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.     

Use of samples differing markedly in salience may encourage use of a single-code/default strategy in matching-to-sample in pigeons

To test the hypothesis that pigeons will only code the more salient sample when samples differ markedly in salience, pigeons were trained with samples consisting of a 2-s presentation of food (highly salient sample) and an 8-s presentation of keylight (less salient sample). During retention testing, pigeons tended to respond at longer delays as if an 8-s keylight sample had been presented. This finding is consistent with use of a single-code/default strategy in which only the 2-s food sample was coded and the comparison associated with an 8-s keylight sample was selected by default in the absence of memory for the salient 2-s food sample. Hence, a marked difference in sample salience appears to encourage use of a single-code/default strategy.     

Many-to-One Matching with Temporal and Hedonic Samples in Pigeons

Pigeons were initially trained with either temporal samples (2- and 8-s keylights) or hedonic samples (food and no food) mapped to line-orientation (horizontal and vertical) comparisons. Delay testing revealed marked retention asymmetries in both groups (i.e., a choose-short effect with temporal samples and a choose-no-food effect with hedonic samples). Next, while both groups continued training on the original task, a second set of samples was added, hedonic for birds originally trained with temporal samples and temporal for birds originally training with hedonic samples. For all birds, food and short samples were associated with one comparison, and no-food and long samples were associated with the alternative comparison (many-to-one, MTO, mapping). This time, delay testing revealed symmetrical retention functions in both groups with both sets of samples, and mediated-transfer testing revealed positive transfer. It was concluded that (1) a common code was used to represent samples associated with the same comparison in the MTO mapping and (2) the content of the codes was unrelated to the identity of the samples.     

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.     

Presence/absence-sample matching by pigeons: divergent retention functions may result from the similarity of behavior during the absence sample and the retention interval

Divergent choose-absence retention functions typically found in pigeons following presence/absence-sample matching have been attributed to the development of a single-code/default coding strategy. However, such effects may result from adventitious differential responding to the samples. In Experiment 1, retention functions were divergent only when differential sample responding could serve as the basis for comparison choice. In Experiment 2, when pecking did not occur during the retention interval, a choose-absence bias was found, but when pecking occurred during the retention interval, a choose-presence bias resulted. In Experiment 3, positive transfer was found when a stimulus associated with the absence of pecking replaced the absence sample but not when a stimulus associated with pecking replaced the presence sample. Thus, presence/absence-sample matching may not encourage the development of a single-code/default coding strategy in pigeons.     

Development of a single-code/default coding strategy in pigeons

We tested the hypothesis that pigeons could use a cognitively efficient coding strategy by training them on a conditional discrimination (delayed symbolic matching) in which one alternative was correct following the presentation of one sample (one-to-one), whereas the other alternative was correct following the presentation of any one of four other samples (many-to-one). When retention intervals of different durations were inserted between the offset of the sample and the onset of the choice stimuli, divergent retention functions were found. With increasing retention interval, matching accuracy on trials involving any of the many-to-one samples was increasingly better than matching accuracy on trials involving the one-to-one sample. Furthermore, following this test, pigeons treated a novel sample as if it had been one of the many-to-one samples. The data suggest that rather than learning each of the five sample-comparison associations independently, the pigeons developed a cognitively efficient single-code/default coding strategy.     

The Role of Asymmetrical Coding of Duration Samples in Producing the Choose-Short Effect in Pigeons

Pigeons were trained on two independent matching-to-duration-samples tasks; one involved 2- and 10-s durations and color choice stimuli, and the other involved 4.5- and 22.5-s durations and line choice stimuli. Accuracy was above chance on mixed-choice probes in which either of the short-duration samples was followed by the two short-associated stimuli. Following explicit training on mixed-choice trials involving choice between the two short- and the two long-associated stimuli, a choose-short effect was demonstrated with both sets of duration samples. These findings are inconsistent with the possibility that the choose-short effect reflects processes of asymmetrical-sample coding and default responding.     

Evidence for detection of one duration sample and default responding to other duration samples by pigeons may result from an artifact of retention-test ambiguity

S. C. Gaitan and J. T. Wixted (2000) proposed that when pigeons are trained on a conditional discrimination to associate 1 duration sample with 1 comparison and 2 other duration samples with a 2nd comparison, they detect only the single duration, and on trials involving either of the 2 other duration samples, they respond to the other comparison by default. In 2 experiments, the authors show instead that pigeons lend to treat the retention intervals (such as those used by Gaitan and Wixted) as intertrial intervals, and thus, they tend to treat all trials with a delay as 0-s sample trials. The authors tested this hypothesis by showing that divergent retention functions do not appear when the retention interval is discriminably different from the intertrial interval.     

Training and testing music skills in a boy with autism using a matching‐to‐sample format

A 16‐year old boy with autism was taught music skills using a matching to sample procedure. He was trained and subsequently tested for the formation of four 4‐member classes, including different visual music stimuli, and Norwegian and Vietnamese labels for different major and minor chords. Four different stimuli sets were trained both in one‐to‐many (OTM) and many‐to‐one (MTO) training structures. Further, we explored if the reaction times to comparison stimuli increased from training to testing. Results showed that the participant formed equivalence classes with music relations. Furthermore, there were small differences only between OTM and MTO with respect to stimulus equivalence responding. The reaction times to comparison stimuli increased from training to testing, and were most pronounced for the equivalence trials. Copyright © 2010 John Wiley & Sons, Ltd.     

Assessing the contributions of S-O and R-O associations to differential-outcome matching through outcome reversals

Pigeons were trained on symbolic matching with 2 samples, 2 pairs of comparisons, and different outcomes for the correct responses within each comparison pair. For one group, the 2 samples were also associated with different outcomes, whereas for another group, they were not. When the response-outcome (R-O) relations for one pair were subsequently reversed, the group trained with differential sample-outcome (S-O) associations was significantly disrupted in its performance on both reversed- and nonreversed-outcome trials. By contrast, the group trained with just differential R-O associations was disrupted only on reversed-outcome trials. These results were replicated when the outcomes on the initially nonreversed trials were then reversed. The findings indicate that differential S-O associations, when present, have a stronger influence on matching performances than differential R-O associations. They are also consistent with hierarchical and configural models of discriminative control.     

A descriptive analysis of baseline and equivalence-class performances under many-to-one and one-to-many structures

The purpose of the present experiment was to describe responding as a function of One-to-Many (OTM) and Many-to-One (MTO) training structures and identify baseline performances correlated with the accuracy level in tests for equivalence class formation. Participants were 42 adults assigned to either the MTO or the OTM groups, trained on 24 baseline relations, and assessed on the emergence of three 9-member equivalence classes. Participants in the MTO group presented similar frequencies of responses to each of the comparisons throughout baseline training. Also, the number of trials required to meet the baseline mastery criterion was negatively correlated with test accuracy. Participants in the OTM group presented more variable frequencies of responses to each of the comparisons (participants tended to select some of the comparisons less often than others at the beginning of the training). In addition, the number of reinforced responses to the node presented as a sample during training was positively correlated with the number of correct responses during testing for the OTM group. The experiment contributed to an in-depth stimulus control analysis of baseline and test performances, and its results have implications for understanding potential sources of variability between the training structures.     

Matching-to-sample abstract-concept learning by pigeons

Abstract concepts--rules that transcend training stimuli--have been argued to be unique to some species. Pigeons, a focus of much concept-learning research, were tested for learning a matching-to-sample abstract concept. Five pigeons were trained with three cartoon stimuli. Pigeons pecked a sample 10 times and then chose which of two simultaneously presented comparison stimuli matched the sample. After acquisition, abstract-concept learning was tested by presenting novel cartoons on 12 out of 96 trials for 4 consecutive sessions. A cycle of doubling the training set followed by retraining and novel-testing was repeated eight times, increasing the set size from 3 to 768 items. Transfer performance improved from chance (i.e., no abstract-concept learning) to a level equivalent to baseline performance (>80%) and was similar to an equivalent function for same/different abstract-concept learning. Analyses assessed the possibility that item-specific choice strategies accounted for acquisition and transfer performance. These analyses converged to rule out item-specific strategies at all but the smallest set-sizes (3-24 items). Ruling out these possibilities adds to the evidence that pigeons learned the relational abstract concept of matching-to-sample.     

Same/different concept learning in the pigeon: the effect of negative instances and prior adaptation to transfer stimuli

Pigeons were trained on a matching-to-sample or oddity-from-sample task with shapes (circle and plus). Half of each group was exposed to “negative instance” trials i.e., for matching birds, neither comparison key matched the sample, and for oddity birds both comparison keys matched the sample. When all birds were transferred to a new task involving colors (red and green), nonshifted birds (transferred from matching to matching, or oddity to oddity) performed significantly better than shifted birds (transferred from matching to oddity, or oddity to matching), but only if they had experienced negative instances of the training concept. When all birds were exposed to negative instances of the transfer task and then transferred to a new color task (yellow and blue), dramatic transfer effects were observed. The effect of pre-exposure to the yellow and blue colors, in order to reduce transfer-stimulus novelty, had a minor effect on transfer.     

Timing in pigeons: The choose-short effect may result from pigeons’ “confusion” between delay and intertrial intervals

In conditional discriminations, when samples differ only in duration, pigeons typically show a choose-short effect (i.e., higher matching accuracy on short-duration-sample than on long-durationsample trials with increasing delay between sample and comparison stimuli). That this effect depends on the similarity of retention interval (RI) and intertrial interval (ITI) houselight illumination conditions has been taken as evidence that pigeons judge duration relative to a temporal background. In the present experiment, pigeons trained with duration samples and with the ITI either illuminated or not showed a choose-short bias only when the RI illumination on test trials was the same as the ITI illumination had been in training. The results support the hypothesis that the choose-short effect results from the pigeons’ confusion between the ITI and the RI.     

Disruption of short-term memory for reinforcement by ambient illumination

Pigeons were trained on a delayed conditional discrimination (DCD) in which choice of one of two simultaneously presented stimuli was reinforced if the trial had been initiated by presentation of a food sample. On trials in which no sample was presented, choice of the other colour was reinforced. Illumination of the houselights during the retention interval was provided in an attempt to interfere with retention of information about the food sample which served as a conditional cue. In two experiments, retention interval illumination produced a greater disruption of DCD performance on no sample trials than on food sample trials. The finding that retention interval illumination disrupts DCD performance on no sample trials suggests that this manipulation does not affect memorial processes since there was good evidence that performance on no sample trials did not depend on remembering what happened at the outset of the trial. Furthermore, the magnitude of the disruption was larger if the illumination immediately preceded the choice stimuli than if it followed presentation of the sample stimuli. These results support the hypothesis that retention interval illumination disrupts DCD performance by interfering with discriminative control of the choice response rather than with memorial processes. In neither study did retention interval illumination impair discriminative autoshaping to keylight stimuli that immediately preceded the food sample and no sample DCD trials.     

Use of an ambiguous-sample procedure to establish a cue to forget in pigeons

Pigeons were trained on a variation of the matching-to-sample task in which on double-sample trials two samples, one associated with each of the comparison stimuli, were presented successively. Responding to the comparison associated with the first sample was reinforced on half the double-sample trials, and responding to the comparison associated with the second sample was reinforced on the remaining half. One of two postsample stimuli was presented following the termination of each colored sample. A vertical line was presented after a correct or target sample, and a horizontal line was presented after an incorrect or interfering sample. With extended training, each bird demonstrated above-chance accuracy on double-sample trials, providing prima facie evidence that one or both of the postsample stimuli exerted control over matching behavior. Experiment 2 provided evidence that the horizontal line functioned as a cue to forget the code activated by the preceding sample stimulus. It was concluded that a condition sufficient to establish a postsample stimulus as a cue to forget is that the postsample immediately follow presentation of a sample that, if it were to control test responding, would lead to nonreinforcement.     

Sources of visual interference in delayed matching-to-sample with pigeons

In two experiments, independent groups of pigeons were trained on an identity matching task involving line orientations as sample and comparison stimuli. For some birds an overhead houselight was illuminated continuously throughout each training session. For other birds the houselight was never illuminated during training sessions. During subsequent testing, the lighting conditions during the delay were the same as in training on some trials, but on other trials they were opposite those of training during either the entire delay (Experiment 1) or during a portion of the delay (Experiment 2). In birds trained with the houselight off, turning the houselight on during the delay produced a large and enduring disruption in matching accuracy. On the other hand, in birds trained with the houselight on, turning the houselight off during the delay produced only a moderate and temporary disruption in matching accuracy. These findings are inconsistent with the prevailing view that retroactive interference in pigeons is a function of a change in illumination level relative to that which prevailed during training. In pigeons, as in monkeys, sustained retoactive interference effects obtain only when the level of illumination is increase during the delay interval.     

Effects of verbal imitation and comprehension training on verbal production

This study sought to determine whether some combination of imitation training and comprehension training was necessary to achieve verbal production or whether comprehension training alone was sufficient to result in verbal production. Fifty-one first- and second-grade subjects were trained to imitate eight words (Spanish nouns) for which there were no referents. An additional set of eight words was trained in a comprehension task where overt verbal rehearsal was prohibited. Once criterion of two successive sessions of 100% performance was reached in training for both imitation and comprehension, training modes were reversed so that items initially trained in imitation were then trained in comprehension andvice versa. Results showed that initial comprehension training did result in some verbal production, whereas initial imitation training, as expected, did not. A marked improvement in verbal production performance was observed when initial comprehension training was followed by imitation training. When initial imitation training was followed by comprehension training, verbal production also resulted but not to the degree or with the consistency of performance which marked the comprehension-then-imitation sequence. Furthermore, comprehension training required more trials to reach a similar level of proficiency when it followed imitation training than when it preceded imitation. These data indicate that initial imitation training interferes with acquisition of subsequent comprehension and production responses and that the preferred training sequence is one which initially focuses on comprehension and follows this with verbal imitation.This study was supported by Grant HD 00870 from the National Institute of Child Health and Human Development and Grant NS 10468 from the National Institute of Neurological Diseases and Stroke awarded to the Bureau of Child Research, University of Kansas, Lawrence, Kansas.     

Control of pigeons' matching-to-sample performance by differential sample response requirements

Pigeons were trained on a matching-to-sample task in which sample hue and required sample-specific observing behavior provided redundant, relevant cues for correct choices. On trials that involved red and yellow hues as comparison stimuli, a fixed-ratio 16 schedule (FR 16) was required to illuminate the comparisons when the sample was red, and a differential-reinforcement-of-low-rates 3-sec schedule (DRL 3-sec) was required when the sample was yellow. On trials involving blue and green hues as comparison stimuli, an FR 16 schedule was required when the sample was blue and a DRL 3-sec schedule was required when the sample was green. For some pigeons, a 0-sec delay intervened between sample offset and comparison onset, whereas other pigeons experienced a random mixture of 0-sec and 2-sec delay trials. Test trial performance at 0-sec delay indicated that sample-specific behavior controlled choice performance considerably more than sample hue did. Test performance was independent of whether original training involved all 0-sec delay trials or a mixture of 0-sec and 2-sec delays. Sample-specific observing response requirements appear to facilitate pigeons' matching-to-sample performance by strengthening associations between the observing response and correct choice.     

Interaction between consecutive learnings: inhibitory avoidance and habituation

Rats were submitted to step-down inhibitory avoidance training and to habituation of a rearing response to a tone with a 2-h interval between the two tasks, and were tested for retention of both tasks on the next day. When animals were trained first in inhibitory avoidance and then in habituation, retention of the avoidance behavior was impaired. When the animals were trained first in the habituation task and then in the avoidance task, retention of the two tasks was normal. The same results were obtained regardless of the order in which the two tasks were presented on the day of testing. This asymmetrical influence of habituation training on inhibitory avoidance retention could be due either to cognitive or, more likely, to task-specific neurochemical interactions.