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poster
Acquisition of adaptive motor skills such as walking involves more thanmuscles and biomechanics. Locomotion over irregular terrain requireshigher level cognitive abilities such as planning, inhibition, andmeans/ends coordination. If the constraints of the ground surface exceedinfants limited ability to keep balance, then they must avoid walking oruse an environmental support to augment their abilities. Previousresearch provides ample evidence for planning and inhibition in younghuman infants on the visual cliff, slopes, and other surfaces (e.g.,Adolph, 1997) and for means/ends coordination in adult primates (e.g.,Kohler, 1925). Here, we examined whether and how young walking infantsrecognize an environmental support as an aid for balance control in anovel locomotor task. Twenty-four 16-month-old infants (12 girls, 12 boys) were encouraged tocross wide and narrow bridges (72, 54, 36, 18 cm) spanning a largeprecipice in the surface of support (91 cm long x 74 cm wide x 60 cmdeep). On half of the 24 trials, a handrail along one edge of the bridgewas available to provide support for locomotion. Parents encouraged theirinfants from the far side of the bridge and an experimenter followedalongside infants to ensure their safety. Bridge widths were chosen sothat all infants could walk easily over the widest bridges, but withoutthe handrail, the narrowest bridge would be difficult for even the mostskillful walkers. We reasoned that if infants recognized that thehandrail augmented their ability to keep balance then they would use thehandrail to walk over the narrowest bridges but not over the widest ones.Repeated measures ANOVA on attempts to walk showed an interaction betweenbridge width and handrail presence indicating that infants were morelikely to walk over the narrowest bridge when the handrail was available.Handrail use decreased linearly with bridge width, providing furthercorroboration that infants viewed the handrail as an aid for balancecontrol on narrower bridges; F(5, 514)3.96, p<.01. In addition tocurtailing attempts to walk based on bridge width, infants hesitatedlonger before embarking onto the narrowest bridge and modified their gaitto cope with walking over it by taking smaller, slower steps; all p<.01.Together, these results provide evidence of higher level cognitiveabilities in the adaptive locomotor behaviors of 16-month-old walkinginfants. Babies planned their movements prospectively based on taskdifficulty, they inhibited their normal walking response by hesitatingbefore crossing the narrowest bridge, and they recognized that anenvironmental structure augmented their own limited abilities and could beused as a means for achieving a goal. Further analyses will examinefactors that affect infants discovery of the handrail as a means foraugmenting balance control - exploration of the handrail prior toembarking onto the bridge, variations in gait while using the handrail(e.g., walking sideways), and individual differences in walking skill,body size, and prior experiences with handrails and stair banisters.
poster
Between crawling on four limbs and walking on two, babies exhibit severaltransitional milestones with erect posture: pulling to a stand, balancingon their own, walking holding caregivers hands, and cruising sidewaysholding onto furniture. Because these transitional skills are temporalprecursors to walking and share the physical similarity of uprightposture, researchers have assumed that they are functionally related towalking, i.e., practice keeping upright balance helps babies learn towalk. To the contrary, we show that developmental milestones that aretemporally related and similar in form may not necessarily share afunctional relationship. In particular, we tested the purported temporaland functional relationships of cruising to crawling and walking.Temporal Relationship. Although most researchers assume that cruisingoccurs between crawling and walking, little normative data actually existsthat compares all three skills. Preliminary data from 145 infants showthat cruising is not a strict temporal bridge between crawling andwalking. Parents of 4.5-18 month-olds reported onset ages for crawling,cruising, and walking and milestones were verified in the laboratory. Allbabies cruised before walking, but only 68% showed the typical pattern ofcrawling before cruising. The others cruised before crawling or cruisedand crawled simultaneously.Functional Relationship. We examined the information infants use to keepbalance while cruising. If cruising facilitates walking by providingpractice with upright balance, then infants should learn walking-relevantfacts about balance control such as information about the lower limbs andfloor. However, if cruising is manually controlled, like crawling, theninfants should attend only to information specifying support for the upperlimbs. We tested 11-month-old cruisers on an adjustable 'gaps' apparatus,presenting gaps of varying width (0-90 cm) in either the floor or ahandrail. In both the floor and handrail conditions, infants began eachtrial in a sideways cruising position. Then an experimenter showed themthe gap in the rail or the floor to ensure that they obtained relevantinformation for balance control. Parents encouraged infants from the farside of the apparatus and an experimenter followed alongside infants toensure their safety. An online, psychophysical staircase procedure(Adolph, 1995) estimated the largest gap each infant could cruise in eachcondition to a 67% criterion. Preliminary results from 10 infants suggest that cruising is not afunctional bridge to walking. Despite being shown gaps at the start ofeach trial, infants appeared oblivious to the fact that balance isimpossible without a floor. In the floor condition, they repeatedlycruised into impossibly large gaps. However, in the handrail condition,the same babies attempted safe gaps and avoided increasingly risky ones. Together, these studies suggest that crawling and cruising may share acommon basis for locomotionmanual control of balanceand that both skillsmay be functionally irrelevant to the problem of maintaining balance whilewalking. More generally, these data demonstrate that developmentalmilestones that appear to be functionally related because of temporal andphysical similarities may, in fact, bear no such relationship.
poster
The role of locomotor experience is fundamental to developmental theoristssuch as E. Gibson, J. Piaget, and A. Freud. However, despite an abundanceof recent empirical evidence linking crawling experience with improvementsin motor, perceptual, cognitive, and social domains, we know little aboutunderlying change mechanisms. Theoretical claims about the role oflocomotor experience cannot be verified because there are no empiricaldata specifying what infants experience. Previous studies have definedcrawling experience only as the number of days since crawling onset. Tounderstand the mechanisms underlying experience-related changes, we need adetailed description of what experience really entailswhere infants crawl,how often they go there, what surfaces and paths they traverse, and howfar they crawl. To redress these deficiencies, we devised a telephone diary method forobtaining parents reports of infants daily activities and locomotorexperience. Our aims were to validate the method and to compile a rich,longitudinal database. Six families participated 1-6 days/week for 4-16weeks. Three babies were observed from their first week of crawling andthree others as more experienced crawlers (4+ weeks). Parents eithertelephoned a time-stamped answering machine to report activities andcrawling experience every hour or two or they gave reports to anexperimenter during nightly telephone interviews. In both cases, anexperimenter probed parents at the end of each day for information missingfrom their reports. Online audio recordings by parents and homeobservations by experimenters demonstrated the reliability of parentsreports. Home blueprints provided information about places to crawl,spatial layout, dimensions of rooms and furniture, and types of floorsurfaces. Locomotor experience comprised a central portion of each infants dailylife. On average, they spent 39.4% of their 11.5 hour days on the floorcrawling and playing. For the remainder, they napped, ate, and were held.Increase in one activity was gained at the expense of another. Allinfants showed predominantly negative correlations between activities andall showed significant negative correlations between time crawling andtime being held (all p<.05). Variability in crawling time was greater inthe three new crawlers (average range53.7% of daily activities) comparedwith the experienced infants (17.0%), suggesting that acquisition ofmobility initially disrupted infants schedules.Infants homes varied widely in places to crawl, ranging from 304.9-1577.6square feet of open crawling space, 5-12 rooms, and 6-20 floor surfaces.Infants with smaller homes visited a larger proportion of rooms andsurfaces. Five infants spent most of their floor time and crawlingexcursions in their familys primary living space (family/living/diningroom area). Most crawling excursions (M86.8%) were one-way trips. Totalcrawling distance/day depended on number of trips rather than trip length.Infants with more trips/hour accumulated greater distances each day thanthose with lower activity levels. Further analyses will examine the relationship between developmentalchanges in crawling skill, body dimensions, locomotor experience andresulting changes in opportunities for learning. The long-term aim ofcompiling such a detailed, longitudinal database is to constraintheorizing about change mechanisms that underlie the link betweenlocomotor experience and psychological development.
poster
Acquisition of locomotor skills in infancy shows repeated patterns ofimprovement and decrement. In their first weeks of crawling, most babiesare poorly skilled. Gait is slow and awkward and many children creepalong using their abdomen for support. Apparently oblivious to theirlimitations, new crawlers plunge headfirst over the brink of cliffs andimpossibly steep slopes (e.g., Adolph, 1997; Bertenthal et al., 1984).After several weeks of crawling experience, infants correctly crawl oversafe ground but avoid risky surfaces. Then, in their first weeks ofwalking, infants again are poorly skilled. Gait is clumsy and unstablewith poor balance control. Moreover, beginning walkers must learn allover again to distinguish safe from risky ground surfaces. Thus, duringearly stages of crawling and walking, infants must rely on caregivers tokeep them safe from falling. In later stages, infants are more able tonavigate potentially risky situations on their own. Given parents role in accident prevention, we tested whether mothers couldaccurately predict their infants crawling skill and motor risk-taking in apotentially risky locomotor taskdescending a 9 foot walkway withadjustable slope (0-90). Twenty-one mothers and their 11-month-oldcrawling infants participated (11 girls, 10 boys). Average duration ofcrawling experience was 13.0 weeks. Using the psychophysical method ofadjustment, mothers set the walkway to the steepest slope they thoughtthat their infants could crawl down successfully (measure of crawlingskill) and the steepest slope they expected their infants to attempt tocrawl down regardless of success (measure of motor risk-taking). Then, weencouraged infants to descend shallow and steep slopes to assess theaccuracy of mothers predictions. Using a modified psychophysicalstaircase procedure (Adolph, 1995), we determined the steepest slopeinfants could actually crawl down successfully and the steepest slopeinfants would attempt to crawl down regardless of whether they succeededor fell. As in previous studies with experienced crawlers, infants displayed a highlevel of crawling skill and highly adaptive avoidance responses when facedwith risky ground surfaces. They successfully crawled down steep slopesand they closely matched attempts to crawl with the probability ofsuccess. There were no differences between girls and boys on eithermeasure: Ms for crawling skill were 23.6 and 20.6 and for motor risktaking were 29.6 and 24.4 for girls and boys respectively. Motherspredictions were extremely inaccurate. The average absolute differencebetween mothers predictions of crawling skill and infants actual crawlingability was 8.6; t(20)5.2; p<.00. The average absolute differencebetween mothers predictions of motor risk taking and infants actualattempts was 15.8; t(20)4.8; p<.00. Mothers pattern of errors fellneatly along gender lines. Mothers of girls predicted shallower slopesfor crawling skill (M13.9) than mothers of boys (M .3); t(19)-2.2,p<.05. Similarly, mothers of girls predicted shallower slopes for motorrisk taking (M .2) than mothers of boys (M32.8); t(19)-2.9, p<.01. Insum, mothers do not track developmental changes in infants locomotorskills and they attribute gender differences to infants where none exist.Results have important implications for accident prevention and forunderstanding the development of gender differences in motor skill inolder children and adolescents.
poster
Introduction. Walking is one of the most important events of infancy; itmarks the transition between infancy and toddlerhood. The emergence ofmotor milestones, such as this, is sometimes argued to be geneticallyprogrammed (Konner, 1985) yet studies have shown that practice cansignificantly affect the age of walking onset in normally developinginfants (Super, 1976; Zelazo, Zelazo, & Kolb, 1972). For infants with Downsyndrome (DS) walking occurs about one year later than in nondisabledinfants. In previous studies we have shown that infants with DS canproduce well-coordinated alternating steps when supported on a motorizedtreadmill, long before they walk independently (Ulrich et al. 1995). Thepurpose of this study was to determine if regular practice on a treadmillcould reduce the delay infants with DS experience when learning to walk.Method. We enrolled 30 infants with DS in this study in a lagged fashion(over 3 years) when they were able to sit alone for 30 seconds. Werandomly assigned each to the Experimental (E) Group or Control (C) Group.All received physical therapy at least every other week; in addition the EGroup received 8 minutes of supported stepping practice on a motorizedtreadmill, provided by their parents, 5 days per week. Every two weeks wetested infants in their homes by administering the BSIDII (motor scale),anthropometric measures, and bimontly videotaping of infants' supportedstepping behavior on the treadmill. We behavior coded the alternatingsteps taken during each test trial via frame by frame analysis of thevideotapes.Results. Over time, infants in the E Group showed a more rapid rise in thenumber of alternating steps taken than the C Group. Infants in the E Groupalso showed more rapid improvement in the stability of interlimb phaserelations of their steps over time. To examine functional motor behaviorswe compared the Groups on the time elapsed between entry into the studyand three motor milestones. Infants in the E Group pulled to standing anaverage of 60.6 (M) days earlier than those in the C Group [F(1,28) 3.01, p<.09; effect size statistic .65]; the E Group began to cruise73.8 (M) days before the C Group [F(1,28) 5.54, p<.03; effect sizestatistic .80]; and the E Group walked 101 (M) days earlier than thosein the C Group [F(1,28) 6.15, p<.02; effect size statistic .83].Discussion. The results of this study show that practice on a treadmillhastened improvement in quality of stepping patterns in infants with DS.Further, practice facilitated the onset of independent walking. Thissuggests that the emergence of this skill is plastic and significantlyimpacted by peripheral factors. These data lead us to argue that complexsystems theory provides a more credible and replete explanation for theacquisition of this skill than simple maturation does.
poster
This study investigated the roles of locomotor experience, walking skill and body size in determining the abilities of 12-month-old toddlers for crossing barriers varying in height. Walking skill was assessed using the footprint method of gait analysis; this is a global measure in which the inked footprint sequences of a toddler's walking pattern are compared to an adult's mature pattern (Adolph, 1995; Adolph, Eppler & Gibson, 1993; Adolph, Vereijken, Byrne & Ilustre, 1996; Boenig, 1977). Such an investigation was of interest for a number of reasons. Previous work, examining the relation between experiential, skill and anthropomorphic variables, and the action capabilities of toddlers has revealed conflicting findings. For instance, Adolph (1995) has found that measures of walking skill best predicted the abilities of 14-month-old toddlers for walking up and down slopes of varying angles. In contrast, the barrier crossing abilities of 18-, 24- and 30-month-old toddlers have been found to be most strongly related to locomotor experience (Kingsnorth & Schmuckler, 1999; Schmuckler, 1996). One possible explanation for the different patterns of findings seen is that the actions in question (i.e., slope ascent and descent, and barrier crossing) are simply too different for direct comparisons to be made between them. Alternatively, it may be the case that the importance of walking skill, itself, changes with age. For children who are just learning to walk (i.e., 14-month-olds), walking skill may be the most influential factor in determining the limits of their abilities. However, once a basic level of skill has been achieved, locomotor experience takes on a greater role. To examine the relation between crossing thresholds and the various experiential, skill and size parameters, the crossing thresholds were normalized and compared as a function of age with matching data previously collected for 18-, 24- and 30-month-old infants (Kingsnorth & Schmuckler, 1999). Factors that are strongly related to crossing thresholds will remove differences in the threshold values, both within an age group, as well as between age groups (Schmuckler, 1996; Warren, 1984). Replicating earlier findings (e.g., Kingsnorth & Schmuckler, 1999; Schmuckler, 1996), barrier crossing was most strongly related to walking experience. At first glance, this finding appears to rule out the developmental path previously suggested, whereby skill is more important in determining the action capabilities of toddlers in the early days of walking. However, it may be the case that the measure of skill being used is much more specific to particular tasks than previously thought. Although the footprint method is thought of as a global measure of walking skill, the actions involved (i.e., repeating a similar movement over and over) are more closely attuned to the motor demands of walking up and down slopes than to the motor demands of barrier crossing. For example, walking on flat ground does not require a child to balance on one foot while swinging the other leg across an obstacle. Perhaps what is needed before comparisons between these two tasks are made is a different measure of skill; one that more accurately assesses the elements involved in crossing a barrier. For instance, assessments of kinematic parameters, such as balance, flexibility and strength, may more accurately reflect the contribution of walking skill in predicting the barrier crossing thresholds of toddlers. One challenge, however, in examining kinematic parameters is the difficulty in using them with very young children; future research may wish to address means of obtaining such information in such a young population.REFERENCES Adolph, K. E. (1995). Psychophysical assessment of toddlers' ability to cope with slopes. Journal of Experimental Psychology: Human Perception and Performance, 21 (4), 734-750. Adolph, K. E., Eppler., M. A., Gibson, E. J. (1993). Crawling versus walking infants' perception of affordances for locomotion over sloping surfaces. Child Development, 64, 1158-1174. Adolph, K. E., Vereijken, B., Byrne, K., & Ilustre, I. (1996, April) Footprint method of gait analyses: New insights into infant walking. Poster presented at the International Conference for Infant Studies, Providence, RI. Boenig, D. D. (1977). Evaluation of a clinical method of gait analysis. Physical Therapy, 57(7), 795-798. Kingsnorth, S. & Schmuckler, M. A. (1999, April) Walking skill versus walking experience as a predictor of barrier crossing in toddlers. Poster presented at the Society for Research in Child Development, Albuquerque, NM.Schmuckler, M. A. (1996). The development of visually-guided locomotion: Barrier crossing by toddlers. Ecological Psychology, 8(3), 209-236. Warren, Jr., W. (1984). Perceiving affordances: Visual Guidance of stairclimbing. Journal of Experimental Psychology, 10(5), 683-703.