The peak-end effect, in which evaluations of experiences are disproportionately influenced by their most intense, most recent, or final moments, is seen consistently in humans but inconsistently in nonhuman primates. Understanding in what species and contexts these biases appear can help us better understand the evolution of these decision-making biases. Previous evidence in monkeys is contradictory, likely due to differences in experimental procedures. Thus, to assess whether capuchin monkeys (Sapajus [Cebus] apella) exhibit such biases, we tested 14 individuals in a manual two-item food sequence task. Across conditions, monkeys consistently preferred to consume the higher value item first, showing a start bias rather than the end bias characteristic of human decision-making and seen in some other primate studies. This preference was strongest among low- and middle-ranking individuals. However, replacing the low-value item with a delay did not affect choices, suggesting that it was discounted or ignored when monkeys were making their decisions. We consider several explanations for why our monkeys show a start bias rather than an end bias, including possible methodological influences on their choices, and how this affects our understanding of the evolution of these biases. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Comments on an article by K. Ighalo & N. Miller (see record 2027-04636-001). In the context of numerous foragers in an environment, the story becomes more complicated. Now, many foragers searching for one cryptic prey type means less of those prey and a greater relative prevalence of other prey that may then be easier to identify by other foragers. As this process plays out and some foragers focus attention on some prey types because those are the ones they first encounter, other foragers then focus on other prey types because they are more prevalent as a result. This can lead to a reduction in competition among the foragers. The article by Ighalo and Miller is about exactly that kind of situation in which individual foragers engage in "attentional character displacement." Ighalo and Miller's model was based on a simplified version of Guided Visual Search, which proposes that individuals engage visual scenes by first processing basic features (such as color and size) across the entire field in parallel. These features are combined with the individual's goals to create a priority map that guides attention toward likely target locations. Ighalo and Miller predicted that attentional character displacement would reduce competition and improve success rates in their group of simulated foragers, and that each individual forager would experience this effect whether those foragers were able to modulate attention or not. They also predicted that this outcome would be modulated by other effects such as group size, the number of prey types available, and how cryptic the prey were. When the simulation included only two types of prey, Ighalo and Miller found that smaller groups foraged more successfully than larger groups, but it also was true that a higher proportion of attention-modulating foragers led to higher success rates across group sizes. What can be concluded is that a cognitive-ecological modeling approach such as that used by Ighalo and Miller shows that competition likely leads to the evolution of search images. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Gibbons (family Hylobatidae) are small apes comprising lar gibbons (Hylobates spp.), crested gibbons (Nomascus spp.), siamangs (Symphalangus syndactus), and hoolocks (Hoolock spp.). These four genera are closely related to one another and to orangutans (Pongo spp.). Gibbon phylogeny and socioecology make them uniquely suited to improve our understanding of the origins of personality factors. Personality trait ratings of lar gibbons, crested gibbons, and siamangs-sufficient data on hoolocks were not available-were analyzed using exploratory factor analyses. All three genera possessed factors labeled Dominance, Extraversion, and Agreeableness. In addition, lar gibbons and siamangs possessed factors labeled Neuroticism and Conscientiousness, lar gibbons possessed a factor labeled Individualism, and crested gibbons possessed factors labeled Dyscontrol and Avoidance. Exploratory factor analysis of the combined data, which included hoolocks, revealed a Conscientiousness factor and four factors-Extraversion, Dominance, Agreeableness, and Neuroticism-that resembled four of the five orangutan personality factors. Genus- and family-level analyses revealed that better subjective well-being and health-both measured using informant ratings-were associated with higher sociability, emotional stability, and conscientiousness. Based on these results, we concluded that social group size and/or arboreality are related to factor structure, Conscientiousness evolved in hominoids 16-20 million years ago (much earlier than previous estimates), and that relationships in humans between personality and psychological and physical well-being have very early origins. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
In animals, high fission-fusion dynamics (FFD) characterize groups in which individuals frequently split into subgroups of different size and composition. Through evolution, this might have led to an increase in specific cognitive skills that allowed individuals to better cope with the challenges they usually experience under such social conditions. This hypothesis has rarely been tested empirically, and therefore we compared 2 species of zebras to assess potential differences in their cognitive skills. The Chapman's zebras (Equus burchelli chapmanni) typically show lower levels of FFD associated with stable multilevel social groups, whereas Grevy's zebras (Equus grevyi) show higher levels of FFD and therefore live in less cohesive groups. We tested 8 Grevy's zebras and 5 Chapman's zebras in experimental tasks assessing their object permanence, short-term memory, inference, and quantity discrimination skills. Our results showed that Grevy's zebras, typically showing higher FFD, performed better than Chapman's zebras, which live in more cohesive groups, in tasks requiring complex inference skills and marginally in quantity discrimination skills. These findings provide preliminary support to the hypothesis that high FFD may be linked to the enhancement of specific cognitive skills also in taxa other than primates. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
This study examined whether saline acts as an aversive stimulus for planarians and how it influences learning and memory. Using saline as an unconditioned stimulus, we first tested conditioned place avoidance. Saline did not support conditioned place avoidance acquisition; instead, it disrupted habituation to initially preferred tactile and visual stimuli. Further experiments assessed the establishment of conditioned place preference using food as the reinforcer with visual cues. Following training, exposure to saline impaired the expression of conditioned place preference for both light and dark contexts, indicating that the disruptive effect of exposure to saline extends beyond habituation. These findings suggest that saline interferes with the expression of learned behaviors through state-dependent retrieval failure caused by physiological changes induced by saline exposure. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
The conjunction fallacy, a well-known cognitive bias, occurs when individuals erroneously judge the conjunction of 2 events as more probable than either event occurring independently (Tversky & Kahneman, 1983). Although this fallacy has been extensively studied in humans, recent research from our lab shows that nonhuman animals, such as rats, also demonstrate this bias (González, Sadeghi, et al., 2023). In González et al.'s study, rats were trained in a feature-positive/feature-negative go/no-go discrimination (A-/AX+; B+/BY-, where A and B were auditory cues and X and Y were visual cues, and + and-indicate that lever pressing was reinforced or not). At test, cues A and B were presented on probe trials with cues X and Y either unoccluded and off or occluded by a metal shield. Responding was low to A and high to B when the light was visible (and off). When the light was occluded, however, this pattern reversed, with high responding to A and low responding to B. This indicated a bias toward expecting the occluded light to be present rather than absent, consistent with a conjunction fallacy. In a go/no-go procedure, however, some trial types are rewarded, whereas others are unrewarded. This reward asymmetry may bias attention to the different cue conditions. Thus, the current study replicated this conjunction bias using a 2-alternative choice procedure where reinforcement was available on all trial types, removing this potential bias. Our demonstration of a strong conjunction fallacy replicated our prior results, setting the stage for parallel studies in rats and humans. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
English speakers respond more quickly to small numbers with a leftward response and large numbers with a rightward response, a phenomenon known as the spatial-numerical association of response codes (SNARC) effect. Two prevailing theories to explain the SNARC effect make contrasting predictions about individual variability. If the SNARC effect stems from stable long-term memory representations, participants in a culturally homogeneous population (e.g., college students in a Western, English-speaking country) should exhibit a culturally consistent left-to-right SNARC with low variability between individuals within a magnitude domain and within individuals across domains. Alternatively, if the effect arises from an online working memory strategy, participants may be expected to show greater variability both between and within individuals, across and within domains. We present the results of three within-subject experiments in which participants engaged in multiple SNARC tasks across eight magnitude domains. Across the three experiments and 17 task presentations, we consistently found substantial variation in the orientation of the relationship between magnitude and space, both within a magnitude domain and across domains, in a culturally homogeneous Western sample. These findings are more consistent with accounts positing a flexible, context-dependent strategy than with those proposing a stable mental number line as an explanation of the SNARC effect. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
The world is full of uncertainty, often requiring decisions that involve unknown outcomes. Responses to uncertainty, or risk, have been widely studied, revealing both species-level and individual differences. Risk studies have focused on a few key species, so to increase taxon diversity, we investigated the risk sensitivity of four female beluga whales (Delphinapterus leucas) living under human care. We presented them with two options that had identical mean value but differed in their respective variability. The safe option provided four fish every time it was selected, and the risky option provided either zero or eight fish with equal probability. Belugas' preferences varied, with two whales preferring the safe option and two whales preferring the risky option. Testing across morning and afternoon sessions revealed that satiation, assumed to be higher in the afternoon due to feeding schedules, exacerbated existing tendencies toward the safe option in two whales, but did not change any of the belugas' overall preferences. In addition, whales maintained their preferences irrespective of what they had received on the previous trial. Therefore, within individuals, neither short (previous trial) nor longer (time of day) term contexts influenced individuals' preferences, suggesting that these differences were stable. Our results emphasize the importance of considering individual differences in animal decision-making. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Comparative cognition can make itself more relevant to those who care largely (or entirely) about humans by making itself less WEIRD and less focused on humans. That feels nonintuitive, I know, but psychology has long wanted to find itself at the table with the so-called "hard" sciences, and those sciences have already addressed their WEIRDness largely because they have not wanted humans to be the main character in their story. This cannot be the goal for psychological science to take humans out of it entirely, or should it be. However, there is a fertile middle ground between humans always being the central character and instead sometimes being a "supporting" character in proper comparative perspective or perhaps in some cases not being a character at all (e.g., for some evolutionary questions in which humans are too distantly related to be relevant to the study of certain phylogenetic or mechanistic questions of closely related species). This approach can facilitate greater appreciation for the need to study cognition across cultures and across species (as well as other potential sentient entities such as those emerging in artificial intelligence). (PsycInfo Database Record (c) 2026 APA, all rights reserved).
In this study of mutual gaze (MG) and emotion, using multiple groups of chimpanzee infants to compare with multiple groups of human infants, we provide a methodology to assess two deeply rooted assumptions: (1) Psychological outcomes in chimpanzees are uninfluenced by socioecological conditions, and (2) samples from humans living in Western, middle-class family settings are adequate representatives of humankind. Even though MG is widely viewed as foundational for social cognition, and gaze becomes coordinated with emotion around 1 year of age, these topics have rarely been studied in 1-year-old chimpanzees. We studied four diverse chimpanzee groups-that is, 1-year-old infants living at Chester Zoo (n = 4), in Gombe National Park (n = 12), at the Primate Research Institute (n = 3), and in a human home (n = 2)-and compared them with three diverse groups of human 1-year-olds: urban-UK (n = 8), subsistence farming-Nso (n = 12), and foraging-Aka (n = 10). MG occurred 22% of the time and did not differ across groups or species. We found no species differences in any infant Emotion or in any MG-Emotion co-occurrence pattern. In three of five types of MG-Emotion co-occurrence, the Primate Research Institute chimpanzee infants differed from at least one of the other chimpanzee groups (we reject Assumption 1), and the UK infants differed from at least one of the other human groups (we reject Assumption 2). We conclude there are meaningful influences of socioecology on the functions of some social cognition outcomes, and, thus, it is necessary to sample multiple diverse groups to detect true species differences. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Exploration encompasses a range of behaviors aimed at gathering information about the environment, which is then encoded and stored in memory. Memory processes support exploration by retaining past experiences, facilitating habituation to novelty, and aiding in the formation and updating of cognitive maps. As aging often leads to changes in memory function, we expected these changes to be detected by analyzing exploratory behaviors. In our experiment, we investigated the behavior of male rats at 2 and 9 months of age. We found that young rats reacted to novel objects with greater intensity and spent more time in the zone where change was introduced. In addition, they moved between the zones more frequently than the older ones. There were no differences in habituation rate, and the reaction to novelty was typical for both ages. However, older rats exhibited higher grooming levels and spent more time in the starting box. The results indicate that basic memory functions are not impaired in older rats, but the level of emotional reactions is slightly elevated compared with measures taken at a young age, which may influence their performance and lead to decreased exploratory behavior. Our findings also suggest that the rats can retain memory traces of events that occurred months earlier and show familiarity with the experimental environment. Our research indicates that behavioral changes associated with memory decline in older individuals may be linked to alterations in emotional regulation. These changes appear to have a neurobiological foundation centered on the hippocampus, where distinct regions process anxiety responses alongside memory functions. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Dexterity, the flexible and precise control of objects, requires the integration of cognitive abilities, motor coordination, and anatomical specializations. Due to the evolutionary significance of the opposable thumb, dexterity research has traditionally focused on primate species. However, based on a review of current knowledge in parrot morphology, cognition, and neurobiology, we propose that parrots represent a highly promising model system for dexterity research. We highlight lineage-specific morphological novelties that turn the parrot beak-and-tongue apparatus into a multifunctional tool, draw comparisons between the parrot tongue and the primate thumb, and showcase existing studies on Goffin's cockatoos that reveal advanced tool-related problem-solving abilities. Characterized by fine motor control, pronounced interindividual variability, goal-directed behavior, flexibility, and the optimization of speed through learning, the Goffin's cockatoo model embodies the core components of dexterity. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Establishing interobserver reliability is a key step for asserting concordance in personality ratings. Yet, typical measures of reliability-such as intraclass correlation coefficients (ICCs)-are not just reflective of whether raters agree on subject variation. Rather, ICC estimates can be influenced by a multitude of data qualities such that high reliability need not demonstrate validity. I explored what our expectations are for ICCs based on the state of published studies' estimates and based on simulations built upon the typical properties of Likert ratings used for nonhuman assessments. I relied on the nonhuman primate personality literature, assembling ICC(3, 1) estimates from 34 publications. I conducted Bayesian meta-analyses, which demonstrate that ICC(3, 1) estimates showed a posterior estimate of 0.31, but that items exhibited high variability. This variability showed concordance with the underlying traits and dimensions, as well as taxonomic distinctions. Simulations, however, demonstrated the complexities of using ICC estimates as a measure of reliability. Furthermore, the simulations showed that neat threshold cutoffs are of poor utility without consideration of the properties of the data and system, namely, the number of raters and subjects, as well as distributions of the item scores. I provide recommendations based on expectations of these data. Nonhuman primate ICC estimates show reasonable values relative to expectations of reasonable true subject variation, in line with repeatability estimations from behavior, physiology, and expectations from human individual differences. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Emotional expressions play an important part in social communication of dogs and humans, but comparative studies between dogs and humans are rare. In addition, little is known about how emotions are perceived across species and how attention is divided among different parts of faces. Here, we compared the gazing behavior of dogs and adult humans toward emotional dog and human facial expressions. Dogs mostly gazed at the eye and nose areas, whereas the humans' focus also included the mouth area. The gazing behavior of both species was affected by the facial expressions and species presented, and they gazed at emotional more than neutral stimuli. Dogs and humans demonstrated attentional bias toward angry and happy eyes of their own species, which highlights the ecological salience of the species and the importance of eyes in reading conspecifics' emotional expressions. For both species, mouths of aggressive dogs were gazed at more than those of angry humans, whereas mouths of happy humans were gazed at more than happy dog mouths. Thus, the mouth area provides important emotional cues for recognizing emotions across species, suggesting the ecological salience of facial expressions connecting to the subcortical visual pathway across mammalian species. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Central to many contemporary theories of language development is the idea that humans possess species-specific cognitive adaptations for understanding directional social cues, whereas contrasting theoretical positions emphasize the influence of domain-general learning mechanisms on this comprehension. We sought to test whether presumptive domain-general learning was sufficient to instill the comprehension of pointing and other cues by asking just how much training is required to train 44 mature, captive chimpanzees to follow deictic cues, using both a complex set of social cues (pointing, head/body orientation, and verbal cue) and a nonsocial cue (an object adjacency). We found that successful performance on an object choice task-a commonly used measure of receptive joint attention capacity-required relatively little explicit training. Thus, if chimpanzees can acquire this understanding with relatively little experience, humans may also acquire receptive joint attention from their learning experiences.
Many species forage collectively, and this will shape how they search for prey. However, theories of visual attention and search image formation have not considered social foraging, and studies of collective foraging rarely consider cognitive constraints. Here, we connected these ideas and present an agent-based model of collective foraging on cryptic prey in agents that either can or cannot form search images. Agents focused on one prey type reduce its local density, biasing other agents to form search images for other prey types. This effect, attentional character displacement, may reduce competition, as foragers occupy separate regions of "attention-space." We found that the ability to modulate attention increases distance in attention-space and reduces competition, improving success rates. Agents that cannot modulate their attention benefit from foraging with those that can. We also found that some top-down control of search is critical to taking advantage of this effect. This cognitive-ecological approach to modeling collective foraging suggests that competition is a critical driver of the evolution of search images. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Probabilistic reasoning-the ability to predict outcomes based on the likelihood of different possibilities-is a key component of numerical cognition and is critical for navigating uncertain environments. However, it is unclear whether this capacity is shared with our closest relatives, the great apes, or with even more distantly related species such as the small apes. Here, we presented two gibbons (Nomascus leucogenys), two siamangs (Symphalangus syndactylus), and three chimpanzees (Pan troglodytes) with a proportional probability task requiring them to reason from the distribution of items in a population to the likely contents of a sample. In contrast to previous research, we ensured that participants could not rely on two salient heuristics-the absolute quantity of the preferred item or majority sampling-to solve the task. We found that individuals of all species were able to distinguish between 0% versus 50% and 50% versus 100%, and that two individuals (one chimpanzee and one siamang) were able to convincingly distinguish between 33% versus 67%. These results suggest that an antecedent to probabilistic reasoning was shared by a common ancestor of humans, great apes, and small apes. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Perceptual categorization is grouping objects based on similar physical features. Otters may use categorization to classify predators, prey, and conspecifics. This study was the first to examine whether North American river otters (Lontra canadensis) are capable of perceptual categorization. Previously, otters at the Seneca Park Zoo were trained to discriminate between a circle and an equilateral triangle in a two-alternative forced-choice task. In the present study, these otters were presented with novel geometric shapes (e.g., an oval and a right triangle) in Experiment 1 and novel drawings of real-world objects (e.g., a tomato and a tent) in Experiment 2 that could be classified into the circle or triangle category. Two otters performed significantly better than chance during Experiment 1 on subsets of the novel test stimuli. In Experiment 2, one otter was able to categorize drawings of real-world objects into two shape categories of circles and triangles, but only when the triangle-like stimuli were composed of straight lines, not when stimuli were composed of curved lines. The results from both experiments suggest that line type (straight vs. curved) and symmetry may have been salient features for the otters. It appears that otters have the ability to perceptually categorize two-dimensional shapes and line drawings, though further research with additional subjects and different stimuli is needed. Better understanding this ability in otters can expand our knowledge of categorization behavior in a variety of nonhuman animals. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
Comparative psychology has its share of historical ironies. A particularly delightful one comes from Lloyd Morgan himself. In Animal Behavior, which was published after An Introduction to Comparative Psychology (which contains Morgan's Canon), he marvels at a digger wasp that picks up a small pebble in her mandibles and uses it as a hammer to pound and tamp the earth sealing her burrow. what does the Canon mean to the scientists who use it today? A recent article in this issue by Voudouris et al. (2025) gives us a first empirical insight. Using systematic surveys, they shed light on what comparative cognition researchers actually think about Morgan's Canon, the associative-cognitive distinction, and the role of parsimony in interpreting animal behavior. Morgan's Canon began as a plea for rigor. Over time, it became a slogan, sometimes a straitjacket, occasionally a scapegoat. But it remains also a guardrail, a guide, and a goad: it guards against overreach, guides control design and interpretation, and goads us to spell out mechanisms. The new survey shows that researchers still value the Canon but use it with more flexibility and less dogmatism than in the past. (PsycInfo Database Record (c) 2025 APA, all rights reserved).
The Producer-Scrounger game proposes that individuals in social foraging situations tend to choose one of two strategies: (a) actively invest effort in searching for resources (producing) or (b) exploit resources discovered by others (scrounging). Models have typically given scroungers an advantage. In Vickery et al.'s (1991) model, remaining food in a patch is equally shared among scroungers regardless of their position or visual range. Similarly, agent-based models assume scroungers have a comprehensive view of the habitat, enabling them to detect all opportunities to exploit resources, while producers move randomly. This study examined the effect of visual range on producer-scrounger dynamics using a computerized behavioral task where four human participants interacted in real time within a virtual habitat. Two groups, differing in food probability (λ80 and λ20), were exposed to four experimental conditions that varied visual range by manipulating the top-down camera angle (45° or 75°) and camera distance (240 or 80 px). Results showed that the producer index was higher when the probability of finding resources increased, and highest in the 75°-240 px condition, where participants had limited depth of view but could better perceive their immediate surroundings. A modified agent-based model that included visual range parameters revealed a similar pattern. These findings highlight the importance of visual range, often underestimated in theoretical models, for producer strategies. (PsycInfo Database Record (c) 2026 APA, all rights reserved).
