Novelty and functional equivalence in superordinate categorization by pigeons

Superordinate categorization via association with a common response was studied in pigeons. Original training paired disparate classes (e.g., people + chairs and cars + flowers) with a common response (Responses 1 and 2, respectively). Reassignment training taught new responses (Responses 3 and 4, respectively) to one component class from each pair (e.g., people and cars). Superordinate categorization was documented in testing when the pigeons made the same responses to the stimuli that were withheld in reassignment training (e.g., chairs and flowers) as they did to the reassigned stimuli themselves (e.g., people and cars) and when the birds transferred these discriminative responses to novel stimuli from all four component classes. Reassignment training with novel stimuli produced effects that were similar to those of reassignment training with familiar stimuli. Superordinate categorization via association with a common response is thus a robust effect that generalizes to novel stimuli from each of the component classes.     

Preliminary evidence for color stimuli discrimination in the Asian small-clawed otter (Aonyx cinerea)

Color discrimination ability can be determined through anatomy or perceptual ability. In this study we tested perceptual ability. Three Asian small-clawed otters (Aonyx cinerea), one male and two females, were trained via operant conditioning to discriminate stimuli within a training task. If they passed criteria for this task, they were tested on as many as six delayed matching-to-sample experimental tasks. These experimental tasks involved comparing varying saturations of the colors blue, green, and red against varying shades of gray, as well as against each other. The male reached criterion on five of the experimental tasks, indicating an ability to discriminate the stimuli. One female participated in only two tasks and did not achieve the criteria as set. The second female did not pass the training task, and thus was not experimentally tested. This study overall showed some early evidence that Asian small-clawed otters may have the ability to learn to discriminate different stimuli on the basis of color cues. Sensory studies conducted on two other otter species and the results of this study indicate that color vision may be a common trait across Lutrinae species.     

Generalization along the dimension of sound intensity in pigeons

Two groups of four pigeons each were trained on a discrimination between two intensities of white noise. The low-intensity group had a 60-dB intensity as the negative discriminative stimulus (S?) and a 70-dB intensity as the positive discriminative stimulus (S+): the high-intensity group had a 95-dB intensity as S? and an 85-dB intensity as S+. Generalization stimuli were all of higher intensity than S+ for the former group and all of lower intensity than S+ for the latter group. The rate of acquisition of the discrimination was faster for the Ss in the high-intensity group. In both groups, the maximum of the generalization function was shifted toward the middle values of the set of test stimuli, away from the training stimuli. Responding showed a decline at the far end of the range of test stimuli. Responding to the positive training stimulus was initially as great as it had been on the preceding training sessions, but became markedly depressed relative to responding to the other stimuli as the test progressed.     

Discrimination and representation of relative numerosity in a bisection task by pigeons

We trained 4 pigeons in a numerical bisection task to discriminate between pairs of keylight flashes with a ratio of 1∶3 (2 vs. 6, 4 vs. 12, and 8 vs. 24) that were presented in a sample phase. Responses to the blue key were reinforced after a sequence of a larger number of flashes, and responses to the white key were reinforced after a sequence of a smaller number of flashes. The intervals between flashes in the sample phase were randomized to attenuate the covariation of temporal cues with flash number. Pigeons responded accurately in each of the discriminations, with typically 85%–90% correct responses. Transfer tests showed that the proportion of large responses increased with number and performance generalized to larger values outside the training ranges. Psychometric functions superposed when plotted on a relative scale, and estimates of Weber fractions were approximately constant, suggesting that variability was scalar. However, contrary to previous research in nonhumans, bisection points were located at the arithmetic, not geometric, mean. Hierarchical logistic regressions confirmed significant control over responding by number beyond that attributable to temporal cues. These results show that pigeons are able to respond accurately in a relative numerosity discrimination with successively presented visual stimuli, although the nature of the numerical representation and response rule remains unclear.     

Stimulus duration and conditioned reinforcing value measured by a learning-tests procedure

The relationship between the duration of stimuli and their conditioned reinforcing effect was investigated using a learning-tests procedure. In Experiment 1, stimuli were the same duration on training (stimulus → reward) and test (choice response → stimulus). Ten- and 30-sec stimuli provided effective differential conditioned reinforcement but 3-sec stimuli did not. In Experiment 2, different pigeons had each combination of the 3- and 30-sec stimuli on training and test trials. Evidence of conditioned reinforcement was obtained only for the birds with 30-sec stimuli on both training and test. The results were interpreted as indicating that stimuli become effective conditioned reinforcers on test trials only when their duration exceeds the duration of differential short-term memory cues resulting from a difference in the events that precede them on training and test trials.     

Cognitive Mechanisms in Children''s Gender Stereotyping: Theoretical and Educational Implications of a Cognitive-based Intervention

The study was designed to test the hypothesis derived from cognitive-developmental theory that multiple classification skill plays an important role in children's gender stereotyping and in their processing of counterstereotypic gender information. Children (N = 75; 5-10 years) were matched on pretest measures of gender stereotyping and multiple classification skill and then assigned to: (1) multiple classification training using nonsocial stimuli, (2) multiple classification training using social stimuli, (3) a rule training intervention, or (4) a control intervention. Children who had acquired multiple classification skill via training with social stimuli and those children trained on rules for occupational sorting showed significantly more egalitarian responding on a subsequent measure of gender stereotyping and superior memory for counterstereotypic information embedded in stories. Additionally, children who had acquired multiple classification skill via training with nonsocial stimuli showed superior memory for counterstereotypic information, despite demonstrating no greater flexibility on the gender stereotyping measure. Both theoretical and educational implications of results are discussed.     

Reductions in resistance to extinction and spontaneous recovery as a function of changes in transportational and contextual stimuli

Thirty rats received 10 sessions of baseline training in which leverpressing was reinforced according to a variable-interval (VI) 60-sec schedule. Twenty-four of the subjects were then assigned to one of four groups that received five sessions of extinction, with groups being differentiated in a 2 by 2 factorial design on the basis of: (1) changes in stimuli accompanying transportation of subjects from home cages to the laboratory and placement in the apparatus, and/or (2) changes in contextual stimuli within the apparatus. During the sixth session of extinction, the transportational and contextual stimuli previously associated with baseline training were reinstated. The remaining six rats experienced changes in both transportational and contextual stimuli but were maintained on the VI 60-sec schedule of reinforcement. Changes in either transportational or contextual stimuli reduced resistance to extinction and spontaneous recovery, and substantial increments in responding occurred upon reinstatement of the transportational and contextual stimuli associated with baseline training. Evidence for summation of the two sources of stimulus change was obtained. Changes in transportational and contextual stimuli produced only a brief disruption in responding when reinforcement of leverpressing was continued.     

Auditorysame/different concept learning by monkeys

Two rhesus monkeys learned the auditory abstract concept ofsame/different. They were trained with 38 different environmental and natural sounds, which were arranged in different combinations as training progressed. Upon transfer to 138 different novel stimuli, they performed as well (78.8% correct) on the first exposure to the novel stimuli as they did (77.3%) with their training stimuli. The comparatively large set of training sounds, contact with the sound source, and a special fading procedure are thought to have contributed to the monkeys’ being able to learn this concept. Implications for species’ similarities/differences in cognitive processing are discussed.     

Further negative findings on facilitated communication

To date, most studies of the efficacy of Facilitated Communication (FC) have been hampered by small samples, limited experience of the subjects with the FC, and diagnostically narrow samples. The present study has a comparatively large sample, and the subjects each had a minimum of one year's experience using FC. Diagnoses of the subjects were also arrayed across a broad spectrum. Pictorial stimuli that had been used as classroom teaching materials were presented to each subject and facilitator under three different conditions of five trials each. Responses were rated by independent judges who were not aware of the stimuli. Support for the communicative value of FC was not found.     

Attentional enhancement in matching-to-sample: Facilitation in matching acquisition by sample-discrimination training

In three experiments, we examined how matching-to-sample by pigeons is affected by discrimination versus nondifferential training between the matching stimuli. In Experiment 1A, pigeons responding differentially to the sample stimuli off-baseline acquired accurate matching performances more rapidly than did pigeons responding nondifferentially to those same stimuli. In Experiment 1B, tests involving reversal of the off-baseline requirements demonstrated that the birds were primarily controlled in their matching choices by the sample stimuli. The results of Experiment 2 showed that off-baseline nondifferential training did not retard acquisition relative to comparable training between stimuli unrelated to the matching task. Together, these results suggest that discrimination training can facilitate matching acquisition by enhancing attention to the sample stimuli.     

Learning-related shifts in generalization gradients for complex sounds

Learning to discriminate stimuli can alter how one distinguishes related stimuli. For instance, training an individual to differentiate between two stimuli along a single dimension can alter how that individual generalizes learned responses. In this study, we examined the persistence of shifts in generalization gradients after training with sounds. University students were trained to differentiate two sounds that varied along a complex acoustic dimension. The students were subsequently tested on their ability to recognize a sound that they had experienced during training when it was presented among several novel sounds varying along this same dimension. Peak shift was observed in Experiment 1, in which generalization tests immediately followed training, and in Experiment 2, in which the tests were delayed by 24 h. These findings further support the universality of generalization processes across species, modalities, and levels of stimulus complexity. They also raise new questions about the mechanisms underlying learning-related shifts in generalization gradients. The sound stimuli from this study are available as .wav files from http://lb.psychonomic-journals.org/content/supplemental.     

Directed forgetting in monkeys

Based on several recent demonstrations of a directed forgetting effect in pigeons, three experiments were carried out in an attempt to demonstrate directed forgetting in three squirrel monkeys. During initial training with a delayed matching-to-sample procedure, retention tests were always given for sample stimuli followed by remember cues (R-cues) and were always omitted for sample stimuli followed by forget cues (F-cues). Retention of F-cued items was tested on probe trials after initial training. The first two experiments examined the effects of R- and F-cues on memory for slide-projected pictures, with different pictures used on each trial of a session. In Experiment 1, a complex design was used in which one or two sample pictures were presented on each trial; when two pictures were presented, both could be R-cued or F-cued, or one could be R-cued and the other F-cued. A simpler design was used in Experiment 2, with only single pictures presented as sample stimuli and half the trials within a session R-cued and the other half F-cued. In both of these experiments, no differential retention of R- and F-cued stimuli was found, even at a retention interval as long as 16 sec. In Experiment 3, a series of studies was performed to test for directed forgetting when only two sample stimuli were used repeatedly throughout training and testing. With two pictures as sample stimuli, clear evidence of directed forgetting was found in Experiment 3b. It is suggested that the directed forgetting effect may arise only when a small set of sample stimuli is used.     

Effects of proactive interference on rats’ continuous nonmatching-to-sample performance

Rats performed a new delayed matching-to-sample task—the continuous nonmatching-to-sample task. A variable number of trials with one stimulus alternated with trials with a second stimulus. A response on the trial following a stimulus change (nonmatch trial) was reinforced. Responses to repeated stimuli were never reinforced. Rats could maximize reinforcement by remembering across the intertriai interval which stimulus was presented on the previous trial. Sequential analysis indicated that interference from previous conflicting trials (proactive interference, PI) reduced response accuracy but did not affect retention: Accuracy was lower on trials following a nonmatch trial than on trials following repeated stimuli. Furthermore, accuracy increased as a function of the time between the to-be-remembered nonmatch trial and the previous interfering trial. However, neither time between trials nor the distance from a stimulus change affected the rate of decline in accuracy over the retention interval.     

Human postdiscrimination gradients: The effects of three-stimulus discrimination training

Young adult subjects were trained in a discrimination involving three pure tones varying in pitch, with two positive stimuli and a negative stimulus located midway between the two. Subjects in the control conditions were trained only with the two positive stimuli. Generalization gradients were bimodal in all cases, but for the control subjects, the modes were at the positive stimulus values, while postdiscrimination gradients were displaced away from the negative stimulus toward the extremes of the continuum. Since, with this procedure, the training and test adaptation levels were the same, the observed displacements are difficult to explain in terms of an adaptation-level account of peak shifts. The observed shifts are more consistent with the conditioning-extinction model which assumes interactions between inhibitory and excitatory gradients. However, overall response rates did not reflect the action of summation processes.     

The impact of individual differences and learning context on strategic skill acquisition and transfer

How individual differences in cognitive ability influence acquisition and transfer of strategic comparison skills was examined as a function of learning difficulty. Using a cognitive test battery, we classified forty-nine participants into three cognitive ability groups. Participants in each group were trained to compare similar (difficult training) or dissimilar (easy training) stimuli and then transferred to compare novel stimuli. Results suggest that overall individual differences in cognitive ability dictate the optimality of strategic skill development, though the effect of training difficulty on transfer performance varies with cognitive ability. Individuals with a midrange of cognitive ability are the most sensitive to the training context. Results are discussed with respect to the characteristics of strategic skills acquired and transferred.     

Oddity of visual patterns conceptualized by pigeons

Pigeons were trained to learn an instrumental oddity-from-sample discrimination involving visual forms. One group, the “few examples” group, dealt with 5 patterns in 40 different combinations. Another group, the “many examples” group, dealt with 20 patterns in 160 different combinations. After both groups had reached asymptotic performance and had learned to operate under partial reinforcement conditions, they were tested for transfer under extinction conditions with two different groups of 5 novel patterns, each in 40 combinations. All animals showed significant above chance transfer to both of these novel stimulus sets. Transfer performance with test stimuli of similar geometric design to training stimuli was better than performance with stimuli of markedly different design. The transfer performance of the “many examples” group was marginally better than that of the “few examples” group, even though the latter’s performance on the training stimuli was better throughout. It is concluded that pigeons can learn to employ an oddity concept and that this may be promoted by the use of many training exemplars. Furthermore, it is inferred that pigeons may normally use a mixture of strategies to solve oddity and identity problems.     

Training reinforcement rates,resistance to extinction,and the role of context in reinstatement

Behavior reduced as a consequence of extinction or intervention can relapse. According to behavioral momentum theory, the extent to which behavior persists and relapses once it has been eliminated depends on the relative training reinforcement rate among discriminative stimuli. In addition, studies of context renewal reveal that relapse depends on the similarity between the training stimulus context and the test stimulus context following disruption by extinction. In the present experiments with pigeons, we arranged different reinforcement rates in the presence of distinct discriminative stimuli across components of a multiple schedule. Following extinction, we attempted to reinstate responding in the presence of those target components with response-independent food presentations. Importantly, we arranged the reinstating food presentations either within the target components or in separate components, either paired with extinction (Experiment 1) or reinforcement (Experiment 2) during baseline. Reinstatement increased with greater training reinforcement rates when the reinstating food presentations were arranged in the target components and the separate components paired with reinforcement during training. Reinstatement was smaller and was not systematically related to training reinforcement rates in the target components when reinstating food presentation occurred in separate components paired with extinction. These findings suggest that relapse depends on the history of reinforcement associated with the discriminative stimuli in which the relapse-inducing event occurs.     

The overshadowing of background stimuli by an informative CS in aversive Pavlovian conditioning with rats

Two experiments investigated the capacity of a nominal CS to overshadow background stimuli. Rats received CS-shock pairings in one compartment of a double-compartment apparatus. After training, the shock compartment was re-presented but in the absence of both the CS and shock, and overshadowing was assessed by measuring the rats’ latency to enter the compartment. In the first experiment, predictive values of temporal cues provided by CS onset and CS offset were manipulated. Rats readily entered the shock compartment, provided shock onset had previously been predicted by CS onset or CS offset. This indicates that background cues in the shock compartment had acquired little associative strength during training. In contrast, rats avoided the shock compartment under every condition in which shock onset had not previously been predicted by either CS onset or CS offset. In the second experiment, a precise temporal cue provided by CS onset was dissociated from other factors arising from CS-shock contiguity. It was found that rats’ reactions to the shock compartment after training was governed by both temporal and contiguity factors. The results are relevant to theories which state that conditioning is a function of a competitive relationship between stimuli present in an animal’s environment during training.     

Integration of cardiac responses to serial stimuli after Pavlovian conditioning in rats

The expression of cardiac responses to sequences of two sounds was studied in restrained rats following discriminative trace or delay conditioning. Stimuli paired with a tail shock 10 sec later (CS1) elicited conditioned bradycardia. Unpaired or neutral stimuli (CS0) elicited mostly tachycardia. Rats did not learn to suppress responding to nonreinforced sequences with an interval of 6 sec between sounds. Responses to the second stimulus were significantly augmented following a CS1 stimulus, but not following a CS0 stimulus. Real-time summation of simple responses provided a more complete and quantitative prediction of dual responses than did resetting or facilitation. These results extend the time range over which summation may be observed from less than 2 sec to at least 16 sec. They appear to be inconsistent with models involving competition between unitary representations of stimuli in short-term memory and suggest the existence of multiple stimulus traces with independent time courses.