VISUAL
PERCEPTUAL
DEFICITS
IN CLUMSY
CHILDREN
CHARLES HULSIE Department of
Psychology.
University
of York,
Hesliogton,
York,
YOI
SDD,
U.K
and
ANNESMART and GEORGINA Physiotherapy
Department.
(Rrcricetf
MORAN
Pictor School, Sale. U.K.
23 Drcrmber
1981)
Abstract-In a previous study clumsy children were found to be impaired in their ability to match the length ofsuccessively presented straight lines. and the ability to perform this task correlated with their degree of motor impairment [3]. The present experiments explore two possible explanations for this pattern of results. One possibility is that this earlier result tapped a memory deficit in the clumsy children. The first experiment shows that the clumsy children still experience difficulties in matching the length of a line to a second line which is simultaneously present. This suggests the difficulty is one of perception and not memory. The second experiment explores whether faulty perception oflength in the clumsy children is related to eye movement problems. No support for this idea was found; with tachistoscopic presentations at durations which exclude subjects making eye movements the clumsy children are still clearly impaired in judging the length of lines.
INTRODUCTION children are a small group who experience severe difficulties in developing adequate skills of movement which cannot be explained in terms of gross sensory defects or general intellectual impairments [ 1, 23. In a previous study [3] we investigated the possible role of perceptual impairments as determinants of clumsiness in a task involving matching the length of lines within and between the modalities of vision and kinaesthesis. The clumsy children, as compared with normal children of the same age and verbal IQ, showed perceptual impairments as indicated by their poor performance on the visual, kinaesthetic and cross-modal judgments of length and also by their low scores on spatial subtests of the WISC. Variations in motor skill correlated with performance on the visual perceptual measures but not with performance on the kinaesthetic or cross-modal tasks. This suggested the interesting possibility that clumsiness in these children may be caused by an impairment of visual perception. The present experiments are concerned with defining more precisely the nature of the visual perceptual problem in these children. In the visual condition of our previous experiment [3], the children were presented with white lines of various lengths in the window of a black box. The stimulus line was then removed and the children directed the experimenter to turn a geared handle on another identical box which caused a white line to extend in an equivalent window. They told the experimenter to stop when theyjudged that the white line produced matched the length ofthe previously presented line. CLWSY
475
476
CHARLESHLLVE. AWE SMUT and GEORC;IU MOKAU
Because of the successive nature of this task as well as requiring the accurate perception of length it also requires adequate visual memory for the length of the stimulus line. It could be, therefore, that the clumsy children’s difficulty with this task was not one of perception, but rather reflected a memory impairment which resulted in inadequate storage of information concerning the length of the stimulus line. The first experiment in this study tests this idea by presenting the stimulus line continuously while the child matches it with another line. If the clumsy children still experience difficulties in performin g this task, we may conclude that their difficulty is a perceptual one and not dependent on the memory requirements of the task. 1
EXPERIMENT
Subjects. Twelve clumsy children and 12 controls matched for age. sex and verbal IQ partrcipated in the experiment. All these children had participated in our previous experiment [3]. In each group there were nme boys and three girls. The clumsy children were selected on the basis ofgood overall IQ and age from amongst a group ofchildren who at the time of the study were receiving physiotherapy. The common factor which had led to these children being referred for treatment was school failure, and several of them were attending a special school because of their educational difficulties. Typically in the first place the children had been referred by their schools to the School Medical Officer who in turn referred them for neurological examination. There were a variety of problems associated with their clumsiness; two were epileptic, two had diagnosed speech problems, one had suffered meningitis as a young child. The control children were selected individually on the basis of age and sex to match a clumsy child from amongst the children attending a primary school in the same area. They were considered by their teachers to be progressing normally in school. Details of the two groups are shown in Table I. All children selected to take part in the study were given a short form of the Wechsler Intelligence Scale for Children (Revised), involving two verbal sub-scales (similarities and vocabulary) and two performance subscales (block design and object assembly). These subscales were selected because, according to a factor analysis of the original WISC, they constitute the best measures ofdistinct verbal and performance abihty factors (MAYWELL [4]). Tests o/‘moror performance. Each child was given a set of live tests of motor performance. Four of the tests (ball rolling, ball throwing. bead threading, and the posting box) were based on those developed by Gt IIIIAY [I]. These four tests were selected because according to GUHRAY [S] they were the ones which best discriminated between normal and clumsy children in his studies. In addition to these four tests, a test of skipping was included. This was an additional test of gross motor skill, which was easy to administer and score, and on the basis of clinical experience appeared likely to discriminate well between clumsy and normal children, Full details of these five tests and the scoring procedures are given in a previous publication [3]. Visual perception oflength. The procedure followed here was very similar to that in the visual condition of our previous study [3] with the exception that the standard stimulus line was present while subjects matched a variable line to it. Appararus Two black perspex boxes were constructed, one for presenting the visual standard stimuli, the other for forming the visual equivalents of the stimuli. Each box was 36 x 3 x 3 in. and in the front of each was a slot (30 x0.25 in.). Through these slots the subjects viewed the standard and comparison stimuli.
Table
N Age V.IQ P.lQ
1. Details
of the ages and IQs of the children
seen in experiments
Control
Clumsy
12 I I yr 0 months (SD. 6.63 months) 93.17 (SD. 14.46) 104.16 (S.D. 22.17)
12 I1 yr 3 months (S.D. 8.01 months) 92.50 (S.D. 15.41) 79.33 (SD. 17.45)
I
and 2
c
P
I .05
N.S.
0.11
N.S.
3.05
VISUAL
PERCEPTUAL
DEFICITS
IN CLUMSY
171
CHILDREN
Behind the aperture in ths box used for presentmg the visual standard stimuli was a bar which had eight equal faces. Alternate faces of the bar were painted black to match the front of the box. On the remaining four faces the standard stimuli consisting ofwhite lines 6.9. 10 and 17 in. long were painted. By turning a knob mounted on theend ofthe box the experimenter could select a particular length ofline and remove it at the end ofthe trial by turning it on one notch. Behind the aperture in the box used for presentmg the variable visual stimulus was mounted a steel measurmg tape painted white. The tape could be extended according to the subject’s directions by the experimenter turning a geared handle on the end of the box. A pointer moved along a scale on the back of the box permitting the subject’s judgment of length to be read off. Procedure
The boxes for presenting the stimuli were placed side by side on a table approximately 3 ft from the subject. The standard stimulus line was shown to the subject and the experimenter then adjusted the variable stimulus gradually until the subject judged it to be the same length as the standard line he was viewing in the adjacent box. Four lengths of stimulus lines were used (6, S, IO and I2 in. long) each length being presented four times to give a total of 16 trials per subject. The order of presentation for the lines was indtvidually randomized for each subject.
RESULTS Motor tests The means and S.D.s for the scores on each test for each group are shown in Table 2. It is apparent that all five tests discriminated clearly between the normal and clumsy children as confirmed by independent r-tests. These clear differences between the normal and clumsy children serve to confirm the accuracy of the clinical diagnosis of clumsiness which served as the basis of group selection, Visual perception
of length
The dependent measure analysed here was absolute error; the difference between the length of the stimulus line and the subject’s reproduction of it. The means and S.D.s of the scores for each of the four lengths of line are shown in Table 3.
Table 2. Means and S.D. for the scores on each test of motor
Control Clumsy r-Value
performance
Ball rolling
Ball throwing
Skipping
Beads
27.50 (6.908) 5.417 (3.964) 9.604
10.33 (1.922) 6.76 (1.422) 5.19 P
92.42 (78.45) 22.58 (32.99) 2.84 P
44.42 (7.868) 75.92 (31.39) 3.372
P
of the two groups Posting box 14.67 (5.821) 25.58 (8.691) 3.615 P
P
Table 3. Means and SD. of the absolute error scores in each condition for the two groups experiment I (errors measured in 0.1 in.)
6 Control Clumsy
0.44 1 (0.316) 0.590 (0.306)
Stimulus 8 0.554 (0.354) 0.854 (0.387)
line lengths (in.) 10 0.762 (0.566) I.009 (0.516)
12 0.927 (0.563) 1.297 (0.732)
of subjects
in
These scores were analysed in a two-way (2 x 4) split-plot analysis of variance in which the factors were groups and length of stimulus line. This analysis revealed a significant effect of groups (F = 6.24; df= 1.22; P < 0.02) confirming that the clumsy children’s performance was worse than the controls’. A signficant effect of stimulus length (F=9.13; df=3. 66; P
In our previous experiment clumsy children were significantly worse than controls in matching the length ofsuccessively presented lines. In the present experiment the procedure was identical except that the stimulus line was continuously available for inspection while matching its length with another line. In this situation the memory requirements of the task are clearly minimized. The finding that the clumsy children still found this task difficult adds to the generality of our previous findings, and indicates that their difficulties are not restricted to tasks with a large memory component. It appears that the clumsy children have appreciable difficulty in simply perceiving the length of visually presented straight lines accurately.
EXPERIMENT
2
Introduction
Experiment 1 has demonstrated that clumsy children perceive the length of lines less accurately than controls. This is an interesting result, because theoretically we might argue that deficits of visual perception, particularly those affecting distance and spatial relationships, might be an important determinant of the clumsy children’s poor motor coordination [3]. It is clear, however, that other explanations for the present pattern of results are possible. We might argue that any causal relationship operates in the opposite direction, with motor co-ordination impairments leading to disturbances of perception. For example it might be that the difficulties of motor control observed in the gross and fine body movements of the clumsy children are associated with comparable difficulties of occulo-motor control; the clumsy children’s perceptual problems might depend upon a disturbance of eye movements. If this were true, a clear prediction follows. We may present a comparable task involving the judgment of length with very rapid exposure durations which exclude the possibility of subjects making eye movements while viewing them. If the clumsy children’s difficulties in judging length are caused by aberrant eye movements, then in this situation their performance ought to be comparable to that of controls. The present experiment tests this prediction.
Snbjects. The same two groups of children participated in this experiment as in the previous one. Procrd~e. Thechild’s task in theexperiment was simply to decide which a a pair ofstraight lines was the longer. On each trial two black lines appeared side by side on a white tachistoscope card for 100 msec and the child responded by putting out his hand on the side on which the longest line appeared. In the other field of the tachistoscope a grey field was constantly illuminated with a central white fixation cross. Before the experimental trials began the subjects were given a series of six practice trials. For these trials a very simple discrimination was presented involving a pair of lines, one 7.0 cm long and the other 3.0 cm long. Nearly all
of
VISL4L
PERCEPTUAL
DEFICITS
IN CLUMSY
CHILDREN
479
the subjects achieved perfect performance here; however. the few children uho dtd make a mistake were sho%n further practice cards until they made six consecutive correct responses. This practice phase served to ensure that all the children understood the task. For the experimental trials three sets of eight cards were prepared. On all these cards the longest line was 7.0 cm long; in the first set theshorter line was 6.0 cm long. tn the second set it was 6.4 cm long. and in the third it was 6.7 cm long. These three sets ofstimulus cards thus required discriminations ofincreasing difficulty. Within each set ofeight stimulus cards the longer line occurred equally often on the right and on the left. The startmg point of each line also varied randomly across cards being either 1.5 or 2.5 cm eccentric to the centre of the viewing field. This meant that subjects had to judge the length ofeach of the lines; reltable judgments could not simply be based upon which line projected furthest from the centre of the card. For theexperimental trials each ofthe stimulus sets was shown twice in random order. giving 16 trials at each level ofdifficulty. Stimulus sets were always shown m order ofdifliculty starting with the easiest set (7.060) followed by the intermediate (7.064) and then the hardest set (7.0-6.7).
RESULTS The mean number of correct responses on each stimulus set for each group are shown in Table4. It appears from these results that the clumsy children are consistently less accurate in this task than the controls, and that the degree of their impairment does not vary with the difficulty of the discrimination required. Since these data are in the form of proportions an arcsin transformation was applied before performing an analysis of variance in which the factors were groups and stimulus set. This analysis revealed a significant effect ofgroups (F=8.13; rif= 1,23; P
Table 4. Means
and S.D. for the number of correct responses in each condition for the two groups in experiment 2 (maximum possible score in each condition= 16)
7.060
Stimulus 7.064
of subjects
set 7.067
Control
13.58 (1.505)
13.33 (1.303)
11.00 (1.954)
Clumsy
11.58 (2.998)
10.50 (2.908)
9.83 (1.899)
Discussiorl The latency to initiate a saccadic eye movement is in the region of 200 msec [6]. This means that with an exposure duration of only 100 msec as in the present experiment we can be sure that thesubjects were not able to move their eyes to inspect the stimulus, Even in these circumstances, however, clumsy children have severe difficulties in judging the length of simultaneously presented lines. This finding allows us to reject the idea that these children’s difficulties in estimating length can be explained in terms of abnormal eye movements made while inspecting the lines.
4SO
CHARLES HULME. .&NE SHRT
GENERAL
and CEORCIX
MOR-\N
DISCUSSION
The present results show that the finding from our previous study that clumsy children have difficulty in comparing the length of successively presented lines has some generality across different experimental conditions. The same difficulty is in evidence when the lines are presented simultaneously, minimizing the memory requirements of the task. and also under conditions of brief exposure which preclude the occurrence of eye movements to inspect the lines. Further research will be necessary to specify more precisely, in terms of information processing models, the nature of the clumsy children’s difficulty in perceiving length. Whatever the precise nature of the visual deficit in the clumsy children, a further question we must consider is whether this deficit may be a cause of their motor co-ordination problems. At the moment all that can be said is that this is consistent with our findings. Given more extensive evidence concerning the nature of the visual perceptual deficits in these children it ought to be possible to design training studies to evaluate this causal hypothesis. If clumsiness in these children depends upon a visual perceptual deficit, and if this deficit can be ameliorated by training, this ought to lead to improvements in motor co-ordination. ~ckno,~lrdym~rnts-We wish to thank Dr. J. SALEM, Area Medical OBicer,Trafford Area Health Authority, and Mr. D. J. HATFIELD,Chief Education Officer. Trafford Borough Council, for their permission to carry out this research. We also thank the children and their parents, teachers and schools for their co-operation, particularly Mr. M. Cox& Longford Park School. Stretford, and Mrs. CAIXF, St. Matthew’s School, Strctford. We thank IA\ MCKINLAY for his help and ANDREW Moslc for useful discussions during the ccmrse of this research.
REFERENCES I. Gurn~av. S. The Clumsy Child. Saunders. London. (975. 2. GOKI)OV, N. and htcK~s~.~\~, I. Who are clumsy children’? In Helpiq Clumsy Childrrrl. N. GOKDOV and I. McK~st.,\v (Editors). Churchill Livingstone, London. 3. HutME C.. BIGGERSTAFF, A., MORI\N, G. and MCKIUL,\Y, I. Visual. kinaesthettc and cross-modal judgements of length in normal and clumsy children. Drcl ~Llrd. Child Neural. In press. 4. MAXWCLL, A. E. A factor analysis of the Wechsler Intelligence Scale for Children. Br. J. rduc. Psycho/. 29, 237-241. 1959. 5. GUHRAY, S. The management of developmental apraxia. Dev/ Med. Chi/d Neural. 20, 643-646, 1978. 6. ALPERS, M. Eye movements. In Handbook oj’Sensory Physioloyy, D. JA>+IFSOSand L. M. HURVICH (Editors), Vol. V11/4, Sensory Psychophysics. Springer, Berlin, 1972.
:
Risumi
Dans une Etude ecaient
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.3 des
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La premiPre
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de
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La seconde expkience
longueur en
que
que les r6sultats
enfants
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les
d’apparier
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chez
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capaciee
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PER< EPT,,,,L UFFICITS
I\1 CLC HSI
C-HILI)Kt\
Zusammenfassung
In einer
vorangehenden
BewegungsstGrung dargebotener ihrer
gerader
motorischen
Erkllrungen
dall bei der
mit
motorischer
zweite
Linie
perzeptueller
ziehung keine
dieses
such
Stiitze:
van
vorgelegt ist und nicht
Linien
wird.
der
werden
Augenbewegungen
hatten beurteilen
Lange hat.
Darbietung die Kinder sollten.
llegt.
iiber immer
AIbglichkeit
Experiment
zeigt,
wenn
die
dal3 die Schwierigkeit Das
bei diesen Fiir
Ausmafl
mdgliche
be1 Kinder”
haben.
folgt,
zum
zwei Eine
Das erste
Daraus
nacheinander
in Korrelatmn
untersucht.
im Gedlchtnis der
zentraler
Llnge
Ged%chtnisstGrung
wurde.
Wahrnehmung
Bei tachistoskopischer
van
eine
gefunden
Natur
ausschlie0en.
und zwar
Ergebnissen
mit
die
Zuordnungsschwierigkeiten
simultan
zu StGrungen
die Lange
dann
Kinder
Experimenten
Untersuchung
ob gestiirte
bewegungen
anzupassen.
Muster
wir
beeintrzchtigt.
In diesen
Behinderung
Kinder
untersucht.
Linien
friiheren
fanden
Ftiigkeit
StGrung.
fiir
ist,
dafl diese
Untersuchung
in ihrer
diese
Experiment
Kinder” Hypothese
Zeiten, noch
zweite
welche
Stiirungen,
eine
Be-
gab es .-Iugenwenn
sie