Origins of the proprioceptive function of vision: visual control of posture in one day old domestic chicks.

Recently hatched domestic chicks control their upright bipedal posture, at least in part, with respect to the flow of visual information at the retina, as do human infants when they first acquire control of the head, of sitting, and of standing. Some implications of the similarity of the proprioceptive function of vision in chicks and in humans for the origins and development of postural control are discussed.     

Visual calibration of posture in normal and motor retarded Down's syndrome infants.

Infants with Down's syndrome are delayed in achieving motor milestones. When they first sit unsupported a discrepancy between visual and mechanical-vestibular indices of postural stability is less disruptive of their balance than in normal infants. Yet when they first stand unsupported, the same discrepancy disrupts balance more in these infants than in the normal infants. The effect of discrepant visual feedback also differs systematically as a function of the infants' experience of the posture. Monitoring posture in relation to a stable visual surround appears to be fundamental to the normal development of motor control.     

The Effect of Posture on Early Reaching Movements

Infants of about 5 months of age who have just mastered the ability to reach succeed more frequently in contacting an object when they are seated upright than when they are supine or reclined. That effect of posture disappears in the subsequent months. Whether that effect can be attributed either to insufficient muscular strength or to insufficient control over the mechanically unstable arm was the subject of the present investigation. Kinematics and electromyography (EMG) of reaching movements of 8 sitting and supine infants at 12, 16, and 20 weeks of age were recorded. Maximum levels of shoulder torque as well as kinematic stability measures were similar in both postures. Coactivation levels and the frequency of on-off switching of muscles turned out to be higher in the sitting than in the supine posture. The authors suggest that the difference in reaching behavior resulted from the degree of error in the feedforward control signal that was allowed by the different postures rather than either insufficient muscular strength or insufficient control over the mechanically unstable arm.     

Two steps forward and one back: Learning to walk affects infants' sitting posture

The transition from sitting to walking is a major motor milestone for the developing postural system. This study examined whether this transition to walking impacts the previously established posture (i.e., sitting). Nine infants were examined monthly from sitting onset until 9 months post-walking. Infants sat on a saddle-shape chair either independently or with their right hand touching a stationary contact surface. Postural sway was measured by sway amplitude, variability, area, and velocity of the center of pressure trajectory. The results showed that for all the postural measures in the no-touch condition, a peak before or at walk onset was observed in all the infants. At the transition age, when peak sway occurred, infants' postural sway measures were significantly greater than at any other age. Further, infants' postural sway was attenuated by touch only at this transition. We suggest that this transient disruption in sitting posture results from a process involving re-calibration of an internal model for the sensorimotor control of posture so as to accommodate the newly emerging bipedal behavior of independent walking.     

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.     

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.     

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.     

Posture and gaze in early mother–infant communication: synchronization of developmental trajectories

Weekly laboratory observations of free play for 13 middle-income mother–infant dyads, from 1 to 6 months of age, were used to study the synchronization of developmental trajectories between infant postural position and gaze direction. Mothers sat in a straight-backed chair while holding infants on their laps and were free to adjust the infant’s posture. Postural position was coded as upright (supported sitting or standing on the mother’s lap) or other (lying, cradling, or being held close to mother). Gaze was coded as either at mother’s face or away. The age of onset of visually guided reaching was also assessed. Results show that there were longer durations of gazing away when the infant was in an upright position. Over the 5 month period of observation, the dyads began with a pattern of non-upright positions accompanied by gaze at mother. Contrary to previous predictions, the developmental shift in the first 6 months from exclusive gazing at mother’s face to gazing away from mother was not synchronized with the development of reaching, but rather with changes in the infant’s posture to more upright positions. The possible role of postural position in fostering positive emotional communication is discussed.     

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.     

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.     

Opportunities for learning and social interaction in infant sitting: Effects of sitting support,sitting skill,and gross motor delay

The development of independent sitting changes everyday opportunities for learning and has cascading effects on cognitive and language development. Prior to independent sitting, infants experience the sitting position with physical support from caregivers. Why does supported sitting not provide the same input for learning that is experienced in independent sitting? This question is especially relevant for infants with gross motor delay, who require support in sitting for many months after typically developing infants sit independently. We observed infants with typical development (n = 34, ages 4–7 months) and infants with gross motor delay (n = 128, ages 7–16 months) in early stages of sitting development, and their caregivers, in a dyadic play observation. We predicted that infants who required caregiver support for sitting would spend more time facing away from the caregiver and less time contacting objects than infants who could sit independently. We also predicted that caregivers of supported sitters would spend less time contacting objects because their hands would be full supporting their infants. Our first two hypotheses were confirmed; however, caregivers spent surprisingly little time using both hands to provide support, and caregivers of supported sitters spent more time contacting objects than caregivers of independent sitters. Similar patterns were seen in the group of typically developing infants and the infants with motor delay. Our findings suggest that independent sitting and supported sitting provide qualitatively distinct experiences with different implications for social interaction and learning opportunities.

Highlights

• During seated free play, supported sitters spent more time facing away from their caregivers and less time handling objects than independent sitters.
• Caregivers who spent more time supporting infants with both hands spent less time handling objects; however, caregivers mostly supported infants with one or no hands.
• A continuous measure of sitting skill did not uniquely contribute to these behaviors beyond the effect of binary sitting support (supported vs. independent sitter).
• The pattern of results was similar for typically developing infants and infants with gross motor delay, despite differences in age.

     

Infants return to two-handed reaching when they are learning to walk

The authors examined whether infants of about 1 year return to 2-handed reaching when they begin to walk independently. Infants (N = 9) were followed longitudinally before, during, and after their transition to upright locomotion. Every week, the infants' reaching responses and patterns of interlimb coordination were screened in 3 tasks involving different adaptive reaching responses. Before the onset of upright locomotion, the infants responded to each task adaptively. Following walking onset, they increased their rate of 2-handed responses in all tasks. The 2-handed responses declined when the infants gained better balance control. The results suggest that infants' return to 2-handed reaching is experience dependent. Those findings are discussed in terms of the integration of new developing motor skills into existing cognitive and motor repertoires.     

Dynamics of the dyad: How mothers and infants co-construct interaction spaces during object play

Studies of dyadic interaction often examine infants’ social exchanges with their caregivers in settings that constrain their physical properties (e.g., infant posture, fixed seating location for infants and adults). Methodological decisions about the physical arrangements of interaction, however, may limit our ability to understand how posture and position shape them. Here we focused on these embodied properties of dyadic interaction in the context of object play. We followed 30 mother–infant dyads across the first year of life (at 3, 6, 9, and 12 months) and observed them during 5 min of play with a standard set of toys. Using an interval-based coding system, we measured developmental change in infant posture, how mothers and infants positioned themselves relative to one another, and how they populated interaction spaces with objects. Results showed that mother–infant dyads co-constructed interaction spaces and that the contributions of each partner changed across development. Dyads progressively adopted a broader spatial co-orientation during play (e.g., positioned at right angles) across the first year. Moreover, advances in infants’ postural skills, particularly increases in the use of independent sitting in real time, uniquely predicted change in dyadic co-orientation and infants’ actions with objects, independent of age. Taken together, we show that the embodied properties of dyadic object play help determine how interactions are physically organized and unfold, both in real time and across the first year of life.     

Lexical Learning May Contribute to Phonetic Learning in Infants: A Corpus Analysis of Maternal Spanish

In their first year, infants begin to learn the speech sounds of their language. This process is typically modeled as an unsupervised clustering problem in which phonetically similar speech‐sound tokens are grouped into phonetic categories by infants using their domain‐general inference abilities. We argue here that maternal speech is too phonetically variable for this account to be plausible, and we provide phonetic evidence from Spanish showing that infant‐directed Spanish vowels are more readily clustered over word types than over vowel tokens. The results suggest that infants’ early adaptation to native‐language phonetics depends on their word‐form lexicon, implicating a much wider range of potential sources of influence on infants’ developmental trajectories in language learning.     

Specificity of learning: why infants fall over a veritable cliff

Nine-month-old infants were tested at the precipice of safe and risky gaps in the surface of support. Their reaching and avoidance responses were compared in two postures, an experienced sitting posture and a less familiar crawling posture. The babies avoided reaching over risky gaps in the sitting posture but fell into risky gaps while attempting to reach in the crawling posture. This dissociation between developmental changes in posture suggests that (a) each postural milestone represents a different, modularly organized control system and (b) infants' adaptive avoidance responses are based on information about their postural stability relative to the gap size. Moreover, the results belie previous accounts suggesting that avoidance of a disparity in depth of the ground surface depends on general knowledge such as fear of heights, associations between depth information and falling, or knowledge that the body cannot be supported in empty space.     

To reach or not to reach? Perception of body effectivities by young infants

Two experiments compared 6‐month‐old infants as they reach for an object. All were proficient reachers but with different levels of sitting ability. The object was presented at various distances, within and beyond reach of the infant. In the first experiment, the scaling of perceived reachability in infants with different postural abilities (i.e. non‐sitter, near‐sitter, and sitter infants) was explored. The second experiment investigated the role of proprioception in the scaling of perceived reachability by non‐sitter and sitter infants. In general, results suggest that perceived reachability is calibrated in relation to the degree of postural control achieved by the infant. Infants demonstrate a sense of their own situation in the environment as well as a sense of their own body effectivities. Both determine the execution, or non‐execution, of reaching for a distal object by young infants. Copyright © 1999 John Wiley & Sons, Ltd.     

Is Segmental Trunk Control Related to Gross Motor Performance in Healthy Preterm and Full-Term Infants?

Abstract

The authors’ aim was to verify the correlation between segmental trunk control and gross motor performance in healthy preterm (PT) and full-term (FT) infants aged 6 and 7?months and to verify if there are differences between groups. All infants were assessed at 6 and 7?months by means of Segmental Assessment of Trunk Control (SATCo) to identify the exact level of segmental trunk control and Alberta Infant Motor Scale (AIMS) to measure gross motor performance. A significant correlation between segmental trunk control and gross motor performance was found in healthy PT infants at 7?months and FT infants at 6?months. PT infants showed a delay on segmental trunk control at 6 and 7?months and in supported standing posture at 6?months compared with FT infants. Segmental trunk control and gross motor performance showed an important relationship in healthy PT and FT infants, mainly in sitting posture.     

A new twist on old ideas: how sitting reorients crawlers

Traditionally, crawling and sitting are considered distinct motor behaviors with different postures and functions. Ten‐ to 12‐month‐old infants were observed in the laboratory or in their homes while being coaxed to crawl continuously over long, straight walkways (Study 1; N = 20) and during spontaneous crawling during free play (Study 2; N = 20). In every context, infants stopped crawling to sit 3–6 times per minute. Transitions from crawling to sitting frequently turned infants' bodies away from the direction of heading; subsequent transitions back to crawling were offset by as much as 180° from the original direction of heading. Apparently, body reorientations result from the biomechanics of transitioning between crawling and sitting. Findings indicate that sustained, linear crawling is likely an epiphenomenon of how gait is studied in standard paradigms. Postural transitions between crawling and sitting are ubiquitous and can represent a functional unit of action. These transitions and the accompanying body reorientations likely have cascading effects for infants' exploration, visual perception, and spatial cognition.     

Lean back and relax: Reclined seating position buffers the effect of frustration on anger and aggression

Frustration is a powerful instigator of anger‐based aggression. We hypothesized that the impact of a frustration on anger and aggressive behavior is reduced in a state of feeling relaxed, which is considered incompatible with the experience of anger. Seventy‐nine participants received frustrating feedback either when sitting upright or sitting in a reclined position and were then given a chance to act aggressively toward the frustrator. Feelings of anger and relaxation were assessed before and after the frustration. Participants in the reclined position felt more relaxed than those sitting upright, which indirectly predicted less aggressive behavior via lower anger. The results are consistent with theories of incompatible states and embodiment and have implications for using body‐related cues to mitigate anger‐based aggression.     

I used to like it but now I don't: The effect of the transfer test in Northern Ireland on pupils' intrinsic motivation

Background. Research has suggested that the pressure of exams could undermine pupils' interest in their subjects, but almost all of this research has been conducted in laboratory settings. The Transfer Test in Northern Ireland provides an unusual opportunity to assess the effects of exam pressure in real life because some 10‐ and 11‐year‐olds sit a Transfer Test to be admitted to grammar school while others are not tested until they are 14. Aim. To assess the effect of exams on pupils' interest in their subjects both during the period before the exam and after the results are known. Sample. The sample comprised 66 pupils preparing to sit the Transfer Test and 55 not preparing for the test. Method. Pupils' interest in their school subjects was assessed by questionnaires administered 2 weeks before the Transfer Test and then again 2 weeks after the results were announced. Results. Surprisingly, prior to sitting the test, there was no significant difference in motivation between the test and no‐test pupils. However, after sitting the test, the motivation of the test pupils decreased significantly relative to their no‐test counterparts, despite the fact that most achieved the grades they needed for admission to grammar school. Conclusions. Exams provide a valuable tool for assessing academic progress, but under some circumstances they can reduce pupils' interest in the subjects they are studying.