Iryna Babik

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 infants 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.

Latent classes in the developmental trajectories of infant handedness.

Handedness for acquiring objects was assessed monthly from 6 to 14 months in 328 infants (182 males). A group based trajectory model identified 3 latent groups with different developmental trajectories: those with an identifiable right preference (38%) or left preference (14%) and those without an identifiable preference (48%) but with a significant trend toward right-handedness. Each group exhibited significant quadratic trends: Those with a right preference increased to asymptote at about 10 months and began decreasing thereafter; those with a left preference increased to asymptote at about 11 months; those without a preference exhibited increasing right-hand use. Since adult handedness reflects different patterns of neural organization which relate to differences in psychological functioning, the observed differences in infant handedness development may relate to differences in the development of infant neurobehavioral organization and functioning. Several methods were used to explore the relation of latent classes to more conventional ways of classifying infant handedness. Classification into handedness groups according to either a monthly z-score or a combination of 4 or fewer months for a handedness index failed to provide reliable estimates of handedness identified by the trajectory analysis. If identified trajectories of handedness development relate to the development of the infants neurobehavioral organization, researchers who assess infant handedness only once in order to relate it to cognitive, social and emotional functioning may risk misclassifying the handedness of as many as 37-45% of infants.

How the development of handedness could contribute to the development of language

We propose a developmental process which may link the development of handedness with the development of hemispheric specialization for speech processing. Using Arbibs proposed sequence of sensorimotor development of manual skills and gestures (that he considers to be the basis of speech gestures and proto-language), we show how the development of hand-use preferences in proto-reaching skills concatenate into object acquisition skills and eventually into role-differentiated bimanual manipulation skills (that reflect interhemispheric communication and coordination). These latter sensorimotor skills might facilitate the development of speech processing via their influence on the development of tool-using and object management abilities.

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).

Infant Hand Preference and the Development of Cognitive Abilities

Hand preference develops in the first two postnatal years with nearly half of infants exhibiting a consistent early preference for acquiring objects. Others exhibit a more variable developmental trajectory but by the end of their second postnatal year, most exhibit a consistent hand preference for role-differentiated bimanual manipulation. According to some forms of embodiment theory, these differences in hand use patterns should influence the way children interact with their environments, which, in turn, should affect the structure and function of brain development. Such early differences in brain development should result in different trajectories of psychological development. We present evidence that children with consistent early hand preferences exhibit advanced patterns of cognitive development as compared to children who develop a hand preference later. Differences in the developmental trajectory of hand preference are predictive of developmental differences in language, object management skills, and tool-use skills. As predicted by Casasanto’s body-specificity hypothesis, infants with different hand preferences proceed along different developmental pathways of cognitive functioning.

Development of role-differentiated bimanual manipulation in infancy: Part 1. The emergence of the skill

This is the first paper in a series of three discussing different aspects of the development of role-differentiated bimanual manipulation (RDBM-two hands performing different but complementary actions on an object). Emergence of RDBM is an important shift in the development of infant manual skills. Trajectories of monthly changes in the number of RDBMs and RDBM hand preference were explored in a sample of 90 (57 males) normally developing infants (30 with a right preference for acquiring objects, 30 with a left preference, 30 with no preference) during the 9-14 month period. Multilevel analysis revealed that infants performed more RDBMs with age, with similar patterns of change in all hand preference groups. A hand-use preference for RDBM became more prominent with age with most right-preferring infants and those without a preference for object acquisition developing right-hand preference for RDBM. Left-preferring infants exhibited more heterogeneity in their hand-use for RDBM.

Development of role‐differentiated bimanual manipulation in infancy: Part 2. Hand preferences for object acquisition and RDBM—continuity or discontinuity?

This second paper in a series of three investigated the development of hand preference for role-differentiated bimanual manipulation (RDBM) relative to the infants hand preference for object acquisition and to the infants hand-use for acquiring the objects used to assess RDBM. The same 90 infants (30 with a right preference, 30 with a left preference, and 30 with no preference to acquire objects) from the first paper were tested from 9 to 14 months for hand preference for acquiring those objects used to assess RDBM and for a hand preference for RDBM. Multilevel analysis revealed that infants with a hand preference for acquiring objects decreased in their use of the preferred hand for object acquisition during the 11 to 14 month interval, which coincided with the development of a hand preference for RDBM. These results are discussed in relation to the cascade theory of hand preference development.

Sitting Together And Reaching To Play (START-Play): Protocol for a Multisite Randomized Controlled Efficacy Trial on Intervention for Infants With Neuromotor Disorders

Background. There is limited research examining the efficacy of early physical therapy on infants with neuromotor dysfunction. In addition, most early motor interventions have not been directly linked to learning, despite the clear association between motor activity and cognition during infancy. Objective. The aim of this project is to evaluate the efficacy of Sitting Together And Reaching To Play (START‐Play), an intervention designed to target sitting, reaching, and motor‐based problem solving to advance global development in infants with motor delays or neuromotor dysfunction. Design. This study is a longitudinal multisite randomized controlled trial. Infants in the START‐Play group are compared to infants receiving usual care in early intervention (EI). Setting. The research takes place in homes in Pennsylvania, Delaware, Washington, and Virginia. Participants. There will be 140 infants with neuromotor dysfunction participating, beginning between 7 to 16 months of age. Infants will have motor delays and emerging sitting skill. Intervention. START‐Play provides individualized twice‐weekly home intervention for 12 weeks with families to enhance cognition through sitting, reaching, and problem‐solving activities for infants. Ten interventionists provide the intervention, with each child assigned 1 therapist. Measurements. The primary outcome measure is the Bayley III Scales of Infant Development. Secondary measures include change in the Early Problem Solving Indicator, change in the Gross Motor Function Measure, and change in the type and duration of toy contacts during reaching. Additional measures include sitting posture control and parent‐child interaction. Limitations. Limitations include variability in usual EI care and the lack of blinding for interventionists and families. Conclusions. This study describes usual care in EI across 4 US regions and compares outcomes of the START‐Play intervention to usual care.

Feasibility and Effectiveness of a Novel Exoskeleton for an Infant With Arm Movement Impairments.

Purpose: To determine whether a novel exoskeletal device (Pediatric-Wilmington Robotic Exoskeleton [P-WREX]) is feasible and effective for intervention to improve reaching and object interaction for an infant with arm movement impairments. Methods: An 8-month old infant with arthrogryposis was followed up every 2 weeks during a 1-month baseline, 3-month intervention, and 1-month postintervention. At each visit, reaching and looking behaviors were assessed. Results: Within sessions, the infant spent more time contacting objects across a larger space, contacting objects with both hands, and looking at objects when wearing the P-WREX. Throughout intervention, the infant increased time contacting objects both with and without the device and increased bilateral active shoulder flexion. Conclusions: (1) It may be feasible for families to use exoskeletons for daily intervention, (2) exoskeletons facilitate immediate improvements in function for infants with impaired upper extremity mobility, and (3) interventions using exoskeletons can improve independent upper extremity function across time.

Development of role-differentiated bimanual manipulation in infancy: Part 3. Its relation to the development of bimanual object acquisition and bimanual non-differentiated manipulation

This third paper in a series of three related developmental trajectories of bimanual object acquisition and non-differentiated bimanual manipulation (NDBM) to patterns of role-differentiated bimanual manipulation (RDBM) development to help identify the sequence of events that might predict (and potentially facilitate) the development of RDBM skill. Ninety infants were tested monthly from 6 to 14 months of age for object acquisition, and from 9 to 14 months for NDBM and RDBM. The results did not support the hypothesis proposing that the onset of RDBM would require decoupling of the hands in unimanual acquisition, but supported the prediction that coupling of the hands in bimanual acquisition would predict increasing expertise in the RDBM skill. The relation between the bimanual object acquisition and RDBM was found to be mediated by NDBM, which prompts the hypothesis that bimanual acquisition of objects facilitates the development of NDBM, which, in its turn, facilitates the development of the RDBM skill.