Pigeon same–different concept learning with multiple stimulus classes.

Two experiments examined the acquisition and transfer of a complex same–different discrimination by pigeons. With the use of a 2-alternative choice task, 5 pigeons were reinforced for discriminating odd-item Different displays, in which a contrasting target was present, from Same displays, in which all elements were identical. Four different types of same-different displays were concurrently tested. The display types differed in their configuration (texture vs. visual search organization), the nature of their elements (small and large colored shapes; pictures of birds, flowers, fish, and humans), and the processing demands required by their global-local element arrangement. Despite these differences, the pigeons learned to discriminate all 4 display types at the same rate and showed positive discrimination transfer to novel examples of each type, suggesting that a single generalized rule was used to discriminate all display types. These results provide some of the strongest evidence yet that pigeons, like many primates, can learn an abstract, visually mediated same-different concept. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of visual context on pattern discrimination by pigeons (Columba livia) and humans (Homo sapiens).

Three experiments examined the role of contextual information during line orientation and line position discriminations by pigeons (Columba livia) and humans (Homo sapiens). Experiment 1 tested pigeons' performance with these stimuli in a target localization task using texture displays. Experiments 2 and 3 tested pigeons and humans, respectively, with small and large variations of these stimuli in a same-different task. Humans showed a configural superiority effect when tested with displays constructed from large elements but not when tested with the smaller, more densely packed texture displays. The pigeons, in contrast, exhibited a configural inferiority effect when required to discriminate line orientation, regardless of stimulus size. These contrasting results suggest a species difference in the perception and use of features and contextual information in the discrimination of line information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Pigeons learn stimulus identity and stimulus relations when both serve as redundant, relevant cues during same-different discrimination training.

The authors taught pigeons to discriminate displays of 16 identical items from displays of 16 nonidentical items. Unlike most same-different discrimination studies-where only stimulus relations could serve a discriminative function-both the identity of the items and the relations among the items were discriminative features of the displays. The pigeons learned about both stimulus identity and stimulus relations when these 2 sources of information served as redundant, relevant cues. In tests of associative competition, identity cues exerted greater stimulus control than relational cues. These results suggest that the pigeon can respond to both specific stimuli and general relations in the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

Conditional same-different discrimination by pigeons: Acquisition and generalization to novel and few-item displays.

The authors explored whether pigeons can learn to discriminate simultaneously presented arrays of 16 identical (Same) visual items from arrays of 16 nonidentical (Different) visual items, when the correct choice was conditional on the presence of another cue: the color of the background. In one experiment, pigeons rapidly learned this task and, after training with arrays created from a 72-icon set, they exhibited nearly perfect transfer to novel testing arrays. In a second experiment, pigeons’ accuracy to 24-, 20-, 12-, and 8-icon arrays during later testing remained as high as accuracy to training arrays; although accuracy declined with 4- and 2-icon arrays, it was still significantly above chance. In both experiments, pigeons’ choice reaction time scores nicely complemented their choice accuracy scores. These results suggest that the conditional discrimination procedure is well suited to disclose same-different discrimination in pigeons and to elucidate the interaction between perception and abstraction in conceptual learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acquisition and transfer of visual texture discriminations by pigeons.

Two experiments investigated texture discrimination in pigeons. In a simultaneous conditional-discrimination procedure, pigeons were reinforced for pecking at a small target region of identically colored form elements embedded in a larger region of distractor elements. These regions differed in either color or shape or differed redundantly in both dimensions. Pigeons readily acquired these discriminations and showed substantial positive discrimination transfer to new displays composed from novel recombinations of training colors and shapes, novel colors and shapes, and novel spatial organizations. The global organization of these displays appeared to be chief property mediating performance. This suggests that pigeons have mechanisms for perceptually grouping regions of similar colors and shapes, and these mechanisms may be similar to the preattentive visual mechanisms proposed for human texture segregation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contrasting object-based and texture-based accounts of same/different discrimination learning with trial-unique stimuli.

Same/different discrimination is a classic task for investigating relational learning in animals. Recent research suggests that pigeons can learn a trial-unique same/different discrimination, which eliminates the opportunity to memorize the training items (Brooks & Wasserman, 2008). The authors conducted three tests to elucidate the role that item-based comparison plays in this trial-unique discrimination. In the first, the authors tested the possibility that pigeons’ same/different discrimination was based on textural features of the displays by creating a single, unitary texture from same and different displays; pigeons failed to discriminate these unitary textural displays. In the second, the authors varied the number of items (mosaics) in the display and the authors reproduced the characteristic decline in performance associated with fewer items. In the third, the authors systematically increased the area of two mosaics to closely match the area occupied by increasing numbers of mosaics; the results obtained with two small items persisted even when the size of the mosaics was increased. These results clearly show that pigeons’ same/different discrimination was based on object-level variability and not on other properties of the displays. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Outcome expectancies as mediators for discriminative responding.

Attempted to identify the mechanism that underlies the differential outcome effect in acquisition and working memory in pigeons. Different outcomes were cued by 2 pairs of colors that also served as initial stimuli in 2 delayed conditional discriminations. The test stimuli were vertical and horizontal lines. Ss were 22 White Carneaux pigeons. The outcomes were arranged so that expectancies based on them would cue the same response patterns to the 2 test stimuli in both problems (consistent conditions) or opposite response patterns (inconsistent conditions). In Exp I, the 2 problems were trained concurrently; acquisition was faster and reached a higher level in the consistent conditions. In Exp II, transfer of a discrimination between pairs of initial stimuli was studied. Transfer based on consistent expectancies was almost perfect, but there was no transfer with inconsistent expectancies. Shifts from inconsistent to consistent training conditions improved performance, and those in the opposite direction worsened performance. It is concluded that expectancies act as mediating cues and control discriminative behavior directly, strengthening or replacing the cues provided by initial stimuli. (French abstract) (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same–different texture discrimination in pigeons: Testing competing models of discrimination and stimulus integration.

The choice behavior of 6 pigeons performing a multidimensional same-different texture discrimination was examined. On each trial, they had to choose among 2 choice hoppers depending on whether a color, shape, or redundant (color and shape) target signal was present or not in a textured stimulus. Receiver operating characteristic (ROC) curves were produced by variations in the a priori signal presentation probabilities across conditions. Quantitative analyses of these ROC curves were used to evaluate different competing theories of discrimination (signal detection vs. high-threshold-default response models) and information integration (independent observations, additive integration, unidimensional models). The results suggested the structure of the pigeons' choice behavior in this same different discrimination was best described by an unequal variance signal detection model involving a unidimensional evidence variable (e.g., degree of difference). (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)     

Timing light and tone signals in pigeons.

Pigeons' ability to time light and tone stimuli was examined in four experiments. In Experiment 1, two groups of pigeons were trained to discriminate between 2- and 8-s durations of lights or tones and then were transferred to reversal or nonreversal discriminations in the alternate modality. Pigeons learned the light discrimination faster than the tone discrimination and showed immediate positive intermodal transfer from tone to light but not from light to tone. In Experiments 2–4, the peak procedure was used to study birds' timing of 15- and 30-s fixed-interval light and tone signals. Peak times on empty trials under baseline conditions closely approximated the length of fixed-interval signals. When pigeons were tested with time-outs and intermodal switches introduced midway through an empty trial, they tended to reset the timing mechanism and begin timing again from 0 s. With both estimation and production procedures, pigeons were less accurate when timing the tone stimuli than when timing the light stimuli. A comparison of these data with data from timing experiments with rats suggests several possible differences in timing processes between pigeons and rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning Processes in Matching and Oddity: The Oddity Preference Effect and Sample Reinforcement.

Eight pigeons learned either matching (to sample) or oddity (from sample) with or without reward for sample responding. The training stimuli were coarse-white, fine-black, or smooth-mauve gravels in pots with buried grain as the reinforcer. Oddity without sample reward was learned most rapidly, followed by matching with sample reward, oddity with sample reward, and matching without sample reward. Transfer was related to acquisition rate: The oddity group without sample reward showed full (equal to baseline) color and texture transfer; the matching group with sample reward showed partial texture transfer; other groups showed no transfer. Sample reward was shown to determine rate of acquisition of matching and oddity and the oddity preference effect. The results are discussed in terms of item-specific associations operating early in learning prior to any relational learning between sample and comparison stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dimensional organization and texture discrimination in pigeons.

Two experiments examined the influence of dimensional organization on pigeons' texture perception, using a simultaneous conditional discrimination procedure. Four pigeons were reinforced for pecking at a small group of target colored shape elements randomly located within a larger array of distractor elements. The target and distractor regions of feature displays differed consistently in color or shape, whereas in conjunctive displays these regions were formed by conjunctive mixtures of the 2 dimensions. In Exp 1, pigeons' target-detection accuracy was higher with feature than with conjunctive displays. In Exp 2, pigeons responded more accurately and humans responded more quickly with feature than with 2 variations of conjunctive displays. These results suggest that the early visual mechanisms mediating the perception of dimensional information are similar for both species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Range effects in successive discrimination.

Examined the discrimination performance of 3 male white Carneaux pigeons, 2 male homing pigeons, and 2 female Oriental frill pigeons with a visual flicker-rate continuum, using a conventional successive discrimination procedure in 2 experiments. In Exp I, responses during the intermediate stimulus value were never reinforced, while responses during stimuli on either end of the continuum were reinforced periodically. In Exp II, responses during stimuli from one end of the continuum were never reinforced, while responses during stimuli from the other end of the continuum were reinforced periodically. Results from both experiments show that discrimination between unchanged positive and negative stimulus values is a function of the range over which the total stimulus set varies. These range effects are comparable to effects found in absolute judgment tasks in human and animal psychophysics. In addition, the range effects are not due to channel capacity but may depend instead on variability in judgment criteria. (30 ref) (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)     

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)     

Imitative Learning of Stimulus-Response and Response-Outcome Associations in Pigeons.

A novel automated procedure was used to study imitative learning in pigeons. In Experiments 1 and 2, observer pigeons witnessed a demonstrator pigeon successfully performing an instrumental discrimination in which different discriminative stimuli indicated which of 2 topographically distinct responses (R1 and R2) resulted in the delivery of seed. The observers were then presented with the discriminative stimuli and given access to the response panel. Observer pigeons' behavior during the discriminative stimuli was influenced by how the demonstrator had responded during these stimuli. In Experiment 3, observers witnessed demonstrator pigeons performing R1 for Outcome 1 and R2 for Outcome 2. Observers then received a procedure designed to devalue Outcome 1 relative to Outcome 2 and were subsequently less likely to perform R1 than R2. These results suggest that pigeons can learn both stimulus response and response-outcome associations by observation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The what and the where of the pigeon's processing of complex visual stimuli.

Eight pigeons were trained on a go-no go visual discrimination involving I S+ and 15 S–s. The 16 discriminative stimuli were black-and-white line drawings created by the factorial combination of 4 different geometric shapes (wedge, cylinder, cone, handle) in 4 different spatial locations (right, left, above, below) in relation to a common shape (cube). All of the pigeons readily learned this complex visual discrimination. Each bird's pecking behavior was controlled by both attributes of the line drawings, but somewhat stronger stimulus control was exerted by the location of the added component than by its shape. Across all 8 pigeons, there was an inverse relation between stimulus control by component shape and component location. These results document pigeons' joint processing of "what" and "where" information in visual discrimination learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responses of pigeon (Columba livia) Wulst neurons during acquisition and reversal of a visual discrimination task.

The avian visual "Wulst" is a target of the ascending thalamofugal visual pathway. In pigeons (Columba livia), lesion damage to the Wulst has little effect on simple visual discriminations, but impairs performance on tasks such as reversal learning. We recorded the responses of single Wulst neurons as pigeons were trained on the acquisition and subsequent reversal of a visual discrimination. Of the 64 units recorded, 54 (84%) displayed a significant difference in firing rate between some component of the task and the intertrial interval that separated trials. More important, 14 units (22%) displayed a significant change in firing rate exclusively to the S+ and/or S- as learning progressed either during acquisition or reversal. The responses of these 14 neurons indicate that learning during initial acquisition was as likely to correlate with a change in firing rate as during reversal, and some neuronal responses could be characterized as representing reward properties together with visual stimulus features. As such, responses of pigeon Wulst neurons indicate a role in representing aspects of learning as much as the physical/perceptual properties of visual stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A prototype effect and categorization of artificial polymorphous stimuli in pigeons

In a go-no-go discrimination task, pigeons were trained to discriminate artificial polymorphous stimuli differing along 3 six-valued features. Exemplars of each category were generated by systematic transformations of the features from a single stimulus, a base pattern (prototype). They were then tested for transfer to novel stimuli including the base patterns. The most pronounced discrimination occurred between the base patterns rather than between the extreme positive and negative stimuli. A distance-from-prototype rule and an additive integration of feature utilities or of feature frequencies are suggested to account for the prototype effect. In Experiment 2, pigeons were trained on a 2-key choice discrimination task, with the base patterns as conditional stimuli. Subsequent testing with distorted stimuli suggested that a distance-from-prototype model best explains the present findings.