Memory for, and salience of, the unique features of similar stimuli in perceptual learning

In two experiments, participants received exposure to complex checkerboards (e.g., AX and BX) that consisted of small distinctive features (A and B) superimposed on a larger common background (X). Subsequent discrimination between AX and BX, assessed by a same-different task, was facilitated when the stimuli were presented on alternate trials in preexposure--a perceptual learning effect (Experiment 1). The hypothesis that this form of exposure results in more accurate representations of the unique features was supported in Experiment 1, which showed that participants were well able to match the color of the feature with its shape. Experiment 2 showed that exposure to A and B in isolation, intermixed with presentations of AX and BX, enhanced the perceptual learning effect, which confirmed that the better encoding of the unique features during intermixed preexposure is a direct cause of the enhanced discrimination observed following preexposure on this schedule.     

The role of stimulus comparison in perceptual learning: An investigation with the domestic chick

In two experiments an imprinting procedure was used to familiarize chicks with two stimuli, A and B, that subsequently served as the discriminanda in a simultaneous discrimination. On the first day of each experiment, subjects either received presentations of A and B that were intermixed within a session (mixed exposure) or presentations of A in one session and of B in another (separate exposure). For half of the subjects in each of the exposure conditions, A and B differed in both colour and form; for the remainder A and B differed in form alone. On the second day of the experiments, the chicks were placed into a cool test apparatus and given training in which approaching A was rewarded by the delivery of a stream of warm air, but approaching B was not. Acquisition of this discrimination was more rapid when A and B differed in two respects than when they differed in form alone. When A and B differed in both colour and form, the heat-reinforced discrimination was acquired more rapidly after separate exposure than after mixed exposure; but when A and B differed in form alone, discrimination learning was more rapid following mixed exposure than separate exposure. The latter finding, that the opportunity to compare stimuli differing in only one dimension facilitates subsequent discrimination learning, is consistent with earlier suggestions (Gibson, 1969) regarding the conditions that promote perceptual learning.     

Analysis of the role of associative inhibition in perceptual learning by means of the same-different task

In Experiment 1a, participants were exposed, over a series of trials, to separate presentations of 2 similar checkerboard stimuli, AX and BX (where X represents a common background). In one group, AX and BX were presented on alternating trials (intermixed), in another, they were presented in separate blocks of trials (blocked). The intermixed group performed to a higher standard than the blocked group on a same-different test. A superiority of intermixed over blocked exposure was also evident in a within-subject design (Experiment 1b) and when the test required discrimination between a preexposed stimulus and the background (e.g., AX vs. X), even if the background changed between preexposure and test (AY vs. Y) (Experiment 2). In Experiment 3, the intermixed/blocked effect was observed when, in preexposure, stimulus presentations were alternated with the background alone (e.g., AX/X). This suggests that the perceptual learning effect is not the consequence of inhibitory associations between unique features but to increased salience of those features. Experiment 4 confirmed this finding and also ruled out an account of the effect in terms of trial spacing.     

Effects of similarity and repetition on memory: registration without learning?

We investigated judgments of the frequency of test items (Y) that were highly similar to studied items (X) to test a prediction made by several memory models: that the judged frequency of Y should be proportional to the judged frequency of X. Whether stimuli were pictures or words, judged frequency of Y was bimodally distributed with 1 mode at zero, suggesting that frequency judgments involve a 2-stage process in which a zero judgment is made if there is a mismatch between retrieved information and the test item. Nonzero judgements, taken by themselves, were consistent with the prediction of proportionality. In 2 experiments, the percentage of zero judgments made to Y increased with repetition of X, but in 2 others the percentage did not change beyond frequency = 1. The percentage of "new" judgments in recognition memory followed this same pattern. Because the judged frequency of X increased even as X-Y discrimination showed no improvement, we characterize the result as "registration without learning."     

Dissociations between ABA-, ABC-, and AAB-renewal of Pavlovian modulation in human sequential feature positive discrimination learning

Using a conditioned suppression preparation, we investigated extinction and aba-, abc-, and aab-renewal of Pavlovian modulation in human sequential Feature Positive (FP) discrimination learning, X → A+/A-. Extinction treatment was administered in the acquisition context a (aaa- and aab-groups) or in a new context b (aba- and abc-groups) and comprised X → A- extinction trials. Discriminative X → A/A responding was lost in all groups when tested in the extinction context. In the aba-group, the discriminative X → A/A responding totally recovered when retested in the acquisition context a. For the aaa-, the aab-, and the abc-group, discriminative X → A/A responding did not reappear when tested for renewal in, respectively, contexts a, b, and c. The demonstration of aba-renewal of extinguished modulation, but not abc- and aab-renewal, suggests that extinction in a context different from the acquisition context and a return to the original acquisition context might both be critical for renewal of Pavlovian modulation in human FP-discrimination learning.     

Temporal order: The effect of single versus repeated presentations,practice, and verbal feedback

Whereas Hirsh and Sherrick (1961) found that experienced Os could judge correctly the temporal order of a sound and a light presented repeatedly when the interval separating them was 20 msec, Hirsh and Fraisse (1964) found that naive Os required about 60 msec for the same accuracy of performance with single presentations of the same pair. This experiment examined the effects of single vs repeated presentations, practice, and verbal feedback on performance in the judgment of temporal order. The results indicate that performance under repeated presentation is significantly better than under single presentation, that learning effects are most pronounced during the first 4 of 16 sessions, and that the effects of feedback appear to depend on the precise wording given the S on how he is to perform.     

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.     

A primacy effect in monkeys when list position is relevant

In Experiment 1 (1a and 1b), Rhesus monkeys (Macaca mulatta) learned lists of two-choice visual discriminations in which list position was relevant to discrimination performance. For example, Stimulus A was the rewarded stimulus if it was presented at List Position 1, but was not rewarded if it was presented at any other position in the list; similarly, Stimulus B was rewarded only at List Position 2, and so on. In learning these lists, all animals showed a marked primacy effect. In Experiment 2 (2a and 2b), Rhesus monkeys and Cynomolgus monkeys (M. fascicularis) learned lists of visual discriminations in which each visual stimulus occupied a fixed position in a list, but list position was not relevant to discrimination performance. For example, Stimulus E was always rewarded, and was always presented at List Position 1. To increase the salience of list beginning as a distinctive event, successive presentations of the list were separated by 24-hr intervals. In Experiment 2 there was no primacy effect, however. These results show for the first time that a primacy effect can be obtained in visual discrimination learning by monkeys. Furthermore, they suggest that it is obtained only when list position is relevant to the discrimination learning task.     

Transfer of inhibition after serial and simultaneous feature negative discrimination training

Three experiments examined the nature of inhibitory learning in Pavlovian simultaneous (A+, XA-) and serial (A+, X → A-) feature negative discrimination prodecures in a conditioned suppression situation with rat subjects. The feature (X) trained with simultaneous procedures readily inhibited suppression conditioned to another excitor (B) that was not involved in the feature negative discrimination with X. But the feature trained with serial procedures showed little or no ability to inhibit suppression conditioned to other excitors. These results were obtained with both between- and within-subjects designs, with a variety of test procedures, and after extinction of the A excitor used to establish the inhibition to X. They suggest that nature of the inhibition learned in feature negative discriminations depends on the temporal arrangement of stimuli. We favored the possibility that inhibitors established using simultaneous stimulus arrangements modulate behavior by acting on a representation of the unconditioned stimulus, but inhibitors established with serial procedures act on particular conditioned stimulus-unconditioned stimulus associations.     

The influence of generalization decrement on the outcome of a feature-positive discrimination

In a feature-positive discrimination subjects receive training in which reinforced presentations of a compound, AB⁺, are intermixed among non-reinforced presentations of one element, A^o. The three reported experiments compared the results of this procedure when using a light or a tone as the feature-positive stimulus, B. In all three experiments, the tone elicited a stronger conditioned response than the light when it was presented alone. The main concern of Experiments 2 and 3 was to examine whether this effect was due to training being incomplete for subjects receiving the light as the B element. In Experiment 2 it was found that extended discrimination training did not diminish the difference between the properties of the light and the tone. Experiment 3 revealed that this effect was not due to differences in the asymptotic associative strength of either A or the compound. It is argued that these results are not readily compatible with contemporary theories of learning, and an alternative account is presented.     

Associative activation of stimulus representations restores lost salience: implications for perceptual learning

In 3 experiments, rats received preexposure to presentations of a compound flavor BX. The effective salience of B was then tested by assessing its ability to interfere with the aversion controlled by another flavor or the tendency to drink a saline solution after the induction of a salt need. It was found that the effective salience of B was maintained when during preexposure, presentations of BX alternated with presentations of X alone. This was true both when BX was presented as a simultaneous compound (Experiment 1) and as a serial compound (X-->B; Experiments 2 and 3); salience was not maintained when the serial compound took the form B-->X (Experiments 2 and 3a). It was argued that the salience of B declines during preexposure but is restored when presentations of X are able to activate the representation of B by way of the associative X-B link.     

Stimulus generalization following extra-dimensional training in educationally subnormal (severely) children.

The use of discrimination learning paradigms in the study of attentional transfer is discussed. The technique of go/no-go discrimination learning followed by stimulus generalization testing is contrasted with the more familiar simultaneous learning paradigm followed by a shift in the relevant cues. In the former paradigm the effect of training a discrimination on one dimension on the slope of the stimulus generalization gradient on an independent gradient dimension (extra-dimensional training) is assessed. A steepening of the gradient relative to appropriate control procedures is taken as evidence of positive attentional transfer. The relevance of the technique to the detailed study of attentional transfer in educationally subnormal (severely) (ESN(S)) children is considered. In Expt. I nine ESN(S) children were trained in a go/no-go discrimination involving stimuli differing in orientation, and were generalization tested on a dimension that was orthogonal, namely hue. Of the six subjects who learnt the discrimination five showed clear decremental gradients on the hue dimension. In contrast a Pseudo-Discrimination group (PD) of eight subjects matched to those in the TD group showed no gradients. These subjects were not trained in the orientation discrimination, but were reinforced for responding on 50 per cent of each of the S+ and S- stimulus presentations. They thus received equal exposure to, but no differential training on, the orientation dimension. An S+ only group of four subjects who received no exposure to the orientation stimuli showed no gradients when stimulus generalization testing on the hue continuum was carried out. The result is discussed in terms of transfer deriving from stimulus control by relational aspects of the stimuli; in terms of control by constant irrelevant stimuli; and in terms of the study of stimulus control in ESN(S) children. In Expt. II the influence of the codability of the colours on the location of the peak of the stimulus generalization gradients in the TD group is investigated.     

Sequential and simultaneous feature positive discriminations: occasion setting and configural learning in human Pavlovian conditioning

Using a conditioned suppression preparation, the authors investigated sequential (X --> A+/A-) versus simultaneous (XA+/A-) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A-US association and the simultaneous discrimination by a feature X-US association. After sequential FP training, extinction of Feature X did not affect discriminative X --> A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4.     

Intertrial interval as a contextual stimulus: further analysis of a novel asymmetry in temporal discrimination learning

Four experiments investigated discrimination learning when the duration of the intertrial interval (ITI) signaled whether or not the next conditional stimulus (CS) would be paired with food pellets. Rats received presentations of a 10-s CS separated half the time by long ITIs and half the time by short ITIs. When the long ITI signaled that the CS would be reinforced and the short interval signaled that it would not be (Long+/Short-), rats learned the discrimination readily. However, when the short ITI signaled that the CS would be reinforced and the long interval signaled that it would not (Short+/Long-), discrimination learning was much slower. Experiment 1 compared Long+/Short- and Short+/Long- discrimination learning with 16-min/4-min or 4-min/1-min ITI combinations. Experiment 2 found no evidence that Short+/Long- learning is inferior because the temporal cue corresponding to the short interval is ambiguous. Experiment 3 found no evidence that Short+/Long- learning is poor because the end of a long ITI signals a substantial reduction in delay to the next reinforcer. Long+/Short- learning may be faster than Short+/Long-because elapsing time involves exposure to a sequence of hypothetical stimulus elements (e.g., A then B), and feature-positive discriminations (AB+/A-) are learned quicker than feature-negative discriminations (A+/AB-). Consistent with this view, Experiment 4 found a robust feature-positive effect when sequentially presented CSs played the role of elements A and B.     

Operant conditioning and discrimination of alpha: some methodological limitations inherent in response-discrimination experiments

Studies on the operant conditioning of central nervous system activity have produced results interpreted as demonstrating that responses, certain properties of responses, or response-produced stimuli can function as discriminative stimuli. It is assumed that the feedback stimulus in biofeedback makes the subject aware of the internal response and that by becoming aware of the response, the subject can acquire voluntary control over it. In this context, awareness is operationally defined as the ability to use the response as a discriminative stimulus. Since direct evidence for the assumed relationship between control and discrimination is lacking, an attempt was made to test the hypothesis that discrimination of a response automatically leads to control over that response. The discriminative stimuli were the presence and absence of occipital alpha electroencephalograph (EEG) activity. Data from two experiments are reported. The first study, employing naive subjects, was designed to answer the following questions: (a) Since pilot data indicated that subjects seemed to match their responses to the more probable type of trial, would increases in the probability of a correct response result when the probabilities of alpha and nonalpha trials were held near .50? (b) If correct responding does increase, would performance of these subjects in an alpha feedback task be enhanced relative to that of subjects not previously given discrimination training? and (c) If subjects could not learn the discrimination task, would feedback training enhance their performance in a subsequent discrimination task? Results from this study indicate that holding the probabilities of alpha and nonalpha discrimination trials near .50 results in an absence of learning curves, but leaves open the possibility that sophisticated subjects are capable of discriminating alpha and nonalpha activity. The second study deals with two questions: (a) Can sophisticated subjects learn to discriminate occipital alpha activity from nonalpha activity? and (b) Does the procedure of providing subjects with salient stimuli, contingent on the presence and absence of alpha activity, establish stimulus control of the presence and absence of alpha activity? Results indicate that it is not possible to conclude that subjects can learn to discriminate alpha and nonalpha activity. However, learning to increase percent-time nonalpha or decrease percent-time alpha with respect to baseline levels by means of EEG-contingent stimulation provides subjects with the ability to suppress percent-time alpha in the absence of feedback. Information gained in both studies through subject interviews indicates that subjects most often acquired their control of alpha activity during feedback by a specific strategy and then used the strategy during the stimulus-control tests.     

Framing inequity safely: Whites' motivated perceptions of racial privilege

Racial inequity was theorized to threaten Whites' self-image when inequity is framed as White privilege but not when framed as anti-Black discrimination. Manipulations of Whites' need for self-regard were hypothesized to affect their perceptions of White privilege but not of anti-Black discrimination. In Experiment 1, White participants reported less privilege when given threatening (vs. affirming) feedback on an intelligence or personality test; in contrast, perceptions of anti-Black discrimination were unaffected by self-concept manipulations. In Experiment 2, threatening (vs. affirming) feedback decreased privilege perceptions only among Whites high in racial identity. Using a value-based self-affirmation manipulation, Experiment 3 replicated the effect of self-image concerns on Whites' perceptions of privilege and provided evidence that self-concerns, through their effect on perceived privilege, influence Whites' support for redistributive social policies.     

Configural learning without reinforcement: integrated memories for correlates of what, where, and when

In 2 experiments we examined the ability of rats to form configural memories of what auditory stimulus (X or Y) was presented where (Context A or B) and when (morning or afternoon). In both experiments, rats received morning presentations of X in Context A and Y in Context B and afternoon presentations of X in B and Y in A. Subsequently, at midday the rats were exposed to trials where X was paired with footshock whereas Y was not. We then assessed the degree of contextual fear in A and B in the morning and the afternoon. In the morning, rats showed more fear in A than in B, and in the afternoon they showed more fear in B than in A. These results indicate that rats can form configural memories that represent what (X or Y) was presented, where (A or B), and when (morning or afternoon).     

Extinction of Within-event Learning Is Contextually Controlled and Subject to Renewal

Five experiments examined within-event learning in rats by inducing an appetite for one of the elements (salt) of a compound stimulus and assessing preference for the other element (almond). Almond preference was conditional upon (1) the almond flavour having been presented in compound with the salt, and (2) the assessment being conducted when the rats were out of sodium balance (Experiment 1). Presentations of the compound in one environment (A) and of the salt and almond elements in a second environment (B) resulted in greater almond preference when rats were tested in A than in B (Experiment 2). Almond preference was reduced when separate presentations of the compound and almond (Experiment 3) or of the compound and salt (Experiment 4) occurred in the same environments but not when these presentations occurred in different environments. Rats exposed to the compound in A and then extinguished to the elements in either A or B showed a reduced almond preference when tested in the extinction environment, but not when tested in the other environment (Experiment 5). Thus, extinction of within-event learning is context-specific and subject to renewal. The results were interpreted in terms of an associative model whereby separate presentations of the elements result in a symmetrical inhibitory link which is contextually gated (Bouton, 1993).     

The Interactive Effects of Task and External Feedback on Practice Performance and Learning

The interactions of task and external feedback on practice performance and learning were examined. While external feedback was consistently beneficial to performance during practice, regardless of the availability of feedback from the task, it was detrimental to learning when the task provided little feedback. External feedback benefited learning only when feedback was also available from the task. In addition, task feedback benefited learning, partially due to its effects on error detection and correction skills. Results suggest the importance of examining the simultaneous provision of feedback from different sources, studying the role of task feedback in learning, and more cleanly assessing learning to avoid confounding it with transient performance improvements.     

Configural learning without reinforcement: Integrated memories for correlates of what,where, and when

In 2 experiments we examined the ability of rats to form configural memories of what auditory stimulus (X or Y) was presented where (Context A or B) and when (morning or afternoon). In both experiments, rats received morning presentations of X in Context A and Y in Context B and afternoon presentations of X in B and Y in A. Subsequently, at midday the rats were exposed to trials where X was paired with footshock whereas Y was not. We then assessed the degree of contextual fear in A and B in the morning and the afternoon. In the morning, rats showed more fear in A than in B, and in the afternoon they showed more fear in B than in A. These results indicate that rats can form configural memories that represent what (X or Y) was presented, where (A or B), and when (morning or afternoon).