4 F isio te ra p ie , M a a rt 1983, d e e l 39, n r 1 CONCEPTS IN EARLY SENSORY DEVELOPMENT S A R A H F O R S Y T H B L A C H A , O.T.(C)* S U M M A R Y V arious f a c to r s w hich c o n tr ib u te to p e r c e p tu a l d e v e lo p m e n t a n d the d o s e re la tio n sh ip o f se n so ry a n d m o to r in flu e n ce s to n o rm a l d e v e lo p m e n t are d iscussed in the h o p e o f e n co u ra g in g th era p ists w h o w o rk in the d e v e lo p m e n ta l f ie l d to in co rp o ra te a p p ro p ria te, g ra d e d se n so ry stim u li in to their tre a tm e n t repertoire. The s e n s o r y -m o to r link a n d the im p o rta n c e o f ta ctile a n d vestibular sy ste m s to the n o rm a l d e v e lo p m e n t o f a p e rc e p tu a l sc h e m a are discussed. The i n te g ra ti o n o f senso ry i npu t is essential to n o r m al m o to r d ev elo pm en t. W he n a n infan t is dep rived o f sensory stimulus, the i m p a c t on m o to r a n d p e rc e p tu a l /c o g n i ti v e d ev elo pm en t is de v as ta tin g (Casler, 1968), subseq ue nt ly h a n d ic a p p i n g the child in u n d e r s t a n d i n g a n d inter act ing with his en v iro nm en t. Two widely recognized a p p r o ac h es , Se ns o r y Integrative T h e r a p y (Ayres, 1972, 1975) a n d N e u r o de v e lo pm e n ta l T he r a p y (B o b a th , 1971; B o b a th and Bo ba th . 1975) e mp ha si ze senso ry aware ne ss a n d i np ut in th eir t her ap y models t o p r o d u c e a p p r o p ri a t e m o t o r a n d / o r ad ap ti v e be h av io u ra l responses. The i nt e g ra ti on o f sensory a n d m o t o r i n f o r m a t io n occurs a t various levels o f the cen tr al ne rv ou s sys tem (CNS). All inco min g in f o r m a t io n is processed by the C N S an d sensory feedback is received f ro m the bo d y m us c u la t u r e to help o r g a n i z e m o t o r o u t p u t . T h is s e n s o r y - m o t o r - s e n s o r y processing prov ides the basis for m o t o r lear ning which, as M o o r e (1972) no ted , may be either cons ciou s or un conscious. Since th er a p y in y o un g childr en frequently a tt e m p t s to activate or elicit un c on sc io u s responses, c o n si d er a tio n must be given t o the effects o f sensory input received d u r i n g tr ea tm e n t. M o v e m en t , which occurs at b o t h a n a u to m a ti c a nd a v o l u n ta r y level (conscious a n d u nc ons cio us ), is essential to the de v el o p m en t of bo d y image a n d , thu s, o u r ability to re sp o n d to the e n v ir o nm en t. P e rc ep tio n o f f o r m an d space is d e p en d e n t on f r eed om o f m o ve m e n t. In a st u d y of physically h a n d ic ap pe d children, Wedell et at. (1972) fou nd a high c or re la ti on betw een a lack of i n de p e nd en t mobility and inability t o perceive size c o n st an c y at a distance. T o develop conce pts o f for m, the child mu st not only view an object as it is presented; he mu st also move a r o u n d it a nd pe rh ap s move it a r o u n d . C h ild re n with n e u r o m o t o r diso rd er s are often deprived o f these lear ning op p o r t u n it i es a n d may receive disto rted fe edback be cause of th eir limited in dep en den t mobility or a b n o r m a l m ov em e nt pa tte rn s. In pr ep ari ng childr en to o b t a i n in f o r m a t io n in dep en den tl y, thera pist s must c o n tr o l a b n o r m a l m o v em e nt t h r o u g h “ h an d li n g ” to minimize the po ten ti al for d is to r tin g senso ry m o t o r learning. The close link between m ov em e nt a n d ve stibular in p u t is i m p o r t a n t wh en pl an n i n g th er a p y p r o g r a m m e s . Since all pe rsonnel deal in g with childr en prov ide ve stibular input wheth er de liberately o r not, its effect on the de vel op in g child ‘ O c cu p a t io n a l T h er a p is t T he O c c u p a t io n a l T h e r a p y D e p a r t m e n t , T he Hos pit al for Sick C h ild re n, T o r o n t o , O n t a r io , C a n a d a Received 28 O c t o b e r 1982. O P S O M M I N G V erskeie f a k t o r e wal b y d ra e to / p e rse p tu e le o n tw ik k e lin g en d ie n o u v er b a n d van sensoriese en m o to rie se in vlo e d e tot n o rm a le o n tw ik k e lin g , w o rd b espreek. DU is o m lerapeute, wat m e t k in d e rs m e t vertraagde o n tw ik k e lin g w erk, aan le m o e d ig o m toepaslike, gegradeerde sensoriese stim u li in h u l be h a n d elin g sre p erto ire insluit. D ie sensoriese m o to r s k a k e l en die belong van die ta ktiele en vestibulere stelsels vir die n o rm a le o n tw ik k e lin g van p e rse p tu ele sk e m a w ord bespreek. also requires close ex am i n at io n . M o o r e (1972) no ted th a t the vest ibu la r system has phylogenetic links with most o f the, m aj o r systems in the body. Ayres (1975) includes specific vest ibu la r th e r a p y as a n integral p a r t o f the tr e a tm e n t model A m b u l a t o r y children seek ve stibular i np ut in their use of p l a y g r o un d e q u ip m e n t, swings a n d m er r y - g o- r o un d s as well as th eir activities, for e xa m p le, ro u g h h ou si n g play, j u m p i n g on beds an d climbing fu rn itu re a n d trees. C he e e t at. (1978) studied the effects of specific vestibular s t i m u l a t i o n o n c h i l d r e n w i t h c e r e b r a l pa ls y an d d e m o n s tr a t e d a n overall i m p r o v e m e n t in m o t o r be haviour over the c o n tr o l grou p. How eve r, f ur th er investigation is needed to identify the lo ng-term impact on vestibulo-ocular fu nc tio n an d o t h e r systems c o nn ect ed with vestibular fun ction , especially in infants. S E N S O R Y M O T O R S E N S O R Y L E A R N I N G S en sor y m o t o r learning co up led with in n at e biological factors assists the nor mal ly d ev elo pi ng child to acqu ir e skills in a nt ig rav it y mobility a n d initial co n cep ts o f b o d y schema, form a n d space. F o r m an y years t her ap is ts viewed mo tor skills a n d sensory i np ut as se pa ra te entities but it is now k n o w n t h a t so m e true s e n so r y - m o t o r trac ts exist within the C N S (Wall. 1970: K o r n h ub e r , 1975). S e n s o r y i n p u t is received t h r o u g h e x t e r o c e p t i v e , p r o pr io cep tiv e and interoceptive receptors t h r o u g h o u t the body. The n o r m al C N S in tegrates ex ter nal i n f o r m a t io n with, feedba ck a b o u t m o t o r o r ch emical reac tio ns m ad e i i respon se to a given stimulus. This o n g o i n g integrative process c on tr i b u t e s to n o r m a l de ve lo pm en t. In the n o r m al per son , ex ter o cep tiv e rece ptors obtain i n f o r m a t io n fro m the e xte rn al world which they tr an s m it to the br a in where it is integrated with sens or y feedback as well as pr eviously stored pe rception. W he n the message is i n ter pr ete d a n a p p r o p ri a te a u to m a ti c p o st u r a l response (righting a n d equ ili br ium reactions) is co up led with planned m o t o r responses, which of ten i n c o r p o r a te cognitive and linguistic do m ai n s. The C N S in stantly receives sensory fe edback a b o u t the a cc u r ac y o f the r e spo nse so th a t a n y ne cessary a d ap t a t i o n can be made. T h r o u g h this c o nt i n ua l sen so ry -m o to r-s en so ry cycle child ren learn a b o u t themselves a n d th eir e n vi ro nm ent , a nd de velop the per cep tua l f o u n d a ti o n s r e qui re d for higher cognitive learning. T A C T I L E S Y S T E M T he tactile system in co r p o r a te s extero cep tive t o u ch and pro p ri o ce p tiv e and kinesthesiatic in f o r m a t io n which is carri ed to the CNS . R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) ph ysio th e ra p y, M a rch 1983, vo l 39, n o 1 5 Ayres (1975) has divided the tactile system into the protective and d i sc r im in at or y systems. 1 he protective system is phylogenetically very old a n d highly develo ped in the newborn infant. It wa rns o f p otenti al h a r m an d produces various responses, such as “ fight or flight” m o t o r reactions. The di sc rim in ato ry system provides i n f o r m a t io n a b o u t the nature, quality, q ua n ti t y an d a r ra n g e m e n t o f stimuli. It gives precise tactile i np ut a b o u t time a n d space. T h r o u g h the combined effects o f touch p r o p r i o c e p ti o n a n d kinesthesia the child develops b o d y image and aw are ne ss o f spatial relationships. The phylogenetically n ew er d i sc r im in at or y system mo dul at es the effects of an d responses to stimuli received thr o u gh the protective system ( s p in ot ha la m ic tracts). d e v e l o p m e n t a l s e q u e n c e In early de ve lo pm en t, the protec tive system is highly active in detecting pain a n d t em pe ra tu r e. T h e n e w b o r n is acutely aw are of ha r d and firm pressure. His responses to light touch are initially nonspecific or generalized unless the light touch is rapid or une xpe cte d in which case the ap pr o pri ate response will be one o f p ro tec tio n. G ra d ua ll y the child learns to give a less generalized respo nse an d in so doing develops an aw'areness ol specific body p a r ts so th at he can be visually att entive to th em an d event ually localize the stimulated area with his hands. The discriminative system progresses sequentially. The newborn d e m o n s tr a t e s his aw ar e ne ss o f i np ut by increasing his activity level or a t t e n t i o n / o r i e n t i n g until he can localize touch through vision. He progresses to develo pin g m an ua l form and space pe rce pti on initially by m o u th i n g objects and later, when up p e r e xt re m it y skills are a d eq u a te , by manipulating them within his visual field. As his cognitive abilities d e v e l o p he d i s t i n g u i s h e s o b j e c t s t h r o u g h stercognosis or to u ch alone an d later t h r o u g h grapliesthesia, i.e. by di scrimin ating shapes d r a w n on the skin. A balance is necessary between the protective and discriminatory systems for s o m a to s e n s o r y events to be transmitted sim ul ta ne o us ly a n d interp ret ed accurately. An imbalance is seen in child ren with di st u r b a n c e in the som atosensory process o r tactile defensiveness (Ayres, 1975). Taptile input has m aj o r social a n d e m ot i on al implications establishing the ch ild ’s identity a n d security within his ■fnvironment. When mobility a n d s u bs eq u e nt ly t ou ch and 'pr ess ure are restricted, the t o u ch pressure re ceptors a d a p t very quickly, decre as ing afferent flow to the CNS . F r o m a developmental t r ea tm e nt viewpoint, it is i m p o r t a n t not only to maintain the balance between the protective an d discriminatory systems bu t also to pr ovi de a d e q u a te mobility so th at pr op ri oce pti vc an d kinesthetic feedback can be integrated in developing per cep tua l d o m ai ns . V E S T I B U L A R S Y S T E M The vestibular system, which is phylogenetically old, detects speed a nd direc tion of m ov em e nt a n d m ay even stimulate m ove m en t in ut ero (Wyke, 1975). Because of its many neural co nn ec tio ns it is essential in developing postural security agai nst gravity, di stinguishing m ove m en t onginating within the self from that o r ig in a tin g in the surrounding visual field an d devel opi ng a fluid b o d y schcma as opposed to a static bod y image. It affects p o st u ra l tone, especially in the cervical area. he vestibular system or m ov em e nt is essential for a ro us al an inhibition of the C N S t h r o u g h its co nn ec tio ns to the r etri cular activ ating system. It is also necessary for the de v elo p m en t of concepts a b o u t the self a nd o u r relationship to o u r e n v ir o nm en t, a n d the ability to sequence high-level tasks. The i n teg rat io n of ve stibular functions with tactile and visual input occurs early in the d e v el o pm en t o f righting and eq uilibriu m reactions. This close link between mov eme nt and so m a to s e n s o r y i n f o r m a tio n is a maj or prerequisite for n o rm al a n tig ra vi ty mobility. The co m b i n e d effect o f all senso ry i np ut results in a de vel op m ent al progres sion o f per cep tua l schemas. Initially the n o rm al child comes to kn ow ho w one p ar t of his body relates to a n o t h e r an d how it relates to gravity. Later he develops c o nce pts of laterality, directi on ali ty and spatial relationships. Eventually, by acc urately j u d g in g distance, size, sh ap e a nd form, the child can move freely. At this stage these conce pts are f u rt h er refined and the child gains the ability to a tte nd to a p a rti cu la r sti mulus in the midst of many. Norm all y, the initial p er cep tu al processes are developed as a result o f sensory and m o t o r integ rat io n, bu t they mu st be linked to meaningful ex periences to be integrated. F U N C T I O N A L A P P L I C A T I O N O F S E N S O R Y D E V E L O P M E N T The n or m al , de velo pin g infant is expo sed to varied tactile, vestibular, visual and a u d it o r y in p u t when his m o th e r cuddles and rocks him a lt e r he has been fed. W hen he is a wa ke his pa re nt s talk to him. High frequency h u m a n speech, variety of speed, pitch a n d rh y t h m will increase his att e n tio n . Par en ts also increase their body's sensory aw are ne ss ol the p a r ts ol his bod y by kissing a n d s tr o k in g his feet and hands, thu s affecting his level of alertness t h r ou g h ves tibular and p r o pr io cep tiv e s t i m ul a tio n ( K o r n e r and T h o m a n , 1972). If the c h ild ’s spatial o r i en t at i o n is altered a n d an a p p r o p r i a t e s t i m u l u s is p r e s e n t e d , visual att entiveness c an be increased. Brazelton (1973) discussed va rio us ad ap ti ve behav iou rs neonat es use in dealing with their e n v ir o n m en t , such as the ability to sell quieten. In ad d it i o n , infants c o nt r ol the input they receive fro m their p a re nt s by the response they m ake to the p a r e n t ’s overtures. F o r e x am p le , wriggling or crying usually p er sua de s the pa re n ts to ch an g e the type of input they are giving. Aware nes s o f be h av io u ra l responses is e s p e c i a l l y i m p o r t a n t w h e n t r e a t i n g i n f a n t s w i t h n c u r o d ev e lo pm e nt a l disorders. As the no r m al infant grows he acqui res a g re ate r repert oir e o f m or e o r less r a n d o m m o v e m e n ts th at bring him into co n ta ct with his own body. W h en he bo bs his head up a nd d o w n while lying p r on e o r being held he will a tt e m p t to fix on visually interesting objects; his neck p r o pr io ce p to r s a nd ve st ib ul a r-o c u la r receptors send o ng oi ng feedback to the C N S a b o u t the n o r m al posit ion o f the head a n d eyes in space. The visual system is extre mel y i m p o r t a n t in contr ol lin g the head a nd its mo veme nts. Fo r this reason, the child must practice co n tro ll in g his eye m o ve m e n ts while receiving ve st ibular input or, in m o re basic terms, while- practising head control. The n o r m al child can pu t his ha nd s to his m o u th when he is 2 to 3 m o n th s old. While lying sup in e he will watch his hand s, thus co n ne cti ng tactile, visual, pr op ri oce pti ve and kinesthetic in f o r m a t io n to achieve early sensory aware ne ss o f the u p p e r extremities. Later, as he holds objects o r a tt e m p t s to reach for th em , he be comes a w a r e ' o f the re lationship between his u p p e r ex trem ities a nd the e n v ir on m en t. Once basic g r a s p i n g a b i l it i e s a r e present he will R ep ro du ce d by S ab in et G at ew ay u nd er li ce nc e gr an te d by th e P ub lis he r (d at ed 2 01 3. ) 6 F isio te ra p ie , M a a rt 1983, de e / 39, n r 1 e xpl or e objects visually a n d orally. This e x p lo r a ti o n is essential for the d e ve lo p m en t o f aw are ne ss of shape, si z ea n d taste with its e m o t i o n a l as so ci ati on s with nutritive a nd n o n ­ nutritive sucking. As m o t o r skills are refined, skilled m a n i p u l a t i o n is used to ex pl o re objects within the visual an d tactile do m ai n s. A l t h o u g h we m ay pro vide the a b n o r m a l child with varied s o m a to s e n s o r y experiences, the n o r m a l child goes far be yo nd this by exper ienc ing things such as e a r t h , wo od , flowers, etc., as he investigates his en vi ro nm en t. As the n e rv ou s system m a t u r e s and n e u r o m u s c u l a r c o nt r ol i mp ro ve s a n d each act is re peated m a n y times, the act io ns will have increasing a ccu rac y a n d in tent ion. As the child’s senso ry aw are ne ss o f his u p p e r ex tr e m i t y a nd his bo dy 's sy m m et ry increases he also learns th at his u p p e r t or so orients a b o u t a cen tr al axis a n d begins to de vel op a midline or ien tat io n. Weight be aring gains reality for him a n d he discovers th at he c an use a su p p o r t i n g surface to initiate m ove m en t. T h r o u g h o u t all of this he discovers h ow the parts of his bo dy m ov e in a c o -o rd i n a te d in d ep e n d en t fashion. F u r t h e r se ns o ry aw ar e ne ss is gained t h r o u g h e x p lo r a to r y play. M a ni pu la tiv e a nd visual skills are used to distinguish the for m of a n object. Gr a d u al ly , the child learns to mat ch similar objects, t hen to a tt a c h a m ea n in g to a n object a n d later to give objects sym bo lic labels. Mu c h o f this de ve lo pm en t d e p e n d s on the ch ild ’s ability to move a r o u n d his e nv ir o n m e n t ind ep en d en tl y a n d reach for objects of interest. As the child’s C N S m atu res , the sensory i n f o r m a t io n he receives beco mes mea ni ng ful a n d integrated so th at he develops a n increasingly m or e sop histicated aw aren ess o f his b o d y a nd the world a r o u n d him. Mobility a n d m ov em e nt in space with bo d y on bod y- ri ghting re actions dev elop a n d the child sta rts to roll a r o u n d a cent ral axis, fu r t h e r devel opi ng the midline orient ati on . G r a du al l y he learns sequenced m o v em e n t such as crawling, which requires the use o f c o u n te r ro t at i o n , an d finally pulling to s t a n d in g so th at he can achieve antig rav it y mobility. This progres sio n requires c o n st a n t senso ry input a b o u t bo d y or i e n t a t i o n in a variety of planes as well as the integrated use of ri ghting a n d eq u ili br iu m reactions, which are an a u to m a ti c m o t o r respo nse to a given sen so ry stimulus. Once the child has achieved i n de p e nd en t m obility he has s i m u l t a n e o u s l y d e v e l o p e d m a n y of th e p e r c e p t u a l prerequisites u p o n which he can star t to de velop more co m pl e x p er cep tu al sche ma a n d cognitive function. In co nc lu sio n it is essential for thera pis ts de aling with C N S - d a m a g e d child ren to be a w ar e o f senso ry d o m a i n s and ho w they influence m o t o r o u t p u t a t b o t h a n a u t o m a t i c a n d a m o t o r p la n ni ng level. As it is m o to r ic ind ep e n de n c e th a t will allow the child to e xpl or e his e n v ir o n m e n t a n d be com e a fu nctional a d ul t, o u r th er a p y mu st in c o r p o r a te age a p p r o p r i a t e a n d gr ad ed sensory stim ul us related to a func tio nal task th a t can be integrated an d retained for future use. References Ayres, A. J. (1972). Senso ry i n te gr at io n a n d learning disorders. Western Psychological Services, Los Angeles. Ayres, A. J. (1975). S e n s o r i m o to r f o u n d a ti o n s o f aca dem ic ability, Eds. C r u i c k s h a n k , W. tyl. a n d H a lla h an , D. P. in: Perc eptu al a n d Lea rn ing Disabilities in Chi ldr en , Vol. 2: R esearch a n d Theory. 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