The Pigeon as a Model of Complex Visual Processing and Category Learning.

Over the past 30 years, behavioral, computational, and neuroscientific investigations have yielded fresh insights into how pigeons adapt to the diverse complexities of their visual world. A prime area of interest has been how pigeons categorize the innumerable individual stimuli they encounter. Most studies involve either photorealistic representations of actual objects thus affording the virtue of being naturalistic, or highly artificial stimuli thus affording the virtue of being experimentally manipulable. Together those studies have revealed the pigeon to be a prodigious classifier of both naturalistic and artificial visual stimuli. In each case, new computational models suggest that elementary associative learning lies at the root of the pigeon's category learning and generalization. In addition, ongoing computational and neuroscientific investigations suggest how naturalistic and artificial stimuli may be processed along the pigeon's visual pathway. Given the pigeon's availability and affordability, there are compelling reasons for this animal model to gain increasing prominence in contemporary neuroscientific research.

Enhanced attention in rats following blast-induced traumatic brain injury.

Purpose: To evaluate visuo-cognitive sequelae following blast-induced traumatic brain injury in a rat model. Methods: Rats were randomly assigned to one of four groups depending on the intensity/quantity of a blast received in a blast chamber: sham (no blast), low intensity (22 psi), medium intensity (26 psi), or three medium intensity blasts (26 psi × 3). After recovery, all subjects were given visual discrimination tasks of increasing complexity, until mastery. After behavioral training, visual function was assessed via spectral-domain optical coherence tomography and pattern electroretinogram, and the extent of retinal damage was quantified via immunohistochemistry of retinal ganglion cells. Results: None of the measures assessing visual function revealed significant differences as a function of blast intensity/quantity. Behavioral training did not disclose short-term effects of blast in general motivation or the development of anticipatory responding. No differences in general learning ability and the number of perseverative errors were observed. However, behavioral training found effects of blast in attentional function; relative to controls, subjects that received blasts were faster in learning to attend to informative (over non-informative) cues in the most difficult visual discrimination task. Conclusion: Blast exposure in rats resulted in increased attention following blast, with no appreciable deficits in visual function. These results are contrary to what is often reported for human clinical populations; as such, more research bridging methodological differences is necessary.

The pigeon as a machine: Complex category structures can be acquired by a simple associative model.

Never known for its smarts, the pigeon has proven to be a prodigious classifier of complex visual stimuli. What explains its surprising success? Does it possess elaborate executive functions akin to those deployed by humans? Or does it effectively deploy an unheralded, but powerful associative learning mechanism? In a series of experiments, we first confirm that pigeons can learn a variety of category structures - some devised to foil the use of advanced cognitive processes. We then contrive a simple associative learning model to see how effectively the model learns the same tasks given to pigeons. The close fit of the associative model to pigeons' categorization behavior provides unprecedented support for associative learning as a viable mechanism for mastering complex category structures and for the pigeon's using this mechanism to adapt to a rich visual world. This model will help guide future neuroscientific research into the biological substrates of visual cognition.

The role of numerical and nonnumerical magnitudes in pigeons' conditional discrimination behavior.

Research on approximate numerical estimation suggests that numerical representations can be influenced by nonnumerical magnitudes. Current theories of numerical cognition differ on the nature of this interaction. The present project evaluated the effect of task requirements on the stimulus control exerted by numerical and nonnumerical magnitudes on pigeons' numerical discrimination behavior. In a series of experiments, we explored the effects of cumulative area and item size on pigeons' numerical discrimination. The effect of cumulative area was assessed by presenting visual displays in which cumulative area and item number were either positively correlated, uncorrelated, or negatively correlated. The effect of item size was evaluated by presenting displays in which the size of individual items was varied across trials. Results confirmed that pigeons' numerical discrimination behavior accorded with Weber's law, a prime indicator of nonsymbolic numerical representation. The results further indicated that pigeons did not use numerical information when nonnumerical magnitudes also provided reliable information to solve the discrimination task. However, task manipulations that rendered the information provided by nonnumerical magnitudes unreliable successfully shifted stimulus control toward numerical magnitudes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Resolving the associative learning paradox by category learning in pigeons.

A wealth of evidence indicates that humans can engage two types of mechanisms to solve category-learning tasks: declarative mechanisms, which involve forming and testing verbalizable decision rules, and associative mechanisms, which involve gradually linking stimuli to appropriate behavioral responses.1,2,3 In contrast to declarative mechanisms, associative mechanisms have received surprisingly little attention in the broader category-learning literature. Although various forms of associatively driven artificial intelligence (AI) have matched-and even surpassed-humans' performance on several challenging problems,3,4,5,6 associative learning is routinely dismissed as being too simple to power the impressive cognitive achievements of both humans and non-human species.6,7,8,9 Here, we attempt to resolve this paradox by demonstrating that pigeons-which appear to rely solely on associative learning mechanisms in several tasks that promote declarative rule use by humans3,10,11,12-succeed at learning a novel, highly demanding category structure that ought to hinder declarative rule use: the sectioned-rings task. Our findings highlight the power and flexibility that associative mechanisms afford in the realm of category learning.

Minding behavior.

Perhaps the most popular definition of psychology is the science of mind and behavior. However, the interrelation between mind and behavior is one of continuing controversy. The present paper examines this enduring issue from the perspectives of George J. Romanes, an early comparative psychologist, Edwin G. Boring, an influential experimental psychologist, and Howard Rachlin, an estimable recent behaviorist. Their respective positions shed considerable light on both the theory and practice of behavioral psychology.

Hierarchical and configural control in conditional discrimination learning.

Considerable discussion has concerned the role of context in conditional discrimination learning. Some authors have proposed that contexts might operate hierarchically on CS-US associations, whereas others have proposed that the context plus the CS might be processed configurally. In the present article, we report the results of two experiments that assessed the role of context on pigeons' conditional discrimination learning. In Experiment 1, we found that our pigeons' responding was inconsistent with hierarchical processing; instead, they may have either relied on local features or on configural compounds comprising the context and the discriminative stimulus presented on each trial. In Experiment 2, we precluded the possibility of using local features by requiring the pigeons to attend to both of the compounds that were simultaneously presented on each trial to solve the task. Methodological and theoretical issues are discussed in light of this work. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Rescorla-Wagner Model: The culmination of Hume's theory of causation.

The associative learning theory of Robert Rescorla and Allan Wagner has been duly celebrated for its 50-year reign as the predominant model in learning science. One special recognition is warranted: its close correspondence with David Hume's associative theory of causality judgment. Hume's rules by which causes come to suggest effects are not only embraced by the Rescorla-Wagner model, but their mechanistic account makes precise quantitative predictions that can be assessed by empirical evidence rather than by speculation and argumentation. Framed in this way, the Rescorla-Wagner model truly represents the scientific culmination of Hume's philosophical theory of causation. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

The Lords of the Rings: People and pigeons take different paths mastering the concentric-rings categorization task.

COVIS (COmpetition between Verbal and Implicit Systems; Ashby, Alfonso-Reese, & Waldron, 1998) is a prominent model of categorization which hypothesizes that humans have two independent categorization systems - one declarative, one associative - that can be recruited to solve category learning tasks. To date, most COVIS-related research has focused on just two experimental tasks: linear rule-based (RB) tasks, which purportedly encourage declarative rule use, and linear information-integration (II) tasks, which purportedly require associative learning mechanisms. We introduce and investigate a novel alternative: the concentric-rings task, a nonlinear category structure that both humans and pigeons can successfully learn and transfer to untrained exemplars. Yet, despite their broad behavioral similarities, humans and pigeons achieve their successful learning through decidedly different means. As predicted by COVIS, pigeons appear to rely solely on associative learning mechanisms, whereas humans appear to initially test but subsequently reject unidimensional rules. We discuss how variants of our concentric-rings task might yield further insights into which category-learning mechanisms are shared across species, as well as how categorization strategies might change throughout training.

It's not all the same to pigeons: Representations of difference may be shared across species.

Pigeons readily learn and transfer same-different discriminations in a variety of experimental paradigms. However, strategically designed probe tests suggest that they might only represent sameness. Here, we provide the first direct evidence that pigeons also represent difference. We first trained pigeons on a conditional same-different discrimination; then, on probe trials, we replaced either the same-item pair or the different-item pair with a familiar, but ambiguous stimulus. On different-cued probe trials, pigeons' choices were controlled by sameness: they reliably rejected the same-item pair, but they did not reliably select the different-item pair. Conversely, on same-cued probe trials, pigeons' choices were controlled by difference: they reliably rejected the different-item pair, but they did not reliably select the same-item pair. Together, these findings demonstrate that pigeons can represent both sameness and difference, providing an important clue to elucidating the evolutionary origins of same-different conceptualization.

Comparative cognition-Conceptual and methodological advancements.

This special issue originally placed a Call for Papers that emphasized the importance of "Conceptual and Methodological" advances in the field of Comparative Cognition. Represented here is a collection of 14 papers that helps to display some of the diversity of ideas and approaches within this flourishing research area. The first paper in this issue, by Gazes and Lazareva (2021), discusses transitive inference learning from the perspectives of: identifying the problems of contextual variables in studying different species; whether associative processes can or cannot fully account for the behavior and, if not, what alternative representational mechanisms might be at work; and, finally, how ecological considerations may support comparative research by suggesting novel theoretical and empirical questions. The next paper, by Loy et al. (2021) investigates questions related to the complexity of learning in invertebrate species, single-celled organisms, and plants. The paper by Rawlings et al. (2021) reviews the literature on cumulative cultural evolution, primarily in nonhuman primate species, and critically evaluates the importance of identifying the essential conceptual and methodological issues in what many have deemed to be a uniquely human form of behavior. The paper by Goto and Watanabe (2021) explores whether the mouse visual system is sensitive to Gestalt principles, using operant discrimination learning tasks similar to those used previously to document Gestalt processing in chimpanzees and humans. Qadri and Cook (2021) use the innovative approach of "adaptive genetic algorithms" to assess the relative importance of different features of a stimulus in controlling organisms' discrimination learning performance. Wittek et al. (2021) introduce a novel method for studying the importance of visual accumulation processes in pigeons when information is presented to a single hemisphere at a time. The paper by Cowie et al. (2021) focuses on a misallocation model of two-step sequence learning in young children and explores from a behavioranalytic viewpoint the implications of assuming that reinforcement might be misattributed to a misremembered response at the beginning of the behavioral sequence. The paper by López-Tolsa and Pellón (2021) explores whether the opportunity to display schedule-induced drinking as an early response within a behavioral sequence might alter the accuracy of temporal control in different-length fixed-interval schedule tasks with rats. Crystal (2021) reviews the literature examining episodic memory in nonhuman species and considers a variety of criteria and methods thought to be crucial for establishing empirical evidence for episodic memory in nonhumans, in general, and rats, in particular. Vila et al. (2021) discuss the use a novel 'hide-and-seek' task in preschool age children to study episodic-like memory; their work illustrates how memory dynamics can change over time in a manner not very unlike what has been demonstrated in other nonhuman research paradigms. The paper by Krichbaum et al. (2021) discusses some of the methodological difficulties one faces in studying spatial cognition in canines. The paper by Castro et al. (2021) uses a complex categorization learning task in which different sets of display features are diagnostic, or not, of category mastery depending upon context. The paper by Vernouillet et al. (2021) explores the formation of same/different concept learning in two species of corvids (pinyon jays and California scrub jays). The final paper, by Lazarowski et al. (2021) examines the possibility of abstract same/different learning in canines using a trial-unique training matching-to-sample procedure with olfactory stimuli. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Two-item conditional same-different categorization in pigeons: Finding differences.

Research on same-different categorization has shown that mastery of tasks of this kind can be strongly affected by the number of items in the training arrays-for both humans and nonhuman animals. Evidence for two-item same-different categorization in pigeons is decidedly mixed: although some investigations have succeeded, others have failed. To date, no research has documented successful conditional same-different categorization using just two items, nor has research explored how pigeons' responses in this paradigm might be influenced by perceptual characteristics of the training stimuli. Through a series of methodological modifications, we provide the first successful documentation that pigeons can perform two-item conditional same-different categorization to a high degree of accuracy; further, they can do so without the support of item repetition. We also show for the first time that the perceptual disparity between the items in pairs of different stimuli plays a key part in pigeons' same-different categorization performance. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Prelimbic cortex maintains attention to category-relevant information and flexibly updates category representations.

Category learning groups stimuli according to similarity or function. This involves finding and attending to stimulus features that reliably inform category membership. Although many of the neural mechanisms underlying categorization remain elusive, models of human category learning posit that prefrontal cortex plays a substantial role. Here, we investigated the role of the prelimbic cortex (PL) in rat visual category learning by administering excitotoxic lesions before category training and then evaluating the effects of the lesions with computational modeling. Using a touchscreen apparatus, rats (female and male) learned to categorize distributions of category stimuli that varied along two continuous dimensions. For some rats, categorizing the stimuli encouraged selective attention towards a single stimulus dimension (i.e., 1D tasks). For other rats, categorizing the stimuli required divided attention towards both stimulus dimensions (i.e., 2D tasks). Testing sessions then examined generalization to novel exemplars. PL lesions impaired learning and generalization for the 1D tasks, but not the 2D tasks. Then, a neural network was fit to the behavioral data to examine how the lesions affected categorization. The results suggest that the PL facilitates category learning by maintaining attention to category-relevant information and updating category representations.

Pigeons proficiently switch among four tasks without cost.

Both humans and pigeons are highly adept at task switching. However, unlike humans, pigeons do not show measurable switch costs: decreased accuracy and/or increased response times when required to switch tasks on successive trials. This striking disparity suggests that humans and pigeons may succeed at task switching via different means: humans may rely on a combination of executive control and associative learning, whereas pigeons may rely solely on associative learning. Here, we further explored the limits of pigeons' associative learning in an expanded task-switching paradigm. We trained pigeons to switch among four tasks, each signaled by two redundant types of task cues. The pigeons benefited from the availability of both task cues despite their redundancy: their accuracies were higher when both cues were available than when only a single cue was available. Additionally, we assessed the possibility that the lack of switch costs reported in the pigeon literature might stem from methodological discrepancies between pigeon and human task-switching paradigms. Across experimental phases, we modified pigeons' trial structures to more closely mimic those typically used in human task-switching research. Despite these modifications, pigeons did not display switch costs, consistent with their sole reliance on associative learning. Overall, our data highlight the power and flexibility inherent in the pigeon's associative learning system. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Should I stay or should I go? Pigeons' (Columba livia) performance of a foraging task has implications for optimal foraging theory and serial pattern learning.

Optimal foraging theory suggests that animals have evolved to maximize their net rate of energy intake; all things being equal, they should leave a current depleting patch when an alternative patch would provide either more or sooner food. In nature, however, typically all things are not equal. For example, uncertainty about the value of alternative patches, time to travel to those patches, and potential dangers incurred in changing patches may delay leaving the depleting patch, when it would otherwise be optimal to do so. We tested the hypothesis that leaving the current patch may be delayed, by providing pigeons (Columba livia) with a continuous choice between a progressive schedule, in which each access to food could be obtained with an increasing number of pecks, and a multiple schedule, in which a colored light signaled the number of pecks required for food. The pigeons could switch from the progressive schedule to the multiple schedule at any time. We asked if pigeons would tend to switch when the signaled multiple schedule required fewer pecks than the next reinforcer provided by the progressive schedule. We found that pigeons tended to switch to the multiple schedule sooner than would have been optimal-one might say they precrastinated. We propose that, on the progressive schedule, the signal to switch was not just the number of pecks required for the next reinforcer but also the more general cue that reinforcement was becoming more difficult to obtain-a form of serial pattern learning. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Assessing Attention in Category Learning by Animals.

Appreciating that varied stimuli belong to different categories requires that attention be differentially allocated to relevant and irrelevant features of those stimuli. Such selective attention ought to be definable and measurable in both humans and nonhuman animals. We first discuss the definition and methods of assessing attention in animals. We then introduce new experimental and computational tools for assessing attention in pigeons both during and after category learning. Deploying these tools, we have found that, like humans, pigeons attend more to relevant than to irrelevant stimulus features during category learning. Nonetheless, unlike humans, post-acquisition assessment reveals that pigeons less selectively attend to deterministic than to probabilistic features of category members, indicating that pigeons' attention is more distributed. Fresh opportunities now exist for more effectively understanding the evolution and mechanisms of categorical cognition.

Selective and distributed attention in human and pigeon category learning.

Attention to relevant stimulus features in a categorization task helps to optimize performance. However, the relationship between attention and categorization is not fully understood. For example, even when human adults and young children exhibit comparable categorization behavior, adults tend to attend selectively during learning, whereas young children tend to attend diffusely (Deng & Sloutsky, 2016). Here, we used a comparative approach to investigate the link between attention and categorization in two different species. Given the noteworthy categorization ability of avian species, we compared the attentional profiles of pigeons and human adults. We gave human adults (Experiment 1) and pigeons (Experiment 2) a categorization task that could be learned on the basis of either one deterministic feature (encouraging selective attention) or multiple probabilistic features (encouraging distributed attention). Both humans and pigeons relied on the deterministic feature to categorize the stimuli, albeit humans did so to a much greater degree. Furthermore, computational modeling revealed that most of the adults exhibited maximal selectivity, whereas pigeons tended to distribute their attention among several features. Our findings indicate that human adults focus their attention on deterministic information and filter less predictive information, but pigeons do not. Implications for the underlying brain mechanisms of attention and categorization are discussed.

Bidirectional conditioning: Revisiting Asratyan's 'alternating' training technique.

The study of bidirectional conditioning began more than a century ago, yet it has failed to take strong root in psychology and neuroscience. We revisit this topic by exploiting E. A. Asratyan's alternating procedure of stimulus presentation, in which both forward (e.g., A â†’ B) and backward (e.g., B â†’ A) training trials are concurrently given, in order to analyze their potential interaction. Specifically, using a two-alternative, forced-choice task, we trained humans and pigeons to learn associations between stimuli depending on whether they were presented as sample stimuli or choice stimuli. Trials were selected from an associative network in which forward and backward associations between sample and choice stimuli were synergistic (bidirectional network) or from an associative network in which these associations were not synergistic (unidirectional network). Humans were faster to learn associations from the bidirectional network than from the unidirectional network; additionally, they performed poorly on unidirectional trials that allowed for the expression of (incorrect) bidirectional associations. Unlike humans, pigeons showed no evidence of bidirectional associations. The reasons for this species difference as well as future directions for research deploying Asratyan's two-way training technique are discussed.

Taking pigeons to heart: Birds proficiently diagnose human cardiac disease.

In two experiments, we trained pigeons (Columba livia) to sort visual images (obtained by clinical myocardial perfusion imaging techniques) depicting different degrees of human cardiac disfunction (myocardial hypoperfusion of the left ventricle) into normal and abnormal categories by providing food reward only after correct choice responses. Pigeons proved to be highly proficient at categorizing pseudo-colorized images as well as highly sensitive to the degree of the perfusion deficit depicted in the abnormal images. In later testing, the pigeons completely transferred discriminative responding to novel stimuli, demonstrating that they had fully learned the normal and abnormal categories. Yet, these pigeons failed to transfer discriminative responding to grayscale images containing no color information. We therefore trained a second cohort of pigeons to categorize grayscale image sets from the outset. These birds required substantially more training to achieve similar levels of performance. Yet, they too completely transferred discriminative responding to novel stimuli by relying on both global and local disparities in brightness between the normal and abnormal images. These results confirm that pseudo-colorization can enhance pigeons' categorization of human cardiac images, a result also found with human observers. Overall, our findings further document the potential of the pigeon as a useful aide in studies of medical image perception.

Pigeons exhibit flexibility but not rule formation in dimensional learning, stimulus generalization, and task switching.

A prominent model of categorization (Ashby, Alfonso-Reese, Turken, & Waldron, 1998) posits that 2 separate mechanisms-one declarative, one associative-can be recruited in category learning. These 2 systems can effectively be distinguished by 2 task structures: rule-based (RB) tasks are unidimensional and encourage analytic processing, whereas information-integration (II) tasks are bidimensional and encourage nonanalytic associative learning. Humans and nonhuman primates have been reported to learn RB tasks more quickly than II tasks; however, pigeons and rats have shown no learning speed differences are thus believed to lack the declarative system. In the present trio of experiments, we further explored pigeons' dimensional category learning. We replicated the finding that pigeons learn RB and II tasks at equal speeds. Further, we found that stimulus generalization performance was equivalent on both tasks. We also explored the effect of switching from one task to another. Task switches between phases of training as well as within individual training sessions posed little difficulty for pigeons; they quickly and flexibly switched their categorization responses with no cost in choice speed or accuracy. Together, our data indicate that, although pigeons may lack the capacity to form explicit dimensional rules, their associative learning system is both powerful and flexible. Further exploration of this associative system would help us better appreciate possible contributions of the declarative system. (PsycInfo Database Record (c) 2020 APA, all rights reserved).