Relationship Between Sensory Stimualtion Stereotypy

J. ment. Defic. Res. (1982) 26, 163-175

RELATIONSHIPS BETWEEN SENSORYSTIMULATION AND

STEREOTYPED BEHAVIOUR IN SEVERELYMENTALLY

RETARDED AND AUTISTIC CHILDRENELIZABETH GOODALL

Department of Child Psychiatry,Institute of Psychiatry, Denmark Hill, London

AND

J . CORBETT

Hilda Lewis House, Bethlem Royal and the Maudsley Hospital, Croydon

INTRODUCTIONPrevious research suggests that environmental stimulation can have different effects onstereotyped, repetitive behaviour in mentally retarded people, depending on the natureof the stereotypies and the stimuli provided (Baumeister & Forehand, 1973; Baumeis-ter, 1978).

This has led to different hypotheses about the nature of stereotyped behaviour. Thefirst is that stereotypies are self-stimulatory, maintaining an optimal level of'arousal' inindividuals who are under-stimulated, and who lack the skills to engage in alternativeactivities due to impaired perception or environmental deprivation. It follows from thisthat the provision of alternative stimulation may reduce the occurrence of stereotypedbehaviour (Forehand & Baumeister, 1970; Berkson & Mason, 1964).

The second main group of 'arousal' theories propose that stereotyped movementsresult from increase in arousal produced by drives such as hunger, or intense stimula-tion from sound or fluorescent light (Kaufman & Levitt, 1965; Levitt & Kaufman,1965; Forehand & Baumeister, 1970; Higenbottam & Chow, 1975; Hollis, 1978;Colman, Frankel, Ritvo & Freeman, 1976). Hutt & Hutt (1965) also suggest thatstereotyped movements may block further sensory input under conditions of chronichigh arousal in autistic children.

Williams & Surtees (1975), have expressed the relationship between stereotypedbehaviour and arousal in the form of a U-shaped curve. They have replaced the concept'arousal' with the more observable 'environmental stimulus level' so that conditions of

Requests for offprints should be addressed to Mrs E. Goodall, Hilda Lewis House, TheBethlem Royal Hospital, 579 Wickham Road, Shirley, Croydon CRO 8DR.Received 19 April 19820022-264X/82/0900-0163$02.00 1982 Blackwell Scientific Publications

163

164 ELIZABETH GOODALL and J. CORBETT

both over-stimulation and under-stimulation are directly related to increases instereotypy. When there is optimal stimulus input , stereotyped behaviour is minimizedand learning is maximized.

There is some experimental evidence to suggest that stereotyped behaviour in thesame individual may be affected differently by different environmental stimuli.Presentation of white light and coloured pictures has been associated with decreasedbody rocking in subjects who had shown increase in this behaviour with soundstimulation (Forehand & Baumeister, 1970).

Recent research has led to renewed interest in the systematic use of sensorystimulation as a reinforcer for various operant behaviour, such as lever pulling or switchtouching, or in the development of more complex skills (Frankel etal., 1976; Freeman,Frankel & Ritvo, 1976; Byrne & Stevens, 1980; Murphy, 1982a, 1982b; Rincoveref a/.,1977). The possible reinforcing nature of stereotyped behaviour has been demonstratedby Rincover (1978), who described a reduction in stereotyped movements by eliminat-ing the sensory feedback that the subject was thought to receive. There have, however,been few systematic studies of the temporal relationships between sensory stimulation,which has been under the subject's control, and the frequency of stereotyped behaviour(Williams, 1975, 1978). Other studies have not monitored the effect of stereotypedbehaviour during sensory stimulation experiments, (Frankel et al., 1976; Freeman etal., 1976).

The peripheral self-stimulation techniques, developed by Campbell (1972), havebeen used in the present study to analyse the relative reinforcing properties of sensorystimuli (continuous and flashing white light, sound and vibration), in mentally retardedsubjects showing stereotyped behaviour. The effect of this alternative stimulation onthe amount of stereotyped behaviour has been examined. Previous experimental evi-dence suggests that the mechanisms underlying stereotyped behaviour and the effectsof sensory stimulation may be different in children showing symptoms of childhoodautism from other children with mental retardation, (Frankel et al., 1976; Freeman etal., 1976; Hut t & Hut t , 1965). In order to explore whether there were any clinicalcorrelations with patterns of response to sensory stimuli, three groups of childrenmatched for mental age were included: a group with Down's syndrome, a group withRubella Embryopathy who had severe sensory defects, and a group with neither ofthese diagnoses. Autistic characteristics were examined across the three groups, andindividual patterns of response to peripheral self-stimulation have been examined inrelation to these and other clinical findings.

METHOD

Subjects *

The subjects were 24 severely mentally retarded children who showed stereotypedbehaviour. There were 11 girls, and 13 boys. Eight subjects were diagnosed as havingDown's syndrome, (mean CA, 15 years 5 months), eight subjects had Rubella

*The authors will provide full details of the clinical characteristics on request.

STIMULI AND STEREOTYPED BEHAVIOUR 165

embryopathy, (mean CA, 14 years 1 month), while eight subjects suffered from mentalretardation of unknown aetiology, (mean CA, 14 years 4 months).

Clinical history

Psychological assessments were carried out using the Bayley Scale of Infant Develop-ment or Merrill Palmer Scales and Reynell Developmental Language Scales whereappropriate. (Down's syndrome, MA range 5-40 months; Rubella subjects, MA range5-19 months; unknown aetiology, MA range 92-38 months).

The children were examined for sensory defects and details of their case historieswere taken from hospital records. Particular notes of any history of epilepsy and detailsof medication were made.

Of the Rubella group, one subject was totally blind and partially deaf, six subjectswere either partially hearing or sighted or both; one subject had only a partial hearingdefect.

None of the Down's or unknown aetiology group had severe sensory defects.The Schedule of Children's Handicaps, Behaviours and Skills (Wing & Gould,

1978) was completed with the ward sister after testing was finished. The VinelandSocial Maturity Score and social age was derived from this schedule. (Down's syn-drome, SA range 10-40 months; Rubella subjects, SA range 10-44 months; unknownaetiology, SA range 13-38 months).Apparatus

Testing took place in an experimental room 2.1 x 3.6 m, containing three chairs, theexperimental table, and recording equipment. The room was illuminated by naturallight, and had an ambient sound level of 40 dB. The apparatus was in two parts; anexperimental table containing a flat removable panel, which could be replaced by aconsole measuring 15 x 32 cm, which had two lamps and a loud speaker fitted into thesloping front surface. At the front of the console was a metal cylinder acting as acapacitance switch. Four pre-determined sensory stimuli could be elicited by thesubject touching the switch. The console was connected to control and recordingequipment by a low voltage cable 5 metres in length.

Stimuli

(a) Continuous white light from a 12 V, 24 W frosted filament lamp of variable intensity.(b) Flashing white light from a xenon-filled photographic flash gun, MFT 110, whichhad a flash voltage of 350 V DC and duration per fiash of 200 ;u,s. The rate of fiash wasset at 6 flashes/s.(c) High frequency synthesised sounds from a tape recording of varying intensity,(approximately 70 dB).(d) Vibration provided by a small electric motor housed in the casing ofthe capacitanceswitch, and which had an eccentric fiy wheel attached to its spindle. (When the motorrotated the cylinder vibrated on rubber sprung mountings. The amount of vibrationwas governed by a variable potentiometer control). The sound level was 63 dB andvibration 30 Hz.

166 ELIZABETHGOODALLandJ . CORBETT

Sensory stimulation was contingent on the cylinder being touched up to a maximumof 5 s. If the switch was touched for longer than this the stimulus would cease, and theswitch would need to be re-touched to receive further stimulation. The number of timesthe switch was touched and the total duration of stimulation in seconds was recordedautomatically.

Design

The experiment was conducted in three stages.(a) Baselinestereotyped behaviour was observed while the child was unoccupied,seated at the table without the console in place.(b) Sensory stimulationStereotyped behaviour and duration of stimulation wererecorded when each of the four sensory stimuli was available.(c) ExtinctionStereotyped behaviour and number and duration of switch touches wasrecorded when stimuli were no longer available.

Procedure

The children were tested every morning (for 3-4 weeks). The subject was sat at the tableby the experimenter, who then remained in the room to make behavioural observations.If the child got up, he was replaced on the chair once only. The observer maintained aslittle contact as possible with the child.

Five 5-minute baseline trials took place over three days, not more than two trialsbeing given on any day.

Eight 5-minute trials took place witheach sensory stimulus, the console being in placein the table top for these trials. Generally three trials were given each day, and allowedfor:(a) light stimuli to be alternated with other sensory modes.(b) each day's testing to start with equal number of trials with each stimulus, but theseto be ordered as randomly as possible.(c) all four stimuli to be presented as evenly as possible throughout the testing period,so that no stimulus was finished several days before the others.

Finally, five 5-minute extinction trials took place over three days, when the consolewas present, but no stimulus was elicited when the subject touched the switch.

Prompting

At the start of the first sensory stimulation trial (which was always white light, in orderto make the conditions the same for each child) the child was seated at the table, and noinstruction was given. Many children spontaneously touched the switch, noticed thestimulus and continued to touch, without prompting.

If the child failed to touch the switch spontaneously minimal systematic promptingwas^iven before the start of the trials. If a child failed to reach a response criterion, hewas not tested further.

Direct observation of stereotyped behaviourA study of the accuracy of samphng methods used in direct observation showed that


momentary (Is) time sampling of behaviour every 10 s gave a percentage duration closeto the percent duration recorded on video tape, and gave consistently less error thaninterval recording, which over-estimated percentage duration (Murphy & Goodall,1980),

Using this method each 5-minute trial gave 30 observation intervals. The timing ofobservation was controlled by audio-cueing. If a behaviour occurred at all during a onesecond observation period, it was scored as being present.

Definition of behavioural categoriesA check list of behaviours was compiled, based on those of Berkson & Mason (1963,1964) and Davis, Sprague & Werry (1969). Behaviours were divided into fivecategories: body/head movements, hand movements, oral stereotypies, eye-poking,and self-manipulation (see Table 1).

Table 1. Individual stereotypies included in each category of behaviour

Category Individual stereotypyBody movements Body rocking, swaying, weaving; head nodding, shaking,

weaving; leaning back, bizarre body or head postures;standing and turning movements.

Hand movements Hand flapping, hand/finger postures and movements, fingerdrumming; hand to mouth, ear, face; pulling and smearingsaliva; tapping mouth.

Oral stereotypies Repetitive speech, sounds, snorting, blowing, puffing,clicking, moaning; mouth, lip, jaw, neck movements; teethgrinding.

Self-manipulation Fingers in mouth, ear; hand over ear, mouth; hand pressedagainst throat; self-pinching biting, slapping, rubbing body;masturbating.

Eye-poking Finger in eye, hand pressing against eye or eyebrow.

It was possible for a child to show more than one distinct behaviour in one category,e.g. hand flap, and hand to face. The number of behaviours observed ranged from twoto six per subject.

Individual behaviours were amalgamated within categories. An 'intervals of occurr-ence score' was obtained for each category of behaviour for each trial (max. score = 30)which was converted into a 'percentage duration' score.

Two further measures were calculated: 'total stereotypy score' for each trial, whichwas the sum of the number of intervals that all categories of behaviour occurred for eachtrial. This took account of the total amount of stereotyped behaviour occurring, asmany children carried out several categories at the same time. 'Absence of stereotypy'was the number of intervals in which no stereotypy at all occurred, and was expressed asa percentage.


Reliability

Inter-observer reliability checks were made, (using audio-cueing) on average, onceevery six trials. (The second observer was experienced in direct observation). Reliability(RTOT) was calculated (for each behavioural category) of the number of intervals inwhich there was agreement and expressed as a percentage of the total number ofintervals (see Table 2).

Many stereotypies occurred infrequently. Occurrence and non-occurrencereliabilities (Rocc and RNON-OCC) (Hartman, 1977) were also calculated.

xlOO.no. of intervals both observers agree on occurrence

% Rocc = 30 - no. of intervals both observers agree on non-occurrence

This stringent procedure accounts for the relatively low occurrence reliabilityscores.

Table 2. Reliabilities for direct observation of behaviour

Mean percentagereliability for totalagreement (RTOT)

Down's (n= 8)

Rubella (n =8)

Unknown (n=8)

91(84-95)

92(88-94)

92(83-98)

Mean percentagereliability for

occurrence of stereotypedbehaviour (Rocc)

64(47-86)

76(64-94)

69(54-85)

Mean percentagereliability for non-

occurrence of stereotypedbehaviour (RNON-OCC)

83(72-93)

89(80-95)

88(81-94)

*The ranges are given in parentheses below mean percentage.

R E S U L T S

Group analysis

Baseline stereotypy. The mean baseline total stereotypy levels (over five trials) for thethree diagnostic groups of children were compared, using one-way analysis of variance.The amount of stereotyped behaviour shown by the children in the Rubella group washigher than that shown by the Down's syndrome and 'unknown' groups. The differ-ence was significant at the 5% level (F = 7.6, d.f. 1 & 21).

Five children failed to reach the response criterion (two rubella and threeunknown). No differences were found in their baseline stereotypy levels compared withchildren who passed the criterion.

Sensory stimulation. Repeat measures, using a three-way analysis of variance, com-pared duration of stimulation, total stereotypy, and absence of stereotypy for diagnostic


groups, sensory stimulation conditions and trials ( =18 . The five children who failedthe criterion and a Down's syndrome child who had incomplete results, wereexcluded). It was found that the duration of stimulation for white light was lower thanthe remaining conditions (vibration, flashing light and sound). This difference wassignificant at the 1% level (F= 9.2123, d.f. 1 & 15, P

170 E L I Z A B E T H G O O D A L L a n d J . CORBETT

been unoccupied and the presence of the switch then might have led to considerableprompting being needed during sensory stimulation trials). However, the meanbaseline stereotypy score was 33.0 (n = 18, cf. extinction score of 30.9, Table 4)showing a classical reversal effect when sensory stimulation was available.

Correlation between stereotypy scores and duration of stimulationThe Pearson correlation co-efficients between duration of stimulation, (mean stimula-tion over trials), and mean stereotypy scores were calculated, taking the 18 subjectstogether, and also taking the subjects in each diagnostic group.

There was a significant negative correlation between amount of light and vibrationsought and total amount of stereotyped behaviour shown by the 18 subjects (Table 5).Similarly, sensory stimulation was positively correlated with absence of stereotypywhich was significant for all four stimulus conditions.

Table 5. Pearson correlation coefficient (r) between sensory stimulation and total stereotypy

All subjects ( = 18)Down's (n=7)Rubella (n= 6)'Other'(n = 5)

Continuouslight (r)

-0.7126t-0.6784-0.8298*-0.9872t

Flashinglight (r)

-0.7263t-0.8126*-0.8615*-0.4445 n.s.

Vibration(r)

-0.6127t-0.7433*-0.6269 n.s.-0.9294*

Sound(r)

-0.4789 n.s.-0.6332 n.s.-0.4868 n.s.-0.2827 n.s.

*P


Unknownaetiology

number ot childronwithsensory proterences

I1 number of childrenwitti no sensorypreferences or whofailed criterionFigure 1. Summary of individualchildren's patterns ^_^ ofresponse. 1 ^ failed criterion; L J nosensory preferences (but passed crite-rion); I I no changes inbehaviour; I J decrease seen in atleast one behaviour for at least onestimulus; fSf^ increase seen in at leastone behaviour for sound (+light),decreases seen in other behaviours orconditions.

No increases in stereotypy were found with vibration or flashing light. The differ-ences in the children's response to vibration and sound neared significance. (P


ably repetitive. None of the children showed imaginative play or elaborate repetitiveroutines. All the children had severe language delays, nine were mute , ten babbledwithout meaning. Only two used two word phrases, but both had delayed echolalia.

No significant associations were found between any of these behavioural abnor-malities and the children's patterns of response to sensory stimuli, seven children hadsome understanding and use of gesture but this was not correlated with their response tosensory stimulation.

Behaviour problems shown by children with limited, or no social awareness, werealso analysed. Significant correlations with response to sensory stimuli were found forthe following items, temper tantrums, aggression and crying or moaning. Presence ofthese behaviours were associated with lack of interest in sensory stimulation.

D I S C U S S I O N

For the subjects as a whole, the amount of time the switch was touched when stimuliwere available, was significantly higher than during extinction trials: all the stimuliwere therefore acting to reinforce switch touching behaviour. The percentage durationfor the continuous light was significantly less than the other stimuli, suggesting that thisstimulus is less reinforcing than flashing light, vibration or sound. There was, however,no difference in the amount of stereotyped behaviour shown when continuous lighttrials were compared with other stimuli.

Stereotyped behaviour increased significantly during extinction, and there was anegative correlation between duration of sensory stimulation and stereotypy. Thesegroup results support the theory that the function of stereotyped behaviour is toincrease self-stimulation, the behaviour being maintained by the reinforcing propertiesof the sensations it produced (Williams, 1978). If an environmental sensory stimulusproved to be more reinforcing than the stereotyped behaviour, the alternative activity(switch touching), upon which this stimulus was contingent, was increased, and thestereotyped behaviour decreased.

The analysis of variance showed no differences in amount of response to sensorystimulation between diagnostic groups (due to the large amount of between subjectvariance).

The Rubella group was found to have a higher baseline stereotypy score which issimilar to previous reports on blindisms in sensorily impaired people (Stone, 1964), butdifferences in baseline stereotypy did not account for those who passed the criterion andthose whose interest in environmental stimulation was so limited that they failed tomeet the criterion.

Although the group analyses support the self-stimulation theory, these maskedindividual differences in stereotypy levels. Some children showed an increase in onebehaviour, in response to a particular stimulus, (sound), while other stereotypedbehaviours decreased. This reaction by four children to sound stimulation is in line withreports in the literature, and supports the arousal hypothesis.

There were also interesting differences in quality of response between individualswhich can be seen in Figure 1, such that the difference in the number of childrenfinding sensory stimuli reinforcing in the Down's and unknown aetiology groups wassignificant. These findings raise questions as to whether the behaviours are functionally


differentiated within individual children, or whether the results may be accounted forby differences in the nature of the stimuli. The dichotomy of response of differentbehaviours within an individual to the same stimulus, has also been noted byRomanczyk & Kistner (1980). Young & Clements (1979), have reported differentpsychophysiological responses occurring in three retardates when engaged in rockingand complex hand movements. The fact that increase in stereotypy with sound stimula-tion only occurred for some subjects, suggests that mechanisms underlying theresponse may be related to clinical differences in the children. In particular, it wasthought possible that the abnormal response to sensory stimuli in the natural environ-ment, shown by children with 'autistic' behaviour, might be reflected in the relation-ship of response of stereotyped behaviour to peripheral stimuli.

The analysis of the HBS schedule did not reveal any significant differences relatingto social and language impairments between those who responded to sensory stimuliand those who did not. There was perhaps an indication that some of those who showedan increase in stereotypy in response to sound were among the less retarded and werethe least socially impaired. The severity of the mental retardation and the small numberof children may be reasons why no correlations between autistic features and responseto sensory stimuli have been found. Other behavioural problems (temper tantrums,aggression, crying or moaning) were, however, correlated with lack of interest insensory stimulation.

All the children lacked imaginative play supporting the results of the CamberwellSurvey which reported a relationship between lack of symbolic play and repetitivebehaviour (Wing & Gould 1979).

The results discussed refiect the problems of experimental design inherent inmental retardation research. Single-case analyses show interesting variations amongindividuals which may be important in understanding the function of stereotypy butinferences about populations can only be made from large numbers. It appears thatstereotypy does not function as a unitary response even within an individual.

Use of sensory stimulation in treatment of mentally handicapped peopleSensory stimuli have been found reinforcing in that they increase the likelihood of asimple switch being touched, and at the same time reduce stereotypy. It is hoped thatthese stimuli will prove reinforcing in teaching more complex tasks, particularly withchildren where conventional reinforcers, such as food or social praise, are ineffective.Equipment has been designed to this end (Goodall et al., 1981; 1982).

S U M M A R Y

The reinforcing properties of four sensory stimuli (continuous and fiashing light,vibration and sound) which were under the subject's control, were examined and theeffect on stereotyped behaviour observed. The subjects were 24 severely retardedchildren in three diagnostic groups; Down's, Rubella and a group which includedneither of these diagnoses. Duration of stimulation with continuous light was signifi-cantly lower than the other three stimuli, but there were no differential effects onstereotypy, nor diagnostic group differences.

174 E L I Z A B E T H G O O D A L L a n d J . CORBETT

Switch touching was significantly reduced and stereotypy significantly increasedduring extinction.

These group analyses are interpreted to support the self-stimulation theory ofstereotypy, but the individual differences in response suggest that all stereotypedbehaviours cannot be regarded as a unitary response class. Individual responses arediscussed in relation to clinical correlations and other theories on stereotypy.

A C K N O W L E D G E M E N T SThe authors would like to thank Dr H. J. Campbell whose original research at HildaLewis House led to this project and for his advice which made this study possible.

Much of this research took place at Queen Mary's Hospital, Carshalton. Theauthors are most grateful to Dr V. Cowie, Dr M. Faulkner, Dr S. Shivanathan, Mrs N.Scott, Mrs B. Thomas, and all the staff for their help and co-operation.

They would particularly like to thank Glynis Murphy, Institute of Psychiatry, forcarrying out the psychological assessments and observing during reliability trials andfor many helpful discussions; Dr Lorna Wing, MRC Social Psychiatry Unit for heradvice and the use of the HBS Schedule, and John Clements for his helpful commentson the paper.

The authors are grateful to Mr Brian Everitt, Biometrics Unit, Institute ofPsychiatry, for carrying out the group statistical analyses and to Mr F. Goldsmith fordesigning the equipment.

This research was supported by a grant from the Mental Health Foundation.

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Relationship Between Sensory Stimualtion Stereotypy

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