Hand preference in a captive island group of chimpanzees (Pan troglodytes)

Morphological cerebral asymmetries in chimpanzee brains, similar to those found in humans, in whom they are associated with speech and handedness, suggest the possibility of functional lateralization in the chimpanzee. This possibility was investigated by examining hand preferences in an island group of five chimpanzees on a series of unimanual and bimanual tasks that are diagnostic of human hand and cerebral dominance. Each subject was tested in a double compartment cage on three unimanual nonsequential, three unimanual sequential, and three bimanual coordination tasks. One of the three unimanual sequential tasks was a bar-press task that is analogous to the commonly used human finger-tapping task. For the unimanual tasks, exclusive of the bar-press, the chimpanzees showed a highly individualistic pattern of hand preference that did not change as a function of task complexity. On the bar-press task, four of five subjects produced higher rates with one hand compared to the other; however, relative hand performance on this task was unrelated to hand preference on the other unimanual tasks. For the group of subjects, performance rates did not differ between the left and right hands; however, a practice effect was observed for the right hand in all subjects. The bimanual tasks also revealed a complex pattern of individual handedness, with no trends apparent for the group as a whole. Consistent with previous findings, the results from these tests on this group of five chimpanzees suggest that cerebral morphological asymmetries in the chimpanzee are not associated with motor dominance as reflected in handedness.     

Handedness in wild chimpanzees

The debate over nonhuman primate precursors to human handedness is unsettled mainly due to lack of data, particularly on apes. Handedness in wild chimpanzees at the Taï National Park Côte d'Ivoire, has been monitored in four tasks. For the simple unimanual ones, reaching and grooming, adults use both hands equally (ambidextrous), while for the more complex unimanual wadge-dipping and the complex bimanual nut-cracking, adults are highly lateralized. These results support the hypothesis that lateralization increases with the complexity of the task. The lateralization is constant for years for each task but may vary in an individual with respect to different tasks. For nutcracking females are more lateralized than males. The ontogeny of handedness for nut-cracking shows many variations in the tendency to use one hand and in the side preferred, until at about 10 years of age, the individual achieves her adult handedness. No population bias toward one side exists in Taï chimpanzees. No heritability of handedness between mother and offspring was observed. Human and chimpanzees handedness are compared.     

Chimpanzees are more skilful in competitive than in cooperative cognitive tasks

In a series of four experiments, chimpanzees, Pan troglodytes, were given two cognitive tasks, an object choice task and a discrimination task (based on location), each in the context of either cooperation or competition. In both tasks chimpanzees performed more skilfully when competing than when cooperating, with some evidence that competition with conspecifics was especially facilitatory in the discrimination location task. This is the first study to demonstrate a facilitative cognitive effect for competition in a single experimental paradigm. We suggest that chimpanzee cognitive evolution is best understood in its socioecological context.     

Odor-sampling time of mice under different conditions

Response accuracy and odor sample times on positive (S+) and negative (S-) trials were recorded for mice trained on a variety of go, no-go odor detection and discrimination tasks. Odor sample time was relatively stable over extended training on the same task, increased during acquisition of difficult tasks, relatively insensitive to reinforcement magnitude, and, in some cases, provided more information regarding task difficulty and discrimination than did response accuracy. Mice generally sampled longer on S- trials in simple odor detection tasks but longer on S+ trials in odor discrimination tasks.     

Factor Analysis of Multiple Measures of Hand Use in Captive Chimpanzees: An Alternative Approach to the Assessment of Handedness in Nonhuman Primates

We tested whether chimpanzee handedness could be characterized as either unidimensional or multidimensional when considered across multiple measures of hand use. We determined for each of 6 different tasks in a sample of 105 captive chimpanzees hand preferences, and subjected the individual hand preference scores to a factor analysis. Five of the 6 tasks loaded on two separate factors that accounted for 54% of the variance. To assess population-level handedness, we calculated handedness indices for the loadings on each factor, for the item loadings across all factors, and for all tasks including ones that did not load on any factor. There is significant population-level right handedness for all 4 indices, which suggests that chimpanzee handedness is multidimensional and not task specific.     

Hand Preferences for a Haptic Task in Chimpanzees (Pan troglodytes)

We tested the hand preferences of 20 chimpanzees (Pan troglodytes) for a haptic task requiring individuals to search for grapes in an opaque bucket filled with water. We compared these data to the hand preferences displayed by the same chimpanzees during reaching and bimanual feeding tasks. The chimpanzees displayed no significant hand preference for the reaching or bimanual feeding tasks, but exhibited a right-hand preference while performing the haptic task. In contrast, New and Old World monkeys display left-hand preferences for similar tasks. We discuss the relevance of these findings for the evolution of handedness in primates.     

Manual Laterality for Simple Reaching and Bimanual Coordinated Task in Naturalistic Housed <Emphasis Type="Italic">Pan troglodytes</Emphasis>

Researchers have shown renewed interest in the study of manual lateralization in chimpanzees. Currently there is no consensus confirming the presence or absence of manual dominance at a species level, mainly for populations in the wild and in semicaptivity. We aimed to evaluate the manual laterality in a group of chimpanzees in an intermediate setting (semicaptivity) via 2 tasks: one simple and unimanual (simple reaching) and the other complex and bimanual (tube task). We replicated the same experiments from Hopkins in a new and different sample of chimpanzees. In simple reaching, the hand is used to gather food and the type of grip and the posture are evaluated. The tube task assesses the hand used to extract food from the tube and the method of extraction (digital or instrumental). Through the handedness index we observed that the subjects show clear and strong individual preferences for both tasks (100% lateralized subjects in the tube task; 86% in simple reaching), although we did not detect population preferences for any of the tasks. However, considering both tasks jointly (multiple evaluation), it was possible to detect, for the first time, skilled manual dominance at a group level in semicaptive chimpanzees in one multitask index and borderline significance in a second multitask index.     

Hand Preference for a Novel Bimanual Coordinated Task During Termite Feeding in Wild Western Gorillas (<Emphasis Type="Italic">Gorilla gorilla gorilla</Emphasis>)

Although the level of handedness in humans varies cross-culturally, humans are generally described as right-handed, which has been considered a uniquely human trait. Recently, captive chimpanzees (Pan troglodytes) have been shown to exhibit right-hand preference when performing bimanual but not unimanual tasks. Less clear is whether this pattern also occurs in wild chimpanzees and other African apes. Using videos (N = 49) of six wild western gorillas (Gorilla gorilla gorilla) feeding on termites at the Mondika Research Center (Republic of Congo), we tested whether they exhibit hand preference when performing unimanual, i.e., reaching for termite mound pieces; bimanual, i.e., “termite tapping”: rhythmically shaking a piece of termite mound with the dominant hand and collecting the termites in the other hand tasks; or hand transfer prior to bimanual tasks, i.e., transferring a piece of termite mound from one hand to the other. All individuals exhibited exclusive hand preference when performing the bimanual tasks, with five of six gorillas preferring the right hand. Conversely, most individuals did not show any manual preference during the unimanual task. In addition, hand preference during hand transfer revealed clear hand dominance of similar strength and direction of those shown for the bimanual task, suggesting that this measure is as sensitive as the bimanual task itself. Thus, we propose “termite feeding” as a novel task to be considered in future hand-preference studies in wild western gorillas. Our results are in concordance with those for chimpanzees and captive gorillas showing hemispheric specialization for bimanual actions in apes.     

Genetic basis in motor skill and hand preference for tool use in chimpanzees (Pan troglodytes)

Chimpanzees are well known for their tool using abilities. Numerous studies have documented variability in tool use among chimpanzees and the role that social learning and other factors play in their development. There are also findings on hand use in both captive and wild chimpanzees; however, less understood are the potential roles of genetic and non-genetic mechanisms in determining individual differences in tool use skill and laterality. Here, we examined heritability in tool use skill and handedness for a probing task in a sample of 243 captive chimpanzees. Quantitative genetic analysis, based on the extant pedigrees, showed that overall both tool use skill and handedness were significantly heritable. Significant heritability in motor skill was evident in two genetically distinct populations of apes, and between two cohorts that received different early social rearing experiences. We further found that motor skill decreased with age and that males were more commonly left-handed than females. Collectively, these data suggest that though non-genetic factors do influence tool use performance and handedness in chimpanzees, genetic factors also play a significant role, as has been reported in humans.     

Population-level right-handedness for a coordinated bimanual task in naturalistic housed chimpanzees: replication and extension in 114 animals from Zambia and Spain

Recently, many studies have been conducted on manual laterality in chimpanzees. Nevertheless, whether nonhuman primates exhibit population-level handedness remains a topic of considerable debate. One of the behaviors studied has been bimanual coordinated actions. Although recent studies have highlighted that captive chimpanzees show handedness at population level for these tasks, some authors have questioned the validity and consistency of these results. The first reason has been the humanization of the samples. The second one has been that the results refer to animals in American biomedical centers and the studies were conducted by the same team [WD Hopkins et al.]. This article aims to assess the laterality in bimanual coordination (tube task) activities in animals housed in an intermediate environment (Chimfunshi, Zambia). This has been conducted by replicating previous studies on similar samples (Mona Foundation, Spain), and then by extending the results to chimpanzees housed in intermediate settings. Individuals were evaluated through four experimental sessions (tests). Results indicated that 86% of the Chimfunshi sample was lateralized (48% RH, 38% LH). Furthermore, the sample showed population-level right-handedness in the mean handedness index, in Test 1, Test 2, and the first half of the study (Test 112). Rearing experience did not have an influence on handpreference. Taken together, the two sample (intermediate settings: Chimfunshi and Mona) results indicate a clear right-handedness. In conclusion, this replication and extension shows that (1) the Mona and Chimfunshi chimpanzees are right-handed in certain conditions, (2) the results are consistent with those obtained by Hopkins in captive settings, (3) the humanization of the samples does not affect manual laterality, (4) females are right-handed at population-level, but not males, and (5) these results reinforce the fact that the complexity of the task plays a dominant role in the expression of hand laterality among chimpanzees.     

Task difficulty,probability, and inter-stimulus interval as determinants of P300 from auditory stimuli

The P300 event-related potential was elicited with auditory stimuli in 4 experiments which manipulated combinations of stimulus target probability (10% vs. 30%), task difficulty (easy vs. hard), and inter-stimulus interval (5 sec vs. 2 sec). P300 amplitude was smaller and peak latency longer for the more difficult relative to the easier tasks across experiments. Increases in stimulus target probability generally diminished P300 amplitude and shortened peak latency more for the easy relative to difficult task conditions. Increasing the number of non-target stimulus tones decreased P300 amplitude reliably, but increased latency only slightly. Task difficulty did not interact with variations in inter-stimulus interval which produced generally weak effects for both amplitude and latency. These findings suggests that P300 amplitude and latency obtained from auditory discrimination paradigms reflect processing difficulty independently of stimulus target probability unless differences in task requirements affect stimulus encoding.     

The Role of Task-Related Learned Representations in Explaining Asymmetries in Task Switching

Task switch costs often show an asymmetry, with switch costs being larger when switching from a difficult task to an easier task. This asymmetry has been explained by difficult tasks being represented more strongly and consequently requiring more inhibition prior to switching to the easier task. The present study shows that switch cost asymmetries observed in arithmetic tasks (addition vs. subtraction) do not depend on task difficulty: Switch costs of similar magnitudes were obtained when participants were presented with unsolvable pseudo-equations that did not differ in task difficulty. Further experiments showed that neither task switch costs nor switch cost asymmetries were due to perceptual factors (e.g., perceptual priming effects). These findings suggest that asymmetrical switch costs can be brought about by the association of some tasks with greater difficulty than others. Moreover, the finding that asymmetrical switch costs were observed (1) in the absence of a task switch proper and (2) without differences in task difficulty, suggests that present theories of task switch costs and switch cost asymmetries are in important ways incomplete and need to be modified.     

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.     

Speed–accuracy trade-offs during foraging decisions in the acellular slime mould Physarum polycephalum

Speed–accuracy trade-offs (SATs) are thought to be a fundamental feature of biological information processing, yet most evidence of SATs comes from animals. Here, we examine SATs in the foraging decisions of an acellular, amoeboid organism: the slime mould Physarum polycephalum. Slime moulds were given a simple discrimination task: selecting the highest-quality food item from a set of three options. We investigated the effect of two stressors, light exposure and hunger, on the speed and accuracy of decision-making. We also examined the effect of task difficulty. When given a difficult discrimination task, stressed individuals tend to make faster decisions than non-stressed individuals. This effect was reversed in plasmodia given easy discrimination tasks, where stressed individuals made slower decisions than non-stressed individuals. We found evidence of SATs, such that individuals who made fast decisions were more likely to make costly errors by selecting the worst possible food option. Our results suggest that SATs occur in a wider range of taxa than previously considered.     

Right‐handed fossil humans

Fossil hominids often processed material held between their upper and lower teeth. Pulling with one hand and cutting with the other, they occasionally left impact cut marks on the lip (labial) surface of their incisors and canines. From these actions, it possible to determine the dominant hand used. The frequency of these oblique striations in an array of fossil hominins documents the typically modern pattern of 9 right‐ to 1 left‐hander. This ratio among living Homo sapiens differs from that among chimpanzees and bonobos and more distant primate relatives. Together, all studies of living people affirm that dominant right‐handedness is a uniquely modern human trait. The same pattern extends deep into our past. Thus far, the majority of inferred right‐handed fossils come from Europe, but a single maxilla from a Homo habilis, OH‐65, shows a predominance of right oblique scratches, thus extending right‐handedness into the early Pleistocene of Africa. Other studies show right‐handedness in more recent African, Chinese, and Levantine fossils, but the sample compiled for non‐European fossil specimens remains small. Fossil specimens from Sima del los Huesos and a variety of European Neandertal sites are predominately right‐handed. We argue the 9:1 handedness ratio in Neandertals and the earlier inhabitants of Europe constitutes evidence for a modern pattern of handedness well before the appearance of modern Homo sapiens.     

Visual and auditory conditional position discrimination in chimpanzees (Pan troglodytes)

Chimpanzee cognition has been studied predominantly through the visual modality, and much less through the auditory modality. The aim of this study was to explore possible differences in chimpanzees’ processing of visual and auditory stimuli. We developed a new conditional position discrimination (CPD) task requiring the association between a stimulus (from either the auditory or the visual modality), and a spatial position (left or right). The stimuli consisted of the face and voice of two individuals well known to the subjects (one chimpanzee and one human). Six chimpanzees participated in both the visual and the auditory conditions. We found contrasting results between the two conditions: the subjects acquired the CPD more easily in the visual than in the auditory condition. This supports previous findings on the difficulties encountered by chimpanzees in learning tasks involving auditory stimuli. Our experiments also revealed individual differences: the chimpanzee with the most extensive experience in symbolic visual matching tasks showed good performance in both conditions. In contrast, the chimpanzee expert in an auditory-visual intermodal matching task showed no sign of learning in either condition. Future work should focus on finding the most appropriate procedure for exploring chimpanzees’ auditory-visual cognitive skills.     

Population-Level Right Handedness for a Coordinated Bimanual Task in Chimpanzees: Replication and Extension in a Second Colony of Apes

The purpose of this study was to evaluate the reliability of previously published findings on hand preferences in chimpanzees by evaluating hand use in a second colony of captive chimpanzees. We assessed hand preferences for a coordinated bimanual task in 116 chimpanzees (Pan troglodytes) at the University of Texas M. D. Anderson Cancer Center and compared them to previously published findings in captive chimpanzees at the Yerkes National Primate Research Center. The new sample showed significant population-level right handedness, which is consistent with previously published findings in the Yerkes chimpanzees. Combined data on the 2 chimpanzee colonies, revealed a significant effect of rearing history on hand preference, with wild-caught chimpanzees showing less right-handedness than captive-born mother-reared chimpanzees. We discuss the results in terms of the role of early environment on the development of laterality.     

Hand preferences on unimanual and bimanual tasks in Tonkean macaques (Macaca tonkeana)

This is the first study to examine hand preferences in Tonkean macaques on a bimanual task. One of our objectives was to continue the move toward greater task standardization, in order to facilitate comparisons between species and studies on handedness. The main aim was to test and determine task robustness, by varying intra‐task complexity. To this end, we administered several different tasks to the subjects: two unimanual tasks (grasping task featuring items of different sizes) and three coordinated bimanual tasks (tube task involving different materials, weights, and diameters). Although we found no significant hand preference in either task at the group level, the macaques were more strongly lateralized for small items than for large ones in the unimanual grasping task. Moreover, the absence of a correlation between these two versions of the unimanual task confirmed the weakness of this grasping task for assessing handedness. Regarding the bimanual tube task, no difference was found between the three versions in either the direction or the strength of hand preference. Moreover, the highly correlated hand preferences between these three versions suggest that the tube task provides a more robust means of measuring manual preferences. Am J Phys Anthropol 152:315–321, 2013. © 2013 Wiley Periodicals, Inc.     

Are right- and left-handedness relevant as general categories in a non-industrialized country?

Whether right- and left-handedness are defined as a function of individual tasks or represent general categories across tasks has been long debated. However, the literature on handedness primarily concerns industrialized societies in which manual work has been extensively automated, and the majority of individuals in those countries do not use their arms and hands intensively for highly specialized tasks on an everyday basis. Thus, the question remains whether results from those countries regarding handedness are transferable to countries where the majority of individuals are still exploiting their lateralized skills. Here, we sampled 506 individuals from 143 locations on the islands of Flores and Adonara, Indonesia, to assess their hand preference for and hand performance on several tasks in order to evaluate, in a non-industrialized country, the level of manual specialization and the relevance of right- or left-handedness as general categories. Generalized-declared handedness was consistent with task-declared handedness across 10 specific tasks and with a measure of strength and a measure of skilfulness, suggesting that general handedness is a valid concept. This hand specialization for tasks is discussed in the context of intense and daily tool use in this agricultural society.     

Fitts' law is not continuous in reciprocal aiming

It takes longer to accomplish difficult tasks than easy ones. In the context of motor behaviour, Fitts'' famous law states that the time needed to successfully execute an aiming movement increases linearly with task difficulty. While Fitts'' explicit formulation has met criticism, the relation between task difficulty and movement time is invariantly portrayed as continuous. Here, we demonstrate that Fitts'' law is discontinuous in reciprocal aiming owing to a transition in operative motor control mechanisms with increasing task difficulty. In particular, rhythmic movements are implemented in easy tasks and discrete movements in difficult ones. How movement time increases with task difficulty differs in both movement types. It appears, therefore, that the human nervous system abruptly engages a different control mechanism when task difficulty increases.