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.

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.

Selective attention in rat visual category learning.

A prominent theory of category learning, COVIS, posits that new categories are learned with either a declarative or procedural system, depending on the task. The declarative system uses the prefrontal cortex (PFC) to learn rule-based (RB) category tasks in which there is one relevant sensory dimension that can be used to establish a rule for solving the task, whereas the procedural system uses corticostriatal circuits for information integration (II) tasks in which there are multiple relevant dimensions, precluding use of explicit rules. Previous studies have found faster learning of RB versus II tasks in humans and monkeys but not in pigeons. The absence of a learning rate difference in pigeons has been attributed to their lacking a PFC. A major gap in this comparative analysis, however, is the lack of data from a nonprimate mammalian species, such as rats, that have a PFC but a less differentiated PFC than primates. Here, we investigated RB and II category learning in rats. Similar to pigeons, RB and II tasks were learned at the same rate. After reaching a learning criterion, wider distributions of stimuli were presented to examine generalization. A second experiment found equivalent RB and II learning with wider category distributions. Computational modeling revealed that rats extract and selectively attend to category-relevant information but do not consistently use rules to solve the RB task. These findings suggest rats are on a continuum of PFC function between birds and primates, with selective attention but limited ability to utilize rules relative to primates.

Precrastination: The fierce urgency of now.

Procrastination is a familiar and widely discussed proclivity: postponing tasks that can be done earlier. Precrastination is a lesser known and explored tendency: completing tasks quickly just to get them done sooner. Recent research suggests that precrastination may represent an important penchant that can be observed in both people and animals. This paper reviews evidence concerned with precrastination and connects that evidence with a long history of interest in anticipatory learning, distance reception, and brain evolution. Discussion unfolds to encompass several related topics including impulsivity, planning, and self-control. Precrastination may be a new term in the psychological lexicon, but it may be a predisposition with an extended evolutionary history. Placing precrastination within the general rubric of anticipatory action may yield important insights into both adaptive and maladaptive behavior.

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.

Nonhuman sequence learning findings argue against Hoerl and McCormack's two systems of temporal cognition.

Hoerl & McCormack propose that animals learn sequences through an entrainment-like process, rather than tracking the temporal addresses of each event in a given sequence. However, past research suggests that animals form "temporal maps" of sequential events and also comprehend the concept of ordinal position. These findings suggest that a clarification or qualification of the authors' hypothesis is needed.

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.

Capuchin monkeys can make and use stone tools.

Scientists hoping to elucidate the origin of human stone tool manufacture and use have looked to extant primate species for possible clues. Although some skepticism has been raised, there is clear evidence that today's capuchin monkeys can make and use stone tools.

Face facts: Even nonhuman animals discriminate human faces.

Humans are commonly believed to have evolved specially adapted neural systems for processing the rich and complex content of faces. However, nonhuman animals-including fish-have also shown a well-developed capacity for discriminating human faces, raising important questions concerning the uniqueness and mechanisms of human face perception.

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.

Using the reassignment procedure to test object representation in pigeons and people.

In four experiments, we evaluated Lea's (1984) reassignment procedure for studying object representation in pigeons (Experiments 1-3) and humans (Experiment 4). In the initial phase of Experiment 1, pigeons were taught to make discriminative button responses to five views of each of four objects. Using the same set of buttons in the second phase, one view of each object was trained to a different button. In the final phase, the four views that had been withheld in the second stage were shown. In Experiment 2, pigeons were initially trained just like the birds in Experiment 1. Then, one view of each object was reassigned to a different button, now using a new set of four response buttons. In Experiment 3, the reassignment paradigm was again tested using the number of pecks to bind together different views of the same object. Across all three experiments, pigeons showed statistically significant generalization of the new response to the non-reassigned views, but such responding was well below that to the reassigned view. In Experiment 4, human participants were studied using the same stimuli and task as the pigeons in Experiment 1. People did strongly generalize the new response to the non-reassigned views. These results indicate that humans, but not pigeons, can employ a unified object representation that they can flexibly map to different responses under the reassignment procedure.

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.

Validating the virtual string task with the gap test.

Relational concepts-such as connectedness-may be easy for human adults to appreciate; but, obtaining evidence of other species' understanding of connectedness has been challenging. One key test of connectedness involves an organism's responding to variants of the string task. Using a virtual string task, we gave pigeons a pair of strings from which to choose: one connected to a full dish of food and a second disconnected from another full dish of food. Our pigeons did not at first choose the connected string under conditions of non-differential reinforcement; later, the birds rapidly learned to choose the connected string under conditions of differential reinforcement. Our results replicate prior findings with real strings and food dishes, thereby demonstrating that pigeons can appreciate the connectedness between a string tether and a dish of food, and attesting to the utility and fidelity of the virtual string task.

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.

Information-seeking behavior: exploring metacognitive control in pigeons.

Metacognitive control may occur if an organism seeks additional information when the available information for solving a problem is inadequate. Such information-seeking behavior has been documented in primates, but evidence of analogous behavior is less convincing in non-primates. In our study, we adopted a novel methodological approach. We presented pigeons with visual discriminations of varying levels of difficulty, and on special testing trials, we gave the birds the opportunity of making the discrimination easier. We initially trained pigeons on a discrimination between same and different visual arrays, each containing 12 items (low difficulty), 4 items (intermediate difficulty), or 2 items (high difficulty). We later provided an "Information" button that the pigeons could peck to increase the number of items in the arrays, thereby making the discrimination easier, plus a "Go" button which, when pecked, simply allowed the pigeons to proceed to their final discriminative response. Critically, our pigeons' choice of the "Information" button increased as the difficulty of the task increased. As well, some of our pigeons showed evidence of prompt and appropriate transfer of using the "Information" button to help them perform brand-new brightness and size discrimination tasks. Speculation as to the contents of pigeons' private mental states may be unwarranted, but our pigeons did objectively exhibit the kind of complex, flexible, and adaptive information-seeking behavior that is deemed to be involved in metacognitive control.

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.

Same-different categorization in rats.

Same-different categorization is a fundamental feat of human cognition. Although birds and nonhuman primates readily learn same-different discriminations and successfully transfer them to novel stimuli, no such demonstration exists for rats. Using a spatial discrimination learning task, we show that rats can both learn to discriminate arrays of visual stimuli containing all same from all different items and transfer this discrimination to arrays composed of novel visual items. These results are consistent with rats' engaging in same-different categorization. As such, they pave the way for investigations into the perceptual, cognitive, and neurobiological substrates of abstract categorization behavior.

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.