Neuropsychologia,1976, Vol. 14, pp. 243 to 246. PergamonPress.Printedin England.
NOTE A COMPARISON CONTROLS
OF LATERALITY USING
VERBAL
EFFECTS DICHOTIC
M. E.
IN DYSLEXICS LISTENING
AND
TASKS
THOMSON
Research Fellow, Department of Applied Psychology, University of Aston in Birmingham, Gosta Green, Birmingham B4 7ET, England (Received
15 May 1975)
Abstract-Dyslexic children and a control group were presented with dichotic listening tasks involving digits, words, reversible words (saw/was), similar words (big/pig) and reversible nonsense syllables (magipam). The control group showed the right ear superiority effect for digits, words, reversible and similar words. The dyslexic group showed no difference or a left ear superiority for these tests, and a right ear effect for the nonsense syllables. These findings suggest that the Dyslexic group showed a less well established dominance of hemispheric function. It is postulated that this lack of cortical hemispheric dominance in the latter group could underlie difficulties in processing a written alphabetic script.
INTRODUCTION CONSIDERABLEresearch
has been reported during the last decade using dichotic listening techniques to investigate differential functioning of the cerebral hemispheres (KIMURA [l], BRYDEN [2] and others). Further research has investigated the relationship between the concepts of cerebral dominance and handedness using these techniques (BRY~EN [3]; SATZ ei al. [4]) as well as differing stimulus material such as melodies and other nonverbal material (KIMIJRA [5] ; CURRY [6]). These techniques represent a means for investigating underlying neurological function (by implication) and relating this to behaviour. One such field of behaviour is that of specific reading disability or dyslexia, in which an etiology based upon cerebral dominance has been suggested (ORTON [7]; CRITCHLEY[S] ; NEWTON [9]), linking with the language lateralization in the cortical hemispheres (ZANGWILL [lo]). Using dichotic listening techniques to investigate this relationship BRYDEN [ll] found that boys with speech and motor function oppositely lateralized have a significantly higher proportion of poor readers than the uncrossed pattern. ZURIF and CARSON [12] concluded that there was no clear relationship between bilateral organization of speech and poor reading, whereas a more recent study by BAKKER [13] found a less established cerebral dominance (using dichotic listening) amongst dyslexic children and the relationship was continuous across the range “non-fluent” through “fluent” readers. The purpose of the present investigation was to attempt to clarify this relationship amongst dyslexics, and to study the dichotic perception of different types of verbal material in dyslexics and controls.
METHOD Subjects
The subjects consisted of 20 children in each group matched individually for age, sex, socio-economic status and intelligence; age range 9-12 yr. The experimental group consisted of children referred to a diagnostic clinic for dyslexic-type language difficulties and had an average reading retardation of 23 yr and average spelling retardation of 3 yr. The control group were on average 1 yr ahead in reading and spelling. Medical and school reports showed that all children had normal hearing. Test procedure
The pre-recorded material was presented dichotically by a Tanberg 2041 stereo tape recorder through Pioneer SE-20a headphones. The earphones were reversed for half the subjects to control for possible channel variations. All stimuli were recorded at the same volume. The stimulus material used was as follows: 243
Tesf I. Digits. Twelve sets consisting of 3 pairs in each set, trials given at 4 set intervals. Subjects recalled digits after every set of 3 pairs. (Ss could report in any order.) Tesr 2. Three letter words. Twenty pairs of 3 letter words controlled for frequency from Thorndyke-Lorge word count. So that words to each ear were as comparable as possible each pair started with the same initial letter (e.g. age/act, him/had, run/red). Subjects recalled words after each set of 4 pairs. Ted 3. Ten pairs of “reversible”
words e.g. saw/was, top/pot.
Subjects recalled words after each set of
2 pairs. Tert 4. Ten pairs of similar words e.g. big/pig, gate/cake. Subjects recalled words after each set of 2 pairs. Test 5. Ten pairs of reversible nonsense syllables e.g. mag/gam, pib/bip. Subjects recalled words aftct each set of 2 pairs.
Stimuli for tests 3 and 4 were chosen as examples of reversals and word confusions often made by dyslexics, similarly for Test 5 using unfamiliar non-meaningful information.
RESULTS These are presented in terms of percentage of correct recall for each ear, for tests 1-5. Levels of significance between the two ears are given for each group. (Mann-Whitney Cl Test.) Table 1 Dyslexic Group
Control Group _____ R
L
R
L
Te.rr I
YO
60
I’ < 0.01
63
69
P n/s
T&I 2
44
32
f’cO.01
30
37
P < 0.05
7&r 3
68
42
P < 0.01
50
48
P n/s
Test 4
70
53
P i 0.01
51
64
P < 0.05
Test 5
34
32
P
40
34
P < 0.05
n/s
The results show a significantly better performance by the right ear in the control group for tests l-4; there being no significant difference in test 5. The dyslexic group showed no significant difference on ear performance for tests 1 and 3. This group showed a significantly better /eft ear performance for tests 2 and 4 and a significantly better right ear performance for test 5.
DlSCUSSION The results of the control group are in agreement with previous research suggesting that verbal material such as digits and words are reported more successfully when presented to the right ear. The dyslexic group, however, showed no clear cut ear dominance for digits and “reversible” words, with a left ear dominance for 3 letter words and “similar” words. These results may be interpreted by suggesting a less clear-cut functional area of the brain (in terms of hemisphere) for verbal material, some verbal material at least, being processed in the right hemisphere. The results of the nonsense syllable test is interesting, in that the dyslexic group show opposite results to the other trends. One interpretation suggests a different process occurring in the dyslexic group, nonsense syllable not being perceived as meaningful verbal material. This may relate to language difficulties in general; non-meaningful and meaningful stimuli appear to be processed in a different manner by children with language difficulties when compared to controls (e.g. MENYUKand LOONEY[14]). In general the results are not inconsistent with the “cerebral dominance” hypothesis on dyslexic difficulties in which it is postulated that language stimuli are not processed consistently in one hemisphere. It could be logical to relate these findings to the underlying brain mechanisms involved with language function, development of skills, and concomitant sensory/motor mechanisms. The individual with inconsistent lateralization of hemisphere function may do less well on sequential, ordered, serial tasks, e.g. written language (NEWTONand THOMSON[15]). A model of the brain which is processing (or selectively perceiving)
NOTB
245
temporal, “patterned”, serial (or verbal) information in the left hemisphere and “global”, spatial (or nonverbal) information in the right hemisphere has broad implications. One of these may be the way in which individuals develop skills such as learning to read, spell and write. The person faced with an ordered symbolic serial task, e.g. sequences containing such phoneme/grapheme constrats as b/d, p/g. t/f, m/w, etc. related arbitrarily to meaning could be perceiving a random representation of these events.
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
D. Cerebral dominance
of verbal stimuli. Can. J. Psychol. 15, 156-165, 1961. BRYDEN,M. P. Ear preference in auditory perception. J. exp. Psychol. 65, 103-105, 1963. BRYDEN,M. P. Tachistoscopic recognition, handedness and cerebral dominance. Neuropsychologia 3, 1-8, 1965. SATZ, P., ACHENBACH,K., PATIXHALL,E. and FENNELL,E. Order of report, ear asymmetry and handedness in dichotic listening. Cortex 1, 377-396, 1965. KIMIJRA, D. Functional asymmetry of the brain in dichotic listening. Cortex 3, 163-178, 1967. CURRY,F. K. A comparison of left handed and right handed subjects on verbal and non-verbal dichotic listening tasks. Cortex 3, 343-352, 1967. GRmN, S. T. Reading, Writing and Speech Problems in Children. Chapman & Hall, 1937. CR~TCHLEY,M. The Dyslexic Child. Heinemann, London, 1970. NEWTON,M. A neuropsychological investigation into dyslexia in Franklin and Naidoo. Assessment and teaching of the dyslexic child. ICAA, 1970. ZANCW~LL,0. Dyslexia in Relation to Cerebral Dominance in Reading Dissability, MONEY,J. (Editor). Johns Hopkins Press, 1962. BRYDEN,M. P. Laterality effects in dichotic listening: relations with handedness and reading ability in children. Neuropsychologia 8,443-450, 1970. ZUR~F,E. B. and CARSON,G. Dyslexia in relation to cerebral dominance and temporal analysis. Neuropsychologia 8,351-362, 1970. BAKKER,P. J. Cortical mechanisms subserving early and fluent reading paper presented at International Federations of Learning Disabilities, Amsterdam, January, 1974. MENWK, P. and LOONEY,P. Relationships among components of the grammar in language disorder. Znt. speech hear. Res. 15,395-406, 1972. NEWTON, M. and THOMSON,M. E. Dyslexia as a phenomenon of written language paper presented at British Association of Applied Linguistics, Edinburgh, 1974. KIMURA,
Des taches sibles
(saw-was),
and the perception
dichotiques
mats
r6versibles
(mag-gam)
des groupes
de contr0le.
Dans
reversibles
et similaires.
et une
supikiorite
Ces constatations nance que sous
ou une
mains
bien
le manque tendre
suggerent Btablie
Dyslektische umgekehrte umgekehrte
que
droite
dyslexiques
pour
le groupe
sens et a une
les mots
, on ne constatait
gauche
pour
les syllables
dyslexique
de ce dernier de l'kriture
ces taches,
sans
presente
h&misphSriques.
du traitement
rever-
on constatait les mats,
dyslexique
l'orkille
hemisph&ique
les difficult&
sans
de contri%e,
de
des fonctions
de dominance
mots
syllabes
les chiffres,
le groupe
superiorit
de l'orcflle
Beutschsprachige
dichotischen
Dans
pour
chiffres,
et des
2 des enfants
le groupe
droite
mats,
(big-pig)
ont BtS donnees
supGrl.orite de l'oreille
pas de difference
comportant
siailaires
sens. une domi-
11 est postule groupe
pourrait
alphabetique.
Zusammenfassung:
Kinder
und
Hijrtest Wrter
Kontrollgruppen
untersucht, (saw/was)
Nonsenssilben
wurden
dabei D &nl.iche
(mag/gam)
mit
einem
wurden
Ziffern,
Yijrter
(big/pig)
angeboten.
Hei
den
Wrter, und Kontroll-
246
NOTE
personen fand sich eine iiberwertigkeitdes rechten Ohres fur Ziffern, Wdrter, Umkehr- und Ahnlichkeitswijrter.Die dyslektische Gruppe lief3keine Seiteniiberlegenheitbei diesen Tests erkennen, und es fand sich eine rechtsohrige tiberlegenheit fur Nonsenssilben. Diese Ergebnisse.sprechen dafiir,daI3Dyslektiker in ihrer, hemispharischen Dominanz eine geringere Auspriigungbesitzen. Es wurde angenommen, daD dieser Mange1 einer hemisphgrischen kortikalen Dominanz bei der letzterwkihnten Gruppe die Schwierigkeiten beim Buchstabenschreiben erklart.
NOTE A COMPARISON CONTROLS
OF LATERALITY USING
VERBAL
EFFECTS DICHOTIC
M. E.
IN DYSLEXICS LISTENING
AND
TASKS
THOMSON
Research Fellow, Department of Applied Psychology, University of Aston in Birmingham, Gosta Green, Birmingham B4 7ET, England (Received
15 May 1975)
Abstract-Dyslexic children and a control group were presented with dichotic listening tasks involving digits, words, reversible words (saw/was), similar words (big/pig) and reversible nonsense syllables (magipam). The control group showed the right ear superiority effect for digits, words, reversible and similar words. The dyslexic group showed no difference or a left ear superiority for these tests, and a right ear effect for the nonsense syllables. These findings suggest that the Dyslexic group showed a less well established dominance of hemispheric function. It is postulated that this lack of cortical hemispheric dominance in the latter group could underlie difficulties in processing a written alphabetic script.
INTRODUCTION CONSIDERABLEresearch
has been reported during the last decade using dichotic listening techniques to investigate differential functioning of the cerebral hemispheres (KIMURA [l], BRYDEN [2] and others). Further research has investigated the relationship between the concepts of cerebral dominance and handedness using these techniques (BRY~EN [3]; SATZ ei al. [4]) as well as differing stimulus material such as melodies and other nonverbal material (KIMIJRA [5] ; CURRY [6]). These techniques represent a means for investigating underlying neurological function (by implication) and relating this to behaviour. One such field of behaviour is that of specific reading disability or dyslexia, in which an etiology based upon cerebral dominance has been suggested (ORTON [7]; CRITCHLEY[S] ; NEWTON [9]), linking with the language lateralization in the cortical hemispheres (ZANGWILL [lo]). Using dichotic listening techniques to investigate this relationship BRYDEN [ll] found that boys with speech and motor function oppositely lateralized have a significantly higher proportion of poor readers than the uncrossed pattern. ZURIF and CARSON [12] concluded that there was no clear relationship between bilateral organization of speech and poor reading, whereas a more recent study by BAKKER [13] found a less established cerebral dominance (using dichotic listening) amongst dyslexic children and the relationship was continuous across the range “non-fluent” through “fluent” readers. The purpose of the present investigation was to attempt to clarify this relationship amongst dyslexics, and to study the dichotic perception of different types of verbal material in dyslexics and controls.
METHOD Subjects
The subjects consisted of 20 children in each group matched individually for age, sex, socio-economic status and intelligence; age range 9-12 yr. The experimental group consisted of children referred to a diagnostic clinic for dyslexic-type language difficulties and had an average reading retardation of 23 yr and average spelling retardation of 3 yr. The control group were on average 1 yr ahead in reading and spelling. Medical and school reports showed that all children had normal hearing. Test procedure
The pre-recorded material was presented dichotically by a Tanberg 2041 stereo tape recorder through Pioneer SE-20a headphones. The earphones were reversed for half the subjects to control for possible channel variations. All stimuli were recorded at the same volume. The stimulus material used was as follows: 243
Tesf I. Digits. Twelve sets consisting of 3 pairs in each set, trials given at 4 set intervals. Subjects recalled digits after every set of 3 pairs. (Ss could report in any order.) Tesr 2. Three letter words. Twenty pairs of 3 letter words controlled for frequency from Thorndyke-Lorge word count. So that words to each ear were as comparable as possible each pair started with the same initial letter (e.g. age/act, him/had, run/red). Subjects recalled words after each set of 4 pairs. Ted 3. Ten pairs of “reversible”
words e.g. saw/was, top/pot.
Subjects recalled words after each set of
2 pairs. Tert 4. Ten pairs of similar words e.g. big/pig, gate/cake. Subjects recalled words after each set of 2 pairs. Test 5. Ten pairs of reversible nonsense syllables e.g. mag/gam, pib/bip. Subjects recalled words aftct each set of 2 pairs.
Stimuli for tests 3 and 4 were chosen as examples of reversals and word confusions often made by dyslexics, similarly for Test 5 using unfamiliar non-meaningful information.
RESULTS These are presented in terms of percentage of correct recall for each ear, for tests 1-5. Levels of significance between the two ears are given for each group. (Mann-Whitney Cl Test.) Table 1 Dyslexic Group
Control Group _____ R
L
R
L
Te.rr I
YO
60
I’ < 0.01
63
69
P n/s
T&I 2
44
32
f’cO.01
30
37
P < 0.05
7&r 3
68
42
P < 0.01
50
48
P n/s
Test 4
70
53
P i 0.01
51
64
P < 0.05
Test 5
34
32
P
40
34
P < 0.05
n/s
The results show a significantly better performance by the right ear in the control group for tests l-4; there being no significant difference in test 5. The dyslexic group showed no significant difference on ear performance for tests 1 and 3. This group showed a significantly better /eft ear performance for tests 2 and 4 and a significantly better right ear performance for test 5.
DlSCUSSION The results of the control group are in agreement with previous research suggesting that verbal material such as digits and words are reported more successfully when presented to the right ear. The dyslexic group, however, showed no clear cut ear dominance for digits and “reversible” words, with a left ear dominance for 3 letter words and “similar” words. These results may be interpreted by suggesting a less clear-cut functional area of the brain (in terms of hemisphere) for verbal material, some verbal material at least, being processed in the right hemisphere. The results of the nonsense syllable test is interesting, in that the dyslexic group show opposite results to the other trends. One interpretation suggests a different process occurring in the dyslexic group, nonsense syllable not being perceived as meaningful verbal material. This may relate to language difficulties in general; non-meaningful and meaningful stimuli appear to be processed in a different manner by children with language difficulties when compared to controls (e.g. MENYUKand LOONEY[14]). In general the results are not inconsistent with the “cerebral dominance” hypothesis on dyslexic difficulties in which it is postulated that language stimuli are not processed consistently in one hemisphere. It could be logical to relate these findings to the underlying brain mechanisms involved with language function, development of skills, and concomitant sensory/motor mechanisms. The individual with inconsistent lateralization of hemisphere function may do less well on sequential, ordered, serial tasks, e.g. written language (NEWTONand THOMSON[15]). A model of the brain which is processing (or selectively perceiving)
NOTB
245
temporal, “patterned”, serial (or verbal) information in the left hemisphere and “global”, spatial (or nonverbal) information in the right hemisphere has broad implications. One of these may be the way in which individuals develop skills such as learning to read, spell and write. The person faced with an ordered symbolic serial task, e.g. sequences containing such phoneme/grapheme constrats as b/d, p/g. t/f, m/w, etc. related arbitrarily to meaning could be perceiving a random representation of these events.
REFERENCES 1. 2. 3. 4.
5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.
D. Cerebral dominance
of verbal stimuli. Can. J. Psychol. 15, 156-165, 1961. BRYDEN,M. P. Ear preference in auditory perception. J. exp. Psychol. 65, 103-105, 1963. BRYDEN,M. P. Tachistoscopic recognition, handedness and cerebral dominance. Neuropsychologia 3, 1-8, 1965. SATZ, P., ACHENBACH,K., PATIXHALL,E. and FENNELL,E. Order of report, ear asymmetry and handedness in dichotic listening. Cortex 1, 377-396, 1965. KIMIJRA, D. Functional asymmetry of the brain in dichotic listening. Cortex 3, 163-178, 1967. CURRY,F. K. A comparison of left handed and right handed subjects on verbal and non-verbal dichotic listening tasks. Cortex 3, 343-352, 1967. GRmN, S. T. Reading, Writing and Speech Problems in Children. Chapman & Hall, 1937. CR~TCHLEY,M. The Dyslexic Child. Heinemann, London, 1970. NEWTON,M. A neuropsychological investigation into dyslexia in Franklin and Naidoo. Assessment and teaching of the dyslexic child. ICAA, 1970. ZANCW~LL,0. Dyslexia in Relation to Cerebral Dominance in Reading Dissability, MONEY,J. (Editor). Johns Hopkins Press, 1962. BRYDEN,M. P. Laterality effects in dichotic listening: relations with handedness and reading ability in children. Neuropsychologia 8,443-450, 1970. ZUR~F,E. B. and CARSON,G. Dyslexia in relation to cerebral dominance and temporal analysis. Neuropsychologia 8,351-362, 1970. BAKKER,P. J. Cortical mechanisms subserving early and fluent reading paper presented at International Federations of Learning Disabilities, Amsterdam, January, 1974. MENWK, P. and LOONEY,P. Relationships among components of the grammar in language disorder. Znt. speech hear. Res. 15,395-406, 1972. NEWTON, M. and THOMSON,M. E. Dyslexia as a phenomenon of written language paper presented at British Association of Applied Linguistics, Edinburgh, 1974. KIMURA,
Des taches sibles
(saw-was),
and the perception
dichotiques
mats
r6versibles
(mag-gam)
des groupes
de contr0le.
Dans
reversibles
et similaires.
et une
supikiorite
Ces constatations nance que sous
ou une
mains
bien
le manque tendre
suggerent Btablie
Dyslektische umgekehrte umgekehrte
que
droite
dyslexiques
pour
le groupe
sens et a une
les mots
, on ne constatait
gauche
pour
les syllables
dyslexique
de ce dernier de l'kriture
ces taches,
sans
presente
h&misphSriques.
du traitement
rever-
on constatait les mats,
dyslexique
l'orkille
hemisph&ique
les difficult&
sans
de contri%e,
de
des fonctions
de dominance
mots
syllabes
les chiffres,
le groupe
superiorit
de l'orcflle
Beutschsprachige
dichotischen
Dans
pour
chiffres,
et des
2 des enfants
le groupe
droite
mats,
(big-pig)
ont BtS donnees
supGrl.orite de l'oreille
pas de difference
comportant
siailaires
sens. une domi-
11 est postule groupe
pourrait
alphabetique.
Zusammenfassung:
Kinder
und
Hijrtest Wrter
Kontrollgruppen
untersucht, (saw/was)
Nonsenssilben
wurden
dabei D &nl.iche
(mag/gam)
mit
einem
wurden
Ziffern,
Yijrter
(big/pig)
angeboten.
Hei
den
Wrter, und Kontroll-
246
NOTE
personen fand sich eine iiberwertigkeitdes rechten Ohres fur Ziffern, Wdrter, Umkehr- und Ahnlichkeitswijrter.Die dyslektische Gruppe lief3keine Seiteniiberlegenheitbei diesen Tests erkennen, und es fand sich eine rechtsohrige tiberlegenheit fur Nonsenssilben. Diese Ergebnisse.sprechen dafiir,daI3Dyslektiker in ihrer, hemispharischen Dominanz eine geringere Auspriigungbesitzen. Es wurde angenommen, daD dieser Mange1 einer hemisphgrischen kortikalen Dominanz bei der letzterwkihnten Gruppe die Schwierigkeiten beim Buchstabenschreiben erklart.
