The Role of Non-Numerical Stimulus Features in Approximate Number System Training in Preschoolers from Low-Income Homes

Recent findings have suggested that adults’ and children’s approximate number system (ANS) acuity may be malleable through training, but research on ANS acuity has largely been conducted with adults and children who are from middle- to high-income homes. We conducted 2 experiments to test the malleability of ANS acuity in preschool-aged children from low-income homes and to test how non-numerical stimulus features affected performance. In Experiment 1, mixed-effects models indicated that children significantly improved their ratio achieved across training. Children’s change in probability of responding correctly across sessions was qualified by an interaction with surface area features of the arrays such that children improved their probability of answering correctly across sessions on trials in which numerosity conflicted with the total surface area of object sets significantly more than on trials in which total surface area positively correlated with numerosity. In Experiment 2, we found that children who completed ANS acuity training performed better on an ANS acuity task compared with children in a control group, but they only did so on ANS acuity trials in which numerosity conflicted with the total surface area of object sets. These findings suggest that training affects ANS acuity in children from low-income homes by fostering an ability to focus on numerosity in the face of conflicting non-numerical stimulus features.     

Development of conditional and equivalence relations without differential consequences

Two experiments were conducted to establish conditional stimulus relations without differential consequences and to test for the emergence of other relations. In Experiment 1, 3 adults responded to match-to-sample displays in which sample-comparison pairs were constant while the second comparison presented with each pair changed periodically across trials. No differential consequences followed any comparison selections. All subjects learned conditional relations between constant samples and comparisons, but results of tests for transitivity in those relations were equivocal. In Experiment 2, 4 children were given unreinforced training and testing similar to that provided to the adults in Experiment 1, with procedural refinements. One child learned conditional relations and demonstrated emergent relations that confirmed the development of two four-member equivalence classes. Another child learned the conditional relations but did not demonstrate any emergent relations reliably. A 3rd child, after reinforced training on two conditional relations, learned four new conditional relations without differential consequences and demonstrated symmetry but not equivalence in the trained relations. The 4th child did not learn the conditional relations. These findings emphasize the importance of careful construction of tests for stimulus equivalence and suggest a need for critical analyses of the apparent emergence of untrained stimulus relations on unreinforced tests that has been observed in several stimulus equivalence studies.     

Emergent conditional discrimination in children: Matching to compound stimuli

This study reports two experiments that first taught preschool children identity-matching to compound sample and compound comparison stimuli. A compound stimulus consisted of a colour and a form superimposed on one another. Test sessions assessed whether children related the form and colour elements of a particular compound stimulus. The test for this was matching to sample in which an arbitrary conditional discrimination was required. A majority of the children selected the correct colour comparison in the presence of each form sample. The children also showed the reverse sample-comparison relations: they matched form comparisons to the corresponding colour samples, respectively. In the context of these arbitrary relations, new colours were paired with the form elements of the samples (Experiment 1), and new form elements were paired with the colour elements of the comparisons (Experiment 2). Subsequent tests assessed whether the new stimulus elements had control over responding when presented as single samples or comparisons. Test results showed that most subjects were able to relate the new stimulus elements to the corresponding colour and form elements, respectively. The study demonstrated that matching to compound stimuli in training and testing conditionsMaygenerate conditional relations between the individual stimulus elements.     

Rule learning in children: Multiple-set training and intermediate-size transposition

Two experiments were conducted in which the subjects were trained to choose the middle-size stimulus in either a single stimulus set or in each of two nonoverlapping stimulus sets. Following criterion, each subject was presented with a series of 12 test trials involving a new stimulus set. In Experiment 1, kindergarten children tended to choose the middle-size test stimulus if the test set consisted of stimuli intermediate in size to the stimuli in the smaller and larger training sets. When the test stimuli were all larger than any of the training stimuli, the probability of choosing the middle-size stimulus increased as the distance between the two training sets increased. Three groups of children participated in Experiment 2: a kindergarten group, a first-grade group, and a first-grade group that experienced middle-size training a year earlier. The distance between training sets and two training procedures affected the three groups in a similar manner during acquisition, but several interactions were obtained during the test. The findings were discussed in terms of the Lane and Rabinowitz (D. M. Lane & F. M. Rabinowitz, Child Development, 1977, 48, 412–426) rule based theory of intermediate-size transposition and suggestions were made as to how children acquire the concept of middle.     

Dimensional stimulus control following brief wavelength training

Pigeons with extensive training pecking a key illuminated by a white line then had brief training with the key illuminated by 555 nanometers. This was immediately followed by a wavelength generalization test in extinction. Dimensional stimulus control about the training wavelength increased with the duration and number of reinforcements given on variable-interval 30-sec and variable-interval 10-sec schedules in Experiment I. In Experiment II, dimensional stimulus control was obtained after only 4 min of wavelength training from birds with prior and independent discrimination training. Experiment III provided groups equated in number of reinforcers with groups in Experiment I and two 8-min duration groups. Analyses, which included results from both Experiments I and III, showed that dimensional stimulus control increased: (a) more rapidly as a function of the duration of variable-interval 10-sec than variable-interval 30-sec reinforcement; (b) at the same rate across variable-interval reinforcement schedules, as a function of the number of reinforcers available during brief wavelength training.     

Stimulus probability and same-different classification

Three experiments investigated the effect of stimulus probability on same-different classification time. In Experiments I and II, subjects made same responses on the basis of name matches of simultaneously presented letters. Half of the same trials involved letters that were also physically identical. Experiment I showed that the presentation probability of specific letters affected name matches and different responses, but not physical matches. Experiment II varied stimulus contrast as well as probability. Contrast had a main effect but did not interact with probability at any level of processing. In Experiment III, subjects were switched to the physical level of processing. Stimuli that now had the same name but differed in case were called different. In this condition, the probability effects obs(irved in Experiment II disappeared. These results are interpreted as demonstrating that stimulus probability has its effect during the process that derives the name of the stimulus from the visual representation. This process takes place before the name comparison is made, and the name comparison process precedes the determination of the different response.     

Blocking observed in human eyelid conditioning

Four eyelid conditioning experiments designed to be comparable to rabbit nictitating membrane (NMR) studies examined the blocking phenomenon in humans. All experiments utilized a within-subjects design, with Stage 1 of discrimination, Stage 2 of compound training, and a final test stage comparing responding to the blocked and non-blocked CSs. In two of the experiments (1 and 4) the comparison was made within subjects over all extinction trials. In Experiment 3 the test phase consisted of further reinforced training of the blocked and non-blocked CSs. These three experiments produced evidence of blocking when all extinction trials were entered into the analysis. Experiment 2, which involved a between-subjects comparison, failed to demonstrate the blocking effect. Wide variability both between and within subjects obscured the experimental effects. Post-experimental questionnaires designed to assess awareness of stimulus relations failed to identify a subjective blocking effect and showed no relationship to conditioned eyelid responding     

The restoration of extinguished avoidance responses

Following extensive signaled shuttlebox avoidance training, Fischer 344 rats were given extinction trials until they reliably stopped responding and, thereafter, they received occasional classical CS-UCS pairings during the course of restoration test trials in which shock was absent. Experiment I demonstrated that the classical contingency was both necessary and sufficient for the complete recovery of such behavior. Experiment II revealed that the degree of recovery was not differentially affected by the frequency of such CS-UCS pairings. However, in Experiment III recovery in the presence of this contingency was shown to depend on the number of previous extinction trials, although even after a large number of such trials, a considerable degree of recovery occurred. These findings demonstrated the central role of the classical CS-UCS contingency in restoring a previously extinguished avoidance response.     

The development of functional and equivalence classes in high-functioning autistic children: the role of naming.

The development of functional and equivalence classes was studied in four high-functioning, preschool-aged autistic children. Initially, all subjects failed to demonstrate match-to-sample relations indicative of stimulus equivalence among two three-member classes of visual stimuli. Then, 2 subjects showed emergence of those relations after they were taught to assign the same name to all members in each class. Next, subjects were taught names for new stimuli outside the match-to-sample format. On subsequent match-to-sample tests, 2 subjects demonstrated untrained conditional relations among the stimuli given a common name. New, unnamed stimuli were then related via match-to-sample training to stimuli from sets of named stimuli. Tests for emergent conditional relations between the new unnamed stimuli and the named stimuli yielded positive results for 1 subject and somewhat mixed results for 3 subjects. Finally, without naming, 2 subjects developed stimulus equivalence among two new three-member classes of visual stimuli. These data suggest that naming may remediate failures to develop untrained conditional relations, some of which are indicative of stimulus equivalence.     

The role of naming in stimulus categorization by preschool children

The purpose of the current study was to assess whether children would categorize pictures when taught the relevant listener and speaker behaviors separately. A category-sort test was used to assess emergent conditional relations. Category-sort trials consisted of looking at (Test 1) or tacting/labeling (Test 2) a sample stimulus and selecting the appropriate comparison stimuli. In Experiment 1, 4 children (3-5 years) were taught to tact pictures of six U.S. state maps as either north or south. An assessment was conducted to determine whether they would (1) correctly categorize or sort when presented with a visual sample and (2) select the correct stimuli when hearing their category names (listener behavior). Two of the children categorized the pictures during Posttest 1 after the initial (pairwise) tact training. The other 2 categorized after receiving additional tact training with all pictures presented together. However, one of them categorized only during Posttest 2. In Experiment 2, 4 children (3-5 years) were taught to select pictures when hearing their category names. An assessment was conducted to determine whether they would (1) correctly categorize or sort and (2) tact the stimuli (speaker behavior). One child categorized the pictures during Posttest 1, and two during Posttest 2. The other child required additional training with all pictures grouped together. When participants failed to categorize, they also failed to tact the pictures accurately. Taken together, results from Experiments 1 and 2 show that both speaker and listener behavior play an important role in stimulus categorization.     

Representation-mediated Inhibitory Learning in the Conditioned-suppression Procedure

In three experiments, rats in group I (for intermixed) were given non-reinforced exposure to two compound stimuli, AX and BX, where A and B represent different auditory cues, and X represents a visual cue. AX and BX were presented in alternation. Group B (blocked) received similar exposure except that subjects experienced a block of AX trials and then a block of BX trials. Subsequent shock reinforcement of A was found to endow B with inhibitory strength in group I, as assessed by retardation (Experiments 1 and 2) and summation tests (Experiment 3). This outcome confirms and extends the results reported by Espinet, Iraola, Bennett, and Mackintosh (1995) and constitutes a further example of mediated learning in which the associative strength of a stimulus is found to be modified as a consequence of training given to some other event with which that stimulus is associated.     

Short-Term Retention of “Surprising” Events By Pigeons

Terry and Wagner (1975) have suggested that the short-term retention of information about an event is enhanced if the occurrence of the event is made unexpected or surprising. Three experiments tested this idea using delayed conditional position (Experiment I) and colour discriminations (Experiments II and III). The subjects were pigeons and the presentation of food was the target event to be remembered. Choice of one of two simultaneously presented stimuli was reinforced if the retention interval had been initiated by presentation of target food. Contrary to Terry and Wagner's claim, retention was superior on probe test trials in Experiments I and II if the presentation of the target food was preceded by a previously established signal for food (CS+) rather than by a stimulus which had not been paired with food (CS-). Experiment III systematically manipulated the signalling conditions used during initial discrimination training. Retention was better following a CS+ presentation if the target food had been signalled during initial discrimination training but worse if the food presentation had been unsignalled. These results do not favour the idea that retention of an event is directly affected by whether or not the target event is surprising.     

Establishing Functional Classes In A Chimpanzee (Pan troglodytes) With A Two-item Sequential-Responding Procedure

A 9-year-old female chimpanzee was trained on a two-item sequential-responding task. Attempts were made with successive-reversal training to establish functional classes. In Experiment 1, the subject was exposed to between-session successive-reversal training in which one of two pairs of stimuli was reversed, and transfer of reversal responding to the other pair was tested with nonreinforcement probe trials. She did not show transfer during the course of reversals. Stimulus control established in the original training was maintained on nonreinforcement probe trials. In Experiment 2, within-session reversals were introduced. She showed transfer from the initially reversed pair to the other. The results were consistent with Vaughan's (1988) results with pigeons on successive discriminations, which indicated the formation of functional classes. In Experiment 3, crossover and wild-card tests were conducted to clarify the stimulus control of sequential responding. The results suggested that the sequential responding was controlled only by the first stimulus of each pair. To establish control by both first and second stimuli, trial-unique stimuli or wild cards were substituted for one of the items of the lists in Experiment 4. Further transfer tests, in which stimuli for the two new pairs appeared, were also given to the subject. She successfully responded to these two merged lists and reversed the order as the result of reversal training.     

Generalization and response latency

The present experiments investigated generalization in a reaction time situation where the generalization stimulus, a tone, preceded the reaction time signal, a light. The hypotheses under investigation were that the duration of the cue stimulus would determine the degree of generalization (Experiment I) and that the response latency independent of the stimulus duration would be related to the amount of generalization (Experiment II). A particular generalization test stimulus (a tone of 40, 45, 50, 60, 65, or 70 dB) was presented only once always following two bar-pressing responses to training stimulus (tone of 55 dB) under each of two conditions of stimulus duration in Experiment I and under each of two conditions of response latency in Experiment II. It was found that under the condition of short response latency generalization was broader.     

Generalization and response latency

The present experiments investigated generalization in a reactio? time situation where the generalization stimulus, a tone, preceded the reaction time signal, a light. The hypotheses under investigation were that the duration of the cue stimulus would determine the degree of generalization (Experiment I) and that the response latency independent of the stimulus duration would be related to the amount of generalization (Experiment II). A particular generalization test stimulus (a tone of 40, 45, 50, 60, 65, or 70 dB) was presented only once always following two bar-pressing responses to training stimulus (tone of 55 dB) under each of two conditions of stimulus duration in Experiment I and under each of two conditions of response latency in Experiment II. It was found that under the condition of short response latency generalization was broader.     

Asymmetrical stimulus control and the mirror-image problem

An analysis of the mirror-image discrimination literature revealed a number of inconsistent and paradoxical results. A unifying conception was proposed and it was argued that lateral mirror-image stimuli constitute a special class of problems on which effective performance is related to the introduction of an asymmetrical event into the task. Some implications were derived and tested in two experiments. First, five different response modes were compared for children required to discriminate two lateral or up-down mirror-image stimulus pairs. Acquisition was significantly faster on the latter problems. On the former, it was shown that responding to just one side of the lateral mirror-image stimuli led to significantly faster learning. Subsequent generalization tests indicated control by one part of the stimulus display for those who responded to one side. Next, Ss unable to learn the problem in Experiment I were given further acquisition trials. Only those children given training designed to promote selective stimulus control learned the problem.     

Enhancement of food-rewarded instrumental responding by an appetitive conditioned stimulus

Four experiments are reported in which a stimulus (with a minimum duration of 60 s) signalling the delivery of “free” food was presented to rats lever-pressing for food available on a variable interval schedule. It was found that responding was enhanced in the presence of the stimulus when the baseline schedule of reinforcement was lean (Experiment I) and that the enhancement was dependent upon the pairing of the stimulus with free food (Experiments II and III). Experiment IV showed that an enhancement could be found after initial training in which stimulus-food pairings were given to subjects that were not concurrently lever pressing for food. It is argued that these results are consistent with the suggestion that an appetitive conditioned stimulus can energise appetitive instrumental behaviour.     

The transfer of specific and general consequential functions through simple and conditional equivalence relations

The purpose of this study was to examine the transfer of consequential (reinforcement and punishment) functions through equivalence relations. In Experiment 1, 9 subjects acquired three three-member equivalence classes through matching-to-sample training using arbitrary visual forms. Comparison stimuli were then given conditioned reinforcement or punishment functions by pairing them with verbal feedback during a sorting task. For 8 of the 9 subjects, trained consequential functions transferred through their respective equivalence classes without additional training. In Experiment 2, transfer of function was initially tested before equivalence testing per se. Three of 4 subjects showed the transfer without a formal equivalence test. In Experiment 3, 3 subjects were given training that gave rise to six new three-member conditional equivalence classes. For 2 of the subjects, the same stimulus could have either a reinforcement or punishment function on the basis of contextual cues that defined its class membership. Experiment 4 assessed whether equivalence training had established general or specific consequential functions primarily by adding novel stimuli in the transfer test. Subjects treated even novel feedback stimuli in the transfer test as consequences, but the direction of consequential effects depended upon the transfer of specific consequential functions through equivalence relations.     

Acquisition and maintenance of autoshaped key pecking as a function of food stimulus and key stimulus similarity.

The results of a number of recent studies suggest that acquisitions of autoshaped key pecking in pigeons is affected by the similarity of the grain-hopper stimulus and response-key stimulus. In Experiment 1 this hypothesis was tested by training independent groups of pigeons to key peck under six different hopper-stimulus and key-stimulus similarity conditions, and three procedures containing either immediate reinforcement, variable delay of reinforcement, or omission of reinforcement for key pecking. Number of trials to acquisition was found to be related to the similarity variable. Maintained responding was affected by the response-reinforcer contingency. This effect was found both within and between subjects. Under two of the contingencies (automaintenance and omission), maintained responding continued to be affected by the similarity of the hopper stimulus and key stimulus. In Experiment 2 pigeons were given omission training with a hopper light on or off. Both acquisition and maintenance of key pecking were facilitated by the presence of the hopper light. The present findings suggest that much of the responding reported in various automatic shaping and training procedures may reflect the effects of key stimulus/food stimulus similarity.     

Conditioned changes in pain reactivity I: A discrete CS elicits hypoalgesia, not hyperalgesia, on the tail-flick test

Prior work suggests that a stimulus which has been paired with an aversive event may elicit either an increase or decrease in pain reactivity. In four experiments we attempted to isolate the variables which determine the direction of the conditioned response. In all experiments, one stimulus was paired with shock (the CS+) while another was nonreinforced (the CS−). Pain reactivity was assessed by measuring tail withdrawal from radiant heat (the tail-flick test). Experiment 1 tested whether the amount of training plays a critical role. We found that the CS+ elicits longer tail-flick latencies irrespective of whether subjects received 6 or 24 CS-US pairings. Although there was some evidence that subjects may exhibit a general hyperalgesia at 2 min after the presentation of the conditioned stimulus, the results of Experiment 2 revealed that this effect was an artifact caused by differences in the amount of time between test trials. The results of Experiment 2 also showed that the difference observed between the CS+ and CS− was not due to a CS− induced hyperalgesia. Rather, it reflects a CS+ induced hypoalgesia. Experiment 3 evaluated whether the time of day at which testing occurs is important. We found that subjects exhibit conditioned hypoalgesia when tested in either the light or dark portion of the light-dark cycle. In Experiment 4 we examined whether it matters if subjects are tested in the training context or a neutral context. We found that subjects exhibit conditioned hypoalgesia during the CS+ irrespective of where they are tested. The results suggest that a CS+ elicits hypoalgesia, not hyperalgesia, on the tail-flick test over a wide range of conditions.