Skin conductance response (SCR) and continuous UCS expectancy data were measured concurrently throughout the experiment. Differential UCS expectancy was found only in the easy discrimination group. Differential SCRs were found in the easy discrimination group as well as in the difficult discrimination group, but not in the 50% contingency control. The difficult discrimination group did not exhibit differential UCS expectancy but did show clear differential SCR. These observations support a dual process interpretation of classical conditioning whereby conditioning on an implicit level can occur without explicit knowledge about the contingencies.     

Effects of discrete-trial and free-operant procedures on the acquisition and maintenance of successive discrimination in rats.

Rats were trained on a successive discrete-trial discrimination between two tonal stimuli to examine the effects of availability of a lever during intertrial intervals. In the discrete-trial condition, in which a lever was removed from the chamber during intertrial intervals, 10-s trials were initiated by the presentation of both discriminative stimulus and lever. In the free-operant condition, in which a lever was present during both trials and intertrial intervals, 10-s trials were initiated only by the presentation of a discriminative stimulus. Experiment 1 employed 50-s intertrial intervals and demonstrated that discriminative performances were acquired faster and maintained better in the free-operant conditions than in the discrete-trial conditions. Experiment 2 employed 5-s intertrial intervals and showed that poor discriminative performances in the discrete-trial conditions were improved. These results indicate that the presentation of a lever to start a trial can overshadow or mask the control by a discriminative stimulus and thereby obstruct the acquisition and maintenance of discriminative performances. Furthermore, the overshadowing or masking effects are strengthened as a function of the duration of intertrial intervals.     

Attention to repeated images on the World-Wide Web: Another look at scanpath theory

The scanpath theory of visual perception was tested using Web pages as visual stimuli.Scanpaths are repetitive sequences of fixations and saccades that occur upon reexposure to a visual stimulus. Since Internet users are exposed to repeated visual displays, the Web provides ideal stimuli to test this theory. Eye movement data were recorded for subjects’repeated viewings of three Web pages over three sessions. Resemblance of eye path sequences was measured with a string-edit method; multidimensional scaling and cluster analysis were used to group sequences. Support was found for the scanpath theory; some clusters included pairs of sequences from the same subject. A repeated measures analysis of variance revealeda statistically significant main effect for stimulus type, with a text-intensive news story page generating more similar sequences than a graphic-intensive advertising page. There was a statistically significant main effect for cross-viewing comparisons, reflecting a linear trend in which eye paths for the same subject became more alike over time.     

Differential autoshaping to common and distinctive elements of positive and negative discriminative stimuli

The learning by hungry pigeons of a discrimination between two successively presented compound visual stimuli was investigated using a two-key autoshaping procedure. Common and distinctive stimulus elements were simultaneously presented on separate keys and either followed by food delivery, S+, or not, S−. The subjects acquired both between-trial and within-trial discriminations. On S+ trials, pigeons pecked the distinctive stimulus more than the common stimulus; before responding ceased on S− trials, they pecked the common stimulus more than the distinctive one. Mastery of the within-display discrimination during S+ trials preceded mastery of the between-trials discrimination. These findings extend the Jenkins-Sainsbury analysis of discriminations based upon a single distinguishing feature to discriminations in which common and distinctive elements are associated with both the positive and negative discriminative stimuli. The similarity of these findings to other effects found in autoshaping—approach to signals that forecast reinforcement and withdrawal from signals that forecast nonreinforcement—is also discussed.     

A search for perceptual differentiation produced by nondifferential reinforcement

In each of four experiments (three using pigeons as the subjects and one using rats) animals in an experimental condition were given exposure to a pair of stimuli that subsequently they were required to discriminate between. During the exposure phase response to either stimulus was consistently followed by reward. These subjects were uniformly found to be retarded in learning the discrimination when compared with control subjects that received equivalent pre-training in the absence of the critical stimuli. These results provide no support for the suggestion that stimuli may become “perceptually differentiated” during the pre-training phase but are consistent with the proposal that novel stimuli possess a high level of associability that declines as a result of experience.     

Tests of a two-stage model of visual matching

Predictions from a model of visual matching were tested in two experiments. The model consists of a wholistic comparison process followed by an element-by-element comparison process. All stimuli are processed by the first stage but only those that permit a decision based on a wholistic comparison produce responses. When discrimination is difficult and a decision cannot be reached by a wholistic comparison, the second stage of processing is initiated. Degree of discriminability and stimulus duration (100 and 1000 msec.) were varied in both experiments. In Exp. 1, the stimulus elements were arranged in a square configuration to facilitate a wholistic comparison. As predicted, the hard-different stimuli took longer to match than the same or easy-different stimuli. The hard-different stimuli presented for 1000 msec. took longer to match than those presented for 100 msec. There was no difference in accuracy between responses to hard-different pairs at the two durations. In Exp. 2, the stimulus elements were arranged in a horizontal row and placed one above the other to facilitate element-by-element comparison. As predicted, these stimuli produced slower and more accurate responses for same and hard-different stimulus pairs only when they were exposed for 1000 msec. Responses to easy-different stimulus pairs were made quickly and accurately.     

Stimulus effects on concurrent performance in transition

Six experimentally naive pigeons were exposed to concurrent variable-interval variable-interval schedules in a three-key procedure in which food reinforcement followed pecks on the side keys and pecks on the center key served as changeover responses. In Phase 1, 3 birds were exposed to 20 combinations of five variable-interval values, with each variable-interval value consistently associated with a different color on the side keys. Another 3 pigeons were exposed to the same 20 conditions, but with a more standard procedure that used a nondifferential discriminative stimulus on the two side keys throughout all conditions. In Phase 2, the differential and nondifferential stimulus conditions were reversed for each pigeon. Each condition lasted for one 5-hr session and one subsequent 1-hr session. In the last 14 conditions of each phase, the presence of differential discriminative stimuli decreased the time necessary for differential responding to develop and increased the sensitivity of behavior to reinforcement distribution in the 1st hr of training; during the last hours of training in each condition, however, the effects of the differential discriminative stimuli could not be distinguished from the effects of reinforcement distribution per se. These results show the importance of studying transitions in behavior as well as final performance. They may also be relevant to discrepancies in the results of previous experiments that have used nonhuman and human subjects.     

Stimulus Comparison and Perceptual Learning: Further Evidence and Evaluation from an Imprinting Procedure

Two experiments used chicks to investigate the role of stimulus comparison in perceptual learning. In Experiment 1, chicks received exposure to two views of a jungle fowl, SV (side view) and BV (back view), intermixed within a session (mixed exposure), exposure to SV in one session and BV in a different session (separate exposure), or no exposure to either view. All chicks then received a heat-reinforced discrimination with SV and BV serving as discriminanda. Chicks given mixed exposure acquired the discrimination more readily than did either those given separate exposure or those given no exposure. In Experiment 2, all chicks received mixed exposure to the two stimuli. For one group the interval between presentations of the stimuli was short (short-mixed), for the other group it was long (long-mixed). Subjects in the long-mixed condition acquired the heat-reinforced discrimination more rapidly than those in the short-mixed condition. These results suggest that the intermixed nature of stimulus exposure is an important determinant of the magnitude of perceptual learning effects.     

Picture book exposure elicits positive visual preferences in toddlers

Although the relationship between “mere exposure” and attitude enhancement is well established in the adult domain, there has been little similar work with children. This article examines whether toddlers’ visual attention toward pictures of foods can be enhanced by repeated visual exposure to pictures of foods in a parent-administered picture book. We describe three studies that explored the number and nature of exposures required to elicit positive visual preferences for stimuli and the extent to which induced preferences generalize to other similar items. Results show that positive preferences for stimuli are easily and reliably induced in children and, importantly, that this effect of exposure is not restricted to the exposed stimulus per se but also applies to new representations of the exposed item.     

On the role of covarying functions in stimulus class formation and transfer of function

This experiment investigated whether directly trained covarying functions are necessary for stimulus class formation and transfer of function in humans. Initial class training was designed to establish two respondent-based stimulus classes by pairing two visual stimuli with shock and two other visual stimuli with no shock. Next, two operant discrimination functions were trained to one stimulus of each putative class. The no-shock group received the same training and testing in all phases, except no stimuli were ever paired with shock. The data indicated that skin conductance response conditioning did not occur for the shock groups or for the no-shock group. Tests showed transfer of the established discriminative functions, however, only for the shock groups, indicating the formation of two stimulus classes only for those participants who received respondent class training. The results suggest that transfer of function does not depend on first covarying the stimulus class functions.     

Critical importance of exposure duration for affective discrimination of stimuli that are not recognized

Previous research has found that repeated exposure to briefly presented visual stimuli can increase the positive affect for the stimuli without enhancing their recognition. Subjects could discriminate target and distractor shapes by affective preference in the absence of recognition memory. This study examined this phenomenon as a function of stimulus exposure duration. Over exposure durations of 0, 2, 8, 12, 24, and 48 ms, the functions for affect and recognition judgments exhibited different temporal dynamics. Target selection by affect was possible at very brief exposures and was influenced little by increasing durations; target selection by recognition required longer stimulus exposures and improved with increasing durations. Affective discrimination of stimuli that are not recognized is a reliable phenomenon, but it occurs only within a narrow band of time. This parametric study has specified the relationship between exposure duration and affect and recognition judgments and has located that temporal window.     

A DISCRIMINATION TRAINING PROCEDURE TO ESTABLISH CONDITIONED REINFORCERS FOR CHILDREN WITH AUTISM

Although conditioned reinforcers are used in many behavioral intervention programs for individuals with developmental disabilities, little research has been conducted to determine optimal methods for establishing conditioned reinforcers. An early method that has received relatively little research attention is to condition a neutral stimulus as a discriminative stimulus and then use the stimulus as a programed consequence during skill acquisition. The current study evaluated the effects of a discrimination training procedure on establishing conditioned reinforcers for three children with autism. For all participants, previously neutral stimuli reinforced behaviors after acquiring discriminative properties during discrimination training. Copyright © 2014 John Wiley & Sons, Ltd.     

Inhibition of fear acquisition in toddlers following positive modelling by their mothers

The present study used an experimental design to investigate the role of modelling as a protective factor in fear and avoidance learning in a sample of 77 toddlers. Mothers and their 12-20-month-old children were randomly assigned to one of three pre-exposure conditions: (1) a modelling group (n=27) observed their mothers responding positively to a fear-relevant stimulus; (2) a stimulus-only group (n=25) were exposed to a fear-relevant stimulus alone; and (3) a control group (n=25) were exposed to neither modelling nor the stimulus alone. Children in all three groups were then subjected to an observational conditioning trial in which the experimenter reacted with fear and disgust toward the stimulus. When subsequently tested for the acquisition of fear, children in the modelling group showed more positive affective reactions and more approach behaviours than either controls or children exposed to the stimulus alone. The results demonstrate that very young children can rapidly form lasting associations between maternal affective reactions and novel, fear-relevant stimuli. Further, positive maternal reactions to a stimulus can over-ride any fear-evoking effect of negative reactions to that stimulus by a stranger.