Wavelength generalization and discrimination in the pigeon

Matching is acquired faster than mismatching by pigeons when salient stimuli are presented manually

Same/different learning by pigeons has been studied using several different procedures. One of these procedures is matching-to-sample or mismatching-from-sample in which responses to a sample stimulus result in the presentation of two comparison stimuli, one of which matches the sample, the other of which does not. In the matching task, choice of the matching stimulus is reinforced. In the mismatching task, choice of the stimulus that does not match the sample is reinforced. Most research that has compared acquisition of the two tasks has not reported a difference between them. Research with transfer of training, in which either the matching stimulus or the mismatching stimulus is replaced with a new stimulus, suggests that the matching stimulus is selected in the matching task, but the matching stimulus is rejected in the mismatching task. In the present experiment, pigeons were trained on either matching or mismatching with salient stimuli presented manually and the reinforcer was presented under a colored slide that covered it. In Phase 1 with a noncorrection procedure and a reinforcer for pecking the sample, pigeons did not acquire either task, however, in Phase 2 they learned both tasks readily without reinforcement for pecking the sample and with a correction procedure. Furthermore, the pigeons learned matching significantly faster than mismatching, suggesting that sameness may be a more natural stimulus relation than mismatching.

Flexible Learning of Matching and Mismatching by Pigeons

When pigeons learn a conditional discrimination in which a sample stimulus indicates which of two comparison stimuli is correct Skinner (1950) proposed that they learn a chain involving the sample, the correct comparison stimulus, and the reinforcer. This implies that they do not learn to reject the incorrect comparison stimulus and the sameness relation between the sample and the correct or the incorrect comparison stimulus plays little role in learning. There is, however, considerable evidence that learning to match or mismatch the sample can transfer to novel stimuli. But there is little evidence that the sameness relation facilitates acquisition. In the present research, pigeons were trained on two 0-s delay conditional discriminations: two matching tasks, two mismatching tasks, or one of each. No differences were found in acquisition, suggesting that consistent matching or mismatching does not facilitate acquisition of conditional discriminations. In testing, when either the correct or the incorrect comparison stimulus in each discrimination was replaced with one of the stimuli from the other task, results suggested that the pigeons in all three groups had learned both to select the correct stimulus and to reject the incorrect stimulus in learning both tasks. It appears that the pigeons may have had learned the tasks based on sample/comparison-stimulus configurations with the sample serving as an occasion setter.

Perceptual variability: Implications for learning and generalization

The generalization of learned behavior has been extensively investigated, but accounting for variance in generalized responding remains a challenge. Based on recent advances, we demonstrate that the inclusion of perceptual measures in generalization research may lead to a better understanding of both intra- and interindividual differences in generalization. We explore various ways through which perceptual variability can influence generalized responding. We investigate its impact on the ability to discriminate between stimuli and how similarity between stimuli may be variable, rather than fixed, because of it. Subsequently, we argue that perceptual variations can yield different learning experiences and that interindividual differences in generalized responding may be understood from this perspective. Finally, we point to the role of memory and decision-making within this context. Throughout this paper, we argue that accounting for perception in current generalization protocols will improve the precision of obtained generalization gradients and the ability to infer latent mechanisms. This can inspire future attempts to use generalization gradients as a (clinical) predictor or to relate them to individual traits and neural correlates and, ultimately, may lead to new theoretical and clinical insights.

Olfactory Generalization in Detector Dogs

Simple Summary

Dogs are valued for their odor detection capabilities in a vast range of fields. They help to find hidden and elusive targets, such as explosives, narcotics, missing persons, and invasive or endangered species, amongst an extensive list. In all these roles, dogs are required to find real target odors that vary somewhat from those with which they were trained. For example, dogs might be trained with an explosive mixture or certain explosive compounds, and then must be able to find homemade explosives of differing compositions or manufacturing processes. This ability, to respond to similar odors in the same way as they would respond to the originally trained odor, is known as generalization. A failure to generalize can result in dogs missing targets in working scenarios. Although generalization is usually desired to some extent, dogs must also discriminate against related odors that are not targets. Therefore, research that investigates factors that can influence dogs’ tendency to generalize, and conversely to discriminate, can inform training strategies to improve detection outcomes. However, this field requires further research with greater application to practical training.

Abstract

Generalizing to target odor variations while retaining specificity against non-targets is crucial to the success of detector dogs under working conditions. As such, the importance of generalization should be considered in the formulation of effective training strategies. Research investigating olfactory generalization from pure singular compounds to more complex odor mixtures helps to elucidate animals’ olfactory generalization tendencies and inform ways to alter the generalization gradient by broadening or narrowing the range of stimuli to which dogs will respond. Olfactory generalization depends upon both intrinsic factors of the odors, such as concentration, as well as behavioral and cognitive factors related to training and previous experience. Based on the current research, some training factors may influence generalization. For example, using multiple target exemplars appears to be the most effective way to promote elemental processing and broaden the generalization gradient, whereas increasing the number of training instances with fewer exemplars can narrow the gradient, thereby increasing discrimination. Overall, this research area requires further attention and study to increase our understanding of olfactory generalization in dogs, particularly detector dogs, to improve training and detection outcomes.

Direct and indirect effects of perception on generalization gradients

For more than a century, researchers have attempted to understand why organisms behave similarly across situations. Despite the robust character of generalization, considerable variation in conditioned responding both between and within humans remains a challenge for contemporary generalization models. The current study aims to investigate the extent to which variation in behavior in a context of generalization can be attributed to differences in perception. We combined a fear conditioning and generalization procedure with a perceptual decision task in humans. We found that the failure to perceive a novel stimulus as different from the trained fear-evoking stimulus led to increased conditioned responding. Furthermore, perceptual errors yielded perceived stimulus-outcome contingencies that differed substantially from the objective contingencies. Final, the impact of a perceptual error was dependent upon these perceived contingencies. These findings suggest that generalization across a perceptual dimension is to a large extent driven by perceptual errors that directly affect behavior but also indirectly as they yield different learning experiences between individuals.

Pigeons (Columba livia) show change blindness in a color-change detection task

Change blindness is a phenomenon whereby changes to a stimulus are more likely go unnoticed under certain circumstances. Pigeons learned a change detection task, in which they observed sequential stimulus displays consisting of individual colors back-projected onto three response keys. The color of one response key changed during each sequence and pecks to the key that displayed the change were reinforced. Pigeons showed a change blindness effect, in that change detection accuracy was worse when there was an inter-stimulus interval interrupting the transition between consecutive stimulus displays. Birds successfully transferred to stimulus displays involving novel colors, indicating that pigeons learned a general change detection rule. Furthermore, analysis of responses to specific color combinations showed that pigeons could detect changes involving both spectral and non-spectral colors and that accuracy was better for changes involving greater differences in wavelength. These results build upon previous investigations of change blindness in both humans and pigeons and suggest that change blindness may be a general consequence of selective visual attention relevant to multiple species and stimulus dimensions.

Reaparecimento de sequências com diferentes números de respostas em contextos de extinção e de variação

RESUMO O reaparecimento de uma resposta previamente extinta quando os reforços para uma resposta alternativa são descontinuados é denominado ressurgência. Foram investigados os efeitos de três variáveis sobre o reaparecimento de sequências de respostas: probabilidade da sequência (alta e baixa), contexto de teste (extinção e variação operante) e número de respostas por sequência (três e cinco). Sequências muito prováveis reapareceram mais frequentemente que sequências pouco prováveis, o reaparecimento da sequência alvo foi mais frequente no contexto de extinção do que de variação e o reaparecimento da sequência alvo variou inversamente ao número de respostas por sequência. O reaparecimento da sequência alvo, entretanto, não foi conceitualizado como ressurgência, uma vez que sua frequência foi menor que a das sequências controle.

Range effects in transient and maintained generalization gradients

In three experiments pigeons were trained to discriminate visual flicker rate stimuli. The stimulus set was varied so that the effects of overall stimulus range and border separation between positive and negative stimuli could be assessed. Experiments 1 and 2 showed that transient generalization gradients were lower in height and flatter with increases in either border separation or overall stimulus range. Border separation and overall range interacted in that the effect of range was greatest with relatively greater border stimulus separation. Experiment 3 showed that increased overall stimulus range reduced the magnitude of positive dimensional contrast in maintained gradients. Flattening of the maintained gradient with increases in stimulus range was similar to flattening of post-discrimination gradients found in Experiments 1 and 2. The results from all experiments indicate that increases in overall stimulus range do not decrease discriminability of unchanged stimulus values. Instead, increases in stimulus range may increase the variability of response or criterial factors in discrimination.

The learning of basic-level categories by pigeons: the prototype effect, attention, and effects of categorization

Pigeons were trained to classify composite faces of two categories created by mimicking the structure of basic-level categories, with each face consisting of an item-specific component and a common component diagnostic for its category. Classification accuracy increased as the proportion of common components increased, regardless of familiar and novel item-specific components, with the best discrimination occurring at untrained original faces used as the common components. A no-categorization control condition suggested that categorization gives rise to equivalence for item-specific components and distinctiveness for degrees of prototypicality. When some item-specific components were shared by exemplars of the contrasting categories, those that were not overlapping between the categories became the effective cues for the pigeons' responses. Implications of these results are discussed in the context of current categorization and associative learning theories.

Steady state responding based upon simple and compound stimuli

Two pigeons were trained to perform discrimination tasks along two dimensions, wavelength of a circular spot of light and orientation of a white line. Discriminability among stimuli along these dimensions was established for both subjects by means of a steady state testing procedure. The two dimensions were then combined by superimposing the white line upon the colored background. Subjects were given a series of tests in which a correct response could be made on the basis of either of the two components of the stimulus compounds. Discriminability among these redundant compound stimuli was found to be better than that among wavelength and tilt stimuli alone. A second series of tests was administered using both redundant and conflicting compound stimuli. The results of this test series are consistent with a response strategy in which subjects first examine both elements of a compound and then emit a choice response on the basis of the element that best predicts reinforcement.

The legacy of Guttman and Kalish (1956): Twenty-five years of research on stimulus generalization

This paper is a selective review of the methods, problems, and findings in the area of operant stimulus generalization over the 25 years since the publication of the original paper by Guttman and Kalish (1956) on discriminability and spectral generalization in the pigeon. The paper falls into five main sections, which encompass the main themes and problems stemming from the Guttman and Kalish work and its immediate successors. The first section addresses the relationship between stimulus generalization and stimulus control, as well as the variety of testing procedures and dependent variables used to measure generalization. The next section reviews the limited literature on the effects of early rearing on the generalization gradient. The relationship between discriminability among test stimuli and the slope of the spectral gradient is discussed in the third section, with emphasis upon recent reassessments of the pigeon's hue discriminability function. The fourth section reviews the topic of inhibitory stimulus control, one which developed with the discovery of the peak shift following intradimensional discrimination training. Problems of definition and measurement are discussed in conjunction with the gradient forms used to index inhibitory control. The last section is devoted to attentional effects and the two principal theories postulated to account for them. A survey of different attentional paradigms is provided and the possible role of constant irrelevant stimuli as a source of control is examined. A brief conclusion summarizes the contribution of the generalization technique toward an understanding of the nature and acquisition of stimulus control.

Generalization of excitation and inhibition after different amounts of training of an avoidance baseline

After acquisition of a treadle-pressing response maintained by an avoidance contingency, four groups of pigeons received interdimensional discrimination training. For two groups, the positive stimulus was a 1000-Hertz tone correlated with the avoidance schedule and the negative stimulus was noise correlated with extinction. The discriminative stimuli were reversed for the other two groups. For two groups, the test stimuli were presented during extinction without any shocks during the test stimuli, for the other two groups, an unavoidable shock was presented during each test stimulus. Generalization was measured daily during discrimination training by randomly substituting each of six test frequencies for the 1000-Hertz tone. When the 1000-Hertz tone was correlated with the avoidance schedule, the number of responses to it increased and the excitatory gradient became steeper as a function of the amount of training. When the 1000-Hertz tone was associated with extinction, the number of responses to it decreased as a function of days of training and the inhibitory gradient became slightly steeper, provided that responding to the test stimulus was elevated by unavoidable shock. The training effects parallel those obtained with positive reinforcement.

Color vision of the budgerigar (Melopsittacus undulatus): hue matches, tetrachromacy, and intensity discrimination

Budgerigars, Melopsittacus undulatus, were trained to discriminate monochromatic lights from mixtures of two comparison lights. The addition of small amounts of UV (365 nm) to blue or yellow lights dramatically changed the color for the birds. Hue matches showed the birds to be dichromatic both at long wavelengths (only P565 and P508 active) and at short wavelengths (only P370 and P445 active because of screening of P508 and P565 by cone oil droplets). In mid-spectrum (only P445 and P508 active), a hue match was achieved, but the results were more complicated because two opponent neural processes were activated. All observed hue matches were in quantitative agreement with calculations of relative quantum catch in the pairs of participating single cones and point to the presence of a minimum of three opponent neural processes. For the hue matches at mid- and short wavelengths, the calculations also predict peak values of absorbance of the cone oil droplets associated with P508 and P445. Relative intensity of the training light affected difficult matches at long but not short wavelengths, likely due to achromatic signals from the double cones. With suitable training, birds could make intensity discriminations at short wavelengths, where the double cones have diminished sensitivity.

Generalization of delayed matching to sample following training at different delays

Four groups of pigeons were trained to perform a delayed matching-to-sample task with a single delay of 0, 2, 4, or 6 s from the outset of training. The longer the training delay, the more sessions were required for all birds to reach the same level of response accuracy. Following initial training, five test sessions that included nonreinforced trials with delay intervals of 0, 2, 4, 6, 8, and 10 s were interspersed between training sessions. Unlike typical forgetting functions in which accuracy decreases monotonically with increasing delay, the forgetting functions from test sessions resembled generalization gradients with the peak of the functions occurring at the training delay. Following additional training for all birds with a 0-s delay, forgetting functions decreased monotonically with increasing delay. The results suggested that remembering can be trained at a specific delay interval, and generalizes to similar delay intervals. Generalization along the temporal dimension of delay may contribute to typical forgetting functions in which accuracy decreases from 0-s delay.

Predicting the extension of equivalence classes from primary generalization gradients: the merger of equivalence classes and perceptual classes

In Experiment 1, 6 college students were given generalization tests using 25 line lengths as samples with a long line, a short line, and a "neither" option as comparisons. The neither option was to be used if a sample did not go with the other comparisons. Then, four-member equivalence classes were formed. Class 1 included three nonsense words and the short line. Class 2 included three other nonsense words and the long line. After repeating the generalization test for line length, additional tests were conducted using members of the equivalence classes (i.e., nonsense words and lines) as comparisons and intermediate-length lines as samples. All Class 2 comparisons were selected in the presence of the test lines that also evoked the selection of the long line in the generalization test that had been given before equivalence class formation. Class 1 yielded complementary findings. Thus, the preclass primary generalization gradient predicted which test lines acted as members of each equivalence class. Regardless of using comparisons that were nonsense words or lines, the post-class-formation gradients overlapped, showing the substitutability of class members. Experiment 2 assessed the discriminability of the intermediate-length test lines from the Class 1 (shortest) and Class 2 (longest) lines. The test lines that functioned as members of an equivalence class were discriminable from the line that was a member of the same class by training. Thus, these test lines also acted as members of a dimensionally defined class of "long" or "short" lines. Extension of an equivalence class, then, involved its merger with a dimensionally defined class, which converted a close-ended class to an open-ended class. These data suggest a means of predicting class membership in naturally occurring categories.

Discrete and continuous measures of dimensional stimulus control

In two sets of experiments, we examined dimensional stimulus control of pigeons' responses to a visual flicker-rate continuum. In the first experiment, responses to a single key were reinforced periodically during stimuli from one half of the stimulus continuum, and responses during other stimuli were extinguished. In the second experiment, two response keys were simultaneously available, with reinforcement for each response alternative associated with different halves of the stimulus continuum. Conditions of the second experiment involved either free-operant or discrete-trial stimulus presentations. Results from these experiments show that positive dimensional contrast appeared in discrimination tasks with one or two response alternatives, but only with free-operant procedures. In addition, discrimination between stimulus classes established by differential reinforcement was assessed as accurately by continuous rate measures as by discrete response choice in the two-alternative situation. The general implication of these experiments is that response rate measures, when properly applied, may reveal sources of variation within stimulus classes, such as dimensional contrast, that are not evident with discrete measures.

Massed and spaced stimulus sequences in dimensional discrimination

In two experiments, pigeons' responding to a visual flicker-rate continuum was established by a maintained generalization procedure. For both experiments, variable-interval reinforcement was available for responses during stimuli from one half of the stimulus continuum while responses during other stimuli were extinguished. The first experiment compared gradients of dimensional stimulus control produced by randomly presented positive and negative stimuli with gradients produced by massed positive and negative stimuli. The second experiment alternated the order of massed stimulus sequences. In both cases, massing of stimulus sequences diminished positive dimensional contrast effects, without seriously disturbing discrimination between positive and negative stimuli. The results indicate that stimulus sequences can have an important role in the production of dimensional contrast effects.

Local contrast in multiple schedules: the effect of stimulus discriminability

A three-ply multiple schedule assessed responding in a standard component as a function of the just-preceding schedule. The principal experimental condition was the difference among the wavelengths signaling the schedule components. Only the pigeons working in a narrow wavelength range showed persistent positive local contrast; that is, response rate during the standard component was higher when that component followed extinction than when it followed itself. Birds in both narrow- and medium-range groups showed persistent negative local contrast; that is, rate was lower following a relatively rich component. The dissipation of positive contrast appeared to be most clearly related to the establishment of differential responding. Negative contrast was inversely related to wavelength differences. Theories pertaining to contrast must account for the role of discrimination in both positive and negative types.

Visual search in the pigeon: hunt and peck method

Pigeons pecked at small forms displayed on an oscilloscope screen under computer control. The birds were required to find a small o amid varying numbers of x forms. A photocell glued to the bird's beak provided a signal to the computer when the beak approached a form, and the computer recorded the time and target of the response. As in some similar studies with human subjects, erros and reaction times increased with number of x forms displayed. The method appears promising for further studies of search and of other processes related to perception and information-processing in birds.

The pigeon's perception of saturation

Three experiments used similar methods to investigate the pigeon's perception of saturation of monochromatic lights. This trial-wise procedure consisted of brief presentations of positive and negative stimuli in random sequence. Pecks to the positive stimuli were occasionally reinforced on a low fixed-ratio schedule. The first study determined absolute thresholds for "white" and monochromatic lights by establishing a discrimination between lights of various radiances and a dark key. Experiment II investigated generalization from a white light to various monochromatic lights under conditions that minimized the use of luminance as a cue. The third experiment examined discrimination of various monochromatic lights along a colorimetric purity continuum; responses to white light were reinforced, while responses to lights that combined white and monochromatic lights in various proportions were not. The results indicated that lights of different wavelength differ in saturation, but that all are discriminable from white. Wavelengths between 550 and 600 nm are least saturated for the pigeon, and saturation increases markedly as wavelength decreases below this region of the spectrum.