Forgetting of visual discriminations by pigeons.

Three experiments examined the forgetting of visual discriminations by 48 Silver King pigeons. The problems consisted of feature discriminations, with dot displays as the discriminative stimuli, and involved a successive go/no-go pecking response. In all 3 experiments, Ss trained to refrain from pecking an S– display resumed pecking at this display after retention intervals. It is argued that these data represent the 1st direct demonstration of forgetting of a discrimination by pigeons. Exp I also showed that the amount of forgetting progressively increased, in a negatively accelerated fashion, over intervals of 1, 10, and 20 days. Also, more S– responses occurred during relearning a reverse discrimination than after relearning a nonreverse discrimination. In Exp II, acquisition was retarded and more forgetting occurred for discriminations that involved more highly similar stimuli. In Exp III, a change in contextual cues between acquisition and retention testing enhanced forgetting when the contextual cues present during original acquisition were conspicuous; when these cues were relatively inconspicuous, a change in context had no effect on forgetting. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Category discrimination of artificial polymorphous stimuli based on feature learning.

Pigeons and humans were trained to discriminate between sets of artificial stimuli defined by a 2-out-of-3 polymorphous concept. Stimuli containing any 2 of 3 positive or negative features were used for training. In Exp 1, pigeons showed complete transfer to stimuli with all 3 positive or negative features and even to stimuli that had 1 of the 3 features replaced with a novel feature. In contrast, humans failed to show transfer to those stimuli. By using a selective reversal procedure for pigeons, Exp 2 revealed that functional equivalence was not formed among either the stimuli or the features. Exp 3 examined how pigeons integrate information from several distinct features to determine the response to any given stimulus. An additive rule and a combination rule were suggested to account for category discrimination by pigeons. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquired equivalence and distinctiveness in matching to sample by pigeons: Mediation by reinforcer-specific expectancies.

Assessed the ability of a reinforcer to mediate an association between 2 stimuli that independently predict the occurrence of that reinforcer (acquired equivalence of cues). In Exp I, 12 male White Carneaux pigeons were trained on shape (plus and circle) and color (red and green) matching-to-sample tasks. Correct responses were systematically reinforced with corn on some trials and wheat on others to establish associations between 1 stimulus from each task and a "common" outcome. Following training, Ss were transferred to a symbolic matching-to-sample task wherein a stimulus from one training task was presented as the sample, and the stimuli from the other training task were presented as comparisons. In the 1st session, experimental Ss made significantly more correct responses than controls (i.e., Ss "matched" stimuli previously associated with a common outcome). Exp II with 18 Ss replicated this acquired equivalence effect and controlled for food preference. Delayed matching-to-sample training demonstrated enhanced memory performance for Ss exposed to different reinforcement contingencies, but this effect was confined to the shape task. Results indicate that a reinforcer can serve as the basis for organizing otherwise unpaired predictive cues in memory and that animals will selectively use differential expectancies as cues for solving complex discrimination tasks, depending on the difficulty of the discrimination. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cognitive precedence for local information in hierarchical stimulus processing by pigeons.

Four experiments investigated the processing of hierarchical stimuli by pigeons. Using a 4 alternative divided–attention task, 4 pigeons were food-reinforced for accurately identifying letters arranged as either hierarchical global- or local-relevant stimuli or as size-matched filled stimuli. Experiment 1 found that task acquisition was faster with local-relevant than global-relevant stimuli. This difference was not due to letter size. Experiment 2 demonstrated successful transfer to a novel irrelevant letter configuration. Experiments 3 and 4 tested pigeons' responses to conflict probe stimuli composed of equally discriminable relevant letters at each level. These tests revealed that all of the pigeons showed a cognitive precedence for local information early in processing, with the pigeons using different cues to initiate the processing of global information. This local advantage contrasts with previously reported results for humans and pigeons but is similar to that reported for nonhuman primates. Alternatives attempting to reconcile these contrasting comparative results are considered. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Categorical discrimination and generalization in pigeons: All negative stimuli are not created equal.

Three experiments investigated categorical discrimination and generalization in pigeons. Multiple FI-extinction training was conducted with a pool of 48 different negative discriminative stimuli (12 slides each of people, flowers, cars, and chairs). The most errors were committed to negative stimuli (S–s) from the same category as the 12 positive stimulus (S+) slides. Such categorical generalization was stronger when the 12 S+s entailed 1 copy of 12 different slides (Exp 2) than when the S+s entailed 12 copies of 1 slide (Exp 1). In addition, reliable but incomplete loss of inhibitory control was observed to novel stimuli chosen from the same category as the S– slides (Exp 3). These results are consistent with perceptual theories of categorical coherence, according to which preexisting similarities among stimuli chiefly determine the acquisition and application of categories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer of a discrimination by pigeons (Columba livia) between pictured locations and the represented environments.

In Exp 1, pigeons (Columba livia) were trained in a successive slide presentation procedure to discriminate between pictures of 2 ends of a room and then trained to find food in the actual room. A congruent-transfer (CT) group learned the spatial discrimination more quickly than an incongruent-transfer (IT) group. In Exp 2's replication we used a simultaneous slide presentation procedure and added a control group. The IT group required significantly more trials than the CT or control groups. In Exp 3, order of the training conditions was reversed. CT and IT conditions had no effect on the speed of acquisition of the discrimination. This indicates that pigeons acquire a representation of spatial locations from pictures, which can then direct behavior, but the direction of transfer observed was unidirectional. This suggests that a discrimination between spatial locations may not be accurately represented in pictorial form. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

On the relationship between differential outcomes and differential sample responding in matching-to-sample.

Four experiments involving 24 experimental pigeons and 24 experimentally naive pigeons examined control over choice by differential sample responding in matching-to-sample with differential outcomes. In Exp 1, Ss initially learned to match with food vs no-food outcomes. Their performances later transferred to other samples to which responding vs not responding had been explicitly reinforced with a single outcome (food). In Exp 2, Ss initially learned to produce the comparisons by pecking 1 sample but not the other. Transfer was then observed to new samples associated with food vs no food (and thus often vs seldomly pecked). Exps 3 and 4 showed that transfer of matching required differential behavior to each sample set and did not depend on explicit conditioning of that behavior prior to acquisition. Results show that differential sample behavior provides a redundant cue for choice in differential outcome matching-to-sample. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same-different texture discrimination and concept learning by pigeons.

Investigated the acquisition and transfer of a "same-different" conditional discrimination using multidimensional visual texture stimuli in pigeons. Using a choice task, 4 pigeons were reinforced for discriminating different displays, created from aggregated differences in element color or shape, from uniform displays, in which all elements were identical. Discrimination of these 2 display types was readily acquired by the pigeons when they were required to locate and peck the contrasting target region of the different displays. The pigeons showed high levels of discrimination transfer to novel texture stimuli both during acquisition and in 2 subsequent transfer tests. The results suggest that pigeons may be able to learn a generalized same-different concept when promoted by the use of large numbers of multielement stimuli during training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeon visual memory capacity.

Four experiments examined visual memory capacity in 13 White Carneaux pigeons. In Exp I, Ss learned to discriminate between 80 pairs of random shapes. Memory for 40 of those pairs was only slightly poorer following 490 days without exposure. In Exp II, 80 pairs of photographic slides were learned; 629 days without exposure did not significantly disrupt memory. In Exp III, 160 pairs of slides were learned; 731 days without exposure did not significantly disrupt memory. In the final experiment, Ss learned to respond appropriately to 40 pairs of slides in the normal orientation and to respond in the opposite way when the slides were left–right reversed. After an interval of 751 days, there was a transient disruption in discrimination. These experiments demonstrate that pigeons have a heretofore unsuspected capacity with regard to both breadth and stability of memory for abstract stimuli and pictures. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extent and limits of the matching concept in monkeys (Cebus apella).

Two experiments with 11 monkeys investigated the extent and limits of the matching concept. In Exp I, 8 Ss that were experimentally naive with regard to visual stimuli were trained on identity matching with a 2-sample set based on 2-dimensional stimuli. On a subsequent test employing 2 new samples, 4 of the 8 Ss applied the matching rule to the new sample stimuli (as defined by a transfer criterion). Three of these Ss showed substantial savings in learning to match the new samples; 2 of the 3 Ss transferred the matching rule when given a 2nd test with 2 new samples, and the 3rd S showed immediate and complete transfer when tested with a 3rd pair of new stimuli. Results indicate a stronger representation of the matching concept in monkeys than has been demonstrated with pigeons, even in comparable assessment conditions. However, in Exp II, 4 Ss from Exp I failed to transfer the matching rule to steady vs flashing green samples, indicating that the matching concept did not immediately extend beyond the general class of visual stimuli with which it was developed. These and related research findings suggest that representation of the matching concept in animals varies along a specificity–abstractness dimension, reflecting the degree to which the concept is tied to the conditions and context of its development. (45 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Comparison of differential reinforcement of low rates (DRL) performance in pigeons (Columba livia) and crows (Corvus brachyrhynchos).

Compared the DRL performance of crows and pigeons in 3 experiments. In Exp I, 4 crows and 3 pigeons were studied under DRL schedules ranging from 10 to 120 sec. A standard pigeon test chamber, with minor modifications for the crow, was used. The crows performed much more successfully, obtaining many more reinforcers and making fewer responses per reinforcement. 2 crows continued to respond effectively up to DRL-120 sec. In Exp II, 3 crows were studied and limited hold requirements were added to the DRL schedules. Each crow showed improved temporal discrimination under this procedure, and the conditional probability curves appeared similar to those for rats. Exp III compared the performance of 3 crows and 3 pigeons under a DRL procedure in which the availability of reinforcement was signaled by a change in key-light color. Both species performed very successfully under this procedure, and the species differences observed in Exp I were essentially eliminated. Overall results suggest that crows can make accurate temporal discriminations in the absence of external cues, while pigeons are dependent on these stimuli for effective responding. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context as a conditional cue in operant discrimination reversal learning.

Five experiments with 68 pigeons investigated the conditions under which contextual stimuli gain conditional control in the discrimination reversal paradigm. In Exp I, Ss learned an operant discrimination in which the positive stimulus (S+) was 555 nm and the negative stimulus (S–) was 576 nm in one context (houselight off plus white noise [HLFN]) and then learned the reversal (S+ 576 nm; S– 555 nm) in another context (houselight on plus tone [HLNT]). Subsequent wavelength generalization testing revealed responding appropriate to each context: The gradients peaked at 555 nm in HLFN and at 576 nm in HLNT. In Exp II, separate groups experienced both visual and auditory context cues, only visual ones, or only auditory ones. The visual cues worked as well as the compound, but the auditory cues gained no conditional control. In Exp III, houselight illumination replaced by white light directly added to the colors serving as discriminative cues. Results suggest that houselight illumination does not gain conditional control by altering the brightness and saturation of the key colors. In Exp IV, HLNT and HLFN gained conditional control over discriminations based on different angles of a white line, but background key color did not. In Exp V, conditional control over a color discrimination was established by contexts consisting of black and white striped walls vs plain walls. Findings suggest that pigeons use diffuse visual cues to identify the place where food-reinforced learning has taken place. (16 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Discrimination of temporal relations by pigeons.

In 4 experiments, pigeons were tested on a duration comparison task involving the successive presentation of two visual stimuli that varied in duration from trial to trial. Following presentation of the durations, 2 choice keys were lit, and reinforcement for choices was based on the temporal relation between durations of the pair. In Exp 1, the range of durations was varied over conditions. Responding changed as an orderly function of the ratio of the 2 durations. There was a decrease in discrimination accuracy as average duration increased over conditions. In Exp 2, Ss were transferred from a task involving spatially differentiated choices to one involving hue-differentiated choices. Performance was similar to that of Exp 1. In Exp 3, Ss were exposed to a single duration range that included many durations from the 4 ranges of Exp 1. Discrimination accuracy was comparable on 3 problem duration categories within this range and declined slightly for problems in the 4th and longest category. Manipulation of absolute reinforcement rate in Exp 4 resulted in no change in discrimination accuracy, suggesting that the decline in accuracy over conditions of Exp 1 could not be attributed to decreases in reinforcement rate that accompanied lengthier durations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Formation of tone–US associations does not interfere with the formation of context–US associations in pigeons.

In four experiments we investigated whether signaled and unsignaled unconditional stimuli (US) presentations resulted in differential context conditioning. Experiments 1 and 2 showed that the presence of a tone during grain presentation facilitated the formation of tone–food associations in pigeons. Experiment 2 also showed that the acquisition of associative value by the tone did not diminish associations between context and the US. Experiment 3 showed that signaled USs did not interfere with the acquisition of context–US associations, and Experiment 4 showed that even when the signal was extensively pretrained, context–US associations could not be blocked. The results of these experiments are inconsistent with conditioning models that require competition between cues and contexts for associative value. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning in rats with caudate-putamen lesions: Unimpaired classical conditioning and beneficial effects of redundant stimulus cues on instrumental and spatial learning deficits.

The effects of caudate-putamen lesions in the rat on conditioning were investigated in 3 experiments. In Exp I, rats with lesions were impaired on a spatial task that required learning to make the correct position response, but no deficit was obtained when the alternatives were differentiated by salient visual cues. Performance remained good even when the visual cues were removed. A classical conditioned suppression paradigm was used in Exp II, and caudate-putamen lesions were found not to impair acquisition of suppression or overshadowing. In Exp III poor instrumental learning in subjects with lesions as retarded acquisition of lever-press responding and depressed variable interval response rates were found. When a light stimulus was present together with reinforced responses, response rates were depressed in the control group (which suggested an overshadowing phenomenon) but were potentiated in the group with lesions. Results show that caudate-putamen lesions did not produce a general deficit in association formation. There was disruption of learning about responses but not stimuli and, moreover, it was found that redundant stimulus cues aided response learning. It appears that for normal subjects, the salience or associability of the response cues may largely-determine the influence of stimuli presented during instrumental conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeon memory: Same/different concept learning, serial probe recognition acquisition, and probe delay effects on the serial-position function.

In Exp I, 2 White Carneaux pigeons were trained with sets of 70 pairs of color-slide stimuli in a same/different task to perform at least 88% correct; 6 different sets were used in successive acquisitions. Ss transferred same/different performance to novel stimuli with 60% accuracy following their 6 acquisitions; further training and daily changes in the training stimuli revealed 71% transfer to novel stimuli. In Exps II and III, 4 Ss were trained (88% criterion) in a serial-probe-recognition task with 3 list items, and the list length was increased with successive acquisitions to 4, 5, and 6 items. Their serial-position functions changed for different delays between the last list item and the test item revealing a recency effect (last items remembered well) for 0-sec delay, recency and primacy effects (first items remembered well) for 1- and 2-sec delays, and only a primacy effect for a 10-sec delay. Results are discussed in relation to human memory performance and theories of memory processing. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer across delayed discriminations: II. Differences in the substitutability of initial versus test stimuli.

In 2 experiments, pigeons were trained on, and then transferred to, delayed simple discriminations in which the initial stimuli signalled reinforcement versus extinction following a retention interval. Experiment 1 showed that discriminative responding on the retention test transferred to novel test stimuli that had appeared in another delayed simple discrimination but not to stimuli having the same reinforcement history off-baseline. By contrast, Experiment 2 showed that performances transferred to novel initial stimuli whether they had been trained on-baseline or off-baseline. These results suggest that the test stimuli in delayed simple discriminations acquire control over responding only in the memory task itself. On the other hand, control by the initial stimuli, if coded as outcome expectancies, does not require such task-specific training. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Performance of goldfish (Carassius auratus) in patterned sequences of rewarded and nonrewarded trials.

Studied the performance of 40 goldfish in 4 experiments with patterned sequences of reward (R) and nonreward (N) for responses to a given stimulus (S3). Trials with 2 other, readily discriminable stimuli, in which response to one was always rewarded and response to the 2nd never rewarded, were interpolated in such a way that the outcome of any S3 trial could not be predicted from the events of the immediately preceding trial. The main purpose was to look for control of response to S3 based on memory of N like that found in previous work with pigeons. In Exps I and II, blocks of R and N trials with S3 were programmed, R trials in the 1st half of each session and N in the last half, or N trials in the 1st half and R in the last half. In Exp III, successive acquisition and extinction of response to S3 was studied, with the N-to-R, and R-to-N transitions either within sessions or between sessions. In Exp IV, the effects of partial and consistent reinforcement on extinction of response to S3 were compared. Results are similar in important respects to those for pigeons, as described by P. A. Couvillon et al (see record 1981-07158-001), but different in their failure to demonstrate control of performance by memory of N. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of previously experienced outcomes on the desire for choice.

Three experiments examined the effects of past choice experiences on the desire for choice. All 480 undergraduate Ss experienced both choice and no-choice trials and were asked whether they preferred to perform a 3rd set of trials under choice or no-choice conditions. Success on the choice and no-choice trials was manipulated to determine the effects of experienced outcomes on perceived choice and control, future expectancies, and the desire for choice. Exp I indicated that desire for choice is affected by past success with choice relative to their past success with no choice. Exp II suggested that perceptions of control are based primarily on past success under choice conditions and that their desire for choice is a consequence of these perceptions rather than of the objective efficacy of choice. Exp III demonstrated that breaking the link between perceptions of past control and future expectancies weakens the effects of past outcomes on the desire for choice. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Retrospective coding in pigeons' delayed matching-to-sample.

In Exp I, 2 groups of 6 White Carneaux pigeons initially learned 0-delay matching-to-sample with identical comparison stimuli (vertical and horizontal lines) but with different sample stimuli (red and green hues or vertical and horizontal lines). Longer delays were then introduced between sample offset and comparison onset to assess whether Ss were prospectively coding the same events (the correct line comparisons) or retrospectively coding different events (their respective sample stimuli). The hue-sample group matched more accurately and showed a slower rate of forgetting than the line-sample group. In Exp II, 20 mixed-breed pigeons were trained (1) with either hues or lines as both sample and comparison stimuli or (2) with hue samples and line comparisons or vice versa. Subsequent delay tests revealed that the hue-sample groups remembered more accurately and generally showed slower rates of forgetting than the line-sample groups. Comparison dimension had little or no effect on performance. Data suggest that pigeons retrospectively code the samples in delayed matching-to-sample. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)