The influence of a hand preference for acquiring objects on the development of a hand preference for unimanual manipulation from 6 to 14 months

Development of hand preferences for unimanual manipulation of objects was explored in 90 infants (57 males) tested monthly from 6 to 14 months. From a larger sample of 380 infants, 30 infants with a consistent left hand preference for acquiring objects were matched for sex and development of locomotion skills with 30 infants with a consistent right hand preference for acquisition and 30 with no preference. Although frequency of unimanual manipulations increased during 6–14 month period, infants with a hand preference for acquisition did more object manipulations than those without a preference for acquisition. Multilevel modeling of unimanual manipulation trajectories for the three hand-preference groups revealed that hand preferences for unimanual manipulation become more distinctive with age, and the preference is predicted by the hand preference for object acquisition. Infants with a right and left hand preference for object acquisition develop a right and left (respectively) hand preference for unimanual manipulation. However, the majority of infants at each month do not exhibit hand preferences for unimanual manipulation that are unlikely to occur by chance, even by 14 months. The results are consistent with a cascading theory of handedness development in which early preferences (i.e., for acquisition) are transferred to later developing preferences (i.e., for unimanual manipulation).     

Development of infant prehension handedness: A longitudinal analysis during the 6- to 14-month age period

Handedness is a developmental phenomenon that becomes distinctively identifiable during infancy. Although infant hand-use preferences sometimes have been reported as unstable, other evidence demonstrates that infant hand-use preference for apprehending objects can be reliably assessed during the second half of the infant's first year of life. The current study provides further insight into the stability of prehension preferences. We modeled individual and group level patterns of prehension handedness during the period from 6 to 14 months of age. We examined the developmental trajectories for prehension handedness in relation to the sampling rate at which preferences are assessed. The results revealed interesting developmental changes in prehension handedness that can only be identified when using monthly sampling intervals. We conclude that using non-linear multilevel models of infant handedness with monthly sampling intervals permit us to accurately capture the developmental changes in manual skills that occur during this period of infancy.     

Age Changes in Interlimb Coupling and the Development of Bimanual Coordination

Changes in interlimb coupling, and their role in the development of bimanual coordination, were studied longitudinally in 6- to 12-month-old infants (N = 6). Infants were observed while they were reaching for simple objects of 2 different sizes. Their use of a uni-versus bimanual strategy for reaching as well as the coupling of their bimanual movements were compared; progress in bimanual coordination of complementary movements was evaluated on 8 different bimanual tasks. The bimanual tasks involved an asymmetrical cooperation between the 2 hands. Although spatiotemporal coupling of bimanual reaching movements did not decrease during the age period studied, infants around 7 months of age used their 2 hands infrequently for reaching. Occurrences of bimanual reaching were particularly low at the session preceding the first bimanual success at a bimanual task. This suggests that the temporal coincidence between greater independence of the 2 hands and progress in bimanual coordination of complementary movements acts in 2 directions: Infants may be more at ease when using their 2 hands in differentiated patterns as the hands move less in synchrony, but, in turn, they may be less likely to move their hands in synchrony as the anticipate mirror manipulations of the object less. The frequency of bimanual reaches increased toward the end of the 1st year. This might have been caused by an increase in the repertoire of bimanual asymmetrical object manipulations and by the fact that the development of bimanual coordination allows infants to manipulate objects with complementary movements even after a bimanual approach toward the object.     

The use of bouts and frequencies in the evaluation of hand preferences for a coordinated bimanual task in chimpanzees (Pan troglodytes): an empirical study comparing two different indices of laterality

Hand preferences for a coordinated bimanual task were assessed in 109 chimpanzees (Pan troglodytes). Hand preference was evaluated for 4 test sessions using bouts and frequencies of hand use to compare the sensitivity of each level of analysis in evaluating individual variation in handedness. Overall, significant population-level right-handedness was found using several different measures of hand use. Handedness indices based on bouts and frequencies were highly and significantly correlated. Moreover, hand preferences were consistent across tests despite efforts to situationally bias preference during each test. Taken together, these data do not support the view that bouts are a better level of analysis for evaluating hand preference. The results further suggest that hand preferences for coordinated bimanual actions are not influenced by situational factors and may reflect an inherent specialization of the left hemisphere for motor skill.     

Heritability of hand preference in chimpanzees (Pan troglodytes): evidence from a partial interspecies cross-fostering study.

Heritability of hand preference was tested in a sample of 188 chimpanzees (Pan troglodytes). Hand preference was measured by coordinated bimanual actions, and concordance percentages were compared between parents and offspring and siblings. Among siblings, concordance percentages were compared for dyads in which both individuals were raised by chimpanzees, both were raised by humans, or 1 was raised in each environment. The results indicated population-level right hand preferences for coordinated bimanual actions. There were no significant associations in hand preference between parents and offspring. In full and maternal half siblings, concordance in hand preference was significantly greater than chance in mother- and human-reared individuals but not in cross-fostered dyads. The cumulative results suggest that the direction of hand preference is heritable in chimpanzees but the mechanism of transmission is not genetic. Several environmental explanations are proposed to explain the findings, including the potential role of maternal cradling bias and in utero fetal position.     

AN ANALYSIS OF REINFORCER SUBSTITUTABILITY USING OBJECT MANIPULATION AND SELF-INJURY AS COMPETING RESPONSES

The concept of reinforcer substitutability proposes a continuum of interactions among reinforcers in a given situation. At one end of this continuum, reinforcers are substitutable, with one reinforcer being readily traded for another. We conducted an analysis of reinforcers that were substitutable with those produced by self-injurious behavior (SIB). Three individuals with profound developmental disabilities, whose SIB appeared to be maintained by automatic reinforcement, participated. Results of three experiments showed that (a) object manipulation and SIB were inversely related when leisure materials and SIB were concurrently available, with participants showing almost complete preference for object manipulation; (b) attempts to reduce SIB using the preferred objects as reinforcers in differential reinforcement contingencies were unsuccessful for all 3 participants; and (c) participants' preferences for SIB or object manipulation systematically changed when reinforcer cost (the amount of effort required to obtain the object) was varied. Results of the three experiments illustrate the importance of examining interactions among concurrently available reinforcers when conducting reinforcer assessments.     

Some determinants of changes in preference over time

Results of longitudinal studies suggest that the stability of preferences varies across individuals, although it is unclear what variables account for these differences. We extended this work by conducting periodic assessments of preference for leisure activities over 3 to 6 months with 10 adults with developmental disabilities. Although previous research has collectively shown that preferences identified via repeated assessment are highly variable, our results showed that preferences were relatively stable for the majority (80%) of participants. In an attempt to identify some environmental determinants of shifts in preference, we provided extended daily access to high-preference items (preference-weakening manipulation) and paired access to low-preference items with social and edible putative reinforcers during brief sessions (preference-strengthening manipulation). Preference assessments continued over the course of these manipulations with 2 participants. Results showed that changes in preference across time could be produced systematically and suggest that naturally occurring changes in establishing operations or conditioning histories contribute to temporal shifts in preference. Implications for preference assessments, reinforcer usage, and planned attempts to change preferences are discussed.     

Hand preference for pointing gestures and bimanual manipulation around the vocabulary spurt period

This study investigated the development of hand preference for bimanual manipulative activities and pointing gestures in toddlers observed longitudinally over a 5-month period, in relation to language acquisition. The lexical spurt was found to be accompanied by an increase in the right-sided bias for pointing but not for manipulation. Moreover, results revealed a significant correlation between hand preference for imperative pointing gestures and manipulative activities in children who did not experience the lexical spurt during the observational period. By contrast, measures of handedness for declarative pointing were never correlated with those of handedness for manipulation. This study illustrates the complex relationship between handedness and language development and emphasizes the need to take the different functions of pointing gestures into account.     

Development of manipulatory skills and the deployment of attention

Two independent tasks, object manipulation and auditory-visual matching, were used to examine the relationship between developing manual action skills and attention to intermodal object properties in 3.5- and 5.5-month-olds. Although handling skills improved with age, with older infants demonstrating more varied manipulation, there were no age differences for the matching task. When grouped by handling skills, a significant interaction between skill and event type was found for the two age groups combined and for 5.5-month-olds alone. Auditory-visual matching of social events did not vary with handling skills, whereas auditory-visualmatching of object events did. Infants at higher skill levels responded similarly to social and object events, whereas less skilled infants' matching preferences were weaker for object events. These findings indicate that infants increase their attention to auditory and visual properties of objects as this information becomes useful for guiding new actions. This effect is independent of age due to considerable individual variability in the development of object handling skills.     

The development of reaching and looking preferences in infants to objects of different sizes.

Reaching and looking preferences and movement kinematics were recorded in 5-15-month-old infants, who were divided into 3 age groups. Infants were presented with pairs of cylinders of 3 different diameters: small (1-cm diameter), medium (2.5-cm diameter), and large (6-cm diameter). Whereas infants between 5 and 12 months of age showed a preference for looking first at the large object, a significant preference for reaching to smaller (graspable) objects was observed in 81/2-12-month-old infants. Kinematic measures suggest that the onset of object-oriented action requires a slowing down of the reach and an extended "homing-in" phase. The divergent looking and reaching preferences in infants at different ages may reflect a dissociation during development of visual processing streams subserving object-related action from those related to visual orienting.     

Unimanual and bimanual tasks and the assessment of handedness in toddlers

The goal of this study was to examine the relations between three different measures of handedness: unimanual reaching, bimanual manipulation and unimanual manipulation. The appropriateness of the task chosen to evaluate handedness was also explored by contrasting different bimanual manipulation tasks for the more or less differentiated (passive\active) roles assigned to each hand. Forty children, between 18 and 36 months of age, were tested in the three conditions. The results show that the degree of bimanual handedness is greater on the bimanual tasks with a strong role differentiation than on the tasks with less differentiation. Bimanual tasks with a strong role differentiation elicited more right‐handedness than unimanual reaching. Among the children who showed handedness in reaching, the correlation between unimanual and bimanual handedness was high, especially for right‐handers. For some tasks, bimanual handedness appeared at the earliest age studied here (18 months), and there was little relationship between bimanual handedness and bimanual skill. In contrast with unimanual reaching, there was no age‐related change in the degree of handedness for either bimanual or unimanual manipulation. There was a bias toward the use of the right hand for unimanual manipulation. It was concluded that grasping is not the best task to employ to look for robust evidence of handedness, and that bimanual tasks offer a better way to estimate handedness in children, as long as the tasks are carefully chosen.     

Visuospatial reaching preferences of common marmosets (Callithrix jacchus): an assessment of individual biases across a variety of tasks

Using multiple measures of hand preference, the authors investigated lateralization at an individual level in 21 common marmosets. Despite showing group biases for sensory and communication functions, these same marmosets did not show a group bias in direction of lateralized hand use. Hand preferences were recorded on four novel reaching tasks requiring different levels of visual guidance and postural control. As found for simple food holding (with the same subjects), they displayed strong individual hand preferences but no group bias indicative of handedness. The strength of hand preference was influenced by task demands: stronger preferences were expressed when subjects adopted a suspended posture, and when "successful" versus "unsuccessful" foraging strategies were compared. Comparisons between visuospatial reaching and simple food holding preferences also revealed that half of the subjects displayed a division of function between the hands/hemispheres; subjects displayed opposing preferences in simple and visuospatial reaching, which would be beneficial for the performance of coordinated bimanual tasks. Given the apparent absence of a selective advantage for handedness, the authors suggest that hand preferences may reflect hemispheric dominance of other cognitive domains (i.e., temperament).     

Emotions within reason: Resolving conflicts in risk preference

This research focused on differential effects of emotional and rational preferences in decision making and how people resolve conflicting risk preferences caused by inconsistency between their emotional reactions to and rational assessment of a risk problem. In addition, effects of the framing of choice outcomes on emotional, rational, and overall risk preferences were examined. Adopting a within-subjects design, Study 1 showed that the emotional choice preference was often the opposite of the rational choice preference and was more risk-seeking than the rational preference. The overall favourability rating for a chosen option was significantly higher when the emotional choice and rational choice were the same than when they were opposed. Emotional preferences were significantly more susceptible than rational preferences to the hedonic tone of risky choice framing. The overall preference was a compromise of the conflicting emotional and rational preferences in some risk domains, and resembled either the emotional preference or the rational preference in other risk domains. Study 2, using a between-subjects manipulation, further confirmed that emotional preference and rational preference had differential effects on risky choice.     

The ontogeny of infant bimanual reaching during the first year

Handedness and pattern of coordination during bimanual reaching were assessed separately for six groups of infants, 7 to 12 months old. Infants reached bimanually for a transparent toy-filled box. On some presentations of the box a low barrier was placed in the path of either the right or left hand, while on other presentations there was no barrier. The youngest and two oldest groups of infants were more likely than the other age groups to perform simultaneous bimanual reaches with no barrier present, but when a barrier was present the 11-month-olds were most likely to continue to perform simultaneous reaches. This suggests that while infants as young as 7 months perform simultaneous reaches, the organization of these reaches may be different than for older infants. Hand-use preference contributed significantly to selection of a lead hand in non-simultaneous bimanual reaching. The 8-month group, which had the highest proportion of infants with a hand preference, was the only group likely to hit the barrier when it was placed on the nonpreferred side. Hand preference may, thus, bias the use of information about what the environment affords for action.     

Manual exploration of objects is related to 7-month-old infants’ visual preference for real objects

The present study examined whether infants’ visual preferences for real objects and pictures are related to their manual object exploration skills. Fifty-nine 7-month-old infants were tested in a preferential looking task with a real object and its pictorial counterpart. All of the infants also participated in a manual object exploration task, in which they freely explored five toy blocks. Results revealed a significant positive relationship between infants’ haptic scan levels in the manual object exploration task and their gaze behavior in the preferential looking task: The higher infants’ haptic scan levels, the longer they looked at real objects compared to pictures. Our findings suggest that the specific exploratory action of haptically scanning an object is associated with infants’ visual preference for real objects over pictures.     

Hand preference in the use and manufacture of tools by tufted capuchin (Cebus apella) and lion-tailed macaque (Macaca silenus) monkeys.

The purpose of this study was to examine hand preference in the use and manufacture of probing tools by tufted capuchin and lion-tailed macaque monkeys (Cebus apella and Macaca silenus). Hand preference for the tool-using sequence was noted in 4 of 5 capuchins (a left-hand preference was noted in 3 ss) and 3 of 4 macaques (a left-hand preference was noted in 2 ss). The monkeys frequently used bimanual action in the initial and final segments of the 3-component task and typically modified tools through coordinated action of the hands and teeth. These data provide evidence consistent with the hypotheses that (a) hemisphere specialization for manual control evolved in primates prior to intensive use of tools by early hominids and (b) monkeys prefer the left hand for precise, visually guided, manipulative actions.     

Perturbations in Action Goal Influence Bimanual Grasp Posture Planning

The authors examined the effects of perturbations in action goal on bimanual grasp posture planning. Sixteen participants simultaneously reached for 2 cylinders and placed either the left or the right end of the cylinders into targets. As soon as the participants began their reaching movements, a secondary stimulus was triggered, which indicated whether the intended action goal for the left or right hand had changed. Overall, the tendency for a single hand to select end-state comfort compliant grasp postures was higher for the nonperturbed condition compared to both the perturbed left and perturbed right conditions. Furthermore, participants were more likely to plan their movements to ensure end-state comfort for both hands during nonperturbed trials, than perturbed trials, especially object end-orientation conditions that required the adoption of at least one underhand grasp posture to satisfy bimanual end-state comfort. Results indicated that when the action goal of a single object was perturbed, participants attempted to reduce the cognitive costs associated with grasp posture replanning by maintaining the original grasp posture plan, and tolerating grasp postures that result in less controllable final postures.     

Behavioral asymmetries of psychomotor performance in rhesus monkeys (Macaca mulatta): a dissociation between hand preference and skill.

Hand preferences were recorded for 35 rhesus monkeys (Macaca mulatta) as they manipulated a joystick in response to 2 computerized tasks. These preferences were then used to contrast 8 left- and 10 right-handed subjects on performance measures of hand skill. Individual hand preferences were found, but no significant population asymmetry was observed across the sample. However, the performance data reveal substantial benefits of right-handedness for joystick manipulation, as this group of monkeys mastered the 2 psychomotor tasks significantly faster than did their left-handed counterparts. The data support earlier reports of a right-hand advantage for joystick manipulation and also support the importance of distinguishing between hand preference and manual performance in research on functional asymmetries.     

Note on hand use in the manipulation of joysticks by rhesus monkeys (Macaca mulatta) and chimpanzees (Pan troglodytes)

In a recent article MacNeilage, Studdert-Kennedy, and Lindblom (1987) proposed that nonhuman primate handedness may be contingent on the specific task requirements with visual-spatial tasks yielding left-hand preferences and fine motor tasks producing right-hand preferences. This study reports hand preferences in the manipulation of joysticks by 2 rhesus monkeys (Macaca mulatta) and 3 chimpanzees (Pan troglodytes). Reach data were also collected on these same subjects and served as a basis for comparison with preference data for manipulation of the joystick. The data indicated that all 5 subjects demonstrated significant right-hand preferences in manipulating the joystick. In contrast, no significant hand preferences were found for the reach data. Reaction time data also indicated that the right hand could perform a perceptual-motor task better than the left hand in all 5 subjects. Overall, the data indicate that reach tasks may not be sensitive enough measures to produce reliable hand preferences, whereas tasks that assess fine motor control produce significant hand preferences.     

End-state comfort in bimanual object manipulation

The present experiment investigated the sensitivity for end-state comfort in a bimanual object manipulation task. Participants were required to simultaneously reach for two bars and to place the objects' ends into two targets on the table. The design of the experiment allowed to dissociate the relative roles of initial means (e.g., the selection of grips) and final postures (e.g., the anticipation of end-states). The question of interest was whether affording different grip patterns for the two hands would introduce a bias away from reaching end-state comfort. Results revealed a strong sensitivity for end-state comfort, independent of the required grip patterns. In particular, end-state comfort was preferred even if this meant selecting different initial means (i.e., different grips) for the two hands. Hence, end-state oriented action planning appears to dominate interaction costs that may result from motor-related, intermanual interference. We infer that movement planning is constrained by action goals (e.g., a comfortable end-posture for both hands), but largely unaffected by the type of motor actions necessary to achieve these goals.