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Open Access Publications from the University of California


The International Journal of Comparative Psychology is sponsored by the International Society for Comparative Psychology. It is a peer-reviewed open-access digital journal that publishes studies on the evolution and development of behavior in all animal species. It accepts research articles and reviews, letters and audiovisual submissions.

Volume 24, Issue 1, 2011

Special Issue Introduction

Paying More Attention to What (Some) Nonhuman Animals and (Some) Humans Can Do: An Introduction to the Special Issue on Individual Differences in Comparative Psychology

In 2009, there was a paper session at the annual meeting of the Southeastern Psychological Association entitled “Animal Minds: Sea Lions and Voles and Bears (and Dolphins and Monkeys), Oh My!” The goal of this session was to present a broad perspective on current research in animal cognition, and in particular to present to the SEPA audience some of the variety of species and tasks that are being used in comparative cognition research today. Beyond accomplishing this goal, however, the session revealed something else that provided the basis for the current special issue.

Special Issue

Mapping Individual Variations in Learning Capacity

Individual differences in learning capacity are evident in humans and most other animals. Traditionally, such differences are described in terms of variations along a relatively small number of psychological dimensions corresponding to behavioral traits. Here, an alternative approach is considered in which individual differences in learning capacity are characterized by spatially sorting behavioral patterns. To illustrate this approach, a two-dimensional self-organizing feature map wasused to analyze patterns in the performances of intact and cortically-lesioned rats engaged in multiple learning tasks. After training, the spatial structure of the map revealed systematic variations inlearning across rats that were related to the degree of brain damage. Individual nodes within the map described prototypical performance profiles that corresponded closely to patterns of learning seen in individual rats, including individuals with idiosyncratic profiles. Techniques that automatically identify modal patterns of performance during learning may provide new insights into the processes that determine what an individual organism can learn.

Individual Differences in Animal Intelligence: Learning, Reasoning, Selective Attentionand Inter-Species Conservation of a Cognitive Trait

Humans’ performance on most cognitive tasks are commonly regulated by an underlying latent variable (i.e., “general” intelligence), and the expression of this latent modulator of cognitive performance varies across individuals. While “intelligence” in humans is easily recognized, a precise definition of this trait has proven elusive, and has impeded efforts to compare the emergence of thi strait across species. Here we describe our efforts to characterize this cognitive trait in genetically heterogeneous laboratory mice. Using batteries of as many as eight learning tasks and various principal component analysis regimens, we have found a robust general factor that accounts fornearly 40% of the variance of individual animals across all tasks. This “” is not attributable to variations in stress reactivity or exploratory tendencies. However, like human intelligence, this general factor covaries with the efficacy of selective attention and working memory capacity. Importantly, we also find that general learning abilities covary with animals’ performance on novel tests of reasoning. In total, this work indicates that learning abilities, attentional control, andthe capacity for reasoning, features that constitute both colloquial and formal definitions of human intelligence, are commonly regulated in individual genetically heterogeneous mice. These results suggest an evolutionary conservation of the qualitative and quantitative properties of intelligence, and indicate that like humans, sub-human animals express individual differences in this trait.

Use of a Touchscreen-mediated Testing System with Mandrill Monkeys

Relatively little is known of the cognitive and perceptual abilities of mandrill monkeys ( Mandrillussphinx sp. ). Here, we document how seven adult mandrills were trained to effectively use a touchscreen mediated testing system. Upon mastering use of this device, subjects were presented with two automated discrimination tasks; one requiring discrimination of the target from an array of distracters using color, the second requiring discrimination by shape. Examination of individual differences in both training and testing performance provided evidence that position in the social hierarchy and circumstances of the testing environment impacted learning. Further, examination of error production revealed that errors were not distributed randomly, with subjects being attracted to a biologically relevant color and a shape that was featurally similar to the target.

Individual Differences in Causal Judgment under Time Pressure: Sex and Prior Video Game Experience as Predictors

Individual differences in the effects of stress on causal attribution were studied in the context of a first-person-shooter video game. Participants were tasked with identifying the source of an explosion by repeatedly choosing among three possible enemy targets that were firing their weapons at random. In each trio of possible targets, the true enemy (the cause) produced these explosions at a delay ofeither 0.5, 1.0, or 2.0 seconds and with a probability of 100%, 75%, or 50%; condition varied across trios of targets. In Experiment 1, half of the participants made these choices while under stress (by being under fire by snipers in the hills surrounding the choice area) and half were not under fire. Men had higher accuracies and shorter latencies, and being under fire produced lower accuracy but had no effect on latency. In Experiment 2, a more explicit form of time pressure was used in which participants had a fixed amount of time in which to make their choice. This form of time pressure succeeded in dramatically reducing decision latency with an associated drop in accuracy. There was unreliable evidence of a higher accuracy for men. Neither experiment revealed a relationship between self-reported video game play and performance. The results suggest that causal decisions are negatively affected by time pressure, and the manipulations affected men and women similarly.

Waiting for Grapes: Expectancy and Delayed Gratification in Bonobos

Responses to delayed rewards vary widely across individuals and have important implications for personality and temperament. Animals may avoid delayed rewards because the future is uncertain. Therefore, expectations about receiving a future reward should influence the response to delayed payoffs. Here, we offered bonobos (Pan paniscus) a delayed gratification task in which food accumulated over time. Once subjects chose to consume the reward, food stopped accumulating. We tested their willingness to wait with a reliable and an unreliable experimenter to vary the subjects’expectations that they would receive the food. Subjects waited less often with the unreliable experimenter but showed individual differences in the degree to which reliability generalized across experimental tasks. These data suggest that the expectations generated about the likelihood of receiving future rewards influence how individuals balance current and future needs.

  • 2 supplemental videos

Individual Modulation of Anti-predator Responses in Common Marmosets

Group living may confer an advantage on prey animals if individuals help maximise protection from predation. Some evidence suggests that age and sex differences may signify role divisions infight/flight responses. We examined whether captive common marmosets ( Callithrix jacchus ), a group-living primate species, might also show sex and age differences in response to predators and presented predator-based visual and auditory stimuli, individually and simultaneously. No significantsex or age differences emerged in any of the behaviour recorded. However, we found strong evidence that there were individual differences in flight/fight responses depending on the stimulus presented. Inpresenting a taxidermic model of a carnivore visually, five (of the 12) marmosets showed behaviour suggesting cautiousness, whereas five other marmosets displayed risk-taking behaviour (scored asclose proximity to stimulus, mobbing vocalisations and short latency to approach and vocalise). Importantly, cautious and risk-taking individuals did not behave consistently in these roles but changed when presented with the auditory stimulus or the visual and auditory stimuli combined.These results suggest that there may be individual differences in assessing sensory cues and levels offear fulness and risk-taking may vary accordingly. Whether or not such differences confer anadvantage on group living species, it is an entirely new finding that the type of sensory stimulation affects and alters behaviour to a significant extent within an individual and within the same group of primates.

Individual Differences in Long-term Cognitive Testing in a Group of Captive Chimpanzees

Seven chimpanzees had participated in cognitive tasks from the time they were approximately 18 months to approximately 16 years of age when the data presented here was analyzed. Testing covered a wide range of tasks, which we categorized broadly as measuring their understanding of aspects of either their social or physical environments. Therefore, we could test whether individuals who excelled on ‘social’ tasks, also excelled on ‘physical’ tests. We also categorized our measures as ones of acquisition, criterion, retention or transfer of skill. Thus, we could determine whether individuals who mastered tasks quickly were also those who performed, remembered and generalized tasks most accurately. We were interested in whether there were consistent patterns in cognitive skills across tasks and measures. Results of our analyses indicate that, as with humans, chimpanzees vary in their performance across some measures, although some differences in cognitive skill between individuals are also consistent across measures and tasks. The results have implications for questions concerning domain generality or specificity of cognitive skills in another primate species.