Longitudinal study of gross-motor development in ...

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Longitudinal study of gross-motor development in blind infants and preschoolers1 Downloaded by [Universitaetsbibliothek Dortmund] at 08:37 08 March 2016

HEINRICH TROSTER, WERNER HECKER and MICHAEL BRAMBRING Universität Bielefeld, Fakultät fur Psychologie und Sportwissenschaft, Poffach 100131, D-33501 Bielefeld, Federal Republic of Germany (Received 1 September 1994) This paper reports on a longitudinal study of gross-motor development in 10 congenitally blind children during the first 3 years of life. Compared to developmental norms for sighted children, five full-term blind children showed only slight delays in postural development, but greater delays in locomotor development. Five preterm blind children (birth weight: 650-1,115 grams) showed major delays in all areas of gross-motor development that increased with age. Both groups deviated from the developmental sequence of sighted children in the acquisition of those skills required for self-initiated changes in posture and position (sitting or standing) and in crawling. Blindness-specific and blindness-nonspecific causal factors are discussed.

The development of blind children during the first years of life is often a source of concern to parents. Disturbances (such as stereotypes, see Troster, Brambring, & Beelmann, 1991a, 1991b) and delays (particularly in motor development) lead these parents to question the appropriateness of their childrearing and give rise to worries about whether their child is multiply handicapped. Any explanation of the causes for deviations in the development of blind children requires a knowledge of blindness-specific development. In the 1960s, Fraiberg (1977) used a longitudinal design to study the development of 10 congenitally blind children up to the age of 3. She found that, compared with sighted children, the acquisition of locomotor skills (crawling, walking) and fine-motor skills (reaching, grasping) was clearly delayed, while the milestones of postural development (sitting, standing) were achieved within the same age range in which they can be observed for the first time in 95% of sighted children. A cross-sectional comparison of the motor development of blind and sighted 9and 12-month-olds (Troster & Brambring, 1993) reported that blind infants did not just show developmental delays in locomotion and fine-motor skills, but also minor delays in posture, particularly in their ability to change position (sitting up, standing up). Translated from German into English by Jonathan Harrow at Bielefeld University.

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HEINRICH TROSTER^ a/.

Research in the field has emphasized delays in locomotor and fine-motor development in blind children. However, comparisons with sighted children provide no information on the causes underlying these observed delays. Is the delayed acquisition of motor skills in blind children a sign of brain damage, the result of inappropriate childrearing, or a direct consequence of the lack of visual perception? The latter can be assumed for those motor skills that require a sensorimotor coordination directed toward distant goals in the external world, such as reaching for an object or purposeful locomotion. As these skills involve a processing of sensory information on the direction and distance of distal goals, blind children have to use audimotor coordination to compensate for the lack of visuomotor coordination. However, this constitutes a conceptual problem for the blind child. To reach for an auditible object, "he or she must infer the identity and substantiality of an object 'out there' when only one of its attributes, sound, is given." (Fraiberg, 1977, p. 159). Thus audiomotor control and coordination, such as that involved in reaching for audible objects or crawling toward audibly localizable goals, requires more far-reaching perceptual and cognitive abilities in blind children than the visuomotor control and coordination of movement in the sighted (e.g., an object concept, see Fraiberg, 1977; Troster & Brambring, 1993). As a consequence the delayed acquisition of locomotor and fine-motor skills in the blind can be regarded as being predominantly a direct consequence of the lack of visuomotor coordination. In contrast, lack of vision has less impact on areas of motor development such as postural skills that require no or only a limited integration of distal sensory information. Therefore, delays in postural development provide more reason for considering non-blindness-specific causes, perhaps additional brain damage. Nonetheless, visual perception also contributes to the early control of posture and the stabilization of balance (see Williams et al., 1986): Experimental studies have shown that sighted infants use visual information on the position of their body in relation to their surroundings to control posture and stabilize their balance while sitting (Butterworth & Hicks, 1977), standing (Forssberg & Nashner, 1982; Lee & Aronson, 1974), and changing posture and position (sitting up, standing up). Visual information should be particularly important for the posture and balance motor system during periods of development in which basal postural skills form as a result of neuromuscular maturation processes; whereas, with more experience and practise, posture and balance should be controlled increasingly by the mechanovestibular system (Butterworth, 1981). Various areas of motor development require a varying degree of compensation for the lack of visual perception in blind children. Compensation can be expected earliest in postural development, because it is largely controlled by the vestibular and proprioceptive system. Correspondingly, blind infants exhibit no or only very slight developmental delays in posture and balance compared to sighted peers (Fraiberg, 1977; Troster & Brambring, 1993). For goal-directed movements in proximal or distal space, in contrast, the lack of specific visual information cannot be compensated completely by other sensory modalities. Because both estimation


MOTOR DEVELOPMENT IN THE BLIND

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of distance and localization of direction are far less precise with hearing than with sight (Ashmead, Clifton & Perris, 1987), limitations in fine-motor skills as well as orientation and mobility remain even in adulthood. Therefore, blind children's developmental delays in the skills in which they have to substitute missing visuomotor control and coordination with audiomotor control and coordination should be viewed primarily as an outcome of blindness-specific developmental conditions. Psychosocial developmental conditions harbor an additional risk for the early development of the blind. Unlike parents of sighted children, parents of blind children frequently cannot draw on their own repertoire of interactions when dealing with their child, because this repertoire has been shaped by vision. Interaction calls for a particular sensitivity toward their child's blindness-specific perceptual conditions and reactions. Because of the widespread lack of reactions directed toward the interaction partner or contact-seeking behaviors in blind infants during the first months (e.g., turning their head or turning their torso, stretching their arms toward the interaction partner, smiling, e.g. Fraiberg, 1977), parents are frequently uncertain about the direction of the infant's attention. In turn, blind infants are frequently unable to recognize reliably whether their parents are attending to them (see Troster & Brambring, 1992). These blindness-specific conditions make it harder for parents to react contingently (see Als, Tronick & Brazelton, 1980; Troster, Brambring, 1992). As a result, parents' efforts to promote their infant's development are confronted with the difficulty of building up an adequate dialogue in an early phase of development. In addition, the absence of visual stimulation — the main source of stimulation for motor activity in the sighted infant — cannot be compensated completely through tactile and auditory channels, so that there is a risk that a blind infant will not receive sufficient stimulation from his or her material and social environment during the phase of development in which basic motor skills form. Alongside blindness and its accompanying psychosocial developmental risks, additional brain damage also has to be considered as a cause for developmental delays in the blind. This applies particularly to preterm blind infants. Prematurity is one of the main risk factors for congenital blindness. Because of the uncompleted vascularization of the retina in premature infants, an overdose of oxygen in an incubator can lead to detachment of the retina (retinopathy of prematurity, ROP; previously called retrolental fibroplasia, RLF). This frequently results in complete blindness (Stages IV and V of RPM; see Bossi & Korner, 1986; Wille, 1981). Because of the other risks generally linked to extreme prematurity (e.g., cerebral intraventricular hemorrhage, hypoxia, apnea, respiratory distress syndrome), blind infants with ROP are at risk of additional brain damage. Available estimations of the incidence of injury and impairments to preterm infants nonetheless vary greatly as a function of the underlying criteria of injury, the diagnostic procedures used, and the length of the period of observation. We shall sketch some of these findings. According to a meta-analysis of 111 studies (Escobar, Littenberg & Petitti, 1991), cerebral palsy was diagnosed in approximately 7.7% of


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HEINRICH TROSTER et al.

preterm infants with a birth weight under 1,500 grams; impairments arose during the course of the first year of life in 25%. Based on a review of 80 studies, Aylward, Pfeiffer, Wright and Verhulst (1989) have estimated the incidence of impairment (abnormal/major dysfunction based on various criteria such as neurologic or neurodevelopmental outcome, sensory dysfunction, and "overall" outcome) in preterm infants with a birth weight under 1,500 grams (very low birth weight) at 14%; and in preterm infants with a birth weight under 1,000 grams (extremely low birth weight), at 19%. According to Beckwith and Rodning (1991), approximately 22% to 25% of preterm infants with a birth weight under 1,000 grams have severe impairments by the age of 2 years. Some studies (Crome, 1958; Potter, 1954; Williams, 1958) have indicated a higher incidence of neurological impairment or intellectual dysfunction in infants with ROP compared to preterm infants (for a review, see Scharf & Adams, 1984). For example, blind infants with ROP seem to have a higher incidence of intraventricular hemorrhage (Brown, Biglan 8c Stretavsky, 1990; Prozianoy, Garcia-Prats, Hittner, Adams & Rudolph, 1981). Vohr and Coll (1985) have diagnosed neurological injury (cerebral palsy, seisures) in 7 out of 14 ROP infants with a birth weight below 1,500 grams, but only in 2 of a control group of 14 sighted preterm infants matched for birth weight. In the seven ROP infants with negative neurological findings, a cerebral injury was suspected because of extreme delays in the acquisition of fine- and gross-motor skills. In a study of 12 blind 1- to 12-year-olds with ROP, Teplin (1988) has found only 4 children with no additional severe impairments. Some authors (e.g., Crome, 1958) have suspected that ROP does not just involve an ophthalmological injury, but is regularly accompanied by a frequently undetected mild cerebral injury. The Present Study

The possible causes of developmental delays in blind children mentioned above reveal the difficulty in discriminating direct effects of blindness from deviations due to inappropriate childrearing or additional brain damage. Information on the impact of a lack of vision can be obtained by studying the development of blind children with no additional impairments who have received an impairment-specific early intervention. However, it is particularly difficult to rule out additional damage, especially during the first year of life. Frequently, no or only unreliable neurological findings are available, so that the researcher has to draw on the reports of parents and early intervention staff (e.g., Troster & Brambring, 1993). The common practice of inferring an underlying brain damage when major developmental delay arises is particularly problematic in blind children, because such inferencies do not take into account developmental deviations due to the absence of visual perception. The available findings indicate that preterm blind children have to be regarded as a special group, because their development is threatened by the risks of prematurity as well as lack of vision. However, we still do not know how far the


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risk factors accompanying prematurity lead to developmental delays above and beyond the effects of blindness. This article presents a longitudinal study on the early development of blind children. The study is part of an ongoing research program that is tracking the perceptual, fine- and gross-motor, socioemotional, cognitive, and language development of 10 congenitally blind children from the first year of life up to school entry at the age of 7. Findings reported here on motor development in the first three years of life should provide information on the impact of blindness and prematurity.

METHOD The research program Early Intervention and Family Counselling for Blind Infants

and Preschoolers2 has been providing regular care and developmental diagnoses to 10 blind children since 1989/1990. The research program has three goals: (a) to provide a detailed description of the development of blind children; (b) to develop and implement an early intervention and parent counseling program; and (c) to evaluate this intervention program. Early intervention and parent counseling focus on four aspects: (a) impairmentspecific counseling of the parents on all childrearing issues and problems in their child's development; (b) helping parents cope with psychosocial problems and conflicts within the family arising from their child's impairment; (c) childcentered early intervention; and (d) promoting an exchange of information and experiences through regular parent meetings. The 10 blind infants entered the early intervention program between the ages of 7.5 and 16.0 months. Up to the age of 36 months, an early intervention therapist visited them in their own home every 2 weeks; from 36 to 48 months, they were visited once a month.3 In December 1993, the children were aged between 4 and 5 years, and some of them were attending mainstreamed preschool. Assessment of Motor Development

The level of perceptual, fine- and gross-motor, socioemotional, language, and cognitive development was assessed at each home visit. The specially developed checklists contained a series of hierarchically ordered items for each area of development and for each age range. The items were adjusted for the impairmentspecific perception and reactions of blind children. In the early intervention The research program Early Intervention and Family Counseling for Blind Infants and Preschoolers is part of the special Research Unit on Prevention and Intervention in Childhood and Adolescence, funded by the

German Research Association (DFG) since 1986. The early interventions were carried out by Andreas Beelmann, Michael Brambring, Susanne Buitenhuis, Gudrun Dobslaw, Martina Hauptmeier, Werner Hecker, Cosima Kurp, Gabriele LicherEversmann, and Angelika Miiller.


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practice, these checklists were used to diagnose intervention needs (Suhrweier & Hetzner, 1993). The early intervention therapists could use their entries to read off the current level of achievement in a motor skill in relation to a criterion (e.g., "reaches for audible objects," "stands well without support") and predict which developmental steps each child would make next in various skills. After each home visit, the therapist recorded whether the child had "not yet mastered/exhibited," "partially mastered/exhibited," or "completely mastered/exhibited" the particular skill/behavior. If the home visit did not provide any opportunity to observe the particular item, the parent was asked. This made it possible to record the first occurrence of motor skills with an accuracy of approximately 14 days. In order to take account of the different effects of lack of vision on individual areas and sections of motor development, we discriminated between basic motor functions and the complex motor skills that develop on the basis of these functions. This should make it possible to differentiate the development of simple basic motor skills that require either no or only slight adaptive substitution for the lack of visuomotor coordination in the child (e.g., sitting, standing, holding on to and letting go of objects, taking first steps while holding on to hand) from later stages of development that predominantly concern the acquisition of complex skills of auditory control and coordination of movements as well as the auditory identification and localization of objects. The checklist for basic motor skills contains observation items on posture and balance (sitting, standing), self-initiated changes in posture and position (sitting up, standing up), basic locomotor skills (crawling, first steps), and basic manual skills (holding, letting go of objects). The complex motor skills evolving from these basic motor functions were assessed with the scales "Orientation and Mobility" (spatial orientation, locomotion) and "Fine-Motor Skills" (localization of and reaching for audible objects). This paper describes the development of basic motor skills in the 10 congenitally blind children in our research program. The age at which each child acquired the individual basic motor skills was contrasted with published developmental norms for sighted children (median, range), insofar as norms were available for identical or similar developmental tasks. This comparison should provide information on the impact of blindness and prematurity on motor development and reveal impairment-specific characteristics in the developmental course of blind children. A comparison with the development of complex motor skills (e.g. orientation and mobility) in sighted children, in contrast, seemed inappropriate, because auditory identification, localization, control, and coordination play only a subordinate role in the everyday life of the sighted child. Sample The 10 children in our longitudinal study were either completely blind since birth or possessed at most light perception. Five children (3 boys, 2 girls) were born


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Table 1 The Sample Full-term blind children (n = 5)

Preterm blind children (n = 5)

2,770-3,650

650-1,115

Period of gestation (in weeks)

38-40

26-29

Age at study onset (in months)

9.0-12.5

7.5-16.0*

Age at end of study (in months)

48.0 - 53.5

49.0 - 54.5*


Birthweight (in grams)

Number of home visits Ophthalmological diagnosis

51-60

50-55

Microphthalmos (2) Anophthalmos (1) Leber's amaurosis (1) cortical blindness (1)

Retinopathy of prematurity (5)

* Age corrected for prematurity

full-term, and the other five (2 boys, 3 girls) were preterm. These children, whose blindness was due to retinopathy of prematurity (ROP), had extremely low birth weights (between 650 and 1,115 grams; period of gestation from 26 to 29 weeks). Table 1 presents some important information on the sample. To control for additional damage, the children underwent pediatric-neurological examinations once a year.4 This examination covered reflexes and coordination, as it was not yet possible to perform a diagnosis with imaging techniques. Up to the most recent examination (November/December, 1993), indications of brain damage had been ascertained in one of the full-term and four of the preterm infants. Suspicions of cerebral injury (microcephalus) have hardened in one preterm infant.

RESULTS

Table 2 compares the age (median, age range) at which postural skills (sitting, standing, change of posture and position) were observed for the first time in The pediatric-neurological examinations were carried out by Dr. Rohlmann at the children's clinic, Bodelschinghsche Anstalt Bethel, Germany.

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Table 2 Postural Development Full-term blind children (n = 5)


Nonhandicapped children (norm data)


Sitting Sits alone, steadily

a

10.0b 10.0-11.5

6.6C 5.0-9.0

Sits alone, good coordination (Plays in sitting position)

a

12.8b 10.0-14.5

6.9C 5.0-10.0

a

12.5 11.5-16.0

7.6d 6.7-10.3

Stands alone, briefly

13.0 12.0-14.0

19.0 18.0-37.5

11.0° 9.0-16.0

Stands alone, firmly

15.5 13.5-21.0

33.0 24.0-41.0

13.1d 11.5-15.7

Remains standing with an object in the hand

16.0 14.0-21.0

34.0 24.0-41.0

e

Standing Stands holding on

Changes in posture and position

Raises self to sitting position

13.3b 11.5-16.0

17.0 10.5-21.5

8.3C 6.0-11.0

Stands up by furniture

12.0 10.5-13.5

18.0 13.0-22.0

8.6C 6.0-12.0

Stands up

17.0 16.0-24.5

36.0 25.0-42.0

12.6C 9.0-18.0

Note. Median age (in months) for the aquisition of postural skills in full-term blind children (n = 5), preterm blind children (n = 5, corrected for prematurity) and nonhandicapped children. Second row: age range. " Attained by all infants at the beginning of the study. b Performed by one 11-month-old at the beginning of the study. c Bayley Scales of Infant Development, (Bayley, 1969), 5%-95% age range. d German version of the Denver Developmental Scales, (Flehmig, 1975), 25%-90% age range. e No available age reports for sighted children.



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the full-term and preterm blind children with developmental norms reported for sighted children. The ages of preterm children were corrected for prematurity. Age reports on the acquisition of sitting were not available for full-term children, because all of them could already sit well when recruited at the age of 9.0 to 12.5 months, and retrospective reports were insufficiently reliable or precise. Likewise, the development of basic fine-motor skills could not be followed up, because, at the beginning of the study, all blind infants were able to hold and let go of an object placed in the hand. The majority of full-term blind children exhibited the skills of posture control and balance stabilization within the 95% age range of nonhandicapped children. On average, they could stand up unassisted approximately 2 months later than their sighted peers. Somewhat longer delays of 4.4 to 5.0 months were observed in self-initiated changes of posture and position: Four children in this group could sit up unassisted and two were able to stand up somewhat later than 95% of sighted children. Compared to the full-term blind children, few of the preterm blind children attained the milestones of postural development within the 95% age range of sighted children. On average, they were able to sit steadily about 4 months later than sighted children, could stand firmly about 20 months later, and there was a long delay before they could sit up by themselves (8.7 months) or stand up by themselves (23.4 months). Compared to the developmental course of sighted children, it was conspicuous that after managing to maintain their balance while standing, blind children took longer to stand up by themselves. While sighted infants who were able to stand briefly took, on average, a further 1.6 months to learn how to stand up by themselves, full-term congenitally blind children took 4 months and the preterm 17 months between standing briefly and standing up by themselves. All full-term blind children and three of the preterm blind children could already stand firmly before they managed to stand up without support. Table 3 compares the locomotor development of the blind children with developmental norms for sighted children. Full-term congenitally blind children were able to walk approximately 3 to 4 months later than sighted children and crawl in a coordinated manner approximately 9 months later. Developmental delays were much longer in the preterm blind children: They took their first unsupported steps 15 months later than sighted children, while they began to crawl in a coordinated manner 13 months later than their sighted peers. Figures 1 and 2 show that the developmental differences between full-term and preterm blind children were larger than those between full-term blind and sighted children. Prematurity seemed to represent a greater risk to motor development than blindness. This was also indicated by the slower pace of development in preterm blind children. While the developmental gap between full-term blind children and their sighted peers tended to decrease over the course of the first 3 years of life, the gap between preterm blind children and nonhandicapped children widened with increasing age. For example, the developmental delay in self-initiated walking was about 15 months in preterm blind children during the

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Table 3 Locomotor Development Full-term blind children (n = 5)


Nonhandicapped children (norm data)

j


Crawling

Maintains balance in all-fours position

11.0* 9.5-15.0

14.0 9.0-19.0

Rocks in all-fours position

12.5" 11.5-16.0

14.3b 11.0-16.0

j

Prewalking progression

13.3b 13.0-17.5

15.5° 15.5-23.5

7.1f 5.0-11.0

Uncoordinated crawling

14.5 12.5-20.5

18.0 14.0-27.5

8.0g 6.0-12.0

Coordinated crawling

19.0 14.0-23.5

22.5 19.5-27.5

9.7' 7.0-13.0

Walking Stepping movements (with both hands held)

12.0 11.0-12.5

13.0 12.0-18.0

8.81 6.0-12.0

Walks with help (with one hand held)

14.0 13.0-14.5

19.5 14.0-22.5

9.6f 7.0-12.0

Walks along furniture

13.5 12.5-15.5

18.5 15.5-22.5

9.6 h 8.4-11.7

Walks alone, three steps

15.5 13.5-18.0

26.5 23.0-41.0

11.7f 9.0-17.0

17.5 • 15.5-20.0

30.0 24.0-41.0

13.6 h

Walks alone, 10 steps

12.3-16.0

Climbing stairs and hopping

Walks up stairs with help

17.5 17.0-20.0

34.3e 24.5-41.0

16.1' 12.0-23.0

Walks down stairs with help

18.0 17.0-26.5

36.5e 26.0-41.0

16.4f 13.0-23.0

Hops on two legs

25.0 20.5-39.0

38.0d 26.5-J9.5

25.7h 23.4-31.5


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Note. Median age (in months) for the aquisition of locomotor skills in full-term blind children (n = 5), preterm blind children (n = 5, corrected for prematurity), and nonhandicapped children. Second row: age range. Performed by two infants at the beginning of the study. b Not observed in one infant.c Not observed in two infants.d Not mastered by two children up to the age of 49.0 or 52.5 months. * Not mastered by one child up to the age of 49.0 months.f Bayley Scales of Infant Development, (Bayley, 1969), 5%-95% age range. g According to Zwiener, Schmidt-Kolmer & Niebsch (1982), 5%-95% age range. h German version of the Denver Developmental Scales, Flehmig (1975), 25%-90% age range.' German version of the Griffiths Developmental Scales, (Griffiths, 1983), 5% -95% age range. j No available age reports for sighted infants.


a

third year of life, while full-term blind children began to walk without support about 3 to 4 months later than sighted children. In preterm blind children, the slower pace of development was accompanied by large interindividual differences in motor development. The age range for the first occurrence of motor skills (Tables 1 & 2) was much larger compared to the other two groups, and it increased with age. Beyond a general developmental delay, specific deviations in locomotor development could also be observed in the blind. While sighted children generally crawled first and then began to walk, four of the full-term blind children first walked and then began to crawl, and we even found that one of them began to crawl and walk at about the same time. Three of the five full-term blind children could climb up stairs before they could crawl in a coordinated manner. On average, the full-term blind children began to crawl in a coordinated way 3.5 months after they had already walked three steps without support. The preterm blind children, who were very late in being able to take their first steps, could all walk holding on to a hand an average of 3.0 months before beginning to crawl in a coordinated way.

DISCUSSION

In the development of their posture and balance control, full-term blind children show only slight delays. Almost all of them attain the milestones of sitting and standing within the age norms of sighted infants. However, they show more marked developmental delays in their ability to change posture and position and in self-initiated locomotion. At the end of the second year of life, however, all full-term blind infants are able to stand up and walk without support. These results are in broad agreement with Fraiberg's (1977) longitudinal study of a group of 10 congenitally blind children with no additional impairments that included who were preterm. As additional brain damage can be ruled out with a high degree of certainty in four of the five full-term blind children in our sample, and all the children in our research program are receiving an intensive, impairment-specific early

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HEINRICH TROSTER etal.

Postural Development


Sits afone, firmly Stands up

Stands alone, briefly Stands up by furniture Raises self to sitting position

Stands holding on Sits alone, good coordination •°- Full-term blind "^•Preterm blind

Sits alone, steadily

"*" Nonhandicapped

6

9 12 15 18 21 24 27 30 33 36

Age in months Figure 1 Median age for the acquisition of postural skills in full-term blind children (n = 5), preterm blind children (n = 5, corrected for prematurity), and nonhandicapped children.


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Locomotor Development

Age in months Figure 2 Median age for the acquisition of locomotor skills in full-term blind children (n = 5), preterm blind children (n = 5, corrected for prematurity), and nonhandicapped children.

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intervention, the causes of the delay in achieving the milestones of motor development in full-term blind children compared to sighted peers need to be sought in the lack of vision. This statement confronts us with the question of the functions of vision for motor development and the possible consequences of its loss for the various areas of motor skills. We can report some indications regarding the specific effects of blindness on motor development: 1.

The lack of visual information as a basis for making fine adjustments to vertical body posture while sitting or standing and for anticipating compensatory movements to stabilize balance after active or passive changes in position (as well as possible limitations in storing information on position in memory, see Shingledecker, 1978) slows down the development of posture and balance in blind children.

2.

Through the absence of visual stimulation, blind children are less extrinsically motivated to engage in motor activities than sighted peers, particularly to change posture and position (e.g., lifting the head when lying on the stomach, sitting up, standing up) or to initiate locomotion (crawling, walking).

3.

The need to find an adaptive substitution for the lack of visual information on the localization of goals in their surroundings and on the coordination of their movements in relation to these goals delays the acquisition of locomotor skills in the blind.

4.

The inability to use visual information from their material and social environment to anticipate and evaluate dangers and risks in their surroundings makes it more difficult for blind children to reduce their initial uncertainty and anxiety regarding self-initiated locomotion. For example, blind infants cannot use visual information to recognize and avoid obstacles in their surroundings. In addition, unlike sighted infants, they are unable to exploit visual information from their social environment (e.g., mother's facial expressions when the infant is confronted with an unknown situation) in the sense of social referencing (see Klinnert, Campos, Sorce, Emde & Svejda, 1983) in order to gain a better appreciation of a new and anxiety-arousing situation.

We still have to explain how far these blindness-specific functional limitations individually affect the motor development of blind children and in what ways blind children compensate them. Their particular deviations from the developmental course of sighted children may be informative here. One example is their difficulty in standing up: The lack of visual information on changes in the position of their body relative to its surroundings and the restriction to the vestibular and proprioceptive system during a phase of development when the skills for changing posture and position form may well be particularly disadvantageous. In addition, their restricted possibilities of anticipating and evaluating dangers and risks may contribute to the fact that blind children only hesitantly begin to stand up or walk unaided although they possess the necessary neuromuscular maturity.


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There are also deviations from the developmental sequence of sighted children in the acquisition of locomotor skills. Four of the five full-term blind children skip the crawling phase and only begin to move forward on all fours after they have already taken their first steps. The preterm blind children can also already walk while holding on to a hand before they begin to crawl in a coordinated manner. Skipping the crawling phase seems to represent a particular characteristic of the development of blind children. The causes of this deviation in locomotor development are unclear. Nonetheless, we can offer the following suggestions: 1. At the age at which sighted infants normally begin to crawl toward visible objects in their environment, blind infants still do not possess an object concept that permits them to associate their auditory perceptions with real objects in the external world. Without the idea that auditory perceptions may indicate real objects in their environment, sound objects (such as a musical box) do not stimulate blind infants to crawl toward them (Fraiberg, 1977). 2.

Because of the exposed position of the head when crawling and the risk of knocking it against obstacles, blind children may avoid this type of locomotion. They cannot use their hands to identify and avoid obstacles when crawling. This explanation is supported by the observation that 5 of the 10 blind children first crawled backwards for several weeks.

3.

Vestibular information is more precise when the head is held upright than when it is horizontal. Perhaps the almost horizontal position of the head and the lack of contact between the trunk and the floor when crawling make it more difficult for blind children to stabilize their balance (R.H. Largo, personal communication, October 18, 1993).

Compared to full-term blind children, the preterm blind children show major developmental delays. In this way, they face a twofold risk: Their development is threatened not only by the lack of sight but also by the risks of prematurity. While sighted preterm infants frequently overcome their initial delay in grossmotor development and catch up with full-term infants of the same gestation age during the first 2 years of life (Barrera, Rosenbaum & Cunningham, 1987; Piper, Byrne, Darrah & Watt, 1989), or the developmental differences to full-term children are compensated and sometimes even overcompensated by correcting chronological age after the second year of life (Den Ouden, Rijken, Brand, Verloove-Vanhorick & Ruys, 1991), the developmental delays in the preterm blind children in our longitudinal study increase over the first 3 years of life - despite the correction of their chronological age. There seem to be two possible explanations for this (Hecker, 1994): The major developmental delays in preterm blind children compared to their full-term blind peers could be due to additional brain damage. This assumption is supported by the indications of brain damage in four of the five preterm blind children reported in the annual pediatric-neurological examinations. However, this is as yet confirmed in only one child. More reliable information could certainly be obtained


76


with computer-assisted tomography (CT scans) or ultrasonography, but it has not yet been possible to carry out these procedures. The growing developmental delay compared to full-term blind children may also be conceived as the outcome of an interaction between the two risk factors (Hecker, 1994). According to this idea, the interaction between blindness and prematurity poses a greater threat to early development than each individual risk added together: Because of the problems with attention and information processing that frequently accompany prematurity (e.g., short attention span, irritability, restlessness, difficulties in sensorimotor coordination, for reviews, see Reckwith & Rodning, 1991; Hoy, Bill & Sykes, 1988), preterm blind children are less able than their full-term blind peers to compensate the lack of vision through other sensory modalities, and, vice versa, their blindness-specific constraints make them less able to balance out the risks of their prematurity than sighted premature children. A greater understanding of the possible interaction between blindness and prematurity could be obtained from studies that try to specify more precisely both the cognitive and perceptual demands confronting blind children in their attempts to compensate for the lack of vision as well as the deficits in information processing that accompany prematurity. References Als, H., Tronik, E. and Brazelton, T.B. (1980). Affective reciprocity and the development of autonomy. Journal of the American Academy of Child Psychiatry, 19, 22-40.

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