Auditory lateralisation vs Speech disorders

AUDITORY LATERALISATION Vs Speech Disorders

Z.M. KURKOWSKI Institute of Physiology and Pathology of Hearing, Warsaw, Poland

4th European Congress of Oto-Rhino-Laryngology, Head and Neck Surgery, Berlin, Germany, May 13-18, 2000

SUMMARY Many scientists believe that stuttering results from incomplete lateralisation of brain functions during the development of speech. Therefore, I assume in this paper that stuttering may be caused by irregular lateralisation of auditory functions. In my research, in addition to the dichotic listening test. I have also used A. Tomatis' audiolaterometer to evaluate auditory lateralisation. The study was performed on 45 stuttering subjects. The use of audiolaterometer revealed left-sided auditory lateralisation in 12 cases, indefinite lateralisation in 20 and right-sided lateralisation in 13 cases.

INTRODUCTION For a long time, stuttering has attracted attention of researchers representing different disciplines of science. Today, the answers to the question concerning the genesis of stuttering as well as effective therapy are still being sought. I think that we should assume that stuttering is a much more complex defect than it is generally believed to be. Many researchers claim that stuttering is caused by incomplete lateralisation of brain func足tions during the process of speech development.

Thus, the assumption made in this work is that stuttering may result from impaired lateralisation of auditory functions.

The studies in this field were carried out mainly with the use of di足chotic listening procedure. However, the outcomes of these studies differ greatly. Some authors [Quinn 1972, Slorach and Nohgr 1973, Gruber and Powell 1974, Dorman and Porter 1975, Pinsky and Me Adam 1980, Webster 1988] tend to agree that right hemisphere plays a more important role in speech functions in stuttering subjects when compared with non-stuttering individuals. Other researchers [Curry and Gregory 1969, Brady and Per-son 1975, Sommers et al. 1975, Rosenfield and Goodglass 1980, Libertau and Daily 1981, Rastatter and Loren 1988] did not observe such a percep足tion pattern.

MATERIAL AND METHOD A. Tomatis audiolaterometer was used for the evaluation of auditory lateralisation in the present work as well as R. Zazzo, Z. Matejack and Z. Zlab tests were employed to assess the lateralisation of hand, eye and leg. The degree and nature of dysfluency were evaluated with P. Luking's Stuttering Diagram. Fortyfive stuttering subjects aged 8-32 years (41 men and 4 women) were included in the study.

4th European Congress of Oto-Rhino-Laryngology, Head and Neck Surgery, Berlin, Germany, May 13-18, 2000

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RESULTS The use of audiolaterometer revealed left-sided auditory lateralisation in 12 cases (26,7%), right-sided lateralisation in 13 cases (28,9%) and indefinite lateralisation in 20 cases (44,4%). Thus, 71,1% patient had problems with auditory processing of speech sounds.

Table 1. Stuttering intensity and auditory lateralisation (mean value obtained in Lucking’s Stuttering Diagram) Stuttering Diagram

Indefinite Left-sided lateralisation lateralisation n=20 n=12

Right-sided latéralisation n=13

General outcome Automatic word séquences

R 140 M 11,67

R 211 M 10,55

R 15 M 1,15

R 22 M 1,10

R 96 M 7,38 R 11 M 0,85

Repeating

Spontaneous speech

R 29 M 2,42 R 38 M 3, 17 R 40 M 3,33

R 41 M 2,05 R 61 M 3,05 R 60 M 3,00

R 20 M 1,54 R 26 M 2,00 R 24 M 1,85

R 90 M 2,00 R 115 M 2,56 R 124 M 2,76

Marginal symptoms

R 18 M 1,50

R 26 M 1,30

R 15 M 1,15

R 59 M 1,51

Reading

R - total

Total n=45 R 447 M 9,93 R 48 M 1,07

M – medium

In the case of left-sided auditory lateralisation, tonic or tonic-clonic stuttering was observed, while clonic stuttering prevailed in subjects with indefinite lateralisation.

As far as lateralisation with respect to hand, eye and leg is concerned, homogenous right-sided lateralisation was found in 8 cases (17,7%), homogeneous left-sided lateralisation was observed in 1 case (2,2%), and in the remaining 36 cases (80,0%) the lateralisation was non-homogenous. Stuttering of the greatest intensity was observed in the cases of non-homogenous lateralisation. It should be remembered that the use of Tomatis method for the investigation of auditory lateralisation does not evaluate the dominance of one hemisphere with respect to speech functions (dominance is understood as superiority of one hemisphere over the other in the regulation of a given mental activity) or specialisation (higher compe­tence of one hemisphere in regulating the aspects of a given mental ac­tivity), but it allows for the assessment of lateralisation of mental activities consisting in hemispheredifferentiated control in the course and organi­sation of behaviour.

4th European Congress of Oto-Rhino-Laryngology, Head and Neck Surgery, Berlin, Germany, May 13-18, 2000

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CONCLUSIONS The diagnosis of stuttering should also include the evaluation of auditory lateralisation. In the case of left-ear or indefinite lateralisation, the use of appropriate methods of auditory stimulation in therapy would be advisable. It is also important to define the causes of incorrect development of auditory lateralisation in children, e.g. wrong mode of education or emotional disturbances.

In the case of stuttering, the coordination of breathing and articula­tion and proper realisation of phonic sequence as a result of wrong direc­tion of information passage or information dispersion may occur. There-fore, left or indefinite auditory lateralisation may explain certain phenomena observed in stuttering patients: l/ Patient's emotional status disturbs fluency as it affects the function of right hemisphere which first receives the signal; 2/ Slower pace of speaking reduces stuttering (echo method) as the possibility of full information flow between right and left hemi­sphere is possible; 3/ The masking of one car brings positive results as unilateral information flow is thus regulated; 4/ Speaking to one's palm pressed against one's car improves fluency but only when right hand is pressed against right car; 5/ The onset of stuttering falls between 3rd and 6th year of life, i.e. at the time which is important for auditory lateralisation maturity 6/ Stuttering occurs more often in boys than in girls (fourfold) - this can be explained by greater expectations of boys to rationally perceive the reality and the fact, pointed out by some researchers, that the speech in women is more frequently lateralised in both hemispheres.

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4th European Congress of Oto-Rhino-Laryngology, Head and Neck Surgery, Berlin, Germany, May 13-18, 2000

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