Hand preferences in unimanual and coordinated-bimanual tasks by tufted capuchin monkeys (Cebus apella).

Hand preferences in 26 capuchin monkeys (Cebus apella) were examined in 2 reaching-for-food tasks under 2 postural conditions. In the 1st task (unimanual), monkeys were required to reach for food from both a quadrupedal and an upright posture. A right-hand bias was found for the upright but not for the quadrupedal condition. In the 2nd task (coordinated bimanual), monkeys were required to extract the food from a hanging Plexiglas tube from both a crouched and an upright posture. A right-hand bias was found for both conditions. A significant increase in right-hand use was noted from the unimanual, quadrupedal, reaching task to the coordinated-bimanual task, with females exhibiting a greater right-hand preference than males. In addition, a significant effect of task complexity on strength in laterality was found. Results are discussed in the context of recent theories on primate laterality. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Multiple measures of motor lateralization in human primates (Homo sapiens).

Laterality was assessed in 100 human (Homo sapiens) subjects through the use of five measures of motoric behavior in three categories: locomotor, manual, postural. Locomotor meaures included leading limb for initiation of walking and whole-body turning. Performance and questionnaire measures were used to assess lateral hand bias. Postural bias was assessed as the weight distribution in quiet standing. Population-level biases on the manual and leading limb measures were to the right; on posture and turning, to the left. Locomotor measure were found to be altered by marching experience. Only the manual measures were correlated. We compare the results with those of nonhuman primate studies (e.g., C. Forsythe et al, see PA, Vol 76:477, G. W. Milliken et al, see PA, Vol 77:9169) that have used similar measures and discuss some patterns of laterality common to human and nonhuman primates. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Bipedal posture and hand preference in humans and other primates.

Hand preference for quadrupedal and bipedal reaching in humans and rhesus macaques (Macaca mulatta) was examined, and the data were compared with postural reaching data that have been reported for 8 other primate species. Population-level biases were found toward use of the right hand for quadrupedal and bipedal reaching in humans and use of the left hand for quadrupedal reaching in rhesus macaques. Rhesus macaques showed a significant shift toward greater use of the right hand for bipedal vs. quadrupedal reaching. Comparisons with other species showed significant variance in the direction and strength of hand preference across reaching postures. The study noted right-hand biases for bipedal reaching in humans, great apes, and tufted capuchins and shifts toward greater use of the right hand for bipedal vs. quadrupedal reaching in great apes, tufted capuchins, and rhesus macaques. These results suggest that posture alters both the direction and strength of primate hand preference and that bipedalism may have facilitated species-typical right-handedness in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Laterality for visual-spatial processing in two language-trained chimpanzees (Pan troglodytes).

Most reviews of laterality in nonhuman primates indicate that hemispheric asymmetries, similar to those found in humans, are not evident. With the growing evidence for cognitive processes germane to language in apes, in addition to their phylogenetic similarity to humans, they appear to be useful candidates for studies of laterality. Laterality for visual-spatial processing in 2 language-trained chimpanzees was investigated with a visual half-field paradigm. Initially, Ss were taught to manipulate a joystick that controlled the movement of a cursor on a computer monitor to a central fixation point. Ss were then taught a visual discrimination based on the location of a short line contained within a geometric form. Testing consisted of systematic presentation rates of 15, 122, and 226 ms to the left and right visual fields. For half of the trials, Ss used their left hand to respond and used the right hand for the remaining trials. Accuracy and reaction time (RT) were the dependent measures. One S demonstrated significantly faster RTs to stimuli presented to the left visual field (LVF) regardless of which hand was used to respond. The other S demonstrated a significant LVF bias when using the left hand to respond. Results are discussed in the context of current theories on the evolution of laterality and its relation to linguistic functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Asymmetries in spontaneous head orientation in infant chimpanzees (Pan troglodytes).

Behavioral laterality in head orientation while sleeping in either a supine or prone posture was examined in 43 chimpanzees (Pan troglodytes) for the first 3 months of life. An overall significant right-side lateral bias was found for head orientation in the supine posture. A trend toward greater right-side bias in females compared with males was observed but failed to reach significance. These data suggest that asymmetries in head orientation are present early in life in chimpanzees, and they may be correlated with functional asymmetries observed in adulthood. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postural effect on manual laterality in different tasks in captive grey-cheeked mangabey (Lophocebus albigena).

The authors examined the effects of task complexity and posture on laterality and compared lateralization during different tasks in 9 captive grey-cheeked mangabeys (Lophocebus albigena) during spontaneous food processing and 3 experimental tasks. Comparisons with data of red-capped mangabeys (Cercocebus torquatus torquatus; semiterrestrial species) were used. Less than half the monkeys were lateralized for simple everyday activities, but 6 were lateralized for complex daily activities. Moreover, all the monkeys were lateralized when performing experimental tasks. Laterality at the group level was found for the bipedal task: Mangabeys were right-handed. Complexity of tasks increases laterality at the individual level. Significant differences between the 2 species of mangabeys were found, allowing us to confirm that postural constraints are a major factor in the emergence of group handedness. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Masking and visual field effects on a lateralized rod-and-frame test.

Investigated whether laterality effects would be affected by poststimulus masking in a rod-and-frame test in which visual stimuli were presented to one side or the other of a central fixation point. 96 Ss (aged 18–28 yrs; 50% female) participated. For half the Ss, stimuli were followed by a blank screen; for the other half, stimuli were followed by a mask. An overall left visual field advantage (LVFA) was found in the task. An interaction of sex of Ss, masking conditions, and frame tilt was also found. Data showed that the sex by angle of frame interaction was significant when a mask was presented after the stimuli, but not when no mask followed the stimuli. Results suggest that the LVFA was only significant when a mask was presented after the stimuli. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lateral bias for rotational behavior in tufted capuchin monkeys (Cebus apella).

This research examined lateral bias for rotational behavior in tufted capuchin monkeys (Cebus apella). A symmetrical distribution of rotational bias was noted, with approximately equal numbers of Ss preferring to turn to the right and to the left. As a group, adults did not exhibit a lateral rotational bias. Immatures preferentially rotated to the left. Across Ss, the strength of rotational bias was positively related to the incidence of right-eyed looking. Rotational bias was not related to hand preference. The finding of analogous age-dependent patterns of rotational bias in capuchins and in humans suggests that the rotational behavior of Cebus apella can be used to model an asymmetric response pattern that has been linked to development in Homo sapiens. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hemispheric specialization in infant chimpanzees (Pan troglodytes): evidence for a relation with gender and arousal

The current study extends previous documentation of behavioral asymmetries in hand-to-mouth, self-consoling behaviors of infant chimpanzees. The underlying source of lateralized hand-to-mouth, self-calming behavior was investigated by comparing individual differences in neonatal arousal levels, regulatory ability, and motor performance with individual differences in the degree of laterality at 3 months. Asymmetrical hand-to-mouth, self-calming behaviors at 3 months of age were significantly related to general arousal at 2 days of age (i.e., the Range of State cluster scores measured by the Brazelton Neonatal Behavioral Assessment Scale). Simply stated, chimpanzees with a right-hand bias in hand-to-mouth behavior exhibited lower arousal at 2 days of age compared with nonright-handed individuals. The only item of the Range of State cluster to distinguish subjects was irritability: Right-handed subjects were less irritable. Previously, a trend was reported with respect to sex differences in the laterality of hand-to-mouth behavior. With the greater number of subjects in the present study, we found that females exhibited a significantly greater right-hand bias for hand-to-mouth behaviors (12 of 13) than did males (9 of 15). We conclude that neonatal arousability, and not regulatory capacity or motor performance, predicts the degree of laterality found in hand-to-mouth, self-calming behaviors in 3-month-old chimpanzees. These data are discussed from the standpoint of early pari-parturitional or intrauterine factors affecting lateralized development.     

Head Orientation position during birth and in infant neonatal period, and hand preference at nineteen weeks

This study of lateral preferences of normal full-term infants found, as predicted, that infants who were delivered from a left occiput anterior or transverse birth position (head turned to the right) exhibited a neonatal right supine head orientation and a right-hand preference in visually guided reaching tasks at 19 weeks. Contrary to prediction, infants delivered from a right occiput anterior or transverse birth position (head turned to the left) did not exhibit a left-sided preference in either neonatal head position or hand preference. Results are discussed in relation to other research which found a right shift in neonates' head orientations and in the distribution of hand preference in the human population. The findings suggest further investigation into the relationship between prenatal and postnatal postural asymmetries and the continuing development of laterality.     

Time course of movement planning: Selection of handgrips for object manipulation.

A goal of research on the cognitive control of movement is to determine how movements are chosen when many movements are possible. The authors addressed this issue by studying how Ss reached for a bar to be moved as quickly as possible from a home location to a target location. Ss generally grabbed the bar in a way that afforded a comfortable posture at the target location (the end-state comfort effect) and with the thumb toward the end of the bar that would be aligned with the target (the thumb-toward bias). The data suggest that Ss chose handgrips by retrieving instances of previous reaches, not by carrying out computations that treated candidate reaches as new behavioral events. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Limb laterality and motor proficiency in children

This investigation examined the premise derived from recent reports, that children who are consistent right-handers are better coordinated than their left- and mixed-sided (inconsistent) peers. The observation of limb laterality was extended to include footedness. Two samples of children (N = 273) (foot laterality/hand laterality), matched for age and sex, were assessed for motor proficiency and compared according to limb preference (right, mixed, left). Overall, results indicated no significant group differences (ps > .05) in composite scores (upper-limb, lower-limb, combination) and total performance, within foot and hand laterality. In view of recent studies (noting differences between laterality groups) and these nonsupportive results, it appears that additional inquiry is warranted before any consensus regarding the association between limb laterality and motor coordination can be established. Suggestions for further inquiry are presented.     

Visual hemifield differences in the perception of letters and contour orientation.

In Exp. I, 10 students were required to recognize capital English letters presented 3– to the left or to the right of a fixation point. In Exp. II, 8 Ss were required to discriminate the orientation of a line presented in either the left or the right visual hemifield. In both experiments Ss displayed a significant right visual hemifield superiority, and a marked positive correlation was observed in the hemifield differences between the 2 recognition tasks. Results suggest that for certain classes of stimuli visual laterality differences may be subserved by a selective contour-tuning mechanism. (French summary) (15 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anxiety and lateral cerebral function.

In an initial experiment with 80 right-handed undergraduates, Ss reporting high anxiety (State-Trait Anxiety Inventory) evidenced a performance decrement that was specific to tasks presented to the right visual half-field. Given this suggestion of left-hemisphere involvement in anxiety, a 2nd experiment with 32 undergraduates examined attentional bias and lateral eye movements; high trait anxiety was associated with a right-ear attentional bias and a low incidence of left lateral eye movements. These observations suggest that anxiety, as an individual difference variable, might entail a lateral shift in cerebral function. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental changes in hemispheric specialization for tactile spatial ability.

64 1st-, 3rd, and 5th-grade children and adults (16 in each group) performed a tactile shape-discrimination task. On each of 40 trials, after exploring a randomly generated nonsense form using only finger motion, Ss judged a tactually presented comparison form as either the same as or different from the 1st stimulus. In Condition 1, a single stimulus form and the comparison form were successively presented to the same hand. In Condition 2, stimulus forms were simultaneously presented to both hands; however, a comparison form was presented to only one hand. Results indicate that the left hand (right hemisphere) was more accurate than the right hand (left hemisphere) for 5th-grade Ss and adults, but no significant differences between hands were found for 1st- and 3rd-grade Ss. Overall, Condition 2 was more difficult than Condition 1, but similar laterality effects were found in both groups. Sex differences were found only in the adult group in which males made somewhat fewer errors than females. These results suggest that the right hemisphere becomes progressively more specialized for tactile spatial ability with increasing age. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous osseous genioplasty and meloplasty

We measured whether males of five species of poeciliid fish made detours to the right or left of a vertical-bar obstacle in order to approach a group of females. Three of these species, Gambusia holbrookiGambusia nicaraguensis and Poecilia reticulata showed a significant bias to the left, whereas Brachyrhaphis roseni and Girardinus falcatus showed a significant bias to the right. When tested for direction of turning in front of an opaque barrier, or when a dummy predator was used as a target in a detour test, G. holbrooki and G. falcatus showed similar biases to the right (opaque barrier) and left (predator), thus suggesting that the difference observed when females were used as a target could arise from species differences in the degree of sexual motivation in a novel environment. The two species that showed bias to the right with the females were less likely to exhibit sexual behaviour when placed in a novel environment. Moreover, manipulation of the factors affecting the relative strength of sexual motivation and of fear of a novel environment, such as how long fish were maintained in captivity or in the test apparatus before being tested, caused shifts in the direction of the lateral asymmetries. These results suggest that the presence of functional asymmetries in behaviour could be widespread among vertebrates and that the direction of such asymmetries tends to be strikingly similar in closely related species, thus supporting the hypothesis of an early evolution of laterality in brain and behaviour.Copyright 1997 The Association for the Study of Animal Behaviour1997The Association for the Study of Animal Behaviour     

Effect of posture on hand preference during experimental food reaching in bonobos (Pan paniscus).

The effect of posture on hand preferences was examined in an experiment with 5 bonobos (Pan paniscus). To obtain a food reward, the animals had to adopt 1 out of 7 different postures. These postures represented an increasing problem to the maintenance of body equilibrium. It was expected that an increasing demand for equilibrium maintenance would elicit individual preferences and a population-level bias. All animals showed an increasing trend toward left-handedness while shifting to a bipedal posture from a seated posture by way of a quadrupedal posture. The importance of bipedalism in the evolution of left- and right-handedness is discussed briefly. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reduction of intergroup discrimination through individuation of the out-group.

Several studies have found that the mere categorization of persons into groups is sufficient to promote intergroup discrimination. Out-group members may be convenient targets of bias because they are more deindividuated than in-group members. If so, then intergroup discrimination may be lessened through individuation of the out-group. In the 1st experiment, 72 undergraduates were divided into groups and were informed that the out-group was either unanimous in its behavior or that one member dissented from the majority. Typical levels of intergroup bias were found in the unanimous condition, but Ss did not discriminate against the out-group when an out-group member dissented. These findings were corroborated and extended in 2 subsequent experiments with 225 Ss. Ss requested assistance from an out-group that had previously frustrated them. Assistance from the out-group was found to be more effective in reducing intergroup bias when the out-group responded as individuals than when it responded as a group. Overall, results indicate that intergroup bias is related to the manner in which persons cognitively structure the out-group. Ss discriminated when the out-group was perceived to be a single entity but behaved more fairly when the out-group was more individuated. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hypnosis, reporting bias, and suggested negative hallucinations.

Examined the role of reporting bias in hypnotic negative hallucinations by using a paradigm in which reporting bias was assessed independently of perceptual change. In Exp 1, highly hypnotizable Ss reported significant loudness reductions when tested for hypnotic deafness. Later, however, these Ss biased their reported loudness reductions in the absence of perceptual change, and their reporting bias scores were almost as large as their hypnotic deafness reports. Ss also biased their ratings of strategy use. In Exp 2, ratings of blindness given in response to a hypnotic negative visual hallucination suggestion were significantly correlated with reporting bias scores obtained in this paradigm. Although hypnotic blindness and hypnotic deafness correlated significantly, the partial correlation between these variables was nonsignificant when reporting bias scores were statistically controlled. Theoretical implications are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)