Emotional behavior during the learning of a contingency task in a chimpanzee

State-transition-free reinforcement learning in chimpanzees (Pan troglodytes)

The outcome of an action often occurs after a delay. One solution for learning appropriate actions from delayed outcomes is to rely on a chain of state transitions. Another solution, which does not rest on state transitions, is to use an eligibility trace (ET) that directly bridges a current outcome and multiple past actions via transient memories. Previous studies revealed that humans (Homo sapiens) learned appropriate actions in a behavioral task in which solutions based on the ET were effective but transition-based solutions were ineffective. This suggests that ET may be used in human learning systems. However, no studies have examined nonhuman animals with an equivalent behavioral task. We designed a task for nonhuman animals following a previous human study. In each trial, participants chose one of two stimuli that were randomly selected from three stimulus types: a stimulus associated with a food reward delivered immediately, a stimulus associated with a reward delivered after a few trials, and a stimulus associated with no reward. The presented stimuli did not vary according to the participants' choices. To maximize the total reward, participants had to learn the value of the stimulus associated with a delayed reward. Five chimpanzees (Pan troglodytes) performed the task using a touchscreen. Two chimpanzees were able to learn successfully, indicating that learning mechanisms that do not depend on state transitions were involved in the learning processes. The current study extends previous ET research by proposing a behavioral task and providing empirical data from chimpanzees.

Don't look back on failure: spontaneous uncertainty monitoring in chimpanzees

During computer-controlled cognitive tasks, chimpanzees often look up at the food dispenser, which activates at the same time as feedback for the correct choice but not for feedback for the incorrect choice. Do these "looking back" behaviors also indicate signs of spontaneous monitoring of their confidence in their choices? To address this question, we delayed the feedback for 1 s after their choice responses and observed their look-back behaviors during the delay period. Two chimpanzees looked up at the food dispenser significantly less frequently when their choice was incorrect (but the feedback was not given) than when it was correct. These look-back behaviors have not been explicitly trained under experimental contexts. Therefore, these results indicate that chimpanzees spontaneously change the frequency of their look-back behaviors in response to the correctness or incorrectness of their own choices, even without external feedback, suggesting that their look-back behaviors may reflect the level of "confidence" or "uncertainty" of their responses immediately before.

Vocal functional flexibility in the grunts of young chimpanzees

All living things communicate yet only humans can be said to communicate using language. How this came to be the case is a fundamental mystery unsolved by contemporary science. Within a human lifetime, language emerges from a complex developmental process. As such, understanding chimpanzee vocal development is essential to understanding the evolutionary roots of language. In human development, language is directly built upon the early capacity for "vocal functional flexibility"-the ability to flexibly express the same vocalizations in different ways to achieve different functions. Primate vocalizations, by contrast, have long been believed to be relatively inflexible regarding both production and function. In this paper, we break new ground by providing evidence for vocal functional flexibility in one of the first systematic studies of early chimpanzee vocal production and function. This finding implies the developmental foundations for language are rooted in our primate evolutionary heritage.

Evaluating Self-Directed Behaviours and Their Association with Emotional Arousal across Two Cognitive Tasks in Bonobos (Pan paniscus)

Self-directed behaviours (SDBs) are widely used as markers of emotional arousal in primates, and are commonly linked to negative arousal, or are used as indicators of stress or poor welfare. However, recent studies suggest that not all SDBs have the same function. Moreover, lateralisation in the production of these behaviours has been suggested to be associated with emotional processing. Hence, a better understanding of the production and the asymmetry of these displacement behaviours is needed in a wider range of species in order to confirm their reliability as indicators of emotional arousal. In the current study, we experimentally evaluated the production and asymmetry of SDBs in zoo-housed bonobos during two cognitive touchscreen tasks. Overall, nose wipes were most commonly observed, followed by gentle self-scratches, and rough self-scratches. The rates of nose wipes and rough self-scratches increased with incorrect responses, suggesting that these behaviours indicate arousal and possibly frustration. Rough self-scratching was additionally more directed towards the left hemispace after incorrect responses. In contrast, gentle self-scratching increased after correct responses in one study, possibly linking it with positive arousal. We also tested if left-handed bonobos showed greater behavioural reactivity towards incorrect responses, but found no evidence to confirm this hypothesis. Our results shed light on potential different mechanisms behind separate SDBs. We therefore provide nuance to the use of SDBs as indicator of emotional arousal in bonobos.

Cognitive enrichment in a social setting: assessing the use of a novel food maze in sanctuary-housed chimpanzees

Foraging devices are effective enrichment tools for non-human primates, as they provide both cognitive and manipulative stimulation that may enhance these animals’ welfare. We assessed the behavioral effects of a novel tool-based enrichment on 14 chimpanzees (Pan troglodytes) housed at Fundació Mona (Girona, Spain). The device consisted of a vertical maze filled with food rewards, which chimpanzees could extract by using tools. We conducted behavioral observations in two conditions over an approximately 2.5-month period: when the food maze was loaded (12 enrichment days), and when it was empty (12 baseline days). Data were collected using 2-min scan sampling and untimed-event focal sampling during two daily sessions of 80 min each. We expected that the chimpanzees’ interest in the enrichment would decrease over time, but that its use would be linked to an increase in the occurrence of species-typical behaviors, a reduction in negative indicators of welfare, and changes in social behaviors. We found that participation widely varied among subjects, being higher in females and decreasing through time. Furthermore, participation was linked to an increase in tool use and a decrease in inactivity, but also to an increase in aggression-related behaviors. In contrast, participation had no effect on the occurrence of abnormal behaviors, social proximity or affiliation-related behaviors. Finally, we detected an increase in self-directed behaviors only when subjects actively interacted with the device. We conclude that, in future studies, these types of devices should be evaluated for longer periods of time and more attention should be paid to individuals’ preferences and abilities.

Artificial Termite-Fishing Tasks as Enrichment for Sanctuary-Housed Chimpanzees: Behavioral Effects and Impact on Welfare

Simple Summary

The welfare of captive animals is nowadays a topic of major concern. In order to express their natural behavioral repertoires, however, animals require complex environments and stimuli which are difficult to reproduce in captivity. To overcome this, environmental enrichment is considered one of the most successful tools to increase behavioral opportunities and enhance animal welfare. In this study, we explored whether providing an artificial termite-fishing task, and whether participation in this task, predicted changes in the solitary and social behavior of sanctuary-housed chimpanzees (Pan troglodytes). We compared chimpanzee behavior when the enrichment was presented to different periods without enrichment. We found that the presence of the enrichment predicted an increase in tool use and feeding behavior and a decrease in inactivity, especially for those chimpanzees with higher participation. However, we did not detect significant changes in abnormal or self-directed behaviors. Furthermore, we found no variation in affiliation- or aggression-related behaviors, but social proximity increased in chimpanzees that participated more. Our results support previous studies demonstrating that artificial termite-fishing promotes species-typical behaviors in captive chimpanzees with no major effects on social activities.

Abstract

Artificial termite-fishing tasks are a common enrichment for captive great apes, promoting species-typical behaviors. Nonetheless, whether these activities are linked to changes in other behaviors and whether these changes persist over time has seldom been investigated. We assessed whether the use of an artificial termite-fishing task was linked to changes in the solitary behavior and social dynamics in two groups of sanctuary-housed chimpanzees (Pan troglodytes). Specifically, we compared chimpanzee behavior during eight enrichment sessions distributed over a two-month period, with similar periods before and after the introduction of the enrichment. Data were collected from combined interval and continuous sampling methods and were analyzed using generalized linear mixed models. We found that participation increased across sessions and that both enrichment and participation predicted an increase in tool use and feeding and a decrease in inactivity, which were all maintained throughout the sessions. Furthermore, participation was positively associated with social proximity, revealing a gathering effect of the task. However, neither enrichment nor participation were linked to changes in abnormal, self-directed, affiliation-related or aggression-related behaviors. Overall, our results support the hypothesis that artificial termite-fishing is a suitable enrichment for captive chimpanzees, maintaining the subjects’ interest and promoting species-typical behaviors, with no negative effects on social activities.

High-Tech and Tactile: Cognitive Enrichment for Zoo-Housed Gorillas

The field of environmental enrichment for zoo animals, particularly great apes, has been revived by technological advancements such as touchscreen interfaces and motion sensors. However, direct animal-computer interaction (ACI) is impractical or undesirable for many zoos. We developed a modular cuboid puzzle maze for the troop of six Western lowland gorillas (Gorilla gorilla gorilla) at Bristol Zoo Gardens, United Kingdom. The gorillas could use their fingers or tools to interact with interconnected modules and remove food rewards. Twelve modules could be interchanged within the frame to create novel iterations with every trial. We took a screen-free approach to enrichment: substituting ACI for tactile, physically complex device components, in addition to hidden automatic sensors, and cameras to log device use. The current study evaluated the gorillas' behavioral responses to the device, and evaluated it as a form of "cognitive enrichment." Five out of six gorillas used the device, during monthly trials of 1 h duration, over a 6 month period. All users were female including two infants, and there were significant individual differences in duration of device use. The successful extraction of food rewards was only performed by the three tool-using gorillas. Device use did not diminish over time, and gorillas took turns to use the device alone or as one mother-infant dyad. Our results suggest that the device was a form of cognitive enrichment for the study troop because it allowed gorillas to solve novel challenges, and device use was not associated with behavioral indicators of stress or frustration. However, device exposure had no significant effects on gorilla activity budgets. The device has the potential to be a sustainable enrichment method in the long-term, tailored to individual gorilla skill levels and motivations. Our study represents a technological advancement for gorilla enrichment, an area which had been particularly overlooked until now. We wholly encourage the continued development of this physical maze system for other great apes under human care, with or without computer logging technology.

Cognitive enrichment for bottlenose dolphins (Tursiops truncatus): evaluation of a novel underwater maze device

Cognitive enrichment is gaining popularity as a tool to enhance captive animal well-being, but research on captive cetaceans is lacking. Dolphin cognition has been studied intensively since the 1950s, and several hundred bottlenose dolphins are housed in major zoos and aquaria worldwide, but most dolphin enrichment consists of simple floating objects. The aim of this study was to investigate whether a novel, underwater maze device (UMD) was cognitively enriching for one group of male and one group of female dolphins at Six Flags Discovery Kingdom, CA. The dolphin's task was to navigate a rubber ball through a maze of pipes, towards an exit pipe. We also tested a modification where an edible gelatine ball fell into the pool once the UMD was solved. The UMD was provided to each group between 8 and 11 times over a 4-week period. Male dolphins used the UMD without prior training, whereas females did not use the UMD at all. Two male dolphins solved the UMD 17 times, using a variety of problem-solving strategies. The UMD had no significant effect on circular (repetitive) swimming patterns, but males spent significantly more time underwater when the UMD was present. Males used the UMD significantly more when it contained the rubber ball, but the gelatine ball stimulated social play. The UMD is a safe and practical device for captive dolphins. It now requires further testing on other dolphins, particularly females, to in order to examine whether the sex differences we observed are a general phenomenon.

Effect of a cognitive challenge device containing food and non-food rewards on chimpanzee well-being

Exploration and problem-solving are highly motivated behaviors in non-human primates, but little research has focused on whether cognitively challenging tasks can enhance primates' psychological well-being, particularly in the absence of food rewards. We evaluated whether a novel cognitive challenge device (CCD) consisting of a maze of opaque tubes enhanced the well-being of a group of six adult chimpanzees housed at ZSL Whipsnade Zoo, UK, over a two-month period. Chimpanzees had the opportunity to interact with two versions of the CCD: the first contained tokens which fell into a transparent chamber when extracted from the CCD and could not be eaten. The second contained unshelled Brazil nuts, which could be extracted and eaten. CCD-use was low over the study, occupying on average 2.5% of observation time. However, compared to baseline levels, chimpanzees exhibited more problem-solving behaviors (directed toward the CCD) and spent significantly more time engaged in social play when the CCD was present. Cage exploration was rare whether the CCD was present or not. Chimpanzees used the CCD (including tool-use) significantly more when it contained tokens. The relationship between the presence of the CCD and self-directed behavior (rough-scratching) was difficult to interpret. Although rough-scratching was significantly higher in the cage when the CCD was present and 18% of these scratching events occurred within one arm's length from the CCD, rough-scratching decreased when device use increased. This study provides a preliminary investigation of the CCD and two reward types, and suggests how the design could be modified to enhance its effects.

Cognitive research in zoo-housed chimpanzees: influence of personality and impact on welfare

We monitored chimpanzee welfare during the introduction of on-exhibit cognitive research training and testing, as measured by behavior and interest in such training, and related individual variation to personality assessments. We observed 11 chimpanzees (six males; five females) over a 16-month period and compared their behavior across three conditions: (1) Baseline (nontraining/research situations) and (2) an on-going, off-exhibit program of Husbandry Training and (3) Research Pod Activities, on-exhibit, group training for cognitive testing. There was considerable individual variation in their interest levels during research sessions; females and those scoring higher for Openness were present more frequently (including those who actively participated and those who observed others participating), but interest did not vary in relation to rates of self-directed behaviors (SDBs), rank, or the level of social disruptions within the group (i.e. large-scale displays or fights). The frequency of SDBs was predicted by the Neuroticism personality factor, but did not differ across baseline and training contexts, indicating that these activities do not negatively impact welfare. We also explored vigilance as an indicator of social uncertainty, but social monitoring did not differ in relation to either social context or rank. Finally, we explored how the specific characteristics of the research context impacted on SDBs; namely, social context, reward contingency, and visual access to keepers. SDBs increased only when visual access to keepers was restricted, suggesting that visual contact reduced uncertainty in novel training contexts. Overall, the introduction of a cognitive research program did not compromise welfare, and the chimpanzees' repeated interest and willingness to participate suggests that the research was enriching.

Executive function in young children and chimpanzees (Pan troglodytes): evidence from a nonverbal dimensional change card sort task

In this article the authors compared chimpanzees' executive function with that of children. They developed a nonverbal dimensional change card sorting task, which indexed the development of executive function. Three pairs of mother and offspring chimpanzees and 30 typically developed 5-year-old children were presented with 2 target stimuli and a test stimulus comprising 2 dimensions (size and shape) on a display; they were required to sort the test stimulus according to 1 dimension (e.g., shape). After 5 consecutive correct trials, the participants had to sort the test stimulus according to the other dimension (e.g., size). The results showed that the chimpanzees often failed to sort the test stimuli according to the first and reversed dimensions. On the other hand, the children were correctly able to use both dimensions. These results indicate that chimpanzees may have less developed executive skills than children.

Assessing the effects of cognitive experiments on the welfare of captive chimpanzees (Pan troglodytes) by direct comparison of activity budget between wild and captive chimpanzees

We investigated the effects of cognitive experiments by direct comparison of activity budgets between wild and captive chimpanzees. One goal of captive management is to ensure that the activity budgets of captive animals are as similar as possible to those of their wild counterparts. However, such similarity has rarely been achieved. We compared the activity budget among three groups of chimpanzees: wild chimpanzees in Bossou (Guinea, n = 10), and captive chimpanzees who participated in cognitive experiments (experimental chimpanzees, n = 6) or did not participate in the experiments (nonexperimental chimpanzees, n = 6) at the Primate Research Institute (Japan). The experimental chimpanzees voluntarily participated in computer-controlled cognitive tasks and small pieces of fruits were provided as rewards. The data from captivity were obtained on the experimental days (weekdays) and nonexperimental days (weekends). In both study sites, we followed each chimpanzee from about 7 a.m. until the time when chimpanzees started to rest in the evening. The behaviors were recorded every 1 min. The results showed that on weekdays, feeding time and resting time of the experimental chimpanzees were almost the same as those of wild chimpanzees. However, for the nonexperimental chimpanzees, feeding time was significantly shorter and resting time was longer than those of the wild chimpanzees. In contrast, no difference was found in feeding time or resting time of the two groups of captive chimpanzees on weekends. The results suggested that the cognitive experiments worked as an efficient method for food-based enrichment.

Emotional consequences when chimpanzees (Pan troglodytes) face challenges: individual differences in self-directed behaviours during cognitive tasks

Self-directed behaviours (SDBs) are said to be indicative of negative emotions. The present study focused on chimpanzees’ SDBs during cognitive experiments in order to investigate how each chimpanzee reacted to his or her errors and to changes in task difficulty. We recorded and analysed the behaviour of six chimpanzees during cognitive experiments at the Primate Research Institute, Kyoto University, in Japan. We compared the rate of SDBs after correct trials versus incorrect trials, and in easy tasks versus difficult tasks. Our results suggest that the chimpanzees’ reactions to making an error and the degree of difficulty of the task varied depending on the individual. Three out of the six chimpanzees exhibited higher rates of SDBs after incorrect trials than after correct trials, and in difficult tasks than in easy tasks whilst the other three did not. This finding suggests that chimpanzees may differ in the degree to which they exhibit internal conflict and we should carefully assess subjective evaluations of task situations; taking these differences into consideration when conducting experimental research in chimpanzees.

Lateralized scratching in chimpanzees (Pan troglodytes): Evidence of a functional asymmetry during arousal

This study evaluated laterality in scratching by chimpanzees (n = 89) during socially arousing circumstances. Hand use and the side of the body scratched was recorded during a baseline and experimental condition. In the experimental condition, chimpanzees were shown a video of other conspecifics sharing, fighting over, and consuming a watermelon. Self-touches were categorized as either rubs or scratches. The chimpanzees showed a significant right hand bias for rubbing and also significantly directed the rubs to the right side of the body. For scratching, the chimpanzees showed no hand preference but a significant bias for scratching on the left side of the body. These results support the view that the right hemisphere regulates the autonomic nervous system during arousal.

Observing Conspecifics Scratching Induces a Contagion of Scratching in Japanese Monkeys (Macaca fuscata)

Although a large number of studies have examined self-directed behaviors (SDBs) such as scratching and self-grooming as nonverbal leakage of negative emotional arousal in humans, few studies have investigated the informative function of SDBs in nonhuman primates. The present study investigated whether viewing another monkey scratching itself elicited negative arousal from conspecific observers in Japanese monkeys (Macaca fuscata). An experimental situation was created in which the target monkey watched a stranger through a small peephole and the observer monkey(s) watched the target in turn. Scratching spread when conspecific observers watched the target scratching itself while performing monitoring behavior. The author proposes that the possible contagion of scratching by monkeys observing another's scratching may involve transmission of a psychological state, a primitive style of empathy.

Effects of cognitive challenge on self-directed behaviors by chimpanzees (Pan troglodytes)

In primates, including humans, scratching and other self-directed behaviors (SDBs) have recently been reported to be differentially displayed as a function of social interactions, anxiety-related drugs, and response outcomes during learning tasks. Yet few studies have focused on the factors influencing SDBs in our closest living relatives, the chimpanzees (Pan troglodytes). Furthermore, no previous experimental study has examined handedness of SDBs as a function of changes in task difficulty. Using matching-to-sample tasks of varying difficulty, the present study examines the effect of manipulations of task difficulty on rates, handedness, and type of SDBs in an experimental study of eight chimpanzees. SDBs were categorized as rubs, gentle scratches, and rough scratches. SDBs increased during difficult discriminations, but only for subjects who started the experiment on an easy discrimination; subjects who started on a difficult discrimination exhibited no differential rates of SDBs as a function of task difficulty. There was a tendency to exhibit relatively more SDBs with the right hand in the more difficult task. Rates of SDBs decreased after auditory feedback signals, suggesting a link between SDBs and uncertainty. Rubs were directed more to the face (trigeminal), and gentle and rough scratches more to the body (spinothalamic), suggesting that face-directed SDBs may index a different motivational basis than scratches. Taken together, these results extend previous research on SDBs to the domain of cognitive stress in nonsocial contexts, demonstrating that SDBs are sensitive to manipulations of task difficulty in chimpanzees.