Formation of transitivity in conditional matching to sample by pigeons

Four homing pigeons were trained over 5 months in a zero-delay, “arbitrary” matching-to-sample procedure with sample and comparison stimuli presented on any of three response keys. Birds were also required to complete a fixed-ratio 10 requirement on both sample and comparison stimuli to terminate their presentation. The procedure resulted in the establishment of relations that were not specifically trained and that can be characterized by the property of transitivity in a stimulus equivalence context. This result was in contrast with the findings obtained from most previous research with nonhuman subjects.     

Differential sample response schedules in the acquisition of conditional discriminations by pigeons

Pigeons were trained on four matching-to-sample tasks with various schedule requirements in effect on the sample key. Differential sample-schedule requirements (a differential-reinforcement-of-low-rates of 3 sec in the presence of one sample and a fixed-ratio 16 in the presence of the other) produced rapid rates of acquisition that did not differ across tasks. Nondifferential sample-schedule requirements (fixed-ratio 1, fixed-ratio 16 or a differential-reinforcement-of-low-rates of 3 sec in the presence of both samples) produced slower rates of acquisition, which depended on the difficulty of the discriminations between samples and between comparisons. Patterns of stimulus and position preferences were influenced both by the comparison stimuli in each task and by the sample-schedule requirements. Detailed analyses of acquisition revealed frequent instances of complete differential sample control of comparison responding at intermediate levels of overall “accuracy”.     

Extending sequence-class membership with matching to sample

Three normal adults were first trained to point sequentially to each member of several pairs of visual stimuli. This baseline training established one class of stimuli to which subjects responded first, and another class of stimuli to which they responded second. Then, in a matching-to-sample procedure, baseline-sequence stimuli served as samples and new visual stimuli served as comparisons. Subjects were trained to choose one group of new comparisons when the sample was a "first" stimulus from the sequence baseline, and to choose the other new comparison stimuli when the sample was a "second" from the sequence baseline. When the new stimuli were then presented as pairs in the posttest, two subjects pointed to them in sequences predictable on the basis of the stimulus-class membership established during matching to sample. The failure of one subject to demonstrate sequential transfer was shown to be a consequence of the failure of the matching-to-sample procedure to establish stimulus classes. The production of sequences that were not directly trained suggested an empirical approach to the analysis of simple grammatical behavior.     

The effect of increased response requirements on discriminative performance of the domestic hen in a visual acuity task.

Six domestic hens were trained in a spatial discrimination task. A controlled reinforcement procedure insured that the ratio of scheduled and obtained reinforcement remained equal. Gray stimuli and gratings ranging in spatial frequency from 1 to 10 cycles per millimeter were presented in seven descending series of probes. The response requirement to the sample key was varied from fixed ratio 1 to fixed ratio 40 in seven experimental conditions. An increase in response requirements from fixed ratio 1 to fixed ratio 5 and fixed ratio 10 resulted in significantly higher accuracy at discriminable grating values. Further increases in response requirements did not consistently improve performance. Generally, response biases increased and occasionally became extreme for probes at finer gratings with increased response requirements.     

Asymmetrical sample training produces asymmetrical retention functions in feature-present/feature-absent matching in pigeons

Pigeons were trained in a matching task in which samples involved presentation of a white line on a green background (feature-present) or on an otherwise dark key (feature-absent). After asymmetrical training in which one group was initially trained with the feature-present sample and another was initially trained with the feature-absent sample, marked retention asymmetries were obtained. In both groups, accuracy dropped precipitously on trials involving the initially trained sample and remained high on trials involving the sample introduced second in training. It was concluded that asymmetrical training encouraged a single-code/default strategy in which only the sample trained initially was coded. Consistent with this conclusion, changing attributes of either sample reduced accuracy to a greater extent in pigeons initially trained with that sample than in pigeons for which that sample was introduced second in training.     

Control by sample location in pigeons'' matching to sample.

Three experiments assessed the impact of sample location in pigeons' matching to sample. Experiments 1 and 2 demonstrated that after line or hue identity matching was acquired to high levels of accuracy with center-key samples, varying sample location across the three keys disrupted performances. The drop in accuracy occurred following both zero-delay and simultaneous training and was mostly confined to trials in which the sample appeared on a side key. Experiment 3 attempted to diminish control by location by training birds to match samples that could appear in any location prior to center-key sample training and moving-sample testing with another set of stimuli. In testing, all birds performed accurately on center-sample trials and on side-key sample trials in which the matching choice appeared on the center key. Accuracy was below chance, however, on side-key sample trials in which the matching choice appeared on the other side key. One implication of the persistent control by sample location in the three-key paradigm is that it precludes the possibility of symmetry because symmetry tests require a change in the locations at which samples and comparisons appear.     

Coding responses and the generalization of matching to sample in children.

Two experiments studied the conditions of stimulus control necessary for the generalization of relational matching to sample. Matching required the selection of comparison shapes rotated 90 degrees clockwise from the orientation of the corresponding sample. In Experiment 1, five children were taught to: (a) code the orientations of samples, (b) transform sample codings to account for the 90 degree rotation, and (c) repeat the transformed sample coding response to a comparison. High levels of generalization occurred with a set of novel stimuli for which stable sample-coding responses were initially available. In another novel set, where stable sample-coding responses were not initially available, low levels of generalized matching were recorded. Matching performance improved after stable coding responses were trained. In Experiment 2, two children and three adults were trained in a form of the matching task that produced poor generalization despite the presence of stable sample-coding responses. Retraining to modify the stimulus control exerted by these coding responses produced an immediate improvement in generalized matching to sample. Results suggest that the generalization of matching is dependent on structure of stimulus control that the component responses exert on each other.     

Effectiveness and persistence of precurrent mediating behavior in delayed matching to sample and oddity matching with children.

Two kinds of mediating behavior were compared with respect to their effectiveness in variable-delay matching-to-sample and oddity-matching tasks. Each of four 5-year-old children was trained to emit either differential or common mediating responses. The differential mediating response consisted of pressing a specific computer key corresponding to either of two possible sample stimuli (a red or a green square). The common mediating response consisted of pressing one of the two response keys regardless of the sample. The differential-response subjects did not show the typical, delay-related decrease in matching-to-sample performance that characterized the behavior of common-response subjects. An oddity-matching task was then introduced, and subjects were instructed to use the mediating keys however they preferred, including not at all. Differential-response subjects continued to respond on the originally trained mediating keys in response to sample presentation and later reversed their choice responding, thus accommodating the oddity-matching requirements. Common-response subjects continued to emit the previously trained mediating response and experienced limited success in oddity matching. Results were interpreted in terms of stimulus control, instructional control, and experimental history.     

MATCHING-TO-SAMPLE PERFORMANCE IN RATS: A CASE OF MISTAKEN IDENTITY?

Three rats had previously acquired a simultaneous matching-to-sample performance with steady and blinking lights. In training, the sample stimulus had always appeared on the middle of three horizontally arranged keys with the comparison stimuli on the side keys. In Experiment 1, the sample stimulus appeared on any of the three keys with the comparison stimuli on the remaining two. The matching-to-sample performance broke down with variable sample and comparison locations; the sample stimulus did not control responding to the comparison stimuli when it appeared on a side key, but it retained control when it appeared on the middle key (as in training). In Experiment 2, the rats were trained with the sample always on the left key. When the sample appeared on either of the trained locations (left or middle key), it retained control for both locations. When the sample then appeared on any of the three keys, as in Experiment 1, sample control did not transfer to the untrained location (right key). The experiments demonstrate that training with fixed sample and comparison locations may establish spatial location as an additional controlling aspect of the stimuli displayed on the keys; stimulus location had become part of the definition of the controlling stimuli. The rats' performance seemed best described as specific discriminations involving the visual stimuli and their spatial locations rather than as identity matching.     

Transfer of pigeons' matching to sample to novel sample locations

This study examined the conditions under which conditional stimulus control by the sample stimuli in three-key matching-to-sample paradigms would generalize across the different possible sample locations. In Experiments 1 and 2, the samples appeared on the left and right side keys during initial training and then on the center key during testing. Transfer of pigeons' matching performances to the center-key samples was evident after both identity and symbolic matching training. In Experiment 3, pigeons trained on symbolic matching with two side-key samples or with a side-key and a center-key sample generally transferred their learned matching performances to those samples when they subsequently appeared in the remaining (novel) location. These results indicate that, when two-choice conditional discriminations are learned with more than one sample location, the visual characteristics of the sample per se predominantly come to control the pigeons' comparison choices. This finding encourages the use of the multiple-location training procedure as a way of reducing control by location, thus providing a more discriminating test of symmetry in animals.     

Effect of delay-interval stimuli on delayed symbolic matching to sample in the pigeon

In Experiment 1, food-deprived pigeons received delayed symbolic matching to sample training in a darkened Skinner box. Trials began with the illumination of the grain feeder lamp (no food sample), or illumination of this lamp, accompanied by the raising of the feeder tray (food sample). After a delay of a few seconds, the two side response keys were illuminated, one with red and one with green light, with positions counterbalanced over trials. Pecking the red (green) comparison produced grain reinforcement if the trial had started with food (no food); pecking red after a no-food sample or green after a food sample was not reinforced. Once matching performance was stable, four stimuli were presented during the delay interval, and their effects on matching accuracy were evaluated. Both illumination of the houselight and the center key with white geometric forms decreased matching accuracy, whereas presentation of a tone and vibration of the test chamber did not. In Experiment 2, pecking the red center key was reinforced with food according to a variable interval schedule. The effects of occasional brief presentations of the four stimuli used in the first experiment on ongoing pecking were assessed. The houselight and form disturbed key pecking, but the tone and vibration did not. Thus, stimuli that interfered with delayed matching also interfered with simple operant behavior. Implications of these results for theories of remembering are discussed.     

Transfer of matching-to-figure samples in the pigeon

Three pigeons were trained on a modified six-key matching-to-sample procedure. The third peck on the figure-sample key (which presented a bird, hand, face, beetle, rabbit, fish, flower, or red hue, as the sample) lighted only one comparison key. Every three additional pecks on the sample lighted another comparison key, up to a maximum of five keys. Pecks on keys of matching figures produced grain. Pecks on nonmatching keys (mismatches) turned off all lights on the comparison keys and repeated the trial. Three figures were used during acquisition. The birds learned to peck each sample until the matching comparison stimulus appeared on one of three comparison stimulus keys, and then to peck that key. Later, five novel stimuli, employed as both sample and comparison stimuli, and two additional matching keys were added. Each bird showed matching transfer to the novel samples. The data suggest that the birds may have learned the concept of figure matching rather than a series of two-component chains or discrete five-key discriminations.     

Sample-specific ratio effects in matching to sample

In a symbolic matching-to-sample task, pigeons were trained using sample-specific, fixed-ratio “observing responses.” Subsequently, in a mixed condition, each sample was presented equally often with each ratio requirement, i.e., the ratios were no longer correlated with the samples. In a second experiment, pigeons were trained initially in the mixed condition and subsequently shifted to the sample-specific condition in which the required ratios were correlated with the samples. Results of both experiments suggested joint control of choices by ratio value and by the exteroceptive stimuli. The discriminative properties of the ratios appeared to outweigh absolute ratio-size effects.     

Sample-stimulus discriminability and sensitivity to reinforcement in delayed matching to sample

Five pigeons were trained in a delayed matching-to-sample task with red and green stimuli. The retention interval between sample-stimulus presentation and the availability of the choice stimuli was varied between 0.01 s and 12 s within each session. The probability of food produced by correct-red and correct-green responses was varied across conditions. Sample-stimulus discriminability and response bias were measured at four different retention intervals. The results of these analyses showed an interaction between the discriminability of the sample stimuli and the control exerted by differential reinforcement. At longer retention intervals, sample discriminability decreased and sensitivity of choice behavior to changes in the red/green reinforcer ratio increased. An analogous relation has been reported in conditional discriminations in which the physical disparity of stimuli has been varied. This correspondence suggests that increasing the delay between presentation of one of two stimuli and an opportunity to respond discriminatively to it may be functionally similar to increasing the physical similarity of the two stimuli.     

Effects of within-class differences in sample responding on acquired sample equivalence

Two experiments examined whether acquired sample equivalence in many-toone matching was affected by variation in sample-response requirements. In each experiment, pigeons responded on either identical or different response schedules to the sample stimuli that occasioned the same reinforced comparison choice (i.e., to the within-class samples). Transfer-of-control tests were then conducted to determine acquired equivalence, or lack thereof, between these samples. In both experiments, there was minimal or no evidence of acquired sample equivalence when pigeons responded differently to the samples within each common-choice class. By contrast, transfer was observed if pigeons responded (a) identically to all sample stimuli, or (b) identically to samples within each common-choice class (viz., to samples that occasioned the same reinforced choice) and differently to samples from different classes (viz., to samples that occasioned different choices). These results may help to explain the recent lack of evidence for response membership in pigeons' acquired equivalence (Urcuioli, Lionello-DeNolf, Michalek, & Vasconcelos, 2006). They also raise questions about the functional sample stimuli and about possible interactions between acquired equivalence and acquired distinctiveness.     

Matching- and nonmatching-to-sample concept learning in rats using olfactory stimuli

Previous research has shown that rats can learn matching-to-sample relations with olfactory stimuli; however, the specific characteristics of this relational control are unclear. In Experiment 1, 6 rats were trained to either match or nonmatch to sample in a modified operant chamber using common household spices as olfactory stimuli. After matching or nonmatching training with 10 exemplars, the contingencies were reversed with five new stimuli such that subjects trained on matching were shifted to nonmatching and vice versa. Following these reversed contingencies, the effects of the original training persisted for many trials with new exemplars. In Experiment 2, 9 rats were trained with matching procedures in an arena that provided for 18 different spatial locations for comparison stimuli. Five subjects were trained with differential reinforcement outcomes and 4 with only one type of reinforcer. Differential outcomes and multiple exemplars facilitated learning, and there was strong evidence for generalization to new stimuli for most rats that acquired several conditional discriminations. Performances with novel samples were generally above chance, but rarely reached the high levels obtained during baseline with well-trained stimulus relations. However, taken together, the data from the two experiments extend previous work, show that rats can learn both match and nonmatch relations with different experimental protocols, and demonstrate generalization to novel sample stimuli.     

On the origins of emergent differential sample behavior

Two experiments evaluated the source(s) of emergent differential sample behavior in pigeons. Initially, pigeons learned two-sample, two-alternative symbolic matching in which different patterns of sample responding were required to produce the comparisons. Afterwards, two other samples nominally identical to the comparisons were added to the matching task. On new-sample trials, completion of either sample-response requirement produced comparison alternatives which were either the same as or different from the alternatives on the familiar-sample trials. Differential responding to the new samples developed only when the comparisons were the same as the familiar samples. The results are consistent with acquired sample equivalence and adventitious reinforcement accounts of emergent sample behavior and are inconsistent with bidirectional transfer (symmetry) between the response patterns explicitly required to the originally trained (familiar) samples and the subsequently reinforced comparisons.     

Asymmetrical sample training and asymmetrical retention functions in one-to-one and many-to-one matching in pigeons

Pigeons were trained in a matching task with either color (group color-first) or line (group line-first) samples. After asymmetrical training in which each group was initially trained with the same sample on all trials, marked retention asymmetries were obtained. In both groups, accuracy dropped precipitously on trials involving the initially trained sample and remained high on trials involving the sample introduced second in training, suggesting that asymmetrical training encouraged a single-code/default strategy in which only the sample trained initially was coded. Pigeons next received concurrent training with the alternate set of samples mapped to the same set of comparisons as were the first set of samples (many-to-one, MTO, procedure). Retention testing revealed no marked retention asymmetries in group line-first whereas marked retention asymmetries occurred with both sets of samples in group color-first. Hence, only birds in group color-first continued to use a single-code/default strategy after MTO training.     

Conditional discrimination in mentally retarded adults: the development of generalized skills.

The development of generalized conditional discrimination skills was examined in adults with retardation. Two subjects with histories of failure to acquire arbitrary matching under trial-and-error procedures were successful under procedures that trained one or more prerequisite skills. The successive discrimination between the sample stimuli was established by training the subjects to name the stimuli. The simultaneous discrimination between the comparison stimuli was established using either (a) standard simple discrimination training with reversals or (b) a procedure in which each of the two sample-comparison relations in the conditional discrimination was presented in blocks of trials, with the size of the blocks decreasing gradually until sample presentation was randomized. The amount of prerequisite training required varied across subjects and across successive conditional discriminations. After acquiring either two or three conditional discriminations with component training, both subjects learned new conditional discriminations under trial-and-error procedures. In general, each successive conditional discrimination was acquired more rapidly. Tests showed that conditional responding had become a generalized skill. Symmetry was shown for almost all trained relations. Symmetry trial samples were ultimately named the same as the stimuli to which they were related in training.     

The effect of asymmetrical sample training on retention functions for hedonic samples in rats

Rats were trained in a symbolic delayed matching-to-sample task to discriminate sample stimuli that consisted of the presence of food or the absence of food. Asymmetrical sample training was provided in which one group was initially trained with only the food sample and the other group was initially trained with only the no-food sample. In addition, within each group half of the rats were trained with an illuminated intertrial interval (ITI) and the remaining rats with a dark ITI. While the retention functions did not differ as a function of which sample was trained first, they did differ as a function of the similarity in the illumination conditions during the ITI and the delay interval. Symmetrical retention functions were obtained when the lighting conditions were similar and slightly asymmetrical retention functions were obtained when the lighting conditions were dissimilar. Probe tests confirmed that features of the no-food sample were attended to and used to generate a memory representation for the no-food sample. The results are not consistent with the hypothesis that asymmetrical sample training encourages coding of the sample introduced initially and default responding to the subsequently introduced sample. Rats generate memory representations for both samples when asymmetrical sample training is given with hedonic samples.