Develop. M d Child Nerrrnl, 1976, 18, 25-30

The Perception of Passive Joint-movements by Cerebral-palsied Children Bill Jones

ments. One aim of the present research is to describe an appropriate psychophysical procedure for evaluating deficiencies of sensation. Clinical testing has ordinarily made use of threshold estimation, a procedure which we now know confounds sensitivity per se and response bias. Response bias is the probability that not all possible responses are equally likely. Undoubtedly the best-developed model from which procedures to separate sensitivity and bias can be derived is the theory of signal detection (e.g. McNicol 1972). Unfortunately, signal-detection methods require quite extensive testing and frequently rely upon the person’s ability to make sophisticated confidence judgements. My aim here is to demonstrate the value of an alternative psychophysical model, Luce’s choice theory (Luce 1963). This model allows independent estimates of sensitivity and bias to be made in a reasonably short space of time, without requiring any very detailed responses from the person tested. To carry out the choice theory analysis, the child need possess only the ability to report the presence or absence of physical stimulation. Good discussions of the relationship-choice theory and signaldetection theory are given by Luce (1963) and by McNicol ( I 972).

Introduction To what extent can cerebral-palsied children appreciate passive movements of the joints? It has been suggested that, as part of a wider pattern of perceptual deficits, cerebral-palsied children suffer a reduced ability to detect imposed forces acting upon the joints (e.g. Skatvedt 1960, Abercrombie 1964). Some such deficiency is often presumed to underlie the motor deficiencies characteristic of cerebral palsy (e.g. Kabat and Knott 1953, Rood 1954, Bobath 1971) and many physiotherapy programmes are based upon passive movements of the linibs with the intention of producing ‘correct’ patterns of impulses from the proprioceptors. (The sensation of passive movement would seem to be subserved by the joint receptors, since Browne et al. (1954) have shown that it is abolished by anaesthetization of the joint capsule.) I have argued elsewhere that the central problem for the cerebral-palsied child is not the defective pick-up of proprioceptive information but the rather different one of being dyspraxic and unable to ‘pre-programme’ sequences of motor commands (Jones 1974’).Be this as it may, one initial test of the efficacy of physiotherapy could be to determine the extent to which physiotherapy improves the child’s ability to detect passive move-

Department of Psychology, Carleton University, Ottawa, Canada K1 S 5M.

25

DEVELOPMENTAL MEDICINE AND CHILD NEUROLOGY.

Method Children Ten children with quadriplegic cerebral palsy were matched for age and sex with 10 non-handicapped children. Some characteristics of the cerebral-palsied group are given in Table I. In all five athetoid children the condition was very marked, of the type sometimes described as ‘choreo-athetosis’ (e.g. Bobath 1960). All had considerable difficulty in maintaining any sustained posture. Intelligence was rated according to general assessments made by classroom teachers. The nonhandicapped children were all of normal intelligence and suffered from no known perceptual or motor deficiencies.

1976, 18

to relax his arm. The experimenter gripped the child’s wrist, said “Ready”, and after a three-second interval (timed with a stopwatch) the experimenter asked “Did I move your arm?” The child simply replied “Yes” or “No”. On half the trials the experimenter moved the child‘s arm slowly through 5” and back to the 90” resting position; on the remainder the experimenter simply gripped the child’s arm but did not move it. Moving the arm in this way rather than by means of some mechanical arrangement enabled the experimenter to judge whether on any trial the child had made a voluntary contraction. Whenever the child did so the trial was repeated. Both right and left arms were tested in the same way, with, for each arm, movement on 50 trials and no movement on 50 trials. The cerebral-palsied children were usually tested in two or three sessions of 15 to 20 minutes each, though conceivably reliable data could be obtained with fewer trials. The non-handicapped children were usually tested in a single session.

Apparatus and Procedure The device used for measuring passive movement consisted of a 20cm plexiglass strip, against which the child rested his forearm. The strip could be moved in the sagittal plane against a protractor to a pin set at an angle of 5”. The pin prevented any further movement. The strip, and consequently the child’s elbow-joint, were initially set at an angle of 90”. To prevent the child seeing what was being done, he was asked to close his eyes. A blindfold was considered but not used as it seemed to cause distress to the children. If a child ‘peeked’, that trial was repeated. The child was told to keep his eyes closed and

Results Conventionally we define a ‘hit rate’ (HR) as the proportion of trials on which the child’s arm was moved and the child reported “Yes”, and a ‘false alarm rate’ (FAR) as the proportion of trials on which the child reported “Yes” though no arm

TABLE I Details of the 10 children with quadriplegic cerebral palsy

I

I

Diagnosis Spastic Spastic Spastic Spastic Spastic Athetoid Athetoid Athetoid Athetoid Athetoid

,

Severity

Intelligence

Moderate Moderate Moderate Moderate Moderate Moderate Severe Severe Severe Severe

7 :6 1O:lO 8:3 1O:l I 9 :9 10:s 10:9 11:l 9:1

Average Bright Bright Bright Low-average Average Bright Average Bright Bright

s:10

i

I

Age (yrs:mths)



Speech

I

Adequate Good Adequate Good Good Poor Poor Poor Poor Poor 1

I

26

13 I 1.L JONES

movement had occurred. Table I I gives both values for each cerebral-palsied child. Values for the normal group are not shown because only three of the 10 children made two errors and one made three errors. Otherwise performance in the normal children was error-free (though see Browne et 01. 1954, and below). Because the variance associated with the non-handicapped population was sufficiently close to zero to render artifactual any statistical comparisons, no comparisons were made between the normal and cerebral-palsied groups. Differences between right and left arms were i n no case statistically significant and all values have been collapsed across the two arms. Non-parametric analysis (Siegel 1956) of hit and false-alarm values for the spastic and athetoid children showed that the two groups did not differ significantly in hit rate (Mann-Whitney U test, U = 9, 11 .274) but did differ significantly i n false alarms ( U = 0, y = .004), in which there was no overlap between the groups (Table 11). Conventional threshold measurement cssentially defines a hit rate. According to choice theory, however, the hit rate by itself is determined by sensitivity and response bias alike. The choice-theory index of perceptual sensitivity (q) is given by :

-

FAR ( I - H -R4)

=Im - ( I - F Aijl

--1’

and the index of response bias (h) by

b = [ (I-HR) (I-FAR) HR (FAR)

As sensitivity increases, 7; will tend to zcro.

When the subject is unbiased, h = 1 . When the subject is biased to say “Yes”, b < 1, and when the subject is biased to say “No”, b ; I . The values of .q and / I obtained for each cerebral-palsied child

TABLE 11 Hit (HR) and false-alarm (FAR) rates for each cerebral-palsied child _ _ _ _~

_ ;

Spastic

Atlirtoid

_ _ _ _ _

Spastic

Aihetoicl

_ ~ _ _ _ _ _ _ _ _ _ _

are shown in Table 111. There is no over!ap between the two groups in terms of either sensitivity or response bias, so that for both -q and h the Mann-Whitney test yields a U value of zero associated with 17 = .004 (Siegel 1956). It is noticeable that sensitivity is very high in the spastic group: two spastic children had maximum sensitivity, while performance by a third child is equivalent to an error rate of only 4 per cent. Three of the five spastic children show no response bias, but all of the athetoid group were stroiigly biased to say “Yes”.

Discussion The results are reasonably clear-cut. Only the athetoid children show any major deficiencies in detecting passive movement. One might have expected these children to be able to detect any passive movement, since flexion or extension of one limb very frequently resulted i n associated movements of the other limbs. (Mettler (1967) has noted, as part of the definition of athetosis, how proprioceptive stimulation is likely to elicit athetoid activity.) These children therefore had an apparently wide range of cues upon which to base their judgements. However, all the children in this group showed in a marked fashion the typical athetoid ‘restlessness’ of the limbs, with the consequence that any particular passive movement may have been superimposed upon a very ‘noisy’ background of continuous and irrelevant

DEVELOPMENTAL MEDICINE A N D CHILD NEUROLOGY.

ably certain that all five athetoid children could follow the procedure. They did not give merely random answers and they did not always reply “Yes”. In short, the nature of athetosis per .se, rather than any associated problems, seems to account for both the sensitivity and bias differences. Procedural differences make it difficult to compare these with other findings. Although Skatvedt’s (1960) figure of deficiencies of joint sensation in 43.7 per cent of her cerebral-palsied group compares well with the present figure of 50 per cent, more detailed breakdown shows considerable discrepancies. Whereas only one of Skatvedt’s four athetoid children had loss of joint sensation, all of the present athetoid group were so deficient. Conceivably there were differences between the two groups in the severity of their athetosis. An equally plausible suggestion, on the basis of the present results, is that the athetoid child’s bias to say “Yes” leads to sensitivity being considerably overestimated in standard threshold procedures. Had I simply reported hit rates which correspond to the classical threshold, the spastic and athetoid children would have been indistinguishable. Skatvedt found deficits of joint sensation in nine out of 27 in her comparable spastic group, whereas I found no important deficiencies in mine. However, the earlier report gives no details of the extent of the deficiency and makes no comparison with a normal population. This comparison could be important, since there is some evidence that a failure to appreciate passive movement is found in a small proportion of the ‘nornial’ population (Browne et ul. 1954). It is possible that improved physiotherapy techniques since the report by Skatvedt in 1960 could account for differences between the two spastic groups. By the same token, physiotherapy may not have resulted in relevant gains for the athetoid children,

TABLE 111 Values of sensitivity to passive movement (.q) and response bias (b) for each cerebral-palsied child

b

-~ ’1 Spastic

1

Athetoid

1976, 18

Spastic j Athetoid

proprioceptive activity. Therefore any particular joint sensations may have been swamped by the general background. This interpretation is supported by the marked bias to say “Yes” shown by all the members of the athetoid group; that is, they tended to report the presence of stimulation even when no imposed movement had taken place. It is clear from Table I that there are many differences between the spastic and athetoid groups, which could account for the superior performance of the former. In general, the athetoid group were more severely affected, and all of that group had poor speech. It would be reasonable to suggest that the increased severity of cerebral palsy in the children in the athetoid group would be associated with lowered sensitivity, and therefore not to take into account the type of condition. However, there is no reason to think that increasing severity should induce a response bias one way or the other. In order to explain the marked tendency of the athetoid children to report the occurrence of a movement, it is necessary to consider the nature of athetosis, in that the child is affected by a continuous barrage of random proprioceptive inputs. Similarly, it is difficult to see speech problems being directly connected to the particular response bias. Theoretically, one could imagine speech problems to be associated with failure to understand or to follow the experimental procedure, but I am reason28

BILL JONES

but this suggestion cannot be supported since it was not feasible to make a treatmentlno treatment comparison. Obviously it is possible to extend the present procedure to other types of passive movement, and in fact it can be applied to any task in which the person has to discriminate or recognize stimuli by making a binary decision (see, for example, Jones et a/. (1976) for the application of choice-theory procedures to some aspects of spatibl perception in the cerebral-palsied). Because there may well

be differences in response bias between different groups of children, it is important in assessing perceptual skills to obtain bias-free estimates of sensitivity. The choice-theory procedures can be recommended as the most efficient available means of separating sensitivity and bias in judgements by handicapped children. Acktionlrdgeiiien/s: This research was supported by grant No. A9946 from the National Research Council of Canada. I would like to thank Mr. S. Campbell for giving me facilities to work in his school.

SUMMARY

Luce’s choice theory provided the psychophysical basis for investigating the ability of cerebral-palsied children to detect passive movement of the elbow joint. The method included testing “yes” responses when the forearm was moved, and ‘false-alarm’ responses of “yes” when no arm movement had occurred. The children were tested with their eyes closed. The results showed that, in general, the children with spastic cerebral palsy had no deficits, or only very minor ones, in passive movement sensation. In contrast, the athetoid children had considerable deficits. I t is suggested that the athetoid child is affected by a continuous barrage of irrelevant proprioceptive information and so finds difficulty in discriminating any particular proprioceptive cue.

RE SUM^ La perception des r?iouvetiietitsarticulaires passifs cliez I’etrfntit itEfirnir riioteur c&ribral La thkorie de choix de Luce a fourni les bases psychophysiologiques d‘une recherche de la capacitk des enfants infirmes moteurs ctrebraux ;i apprkier les mouvements passifs du coude. La methode utilisait des reponses “oui” quand I’avant-bras etait bougC mais appriciait Cgalement les ‘fausses’ riponses de “oui” quand aucun mouvement du bras n’etait en fait survenu. En general, les resultats ont montre que les enfants spastiques ne prtsentaient pas de deficit, ou seulement des deficits mineurs dans la sensation des mouvements passifs. Les enfants athetosiques, au contraire, prksentaient des deficiences considkrables. I1 est suggere que les enfants athetosiques se trouvent en face d’un barrage continuel d’informations proprioceptives inadequates et que de ce fait, il lui est difficile d’analyser n’importe quelle information proprioceptive. ZUSAM MENFASSUNG

Die Erfnssutig passiwr Geletik he\ivgunget.lr riurcli Kitidcr tirit Cercbralpnrese Die ‘Wahl’-Theorie von Luce gibt die psychophysische Grundlage, die Fahigkeit von Kindern mit Cerebralparese zu untersuchen, passive Bewegungen des Ellenbogengelenks zu erfassen. Die Methode enthalt als Test sowohl die “Ja”-Antwort bei Bewegung des Armes wie auch die ‘Falscher Alarm’-Antwort des “Ja”, wenn der Arm in Wirklichkeit nicht bewegt wurde. Im allgemeinen ergaben die Resultate, da13 spastische Kinder keiiie 29

DEVELOPMENTAL MEDICINE A N D CHILD NEUROLOGY.

1976, 18

oder nur sehr geringe Ausfallserscheinungen der Empfindung fur passive Bewegungen hatten. Athetoide Kinder jedoch zeigten betrachtliche Ausfalle. Es wird gefolgert, daB das athetoide Kind eine kontinuierliche Sperre nicht zutreffender proprioceptiver Information hat und damit Schwierigkeiten, irgendeinen besonderen proprioceptiven Zweig zu unterscheiden. RESUMEN

La percepcidti de nroviniieritos pasivos por nin’os con pardisis cerebral La teoria de la seleccibn de Luce proporciono la base psicofisica para investigar la habilidad de niiios con paralisis cerebral de detectar movimientos pasivos de la articulacidn del codo. El mitodo incluia el test de respuesta con “si” cuando el antebrazo era movido y de respuesta de ‘falso brazo’ con “si” cuando no habia tenido lugar ninglin movimiento de brazo. Los resultados en general eran que 10s niiios espasticos no sufrian dificits, o solo muy pequeiios, en la sensacibn de movimiento pasivo. En cambio, 10s niiios atetbsicos eran muy deficitarios. Ello sugiere que el nifio atetbsico se encara con una barrera continua de informacion propioceptiva sin valor y por ello encuentra dificultad para discriniinar cualquier dato propioceptivo particular. REFERENCES Abercrombie, M. L. J. (1964) Perceptuul and Visuoniotor Disorders in Cerebral Palsy. Clinics in Developmental Medicine, No. 11. London: S.I.M.P. with Heinemann Medical. Bobath, K. (1960) ‘The nature of the paresis in cerebral palsy.’ In Child Neurology and Cerebral Palsy. Little Club Clinics in Developmental Medicine No. 2. London : S.I.M.P. with Heinemann Medical. - (1971) ‘The normal postural reflex mechanism and its deviation in children with cerebral palsy.’ Physiotherapy, 57, 5 15. Browne, K., Le:, J., Ring, P. A. (1954) ‘The sensation of passive movement a t the metatarso-phalangeal joint of the great toe in man.’ Journd ofPhysiology, 126,448. Jones, B. (1974) ‘The importance of memory traces of motor efferent discharges for learning skilled movements.’ Developmental Medicine and Child Neurology, 16, 620. - Thompson, M., Kabanoff, B. (1976) ‘Judgements in auditory space by spastic children: the application of choice theory procedures.’ Journal of Child Psychology and Psychiatry (in the press). Kabat, H., Knott, M. (1953) ‘Proprioceptive facilitation technique for treatment of paralysis.’ Physical Therapy Review, 33,53. Luce, R. D. (1963) ‘Detection and recognition.’ In Luce, R. D., Bush, R. R., Galanter, E. (Eds.) Handbook of Mathematical Psychology, Vol. I , New York: Wiley. McNicol, D. (1972) A Primer ofSignal Detection Theory. London: Allen & Unwin. Mettler, F. A. (1967) ‘Cortical-subcortical relations in abnormal motor functions.’ In Yahr, M. D., Purpura, D. P. (Eds.) Neurophysiological Basis of Normal and Abnormal Motor Activities. New York: Raven Press. Rood, M. S. (1954) ‘Neurophysiological reactions as a basis for physical therapy.’ Physical Therapy Review, 34,444.

Siegel, S . (1956) Nonparanzefric Statisficsfor the Behavioral Sciences. New York : McGraw-Hill. Skatvedt, M. (1960) ‘Sensory, perceptual and other non-motor defects in cerebral palsy.’ In Child Neurology and Cerebral Pulsy. Little Club Clinics in Developmental Medicine No. 2. Spastics Society with Heinemann Medical.

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The perception of passive joint-movements by cerebral-palsied children.

Luce's choice theory provided the psychophysical basis for investigating the ability of cerebral-palsied children to detect passive movement of the el...
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