Significant Hand Preferences Research Articles

Hand preference in unimanual and bimanual coordinated tasks in wild western lowland gorillas (Gorilla gorilla gorilla) feeding on African ginger (Zingiberaceae).

Bimanual coordinated behaviors are critical for detecting robust individual hand preference in nonhuman primates but are particularly challenging to observe in the wild. This study focuses on spontaneous feeding behavior on African ginger (Aframomum sp. and Renealmia sp.), which involves a unimanual task (reaching and pulling out a ginger stem) and a bimanual coordinated task (extracting pith from a ginger stem) by wild western lowland gorillas. Study subjects were 21 gorillas in the Moukalaba-Doudou National Park, Gabon. We examined whether they exhibit significant hand preference at the individual and group levels for both tasks. Sixteen gorillas showed significant hand preference in the unimanual task, whereas all 21 individuals showed significant hand preference in the bimanual coordinated task. Hand preference was significantly stronger in the bimanual coordinated task than in the unimanual task. It is noteworthy that gorillas showed a significant right-hand preference at the group level for the bimanual task (roughly 70% of the subjects). This study confirmed that bimanual coordinated tasks are more sensitive in detecting hand preferences in nonhuman primates. In addition to the bimanual nature of the task, the precision grip for processing and the importance of African ginger as a food resource might influence the expression of hand preference. Evidence of a group-level right-hand preference may support the "postural origins theory." Because all wild African great apes feed on the pith of African ginger, comparing this task and its hand preferences can contribute toward a better understanding of the evolution of handedness in Hominidae.

How Target Animacy Affects Manual Laterality in Hylobatidae: The First Evidence in Northern White-Cheeked Gibbons (Nomascus leucogenys)

Our study presents the first evidence on how target animacy impacts on manual laterality in the Hylobatidae and contributes to filling the knowledge gap between monkeys and great apes in primate evolution of emotional lateralization. Eleven captive individuals of northern white-cheeked gibbons (Nomascus leucogenys) were chosen as focal subjects. There were significantly more ambipreferent individuals than left/right-handed individuals for both inanimate (χ²(1, n = 11) = 7.364, p = 0.007) and animate (χ²(1, n = 11) = 4.455, p = 0.035) targets, meaning no significant group-level hand preference. The right hand was more frequently used than the left hand for inanimate targets whereas the left hand was more frequently used than the right hand for animate targets, although the interaction between target animacy and hand use was not significant (proportion: F1, 10 = 0.283, p = 0.607; rate: F1, 10 = 0.228, p = 0.643). Our findings in N. leucogenys could not fully support either the tool use theory or the right hemisphere hypothesis.

Preferential hand use by captive chimpanzees (Pan troglodytes) in manual and tool digging

Digging for underground storage organs of plants has been reported in various populations of wild chimpanzees (Pan troglodytes). However, it is unknown so far whether chimpanzees display lateral biases in manual digging as direct observations of this behavior are still lacking. It was therefore the aim of the present study to assess, for the first time, hand preferences for digging in a group of nine captive chimpanzees. We found that with only one exception, all individuals engaged in manual digging for buried food. Five individuals displayed a significant right-hand preference, two a significant left-hand preference, and one was ambidextrous. No apparent differences between males and females were found with regard to the direction or strength of hand preferences for manual digging. Only one out of four parent–offspring pairs was congruent in their preferred hand for manual digging. Three of the eight chimpanzees who dug manually also used tools in order to excavate buried food. Among those three individuals, one displayed a significant right-, one a significant left-hand preference, and one was ambidextrous. Only one of these three chimpanzees was consistent in preferring the same hand for manual and tool digging. The present findings are in line with the notion that chimpanzees display significant hand preferences at the individual level for haptic-guided behaviors, with a tendency for the right hand.

Hand preferences and differences in extractive foraging in seven capuchin monkey species.

Tool use and extractive foraging could be drivers for right hand use preference. The robust capuchins, Sapajus, are more specialized for destructive and extractive foraging than the gracile capuchins, Cebus. Thus, we predicted them to show right-hand preference and higher rates of extractive foraging when compared to the gracile capuchins. We hypothesized that capuchins that evolved in dry habitats are predisposed to show higher rates of extractive foraging and right-hand preference. We employed the tube task (152 individuals) and an extractive foraging task (212 individuals) in seven species of capuchins in captive settings. Data on hand preference and extractive foraging were collected using focal and scan sampling, respectively. Contrary to our hypothesis, S. libidinosus showed significant left hand preference, while S. robustus and S. flavius showed a right hand preference. The species S. xanthosternos, S. flavius, and S. robustus engaged in extractive foraging significantly more often than S. apella, S. libidinosus, and Cebus albifrons. As expected, the gracile capuchins showed significant higher left-hand bias when compared to the robust capuchins. The findings from this study is the first indication of left-hand population level laterality in S. libidinosus, a species that evolved in an environment selecting for increased tool use. Although tool use has been associated with population level right handedness, or a strong trend to use the right hand, our results suggest the link between tool use and right-hand preference is simplistic, at least in Sapajus. The ultimate explanation for the differences in hand preference across species might be due to differences in use of key food resources. We suggest that capuchin monkeys from the Atlantic forest evolved under a stronger selective pressure for high reliance on bimanual feeding and extractive foraging, which requires more sequential actions and planning, than those species from the Amazonia forest and Caatinga/Cerrado dry forest.

Hand preferences in two unimanual and two bimanual coordinated tasks in the black-handed spider monkey (Ateles geoffroyi).

Spider monkeys are interesting to study with regard to hand preferences, as they are one of the few primate species that lack a thumb and, thus, are unable to perform a precision grip. Further, being platyrrhine primates, they also largely lack independent motor control of the digits and, thus, have only limited manual dexterity. It was therefore the aim of the present study to assess hand preferences in black-handed spider monkeys (Ateles geoffroyi) in 4 tasks differing in task demand: simple unimanual reaching for food and 3 versions of the widely used tube task, including 2 bimanual versions that differ from each other in the degree of fine motor control needed and a unimanual version that does not require coordinated action of the hands. We found that black-handed spider monkeys display significant hand preferences at the individual, but not at the population, level. This was true both in the 2 bimanual coordinated tasks and in the 2 unimanual tasks. Further, our results show that the majority of animals were consistent in the hand they preferred in these 4 tasks. Our findings only partially support the notion that task demand positively correlates with strength of hand preference. Finally, we found that the index finger was the most frequently used digit in all 3 tube tasks, although the animals also used other digits and 2- and 3-finger combinations to extract food from a tube. We conclude that limited manual dexterity does not prevent spider monkeys from displaying strong and consistent hand preferences at the individual level. (PsycINFO Database Record

Hand preference on unimanual and bimanual tasks in Barbary macaques (Macaca sylvanus)

The presence of group-level handedness in non-human primates remains controversial, as different studies have produced inconsistent results. Bimanual coordinated tasks have been found to elicit more pronounced hand preferences than simple unimanual tasks. The aim of this study was to examine manual lateralization in a group of 15 Barbary macaques during unimanual and bimanual tasks. In the unimanual task, data on simple food reaching in a foraging context were collected. During the bimanual task, macaques had to use one hand to hold a tube-shaped apparatus while reaching with the other hand to retrieve the food inside it. Data on the hand use to retrieve food were collected. First, no significant group-level hand preference was found for the unimanual task. However, a significant right hand bias was evident for the bimanual task. At the individual-level, approximately 47% and 67% of the subjects had a significant hand preference in the unimanual and bimanual task respectively. The strength of the hand preference was greater in the bimanual than in the unimanual task. Findings of this study add Macaca sylvanus to the other species showing a right hand preference for coordinated bimanual tasks. Moreover, our results add to the growing body of evidence that bimanual tasks are more suitable and valid measures to investigate handedness in non-human primates.

Laterality of Grooming and Tool Use in a Group of Captive Bonobos (Pan paniscus)

Humans exhibit population level handedness for the right hand; however, the evolution of this behavioral phenotype is poorly understood. Here, we compared the laterality of a simple task (grooming) and a complex task (tool use) to investigate whether increasing task difficulty elicited individual hand preference among a group of captive bonobos (Pan paniscus). Subjects were 17 bonobos housed at the Columbus Zoo and Aquarium. Laterality of grooming was recorded using group scans; tool use was recorded using all-occurrence sampling. Grooming was characterized as unimanual or bimanual, and both tasks were scored as right-handed or left-handed. Most individuals did not exhibit significant hand preference for unimanual or bimanual (asymmetrical hand use) grooming, although 1 individual was lateralized for each. For the 8 subjects who engaged in termite fishing enough for statistical testing, 7 individuals exhibited significant laterality and strong individual hand preference. Four subjects preferred their left hand, 3 preferred their right, and 1 had no preference. Grooming, a simple behavior, was not lateralized in this group, yet a more complex behavior revealed a strong individual hand preference, and these results are congruent with other recent findings that demonstrate complex tasks elicit hand preference in bonobos.

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.

Hand preference for tool-use in capuchin monkeys (Cebus apella) is associated with asymmetry of the primary motor cortex.

Skilled motor actions are associated with handedness and neuroanatomical specializations in humans. Recent reports have documented similar neuroanatomical asymmetries and their relationship to hand preference in some nonhuman primate species, including chimpanzees and capuchin monkeys. We investigated whether capuchins displayed significant hand preferences for a tool-use task and whether such preferences were associated with motor-processing regions of the brain. Handedness data on a dipping tool-use task and high-resolution 3T MRI scans were collected from 15 monkeys. Capuchins displayed a significant group-level left-hand preference for this type of tool use, and handedness was associated with asymmetry of the primary motor cortex. Left-hand preferent individuals displayed a deeper central sulcus in the right hemisphere. Our results suggest that capuchins show an underlying right-hemisphere bias for skilled movement.

Patterns and laterality of hand use in free-ranging aye-ayes (Daubentonia madagascariensis) and a comparison with captive studies

We observed hand use in free-ranging aye-ayes (Daubentonia madagascariensis) on an island in the Mananara River, eastern Madagascar. The results were compared with those of two conflicting studies on hand laterality in captive aye-ayes. We argue that patterns of hand preference in wild aye-ayes are comparable to those of captive animals and that discrepancies between studies are—at least partly—caused by different ways of collecting and processing data. Aye-ayes fit Level 2 of the categories of hand laterality described by McGrew and Marchant (Yearb Phys Anthropol 40:201–232, 1997), with some individuals showing significant hand preference, but with the proportion of right- to left-preferent animals being very close to 1:1. We observed hand preference to be consistent for two of the most frequent behaviors, tapping and probing with fingers. Reaching and holding objects in hands is rare in aye-ayes, and the patterns of hand use in aye-ayes are therefore not directly comparable with those of other prosimians in which laterality has been studied. We detected no effect of sex on hand preference and were unable to determine whether there is an effect of age. The posture adopted by the animals did not influence hand preference.

Hand preferences in Barbary macaques (Macaca sylvanus)

Nearly 90% of humans are right-handed, raising the question of the evolutionary origins of this trait. While lateralisation of certain actions appears to be widespread in vertebrates, the question of whether nonhuman primates exhibit hand preferences at the population level is often contested. We observed Barbary macaques (Macaca sylvanus) living in the outdoor enclosure “La Forêt des Singes” at Rocamadour, France, while performing simple unimanual and coordinated bimanual tasks. For the unimanual task, we recorded continuously which hand they used reaching for grains. For the coordinated bimanual tasks, a semi-transparent box and a tube baited with peanut butter were presented to the macaques and the hand used to open the box or reach into the tube, respectively, was recorded. We found no significant hand preference in any of the tasks at the population level, but found individual hand preferences, the extent of which varied among individuals. For the unimanual, but not the bimanual task, we found that the handedness index increased with age. Our results add to the growing body of evidence that monkeys do not show hand preference at the population level.

Experimental field study of hand preference in wild black-horned (Cebus nigritus) and white-faced (Cebus capucinus) capuchins: evidence for individual and species differences

In this experimental field investigation, we compare the degree to which wild capuchins in Brazil (Cebus nigritus) and Costa Rica (Cebus capucinus) exhibit individual- and population-level handedness during three visually-guided tasks. These tasks required reaching to remove a large leaf covering a hidden food reward, seizing the food reward, and manipulating a tool (pulling a wooden dowel) in order to obtain access to an embedded food reward. Studies in some populations of captive capuchins indicate evidence for both individual hand preferences and population-level handedness. In this study, six of eight wild C. capucinus and six of seven wild C. nigritus exhibited a significant hand preference during individual tasks, but no individual exhibited a consistent preference across all three tasks. Task-specialization, or the tendency for most individuals in the same group or population to use the same hand to accomplish a particular task, also was evaluated. Cebus nigritus showed a significant bias toward the use of the right hand in removing the leaf. Although the number of individual capuchins in both species that manipulated the dowels was limited (N = 7), each individual that manipulated the dowels in eight or more instances had a positive handedness index, suggesting a greater use of the right hand to accomplish this task. Overall, our results provide preliminary support for individual- and population-level handedness in wild capuchin monkeys.

Consistency of hand preference across low‐level and high‐level tasks in Capuchin monkeys (Cebus apella)

Numerous studies investigating behavioral lateralization in capuchins have been published. Although some research groups have reported a population-level hand preference, other researchers have argued that capuchins do not show hand preference at the population level. As task complexity influences the expression of handedness in other primate species, the purpose of this study was to collect hand preference data across a variety of high- and low-level tasks to evaluate how task complexity influences the expression of hand preference in capuchins. We tested eleven captive brown capuchin monkeys (Cebus apella) to determine if they show consistent hand preferences across multiple high- and low-level tasks. Capuchins were expected to display high intertask consistency across the high-level tasks but not the low-level tasks. Although most individuals showed significant hand preferences for each task, only two of the high-level tasks that involved similar hand motions were significantly positively correlated, indicating consistency of hand preference across these tasks only. None of the tasks elicited a group-level hand preference. High-level tasks elicited a greater strength of hand preference than did low-level tasks. No sex differences were found for the direction or strength of hand preference for any task. These results contribute to the growing database of primate laterality and provide additional evidence that capuchins do not display group-level hand preferences.

Hand preferences in captive orangutans (Pongo pygmaeus)

The strength of the evidence for population-level handedness in the great apes is a topic of considerable debate, yet there have been few studies of handedness in orangutans. We conducted a study of manual lateralization in a captive group of eight orangutans (Pongo pygmaeus) ranking the degrees of manual preference according to a defined framework. We analyzed five behavioral patterns: eat (one- and two-handed), make/modify tool, oral tool-use, and manual tool-use. Although some individuals showed significant manual preferences for one or more tasks, at the group-level both one-handed and two-handed eating, oral tool-use, and make/modify tool were ranked at level 1 (unlateralized). Manual tool-use was ranked at level 2, with four subjects demonstrating significant hand preferences, but no group-level bias to the right or left. Four subjects also showed hand specialization to the right or left across several tasks. These results are consistent with most previous studies of manual preference in orangutans. The emergence of manual lateralization in orangutans may relate to more complex manipulative tasks. We hypothesize that more challenging manual tasks elicit stronger hand preferences.

Laterality of hand function in naturalistically housed chimpanzees (Pan troglodytes)

Studies of laterality of hand function in chimpanzees (Pan troglodytes) have the potential to tell us about the origins of handedness in Homo sapiens. However, the data are confusing, with discrepancies present between studies done in the field and the laboratory: the former show wild chimpanzees to be unlateralised at the population level, while the latter show captive chimpanzees as lateralised at the population level. This study of 26 semi-free ranging chimpanzees of Chester Zoo, UK, aimed to investigate a situation between the wild and captivity and provided ethological data for 43 categories of spontaneous manual use and 14 categories of tool use. Other variables recorded were subordinate hand activity, whether the subject was arboreal or terrestrial, and the identity of the subject. Using switching focal subject sampling, 23,978 bouts of hand use and 1,090 bouts of tool use were recorded. No population-level handedness was present for manual non-tool use activities in the naturalistically housed chimpanzees of Chester Zoo in a similar way to studies of wild chimpanzees. However, about half of the individuals were lateralised to one side or the other for the foraging behaviours of pick up, eat, and pluck. Using a modified version of McGrew and Marchant's (1997) Laterality Framework, these results are comparable to some wild and captive populations for similar foraging tasks. Bimanuality was rare and thus prevented comparison with captive experimental studies that have reported population right handedness. Behaviour involving contact with water elicited stronger lateralisation. Chester chimpanzees were more likely to exhibit hand preferences for manual tasks with increasing age but there were no effects of sex or rearing history on hand specialisations in adult individuals. Lateralisation was biased in tool use, which evoked significant left hand preferences in half the individuals, with no effect of age. Results are discussed comparatively with reference to methodological and developmental issues. Longitudinal studies of hand use are needed to increase our understanding of laterality of hand use in chimpanzees.

Reach and posture hand preferences during arboreal feeding in sifakas (Propithecus sp.): A test of the postural origins theory of behavioral lateralization.

Sixteen sifakas (11 Propithecus verreauxi coquereli, 2 Propithecus verreauxi verreauxi form majori, and 3 Propithecus tattersalli) were videotaped as they fed on leaves in an arboreal context. The hand used to feed and the hand used to maintain postural stability was coded. For each subject, the lateral bias of the hand used to feed was opposite the hand used in postural support. Seven sifakas displayed no bias for feeding or posture-related hand use, 7 sifakas displayed significant feeding-related reach preferences for pulling branches to the mouth (5 left- and 2 right-hand preferences), and 9 sifakas exhibited significant hand preferences for postural support (2 left-, 7 right-hand preferent). Although these data do not strongly support the postural origins theory of behavioral lateralization, the modal preference pattern for sifakas that displayed significant hand preferences for posture and feeding involve a left bias for feeding and a right bias for postural support. s reserved).

Leading-limb preferences in marmosets (Callithrix jacchus): Walking, leaping and landing

The leading-limb preferences of 17 common marmosets (Callithrix jacchus) when they initiated and terminated locomotion were determined from video recordings of the subjects walking on, leaping off, and landing on a plexiglas platform. In a majority of sequences, 11 of 17 subjects landed with the right hand and foot contacting the plexiglas substrate before the left hand and foot. Of the 17 subjects, 8 initiated leaping with the right side of the body, whereas only 3 subjects significantly preferred to initiate leaping with the left hand and foot. Leading-limb preferences displayed during landing were positively correlated with those displayed for leaping and walking, although only two subjects displayed significant leading-limb preferences when walking. By contrast, hand preferences for initiating and terminating locomotion were not related to hand preferences for food holding; 16 of 17 marmosets displayed strong and significant hand preferences for food holding, even though many did not show leading-limb preferences for walking, leaping, or landing. These data seem to suggest that the right arm is stronger in marmosets. The right arm is used initially to decelerate the body and absorb the impact of contact with the landing substrate. The tendency for the right arm to be stronger is balanced by a tendency for the left leg to be stronger (providing the force needed for leaping).

Patterns of lateralized hand use in an arboreal primate, Simias concolor.

Studies of hand use in nonhuman primates suggest that several species exhibit hand preferences for a variety of tasks. The majority of studies, however, focus on the lateralized hand use of captive nonhuman primate populations. Although captive settings offer a more controlled environment for assessing hand preferences, studies of wild populations provide important insights into how handedness is affected by natural environmental conditions and thus potential insights into the evolution of handedness. To investigate handedness in a population of wild nonhuman primates, we studied patterns of lateralized hand use during feeding in four simakobu monkeys (Simias concolor), an arboreal species inhabiting the Mentawai Islands, Indonesia. Our data show that individual variation in hand preferences for feeding existed among our study animals. In addition, each simakobu expressed a significant hand preference for supporting itself on a branch during feeding, an uncoordinated bimanual task. This bias was most prevalent when the branch used for support was a main branch rather than a terminal branch. When both hands were employed in a coordinated bimanual feeding activity (bimanual manipulation), only two subjects showed a significant bias for feeding. Our data suggest that these individuals are more likely to express significant hand preferences when feeding from stable, rather than precarious, positions within the canopy.

Development of hand preferences in marmosets (Callithrix jacchus) and effects of aging.

The authors investigated the development of unimanual hand use and hand preferences during feeding in 15 marmosets (Callithrix jacchus), ages birth to 51-70 months. Bimanual hand use was common at 1-2 months, but by 5-8 months unimanual holding had developed and so had significant hand preferences. Half of the marmosets preferred to pick up and take food to the mouth with the left hand, and half preferred the right hand. Individuals maintained the same hand preference at all ages examined. Significant relationships were also found between the postures adopted during feeding and the direction of hand preferences displayed by juvenile marmosets. There was a positive correlation between increased suspension and increased left-hand preference, and a negative correlation between increased feeding in a tripedal posture and increased left-hand preference. These results are discussed in terms of motor development and hemispheric specialization.

Hand preferences in unimanual and bimanual feeding by wild vervet monkeys (Cercopithecus aethiops).

Lateral preference was examined in spontaneous feeding actions in 2 troops of wild vervet monkeys (Cercopithecus aethiops). Processing of 4 foods (termites, leaf shoots, sugarcane, and fruit) was studied. Actions included unimanual reaching to moving objects, operating from an unstable posture, and coordinated bimanual processing. Between 19 and 31 subjects were available, according to the task. In 2 tasks, laterality of 2 independent stages was measured separately, giving 6 measures in all. On 4 of these measures, most monkeys were ambipreferent, and only a few showed significant hand preferences. Only for termite feeding and detaching material from fruits did the majority show significant lateralization; no tasks elicited exclusive use of 1 hand. Preference appeared labile, because in 2 tasks, population trends reversed with increasing age. No population trends to left or right were found; instead, these monkeys showed ambilaterality, with lateralization associated with task complexity.