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)     

Stimulus selection and irrelevant stimuli in discrimination learning by pigeons.

Studied discrimination learning in 2 experiments with 32 and 16 White Carneaux pigeons. Exp. I confirmed that Ss trained in a free-operant situation produce a sharper gradient of generalization around a specific irrelevant stimulus if they are given true discrimination (TD) training than if given pseudodiscrimination (PD) training. An additional pair of groups, however, showed that this difference could be eliminated if, after initial training but before the test for generalization, both TD and PD Ss were given TD training on an entirely independent set of stimuli. This suggests that the normally flat PD gradient may represent a test effect: control by the specific irrelevant stimulus is masked by other more powerful irrelevant stimuli that are only suppressed by TD training. Exp. II demonstrated that in a discrete-trial situation, PD training results in a sharper gradient than does TD training, suggesting that the other unidentified irrelevant stimuli are present only in free-operant situations. (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rotational object discrimination by pigeons.

Four experiments examined the discrimination of directional object motion by pigeons. Four pigeons were tested in a go/no-go procedure with video stimuli of geons rotating right or left around their central y-axis. This directional discrimination was learned in 7 to 12 sessions and was not affected by changes in object starting orientation, but did require the coherent ordering of the videos’ successive frames. Subsequent experiments found no or little transfer of this motion discrimination to novel objects. Experiments varying the speed of rotation and degrees of apparent motion per frame revealed that both factors strongly affected the discrimination. Finally, tests with partial occlusion of different portions of a rotating object suggested that the majority of the object was likely involved in determining rotational direction. These experiments indicate that pigeons can exclusively use motion cues to judge relative object motion. They also suggest the pigeons may have used a specific representation of the motion sequences of each object to make the discrimination. (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)     

Generalized auditory same-different discrimination by pigeons.

Three pigeons were trained in a successive same/different (S/D) procedure using compound auditory stimuli (pitch/timbre combinations). Using a go/no-go procedure, pigeons successfully learned to discriminate between sequences of either all same (AAAA...or BBBB...) or all different (ABCD...) sequences consisting of 12 sounds. Both pitch and timbre were subsequently established as controlling dimensions. Transfer tests with novel stimuli revealed a generalized basis for the discrimination (novel pitch/timbre combinations, novel pitches, novel instruments, and complex natural & man-made sounds). These results indicate for the first time that pigeons can learn generalized same/different discriminations in a nondominant modality. When combined with earlier visual results, they support a qualitative similarity among birds and primates in their capacity to judge this type of fundamental stimulus relation across different modalities. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditional discrimination learning by pigeons: The role of simultaneous versus successive stimulus presentations.

A series of experiments investigated the development of a conditional discrimination involving a blue or red keylight and a subsequently presented vertical or horizontal line. Pigeons trained in a single reversal paradigm failed to learn the conditional task despite manipulations that assured continued attention to the colors by reinforcing responding to them and other manipulations that reduced both the short-term and long-term memory requirements inherent in the task. If the colors both preceded and overlapped the lines, the Ss learned a conditional discrimination, but it involved only the overlapping component of the color and the lines. The sequential conditional discrimination was acquired only when training involved frequent reversals. The difficulty of learning a sequential conditional discrimination, relative to a simultaneous one, presumably reflects the true hierarchical nature of the task; simultaneous conditional tasks are not necessarily hierarchical. (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)     

Polarized light discrimination by pigeons and an electroretinographic correlate.

Pigeons placed in a multiple-key Skinner-box could be trained to choose reliably keys that were aligned in a specific way with the polarization axis of an overhead, randomly rotating light source. Two experiments were conducted with a total of 15 Ss (Columba livia). On the basis of these results and those of additional control experiments, it is concluded that pigeons can discriminate the axis orientation of linearly polarized light and, furthermore, that they can orient themselves spatially by this cue. Electrophysiological recording experiments show that the shape of the b-wave of the pigeons' electroretinogram is affected by the axis orientation of linearly polarized flash stimuli. This phenomenon seems to be due to the presence of retinal polarization analyzers that may be tied to color vision mechanisms. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distance and magnitude effects in sequential number discrimination by pigeons.

Number discrimination experiments with humans and monkeys have revealed distance and magnitude effects. When required to choose the more frequently occurring stimulus between two stimuli presented repeatedly in sequence, accuracy improves as the distance between number increases (distance effect) and decreases as distance is held constant and the size of the numbers increases (magnitude effect). These effects were shown in three experiments reported with pigeons as subjects. It was shown that a single model based on discrimination between noisy numerical representations could account for both the primate and bird findings. To model the pigeon data, an additional decay parameter was necessary to account for strong recency effects found for the influence on choice of terminal stimuli presented in a sequence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of drive and incentive magnitude on serial discrimination reversal learning in pigeons and chickens.

32 Seabright bantam chickens and 32 White Carneaux pigeons completed 20 problems of a serial discrimination reversal (SDR) task. 4 levels of drive and 2 levels of incentive were combined in a factorial design. Both species' SDR performance was affected by drive but not incentive. However, drive affected interspecies performance differently. Optimal error reduction occurred for pigeons at 14% weight loss, and for chickens at 22% weight loss. Findings suggest that the effects of procedural variables on SDR behavior can be equated across species and that such equation is necessary before meaningful interspecies comparisons can be made. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual differentiation during categorization learning by pigeons.

In Experiment 1, pigeons were trained to categorize two sets of variable stimuli (black and white checkerboard patterns), constructed by random distortions of two prototype patterns. They were subsequently trained on new discriminations, between two new exemplars of their positive category, two new exemplars of their negative category, or two control checkerboard patterns. The new exemplars of their familiar categories were easier to discriminate than the wholly novel stimuli, although this difference was significant only for exemplars of their previously negative category. In Experiment 2, pigeons were initially trained on a discrimination between two prototype checkerboards; they subsequently learned to discriminate between two distortions of their negative prototype more rapidly than between two control patterns. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Auditory intensity discrimination in blackbirds and pigeons.

Three male and 3 female redwing blackbirds, 2 male brown-headed cowbirds, and 2 male White Carneaux pigeons were trained with operant conditioning techniques to respond to small increases in the intensity of pulsed tone trains at 3 frequencies: .5, 1.0, and 2.0 kHz. All 3 species produced similar intensity difference limens (DLs) at the frequencies tested. Intensity DLs decreased as sensation level (intensity level above absolute threshold) increased at all 3 frequencies, with the slopes of these sensation level functions being greatest at 2.0 kHz. The median intensity DLs at 50 db sensation level were 3.3, 2.7, and 2.9 db at .5, 1.0, and 2.0 kHz, respectively, averaged over the 3 species. Some Ss were also required to detect decreases in intensity. They produced intensity DLs 2–3 times larger than the DLs obtained when these same Ss were required to detect increases in intensity. Avian intensity DLs generally appear to be 1–2 db higher than the DLs of those mammals that have been tested (rat, cat, monkey, humans). (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Same/different abstract-concept learning by pigeons.

Eight pigeons were trained and tested in a simultaneous same/different task. After pecking an upper picture, they pecked a lower picture to indicate same or a white rectangle to indicate different. Increases in the training set size from 8 to 1,024 items produced improved transfer from 51.3% to 84.6%. This is the first evidence that pigeons can perform a two-item same/different task as accurately with novel items as training items and both above 80% correct. Fixed-set control groups ruled out training time or transfer testing as producing the high level of abstract-concept learning. Comparisons with similar experiments with rhesus and capuchin monkeys showed that the ability to learn the same/different abstract concept was similar but that pigeons require more training exemplars. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Feature-positive discrimination learning.

In Experiments 1, 2, and 3, pigeons were trained with an ABC+ BCo discrimination, in which three stimuli, A, B, and C, were presented together and paired with food, and the compound BC was followed by nothing; they were also trained with a DEF+ Eo Fo discrimination in which stimuli E and F were presented separately and followed by nothing, whereas the compound DEF was paired with food. On completion of discrimination training, test trials with the feature A consistently revealed a higher rate of responding than with D. In Experiment 4, reinforced presentations of D were intermixed with the DEF+ Eo Fo discrimination. Test trials revealed that E enhanced responding when it was paired with F, but it had the opposite effect when paired with D. The results are seen as being more consistent with a configural than an elemental model of conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impaired place learning and unimpaired cue learning in hippocampal-lesioned pigeons.

Hippocampal processing is often crucial for normal spatial learning and memory in both birds and mammals, suggesting a general similarity in avian and mammalian hippocampal function. However, few studies using birds have examined the effect of hippocampal lesions on spatial tasks analogous to those typically used with mammals. Therefore, we examined how hippocampal lesions would affect the performance of pigeons in a dry version of the water maze. Experiment 1 showed that hippocampal-lesioned birds were impaired in acquiring the location of hidden food in the maze. Experiment 2 showed that hippocampal-lesioned birds were not impaired when a single cue indicated the location of hidden food. These results support the notion that avian and mammalian hippocampal functions are quite similar, in terms of the tasks for which their processing is crucial and the tasks for which it is not. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Texture discrimination with and without abrupt texture gradients.

Assessed whether effortless, visual texture discrimination relies on the detection of gradients between 2 textures in 2 experiments using a total of 32 undergraduates with manipulations that smoothed (Exp 1) or interrupted (Exp 2) the gradient between textures comprising L- and X-type micropatterns. Compared to discrimination performance when there was an abrupt discontinuity between juxtaposed textures, performance declined moderately (about 10%) when the texture boundary was smoothed. Abrupt texture gradients are not a necessary condition for the asymmetrical discrimination of 2 textures. Results indicate that, in certain instances, texture discrimination may involve pattern classification-like processes that are operative in the absence of texture gradients. (French abstract) (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)     

Amphetamine-like discrimination stimulus effects of ephedrine and its stereoisomers in pigeons.

This study assessed the discriminative stimulus effects of (±)-ephedrine and its stereoisomers in pigeons discriminating 1.0 mg/kg of amphetamine from saline. Amphetamine, (±)-, (-)-, and (+)-ephedrine, and cocaine occasioned greater than 80% drug-key responding with the following rank order of potency: amphetamine > cocaine > (-)-ephedrine ≥ (±)-ephedrine ≥ (+)-ephedrine. Neither the α-adrenergic antagonist, phentolamine, nor the β-adrenergic antagonist, propranolol, antagonized the effects of amphetamine or (±)-ephedrine. In contrast, the dopamine receptor antagonist, haloperidol, antagonized the discriminative stimulus effects of amphetamine and (±)-ephedrine as well as those of (-)- and (+)-ephedrine. These results indicate that, like cocaine, (±)-ephedrine and its stereoisomers share discriminative stimulus effects with amphetamine. Moreover, these effects appear to be the result of increased activity in dopaminergic systems. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of blackout position and discrimination training initiation on dimensional control by S- in pigeons.

Blackouts were imposed during the S- component of an interdimensional discrimination and consisted of (a) response prevention (RP), in which attempted responses produced blackouts and prevented completion of response sequences; (b) response contingent blackout (RC-BO), in which completed responses produced blackouts; or (c) control (C), in which responses had no programed consequences. Ss were 36 White King pigeons. Postdiscrimination generalization tests showed that, under early S- introduction, both RP and RC-BO completely blocked dimensional control in relation to relatively weak control established in the C condition. With late S- introduction, relatively strong dimensional control established by the C procedure was reduced by both RP and RC-BO. The RP procedure did not produce significantly less dimensional control than RC-BO under either early or late discrimination initiation. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)