Spatio-temporal parameters in infant's reaching movements are influenced by body orientation

Many studies have demonstrated that the seated position is more effective in promoting reaching movements when compared with supine. The aim of this longitudinal study was to verify the effect of seated and supine positions on spatio-temporal parameters of reaching in 4-6-month-old infants. Four infants were observed during reaching trials in both positions. A total of 235 reaches were analyzed by using the 3D movement reconstruction. Our results showed that frequency of reaching and straightness index increased over age. Significant differences between the positions were observed at 4 months, when the frequency increased and the duration and deceleration time decreased in the seated position. There were no significant differences at 5 and 6 months. These findings suggest that young infants are able to change kinematical parameters of reaching to adapt themselves to intrinsic and extrinsic constraints (i.e. age and position).     

Not just playing around: Infants’ behaviors with objects reflect ability,constraints, and object properties

This study describes infants’ behaviors with objects in relation to age, body position, and object properties. Object behaviors were assessed longitudinally in 22 healthy infants supine, prone, and sitting from birth through 2 years. Results reveal: (1) infants learn to become intense and sophisticated explorers within the first 6 months of life; (2) young infants dynamically and rapidly shift among a variety of behavioral combinations to gather information; (3) behaviors on objects develop along different trajectories so that behavioral profiles vary across time; (4) object behaviors are generally similar in supine and sitting but diminished in prone; and (5) infants begin matching certain behaviors to object properties as newborns. These data demonstrate how infants learn to match their emerging behaviors with changing positional constraints and object affordances.     

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45°), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints—the intrinsic limb dynamics—in creating coordinated limb behavior out of nonspecific muscle activations.     

Moving into tummy time,together: Touch and transitions aid parent confidence and infant development

“Back to sleep” messages can reduce prone practice for infants, with potential for motor delay and cranial deformation. Despite recommendations for “tummy time,” young infants fuss in prone, and parents report uncertainty about how to help infants tolerate prone positioning. We hypothesized that a Child'Space Method lesson, teaching proprioceptive touch and transitions to prone, would facilitate prone tolerance, parent behavioral support, and parent self-efficacy. This randomized study recruited parents (N = 37) of 2- to 5-month-old infants. On two visits, parents answered questions about infant behavior and parent experience, and played with their infant. Lesson group parents had the lesson following the first free play. One week later, lesson parents reported that infants tolerated more prone time and that parents showed more supportive behaviors in bringing infant to prone, as compared to waiting parents. Lesson parents’ efficacy, and infant behavior during play, trended in the hypothesized direction. The study demonstrated how a lesson in preparatory touch, and gradual transitions, promoted infant prone tolerance and also parent support of rolling, side-lying, and prone positioning. The lesson could be incorporated in parent education and early pediatric visits, helping infants and parents negotiate the prone challenge and setting the stage for further parent support of infant development.     

Adaptive Dynamics of the Leg Movement Patterns of Human Infants: I. The Effects of Posture on Spontaneous Kicking

This is the first of two articles in which we describe how infants adapt their spontaneous leg movements to changes in posture or to elicitation of behaviors by a mechanical treadmill. In this article, we compare the kinematics of kicks produced by 3-month-old infants in three postures, supine, angled (45 degrees ), and vertical, and examine the changes in muscular and nonmuscular force contributions to limb trajectory. By manipulating posture we were able to assess the sensitivity of the nascent motor system to changes in the gravitational context. The postural manipulation elicited a distinct behavioral and dynamic effect. In the more upright postures, gravitational resistance to motion at the hip was 4 to 10 times greater than resistance met in the supine posture, necessitating larger muscle torques to drive hip flexion. Kicks produced in the vertical posture showed a reduction in hip joint range of motion and an increase in synchronous joint flexion and extension at the hip and knee. At the same time, hip and knee muscle torques were also more highly correlated in kicks performed in the vertical than in the supine or angled posture. This increased correlation between muscle torques at the hip and knee implicates anatomical and energetic constraints-the intrinsic limb dynamics-in creating coordinated limb behavior out of nonspecific muscle activations.     

Kinesthetic estimation of the main orientations from the upright and supine positions

This work investigated the accuracy of the perception of the main orientations (i.e., vertical and horizontal orientations) with the kinesthetic modality--a modality not previously used in this field of research. To further dissociate the influence of the postural and physical verticals, two body positions were explored (supine and upright). Twenty-two blindfolded participants were asked to set, as accurately as possible, a rod to both physical orientations while assuming one of the two body positions. The horizontal was perceived more accurately than the vertical orientation in the upright position but not in the supine position. Essentially, there were no differences in the supine position because the adjustments to the physical vertical were much more accurate than they were in the upright position. The lower accuracy in the estimation of the vertical orientation observed in the upright position might be linked to the dynamics associated with the maintenance of posture.     

Influence of Different Sitting Positions on Healthy Infants' Reaching Movements

The authors analyze the influence of different sitting positions (ring and flexion) on the reaching performance (spatiotemporal variables) of full-term infants 6 and 7 months old. In addition, they correlated level of trunk control, measured by the Segmental Assessment of Trunk Control, with performance during reaching. The different sitting positions only influenced the reaching movements of 6-month-old infants, who showed the best performance in the ring position. However, this influence was observed only for the trunk displacement, deceleration time, movement units, straightness index and mean velocity. In contrast, there was no influence of positions on 7-month-old infants’ reaching performance. Regarding the correlations, it was observed that infants with more level of trunk control showed a better performance when reaching, regardless of position and the age assessed.     

Effects of prone and supine positions on sleep state and stress responses in preterm infants

Aim

The purpose of the study is to assess the influence of prone or supine position on sleep states and on withdrawal and approach reactions of preterm infants.

Methods

Thirty-two preterm infants from Meir Medical Center, Israel, mean post menstrual age 30.37 ± 2.57, mean birth weight 1250 g ± 313.86, participated in the study. Infants were studied during 48 h. Positions (prone and supine) were alternated every 3-4 h after feedings. Sleep states were assessed by Actigraph measurement and by two daily 30-min Naturalistic Observations of Newborn Behavior (NONB) to confirm sleep states and for recording the behavioral reactions (approach and withdrawal).

Results

In the prone position there were more approach reactions as compared to withdrawal reactions (p < .001) while in the supine position, the approach and withdrawal reactions were comparable. In the prone position more sleep patterns (deep sleep, light sleep, drowsy) were observed as opposed to more awake patterns (quiet awake, active awake and agitated fussy) that were seen in the supine position.

Conclusions

Clinical implications encourage placing the preterm infant in the prone position while in the NICU. This enables important achievements such as longer periods of quality sleep, and production of adaptive self-regulatory reactions.     

Infant behavioral responses to infant-directed singing and other maternal interactions

Seventy, 6-9-month-old infants were videotaped during six interactions: mother sings assigned song, "stranger" sings assigned song, mother sings song of choice, mother reads book, mother plays with toy, and mother and infant listen to recorded music. Infant-directed (ID) singing conditions elicited moderately positive cognitive behavior, low levels of positive physical behavior and minimal amounts of vocal behaviors, mostly negative. Across all conditions, cognitive scores remained positive at low to moderate levels. Physical responses were most positive during book and toy, most negative during recorded music, and differed by gender, especially during ID singing. Vocally, infants responded positively to toy, and 8-month-old infants vocalized more than younger infants, particularly during ID singing conditions. ID singing appears just as effective as book reading or toy play in sustaining infant attention and far more effective than listening to recorded music, while interactions involving objects may provide opportunity for shared attention.     

Mother-infant responsiveness: timing, mutual regulation, and interactional context

Mutual regulation during the naturalistic interaction of 150 mothers and their 4-month-old infants was investigated from a dynamic systems perspective. Microanalyses of a wide range of behaviors and analysis of contingencies indicated that a 3-s time period best captured contingencies. Both mothers and infants communicated primarily through vocal signals and responses, although maternal touches and infant looks also elicited responses. Although more expressive mothers did not have infants who behaved similarly, levels of contingent responsiveness between partners were significantly associated and occurred within distinct behavioral channels, suggesting coregulated interactional processes in which contingently responsive mothers shape their infants' communications toward mutual similarity. Mothers were more influential than infants over object play, whereas infants were more influential than mothers over expressive behavior. Interactional context consistently influenced contingent responsiveness; there was less mutual responsiveness when the infant was exploring, being held, or looking.     

Infant positioning: A brief review

The American Academy of Pediatrics (2016a) has made several recommendations regarding the safe positioning of infants by caregivers, including placing infants in a supine position for sleep and in prone for supervised periods of tummy time. However, caregivers may have difficulty adhering with these recommendations. A small, but growing, number of behavior analytic studies have examined these infant safety recommendations and strategies for increasing adherence. This review describes behavior analytic research on infant positioning and provides suggestions for future research.     

Infants of “depressed” mothers interact better with their nondepressed fathers

To determine whether infants of “depressed” mothers interact better with their nondepressed fathers, twenty-six 3- to 6-month-old infants were videotaped during face-to-face interactions with their parents. The “depressed” mother group consisted of twelve 3- to 6-month-old infants and their “depressed” mothers and nondepressed fathers. The control group was composed of 14 nondepressed mothers and nondepressed fathers and their 3- to 6-month-old infants. In the “depressed” mother group, the nondepressed fathers received better interaction ratings than the “depressed” mothers. In turn, the infants received better interaction ratings when they interacted with their nondepressed fathers than with their “depressed” mothers. In contrast, nondepressed fathers and mothers and their infants in the control group did not differ on any of their interaction ratings. These findings suggest that infants' difficult interaction behaviors noted during interactions with their “depressed” mothers may not extend to their nondepressed fathers. The data are discussed with respect to the notion that nondepressed fathers may “buffer” the effects of maternal depression on infant interaction behavior.     

Effects of access to a stimulating object on infant behavior during tummy time

Placing infants in a prone position for "tummy time" often is recommended to ensure appropriate infant development and to combat the effects associated with infants spending extended periods of time in a supine position. However, tummy time may be associated with inappropriate infant behavior such as crying and noncompliance. We provided continuous access to a preferred stimulus to decrease negative vocalizations and to increase the duration of an infant's head being elevated during tummy time.     

The beginning of conversation: Early patterns of mother-infant vocal responsiveness

Microanalytic techniques were used to characterize the structure of the prespeech communication of 4-month-old infants and their mothers. Two observers continuously recorded the interactive behavior of mothers and their infants during hour-long observations in the homes of 25 families. Loglinear models were used to examine the extent to which the vocal behavior of one person was conditional upon the vocal behavior of the partner. Within the limits of this microanalytic approach, analyses indicated that patterns of mother-infant vocal exchange were structurally similar to patterns of adult conversation. Initial vocal responses were followed by suppression of vocalization, allowing the partner to join the conversation. The comparative effectiveness of vocal behavior as an elicitor of vocalization and as a response to vocalization was shown for mothers and infants relative to the other behaviors observed. Vocalization served as a modulator of visual attentiveness: When the partner was not visually attentive, vocalization elicited visual attention.     

Discrimination learning during the first year: stimulus and positional cues

In four studies, 3-, 6-, and 9-month-old human infants were tested in a discrimination learning task in which visual fixation to a particular stimulus or lateral position was reinforced with an auditory stimulus. In Experiment 1, all age groups exhibited acquisition, extinction, and reinstatement of fixation to the reinforced target or position. Experiment 2 revealed that 3-month-olds retained the positional discrimination but not the stimulus discrimination after a 5-min delay between acquisition and extinction; older infants retained both types of discriminations. In Experiments 3 and 4 we investigated a possible developmental shift in the dominance of positional versus stimulus cues by training infants on displays in which stimulus and position were confounded and then by dissociating the cues on test trials. Results from both experiments indicated positional cue dominance for young infants and stimulus cue dominance for older infants. The findings are discussed in terms of differences in the attentional demands elicited by proprioceptive versus exteroceptive cues.     

Infant and adult perceptions of possible and impossible body movements: An eye-tracking study

This study investigated how infants perceive and interpret human body movement. We recorded the eye movements and pupil sizes of 9- and 12-month-old infants and of adults (N=14 per group) as they observed animation clips of biomechanically possible and impossible arm movements performed by a human and by a humanoid robot. Both 12-month-old infants and adults spent more time looking at the elbows during impossible compared with possible arm movements, irrespective of the appearance of the actor. These results suggest that by 12months of age, infants recognize biomechanical constraints on how arms move, and they extend this knowledge to humanoid robots. Adults exhibited more pupil dilation in response to the human's impossible arm movements compared with the possible ones, but 9- and 12-month-old infants showed no differential pupil dilation to the same actions. This finding suggests that the processing of human body movements might still be immature in 12-month-olds, as they did not show an emotional response to biomechanically impossible body movements. We discuss these findings in relation to the hypothesis that perception of others' body movements relies upon the infant's own sensorimotor experience.     

Self-Sitting and Reaching in 5- to 8-Month-Old Infants: The Impact of Posture and Its Development on Early Eye-Hand Coordination

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.     

Self-sitting and reaching in 5- to 8-month-old infants: the impact of posture and its development on early eye-hand coordination

The relation between progress in the control of posture (i.e., the achievement of self-sitting posture) and the developmental transition from two-handed to one-handed engagement in infant reaching was investigated. Two groups of 5- to 8-month-old infants, who were either able or yet unable to sit on their own, were videotaped while they reached for objects in four different posture conditions that provided varying amounts of body support. Videotapes of infant reaches were microanalyzed to determine the relative engagement of both hands during reaches. Results demonstrate the interaction between postural development and the morphology of infant reaching. Nonsitting infants displayed symmetrical and synergistic engagement of both arms and hands while reaching in all but the seated posture condition. Sitting infants, by contrast, showed asymmetrical and lateralized (one-handed) reaches in all posture conditions. Results also show that, aside from posture, the perceived spatial arrangement of the object display is a determinant of infant reaching. Combined, these results are discussed as evidence for the interaction between postural and perceptual development in the control of early eye-hand coordination.     

Choosing the shortest way to Mum: auditory guided rotation in 6- to 9-month-old infants

The purpose of this study was to investigate the use of auditory information for rotation of the shortest way in twelve 6- to 9-month-old sighted infants. Behavior was manipulated by means of an auditory stimulus presented in four different directional angles (90°, 112.5°, 135°, and 157.5°) to the right and to the left behind the infants, and in one non-directional angle (180°). Infants lay in a prone position and had magnetic trackers fastened to the head and body which measured their rotation direction and angular velocity. The results showed that infants not only consistently chose the shortest over the longest way, but also rotated with a higher peak angular velocity as the angle to be covered between themselves and the goal increased. The results did not show significant preferences for one particular rotation direction. The study can contribute to the understanding of the auditory system as a functional listening system where auditory information is used as a perceptual source for prospectively guiding behavior in the environment.     

Development of sensitivity to information for impending collision

Infants were tested in three experiments to study the development of sensitivity to information for impending collision and to investigate the hypothesis that postural changes of very young infants in response to an approaching object are of a tracking rather than of a defensive nature. Experiment 1 involved the presentation of three types of shadow projection displays, specifying (1) collision, (2) noncollision, and (3) a nonexpanding rising contour, to infants from 1 to 9 months of age. Avoidance of collision appears to be absent in 1- to 2-month-olds, begins to develop in 4- to 6-month-olds, and is present in 8- to 9-month-old infants. In Experiment 2, 1- to 2-month-old infants were presented with optical expansion patterns which specified collision and noncollision. The top contour of these displays stayed at eye level. No significant difference was observed between reaction to the collision and the noncollision displays, suggesting that the young infants were tracking the displays and not attempting to avoid collision. Experiment 3 was designed to determine whether an approaching real object might elicit an avoidance response in infants not sensitive to an optical display specifying collision. No evidence of avoidance behavior was observed in the 1- to 2-month-olds; however, avoidance, as indexed by blinking, does appear to be present at 4 months of age.