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).

Focusing and shifting attention in pigeon category learning.

Adaptively and flexibly modifying one's behavior depending on the current demands of the situation is a hallmark of executive function. Here, we examined whether pigeons could flexibly shift their attention from one set of features that were relevant in one categorization task to another set of features that were relevant in a second categorization task. Critically, members of both sets of features were available on every training trial, thereby requiring that attention be adaptively deployed on a trial-by-trial basis based on contextual information. The pigeons not only learned to correctly categorize the stimuli but, as training progressed, they concentrated their pecks to the training stimuli (a proxy measure for attention) on those features that were relevant in a specific context. The pigeons selectively tracked the features that were relevant in Context 1-but were irrelevant in Context 2-and they selectively tracked the features that were relevant in Context 2-but were irrelevant in Context 1. This adept feature tracking requires disengaging attention from a previously relevant feature and shifting attention to a previously ignored feature on a trial-by-trial basis. Pigeons' adaptive and flexible performance provides strong empirical support for the involvement of focusing and shifting attention under exceptionally challenging training conditions. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Not all exceptions are created equal: Learning of exceptions in pigeons' categorization.

Learning of exceptions - those items that violate a known regularity - takes longer than learning of rule-following items. Studies reporting this disparity have used exceptions that share most of their features with members of the opposite category (crossover exceptions). Yet, exceptions can be distinctly different from members of their own category and other categories as well (oddball exceptions). Here, we trained two groups of pigeons to discriminate two categories containing regular and exception items. For one group, the exceptions were crossovers, whereas for the other, the exceptions were oddballs. Pigeons learned to classify the oddball exceptions faster than the crossover exceptions. Moreover, the regular items were learned more quickly than the crossover exceptions, but more slowly than the oddball exceptions. Deviation from the rule per se is not why exceptions are typically more difficult to learn. Rather, confusability with members of the opposite category hinders learning, whereas distinctiveness facilitates learning.

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.

The role of category density in pigeons' tracking of relevant information.

Prior categorization studies have shown that pigeons reliably track features that are relevant to category discrimination. In these studies, category exemplars contained two relevant and two irrelevant features; therefore, category density (specifically, the relevant to irrelevant information ratio) was relatively high. Here, we manipulated category density both between and within subjects by keeping constant the amount of relevant information (one feature) and varying the amount of irrelevant information (one or three features). One group of pigeons started with low-density training, then proceeded to high-density training, and finally returned to low-density training (Low-High-Low); a second group of pigeons started with high-density training and then proceeded to low-density training (High-Low). The statistical density of the category exemplars had a large effect on pigeons' performance. Training with high-density exemplars greatly benefitted category learning. Accuracy rose faster and to a higher level with high-density training than with low-density training; the percentage of relevant pecks showed a very similar pattern. In addition, high-density training (in the Low-High-Low group) led to an increase in performance on the more difficult low-density task, an observation reminiscent of the easy-to-hard effect. These results illuminate factors affecting pigeons' accuracy and tracking of relevant information in visual categorization.

Cognitive flexibility and memory in pigeons, human children, and adults.

This work examines cognitive flexibility using a comparative approach. Pigeons (Experiment 1), human children (Experiment 2a), and human adults (Experiment 2b) performed a task that required changing responses to the same stimuli twice across the experiment. The results indicate that all three groups demonstrated robust memory for learned information. In addition, pigeons showed comparable and substantial perseveration following both response shifts. In contrast, both children and adults exhibited some perseveration following a first response shift, while exhibiting no cost following the second response shift. These findings are discussed in relation to memory-based theories of cognitive flexibility, according to which perseveration occurs as a result of competition between long-term and working memory, revealing important differences in memory and cognitive flexibility between species.

Dorsal hippocampus is necessary for visual categorization in rats.

The hippocampus may play a role in categorization because of the need to differentiate stimulus categories (pattern separation) and to recognize category membership of stimuli from partial information (pattern completion). We hypothesized that the hippocampus would be more crucial for categorization of low-density (few relevant features) stimuli-due to the higher demand on pattern separation and pattern completion-than for categorization of high-density (many relevant features) stimuli. Using a touchscreen apparatus, rats were trained to categorize multiple abstract stimuli into two different categories. Each stimulus was a pentagonal configuration of five visual features; some of the visual features were relevant for defining the category whereas others were irrelevant. Two groups of rats were trained with either a high (dense, n = 8) or low (sparse, n = 8) number of category-relevant features. Upon reaching criterion discrimination (≥75% correct, on 2 consecutive days), bilateral cannulas were implanted in the dorsal hippocampus. The rats were then given either vehicle or muscimol infusions into the hippocampus just prior to various testing sessions. They were tested with: the previously trained stimuli (trained), novel stimuli involving new irrelevant features (novel), stimuli involving relocated features (relocation), and a single relevant feature (singleton). In training, the dense group reached criterion faster than the sparse group, indicating that the sparse task was more difficult than the dense task. In testing, accuracy of both groups was equally high for trained and novel stimuli. However, both groups showed impaired accuracy in the relocation and singleton conditions, with a greater deficit in the sparse group. The testing data indicate that rats encode both the relevant features and the spatial locations of the features. Hippocampal inactivation impaired visual categorization regardless of the density of the category-relevant features for the trained, novel, relocation, and singleton stimuli. Hippocampus-mediated pattern completion and pattern separation mechanisms may be necessary for visual categorization involving overlapping irrelevant features.

Unsupervised learning of complex associations in an animal model.

Supervised learning results from explicit corrective feedback, whereas unsupervised learning results from statistical co-occurrence. In an initial training phase, we gave pigeons an unsupervised learning task to see if mere pairing could establish associations between multiple pairs of visual images. To assess learning, we administered occasional testing trials in which pigeons were shown an object and had to choose between previously paired and unpaired tokens. Learning was evidenced by preferential choice of the previously unpaired token. In a subsequent supervised training phase, learning was facilitated if the object and token had previously been paired. These results document unsupervised learning in pigeons and resemble statistical learning in infants, suggesting an important parallel between human and animal cognition.

Feature predictiveness and selective attention in pigeons' categorization learning.

Prior categorization studies have shown that pigeons reliably track features that are perfect predictors of category membership (Castro & Wasserman, 2014, 2016a). One might further ask whether pigeons would also track features that are relevant, but imperfect predictors of category membership. In our present project, pigeons had to categorize multiple exemplars from 2 different artificial categories, in which the exemplars were composed of 4 different features that were associated with 1 of 2 different report responses. Each exemplar contained 1 feature that perfectly predicted category membership; 1 feature that imperfectly predicted category membership; and, 2 irrelevant features that did not predict category membership. We monitored pigeons' choice accuracy as well as the location of their pecks to each of the 4 exemplar features to determine to which attributes the birds attended. As categorization accuracy rose, pecks to the perfect predictor of each category rose as well. Pigeons also showed evidence of attending more to the imperfect predictor than to the irrelevant features, but to a lesser degree. Overall, our results provide evidence of selective attention in pigeons' categorization behavior. (PsycINFO Database Record

Chrysippus's pigeon: Exclusion-based responding in an avian model.

Inference by exclusion can be exhibited by deductively responding to new stimuli that are presented in the context of familiar stimuli. We investigated exclusion-based responding in pigeons using a 2-alternative forced-choice discrimination task. In Phase 1, pigeons learned to associate 2 stimuli (A and B) with Response 1 and 2 stimuli (C and D) with Response 2. Following successful acquisition of these stimulus-response pairings, pigeons advanced to Phase 2, in which stimuli A and B were now reassigned to Response 2. Based on their Phase 1 training, pigeons should initially choose Response 1 when presented with A and B in Phase 2 (this response is now incorrect, but the birds would not yet have had the opportunity to learn the new stimulus-response associations). Also, in Phase 2, stimuli E and F-new stimuli replacing stimuli C and D-were concurrently presented and assigned to Response 1. Without prior training, pigeons' initial responding to E and F in Phase 2 should be at chance. However, if the pigeons were to apply an exclusion rule (stimuli E and F stand in opposition to stimuli A and B), then they might initially choose Response 2 for new stimuli E and F because they are concurrently choosing Response 1 for stimuli A and B. If that is the case, then choice accuracy for stimuli E and F should also be below chance. Indeed, our pigeons responded at reliably below chance levels to stimuli E and F, consistent with their exhibiting an exclusion rule-based strategy, which could actually arise from a more mechanical underlying process such as acquired equivalence formation. (PsycINFO Database Record

Executive control and task switching in pigeons.

Flexibly adjusting one's behavior depending on the task at hand is a hallmark of executive function. In two experiments, we explored pigeons' cognitive flexibility to concurrently perform two complex categorization tasks: a numerosity discrimination (where number was the relevant dimension and variability was the irrelevant dimension) and a variability discrimination (where variability was the relevant dimension and number was the irrelevant dimension). The flexibility of pigeons' behavior was evidenced by their rapid, on-demand switching between tasks within training sessions. In addition, in Experiment 1, pigeons more accurately performed the numerosity task with arrays of different stimuli than with arrays of same stimuli and they more accurately performed the variability task with arrays of 16 stimuli than with arrays of 6 stimuli. In Experiment 2, when the magnitudes of the relevant and irrelevant dimensions were congruent, pigeons' accuracy was higher than when the magnitudes were incongruent. Thus, the irrelevant dimension facilitated target discrimination performance when its magnitude matched the magnitude of the correct choice. These cross-task interactions suggest that a common computational mechanism underlies both discriminations. Pigeons' cognitive complexity and flexibility-even in the absence of a prefrontal cortex-indicates that other avian brain areas can support behaviors emblematic of executive functioning.

Anterior cingulate cortex inactivation impairs rodent visual selective attention and prospective memory.

Previous studies showed that the anterior cingulate cortex (ACC) plays a role in selective visual attention. The current study further examined the role of the ACC in attention using a visual cuing task with task-relevant and task-irrelevant stimuli. On every trial, 2 stimuli were presented on the touchscreen; 1 was task-relevant and the other was task-irrelevant. Rats were trained to attend to the task-relevant stimulus over the task-irrelevant stimulus to determine which side of the touchscreen should be selected for reward. After the rats were well-trained, cannulas targeting the ACC were implanted bilaterally for infusions of PBS or muscimol. When the ACC was functionally intact, high task performance was correlated with the anticipatory touches toward the reward; rats touched the stimulus proximal to the correct side more often, regardless of its task-relevancy. Analysis of the presurgery training data showed that rats developed anticipatory touches during training. Linear discriminant analyses of the touches also showed that the touches predict rats' choices in trials. With muscimol infusions, choice accuracy was impaired and the anticipatory touches toward the correct response location were less frequent. A control experiment, in which there were no irrelevant stimuli, showed no effects of ACC inactivation on choice accuracy or anticipatory touches. These results indicate that the rat ACC plays a critical role in reducing distraction from irrelevant stimuli as well as in guiding attention toward the goal locations.

Attentional shifts in categorization learning: Perseveration but not learned irrelevance.

Once a categorization task has been mastered, if features that once were relevant become irrelevant and features that once were irrelevant become relevant, a decrement in performance-a shift cost-is typically observed. This shift cost may reflect the involvement of two distinguishable factors: the inability to release attention from a previously relevant feature (i.e., attentional perseveration) and/or the inability to re-engage attention to a previously irrelevant feature (i.e., learned irrelevance). Here, we examined the nature of this shift cost in pigeons. We gave four groups of pigeons a categorization task in which we monitored their choice accuracy; at the same time, we tracked the location of their pecks to the relevant and irrelevant attributes of the stimuli to determine to which attributes the birds were attending during the course of learning. After identical training in Phase 1, the roles of the relevant/irrelevant features were changed in Phase 2, so that one group could show only learned irrelevance, a second group could show only attentional perseverance, a third group could show both, and a fourth control group could show neither of these effects. Results disclosed evidence of attentional perseverance, but no evidence of learned irrelevance, either in accuracy or in relevant feature tracking. In addition, we determined that pigeons' allocation of attention to the relevant features followed rather than preceded an increase in choice accuracy. Overall, our findings are best explained by theories which propose that attention is learned and deployed to those features that prove to be reliable predictors of the correct categorization response (e.g., George and Pearce, 2012; Kruschke, 2001; Mackintosh, 1975).

Object-specific and relational learning in pigeons.

Abstract or relational stimulus processing requires an organism to appreciate the interrelations between or among two or more stimuli (e.g., same or different, less than or greater than). In the current study, we explored the role of concrete and abstract information processing in pigeons performing a visual categorization task which could be solved by attending to either the specific objects presented or the relation among the objects. In Experiment 1, we gave pigeons three training phases in which we gradually increased the variability (that is, the number of object arrays) in the training set. In Experiment 2, we trained a second group of pigeons with an even larger number of object arrays from the outset. We found that, the larger the variability in the training exemplars, the lesser the pigeons' attention to object-specific information and the greater their attention to relational information; nevertheless, the contribution of object-specific information to categorization performance was never completely eliminated. This pervasive influence of object-specific information is not peculiar to animals, but has been observed in young children and human adults as well.

Pigeons' tracking of relevant attributes in categorization learning.

Most theories and experimental investigations of discrimination learning and categorization, in both humans and animals, hypothesize that attention must be allocated to the relevant attributes of the training stimuli for learning to occur. Attention has conventionally been inferred after learning has transpired rather than examined while learning is transpiring. We presented pigeons with a visual categorization task in which we monitored their choice accuracy through their responses to different report buttons; critically, we tracked the location of the pigeons' pecks to both the relevant and irrelevant attributes of the training stimuli using touchscreen technology, in order to find out where the birds may have been attending during the course of categorization learning. Pigeons readily mastered the categorization task; most importantly, as training progressed, they increasingly concentrated their pecks on the relevant features of the category exemplars, suggesting that the birds were tracking the relevant information to solve the task. When either new irrelevant features were introduced (Experiment 1) or when new relevant features were introduced and later the discriminative value of these new relevant features was reversed (Experiment 2), pigeons' choice accuracy and peck tracking were strongly affected. These results help elucidate the dynamics and interplay of attention and learning; they also suggest that peck tracking can be a suitable measure of the allocation of attention in pigeons, much as eyetracking is deemed to be a suitable measure of attention in humans.

Pigeons exhibit contextual cueing to both simple and complex backgrounds.

Repeated pairings of a particular visual context with a specific location of a target stimulus facilitate target search in humans. We explored an animal model of this contextual cueing effect using a novel Cueing-Miscueing design. Pigeons had to peck a target which could appear in one of four possible locations on four possible color backgrounds or four possible color photographs of real-world scenes. On 80% of the trials, each of the contexts was uniquely paired with one of the target locations; on the other 20% of the trials, each of the contexts was randomly paired with the remaining target locations. Pigeons came to exhibit robust contextual cueing when the context preceded the target by 2s, with reaction times to the target being shorter on correctly-cued trials than on incorrectly-cued trials. Contextual cueing proved to be more robust with photographic backgrounds than with uniformly colored backgrounds. In addition, during the context-target delay, pigeons predominately pecked toward the location of the upcoming target, suggesting that attentional guidance contributes to contextual cueing. These findings confirm the effectiveness of animal models of contextual cueing and underscore the important part played by associative learning in producing the effect. This article is part of a Special Issue entitled: SQAB 2013: Contextual Con.

Effects of training condition on the contribution of specific items to relational processing in baboons (Papio papio).

Relational processing involves learning about the relationship between or among stimuli, transcending the individual stimuli, so that abstract knowledge generalizable to novel situations is acquired. Relational processing has been studied in animals as well as in humans, but little attention has been paid to the contribution of specific items to relational thinking or to the factors that may affect that contribution. This study assessed the intertwined effects of item and relational processing in nonhuman primates. Using a procedure that entailed both expanding and contracting sets of pictorial items, we trained 13 baboons on a two-alternative forced-choice task, in which they had to distinguish horizontal from vertical relational patterns. In Experiment 1, monkeys engaged in item-based processing with a small training set size, and they progressively engaged in relation-based processing as training set size was increased. However, in Experiment 2, overtraining with a small stimulus set promoted the processing of item-based information. These findings underscore similarities in how humans and nonhuman primates process higher-order stimulus relations.

Pigeons learn virtual patterned-string problems in a computerized touch screen environment.

For many decades, developmental and comparative psychologists have used a variety of string tasks to assess the perceptual and cognitive capabilities of human children of different ages and different species of nonhuman animals. The most important and widely used of these problems are patterned-string tasks, in which the organism is shown two or more strings, only one of which is connected to a reward. The organism must determine which string is attached to the reward and pull it. We report a new way to implement patterned-string tasks via a computerized touch screen apparatus. Pigeons successfully learned such virtual patterned-string tasks and exhibited the same general performance profile as animals given conventional patterned-string tasks. In addition, variations in the length, separation, and alignment of the strings reliably affected the pigeons' virtual string-pulling behavior. These results not only testify to the power and versatility of our computerized string task, but they also demonstrate that pigeons can concurrently contend with a broad range of demanding patterned-string problems, thereby eliminating many alternative interpretations of their behavior. The virtual patterned-string task may thus permit expanded exploration of other species and variables which would be unlikely to be undertaken either because of inadequacies of conventional methodology or sensorimotor limitations of the studied organisms.