Verbal and nonverbal auditory processing among left- and right-handed good readers and reading-disabled children

Nrurop.,);chologla, Vol. 27. No. 11.12. PP. 1357-1371, 1989 Printed m Great Britain.

c

0028-3932’89 $3.00+0.00 1989 Pergamon Pm5 plc

VERBAL AND NONVERBAL AUDITORY PROCESSING AMONG LEFT- AND RIGHT-HANDED GOOD READERS AND READING-DISABLED CHILDREN* JOHN E. OeRzuT,t tCollege

of Education, $Flowing (Rrcuired

PAMELA

F.

CoNRADt and

CAROL

University of Arizona. Tucson, Arizona. Wells Schools, Tucson, Arizona, U.S.A. I I Octohrr

A. BOLIEK$ U.S.A.; and

1988: accepted 10 July 1989)

Abstract-Cerebral lateralization of left- and right-handed good readers and left- and right-handed reading disabled was examined with a sample of 60 children who ranged in age from 7713 years via a dichotic selective attention task (free recall, directed left, directed right) using consonant-vowel (CV) and tonal stimuli. Several ANOVAs were conducted to evaluate gender, reader group, handedness, and stimuli effects of left- and right-ear reports across dichotic conditions. Results indicated males outperformed females across stimuli and conditions regardless of handedness and all subjects recalled more tonal stimuli than CV stimuli. More importantly, the expected REA (left hemisphere processing) was found for CV stimuli only by right-handed good readers across all three dichotic conditions. The left-handed good readers and left-handed reading-disabled children were left ear (LE) dominant in free recall and in the directed left conditon, but were right ear (RE) dominant in the directed right condition. Conversely, right-handed reading-disabled children produced a REA during free recall and directed right conditions, but were LE dominant m the directed left condition. In contrast, a significant LEA (right hemisphere processing) was found for tonal stimuli across all dichotic conditions for all four groups. These findings lend support to the hypothesis that attentional factors have a greater influence on auditory processing of verbal than nonverbal stimuli for various groups of children and also suggest reversed or bilateralized processing abilities for language in strongly left-handed children with sinistral relatives.

MAJOR theories of lateralization have provided the groundwork for various hypotheses about the relationship between cognitive deficits in children and cerebral organization. Briefly, a verbalLnonverba1 or structural theory was proposed by KIMURA [21, 22, 231 which stressed the anatomical differences between the hemispheres at birth from which functional differences could be measured. The attentional-bias or cerebral activation model proposed by KINSBOURNE [25, 271 suggested that asymmetries of perception and performance depend on relative levels of arousal in the two hemispheres such that one or the other dominates processing. M~SCOVITCH 1341 proposed an information-processing theory which suggested that lateralization does not occur at the early sensory input stages of processing but does occur at later or deeper stages of processing. Finally LENNEBERG [32] proposed a developmental or maturational element, whereby the functions of the left hemisphere gradually develop and are well-established by puberty.

*The authors wish to thank the children and teachers of the Tucson Unified School District for their participation and cooperation in the study. $Correspondence should be addressed to John E. Obrzut, Program in Educational Psychology, College of Education, University of Arizona, Tucson, AZ 85721, U.S.A. 1357

1358

JOHN

E. Oe~z~;r, PAMELA F.

COURAII and

CAROLA. BOLI~K

KRASHEN [30] later found that this specialization for language is actually completed by the age of five. However, through systematic study with listening asymmetries, the relationship between cognitive deficits in reading-disabled children and cerebral organization has indicated that exclusive reliance on any one model does not satisfactorily account for all the data. For example, although several early dichotic listening studies reported increases in “ear effect” with age and concluded that reading-disabled children show delays in left hemisphere development [2,43], other investigators have found no developmental trends in normal and reading-disabled subjects ranging in age from 5 to late adolescence [ 19,20, 371. Critical analyses of past studies also reveal that the dichotic listening procedure allows the subject to use his or her own strategies for coping with the tasks. Therefore, it is often difficult to determine if differences in the overall magnitude of the ear advantage between good and poor readers are the result of language lateralization or due to differences in strategies used to deal with perceptual information 131. In this regard, results from recent studies comparing normal and reading/learning-disabled children have indicated that, while normal children are less able to attend to verbal stimuli received in the nondominant ear, reading-disabled children show an attentional bias on dichotic tasks when asked to focus their attention to a particular stimulus [37, 381. However, studies employing this same paradigm have been unable to strictly replicate these results perhaps due to the use of divergent populations. For example, HUGDAHI. and ANDERSON [ 171 compared a group of normal adults with children (mean age 8 years and 10 months) and found a significant REA in both age groups during the free recall and forced-right conditions, but found a marked disparity between the ages during the forced-left condition. In this condition, the adult group revealed significantly more correct responses from the LE input whereas the children did not reveal a significant eardifference during the forced-left condition. With a sample of normal boys and girls, ANIERSSON and HUGDAHL [I] found that during the forced-left condition, boys reported more items from the RE at age 8 but not at age 9, whereas girls reported an equal number of items from both ears at both age levels perhaps indicating that boys show more ability than girls to laterally shift attention. Finally, HUGDAHI. and ANDERSSON [18] found a REA for CV syllables in various reading performance groups during free recall and forced-right recall conditions similar to that found by ORRZUT rt ul. 137, 381. However, unlike the results obtained by Obrzut et al., who found that male children with impaired reading ability reported more correct responses from the LE input during the forced-left condition, these authors found the REA to be more marked in their immature male readers (but not female readers) at age 8 but less so at age 9, especially for boys. Thus, while these results arc somewhat discrepant from those of OBRZXJTet ul. 137,383 likely due to differences in subject populations, the available data do reveal a complex relationship between hemisphere asymmetry, reading ability, gender, and attentional biases than is generally acknowledged in the literature [ 181. Furthermore, it has recently been reported that the type of stimuli used in dichotic studies also affects the magnitude and direction of the ear differences reported [35]. Thus, different stimuli may tap abilities related to attention or auditory short-term memory IJ

11.

Although differences in performance are consistently reported, the research fails to clarify whether these discrepancies are the result of neurological deficits, developmental delays in lateralization, incomplctc cerebral dominance, attentional shifting, or poor information processing. It is likely that the differences are not related to a single causative factor but arc

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1359

the result of the interaction of several factors or deficits that may be characteristic of reading disabilities. While trends in information processing and attentional mechanisms have been identified and validated, the majority of studies have been directed at understanding verbal processing in normal and reading-disabled children. However, a number of investigators have reported robust and reproducible left ear advantages (LEAS) in the perception of dichotically presented pitch and tonal (nonverbal) stimuli among normal adults 17, 8. 9, 10, 121, but research in the perception of nonverbal stimuli with child populations has been virtually nonexistent. Also, noticeably absent from the dichotic literature on cerebral lateralization of normal and reading-disabled children is the question of the influence of handedness on ear preference. The contribution of handedness and familial sinistrality to laterality effects on dichotic listening tasks have produced mixed results. Most studies ofleft-handers thus far have shown right ear preference in adults with no left-handed relatives, but studies with individuals having sinistral relatives have shown either right ear preferences [31], no consistent ear dominance [15], or a smaller right ear preference for verbal stimuli [33]. DEE [4] reported that weak left-handers showed a LEA for verbal, dichotic stimuli whereas strong lefthanders, like right-handers, showed a REA. Other researchers have concluded that it is the strong left-handers who show a LEA in dichotic listening 129,421. DEMAKESTand DEMARFS~ [S. 61 found that strongly left-handed (i.e. familial sinistrality) subjects exhibited a LEA but that moderately lateralized subjects failed to show an ear advantage for verbal material. These researchers also noted that strongly right-handed subjects consistently demonstrated the largest REA. Lastly, HUGDAHL and ANDERSS~N1161 found a significant LEA for sinistral subjects and concluded that right hemisphere dominance for language is not related to a single factor but is dependent on the interaction of handedness, gender, familial sinistrality, and hand posture in writing. ORRZUT et a!. 1361 also reported a LEA in strongly left-handed children for dichotically presented verbal stimuli but found that they were susceptible to attentional shifting. Therefore, right hemisphere processing of language among left-handers may be related to manipulation of attentional strategies. In summary. the research is sparse or nonexistent regarding handedness and right hemisphere processing in reading-disabled children. Neuropsychologically, specific reading disability (i.e. developmental dyslexia) has been conceptualized as resulting from strictly a language or left hemisphere processing deficit. In this light, the present study was designed to provide initial findings and hypotheses about the interactions of handedness and attention on verbal urztl nonverbal processing tasks for both left and right-handed good readers and reading-disabled children.

METHOD SuhjecYs A sample of 60 elementary school students ranging in age from 7 years and 1 month to 12 years and X months (M= 10 years, 5 months; SD= 1 year, 8 months) participated in the study. Thirty reading-disabled subjects (15lcfthanded and 15 right-handed) were matched on the basis ofchronological age and handedness with IS left-handed and I5 right-handed good readers. Table 1 presents the gender, age. and IQ of the subJect pool. The reading-disabled children were selected on the basis of extensive psychoeducational assessments. Standard scores for reading-disabled students, as assessed by the Woodcock Johnson Psychoeducational Battery (WJPB) [46]. were M = 74.X3; SD =9.2X and A4 = 84.80, SD = 1 I .92 for reading and mathematics, respectively. Reading scores were significantly lower than math scores. I (I. 29)=4.36, P
I360

JOHN E. OBKZLT, PAMELA F. CONRAD and CAROL A. BOLIEK

Table

Group Right-handed good readers Left-handed good readers Rtght-handed reading-disabled Left-handed reading-disabled

I. Means and SD for age and IQ by sample groups Gender M F 4 I 9 II

II 8 6 4

IQ

Age M 10.27 IO.47 10.50 10.80

SD

1.40 1.41 I .08 I .69

M

SD

116.27 104.67 97.80 YI .20

9.84 13.76 13.36 8.35

teachers as a result of reading failure. After referral, all 30 students were evaluated by a multidisciplinary team to determine whether students exhibited a pattern of learning disabilities characteristics. Student’s abilities were evaluated using standardized tests, informal test instruments, samples of classroom work, and observations of classroom behavior. Specific abilities assessed included some of the following: (a) academic performance; (b) intelligence; (c)study and work habits: (d) organizational skills: (e) short- and long-term memory; (f) receptive and expressive language skills; and comprehension ability. Additionally, reading-disabled students were defined as students possessing: (a) average intellectual abilities on the WISC-R (FSIQzX5); and (b) demonstrating a significant discrepancy (> 2-year delay) in reading achievement, as delined by IQ/achievement discrepancies of more than one SD. Only subjects who experienced specific reading disabilities of an auditory linguistic nature as determined further by speech and language specialists were included in this sample (see [40] for criteria). Subjects who presented with a profile of visuo-spatial learning deficits were not selected. The good readers were selected on the basis of teacher recommendation, achievement scores in reading ofgreater than the 75th percentile on the district wide administration of the Iowa Test of Basic Skills, and scores ofgreater than 90 on the Peabody Picture Vocabulary Test-Revised (PPVT-R ), a screening measure of receptive vocabulary, which may overestimate general intelligence as measured by more comprehensive test batteries. Teachers described these subjects as above-average readers with strong study skills and consistently good marks in reading. The medical records ofall subjects were initially screened and no subject was included ifheishc had: (a)a htstory of seizures or other neurologic disorders. or (b) a history of speech/hearing impairments. Handedness was established by observing each child’s preference for eight activities included on the Edinburgh Handedness Inventory 1391: writing. cutting with scissors. drawing. using a spoon, using a knife. brushing teeth, throwing a ball. and removing the lid from the box. Both left- and right-handed subjects performed all eight tasks with their dominant hand. In addition. left-handed children were screened for familial sinistrality (F + ) and were only included in the final sample if they had one or both biological parents who were left-handed.

Two dichotic tapes synchronized for onset. duration, and amplitude were used in the dichotic listening task. One tape obtamed from Audiotec of St Louis, consisted of 30 pairs of synthesized consonant vowel (CV) syllables dilfcring only in initial consonant (i.e. ba;da/ka,‘ta,‘pa;ga/) and was used as verbal stimuli. The second tape used as nonverbal stimuli invjolved the serial presentation of two tones. one at 1650 Hz (low) and the other at 1750 Hz (high). This tape was derived from the work of Efron et ctl. [8].* All dichotic stimuli were presented through a TEAC A-2300SX 2-channel tape recorder and were rcccivcd through Koss K-6 stereophonic headphones at a hearing amplitude of 70 dB SPL(A). A calibration tone on the individual dichotic tapes was used to monitor each channel. The ambient noise level was maintained at approx 40 dB SPL(A). The presentation of the CV syllables represented all possible nonidentical pairings of the dichotic stimuli. with an interpair stimulus interval of6 sec. In the tone task, the sequence high;low was heard at one ear and, ~imultaneoualy. the sequence low,‘high was heard at the other ear, the presentation of the 30 dichotic trials 7 randomized bctwccn cars. Although the total set ofstimuli was two, “high- low” vs “low high”, it was assumed that a \uhjcct idcntificd the stimuli on each trial which was most perceptually salient rather than identifying the stimuli through an rnferential process. This assumption is based on task requircmcnts (only one response was requested per trial) and the nature of the stimuli (close spattal separation of speech frequencies).

Each sub.jcct was examined individually in a quiet room. The CV dichotic task was introduced by stating: “You will hear one word in the left ear and another word in the right car at the same time on all trials. It will sound like two pcoplc are talking to you at the same time”. Each child was then shown the list of CV syllables typed on a sheet of paper. After the examiner pronounced the words. the subject was asked to repeat them. The tonal task was introduced by stating: “you will now hear two tones in each car at the same time on all trials. One tone will be higher

*The tone tape was obtained

from M. P. Bryden at the IJniversity

of Waterloo.

Waterloo.

Ontario.

Canada.

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than the other. Yourjob is to tell me whether you heard ‘high low’ or ‘low-high’ tones”. Each child was then given 15 monaural trials to provide practice and to ensure that he or she could make the discrimination between “high” and “low” tones. Most subjects required two or three monaural trials in order to reach 95% accuracy. Three conditions were employed for each of the stimulus tapes in an attempt to assess the child’s ability to direct attention. In the free recall (FR-control) condition, the child was asked to listen to both ears and report what was heard after each stimulus presentation. The second condition involved directing the child to listen only to the left ear (DL) and report what was heard, while the third condition directed attention to the right ear (DR). The order oftrial presentations was counterbalanced for all six possible combinations (FR-DL-DR, FR -DR DL, DR-DL-FR, DR-FR-DL, DL DR-FR, DL-FR-DR). During all trials, children were instructed to maintain their gaze straight ahead (central hemispace). In the CV stimulus presentation, each child was presented with a total of 90 trials, with 30 trials in each condition. There were 15 monaural trials initially given each subject at the beginning of the tonal stimulus presentation, followed by 138 test trials46 per condition. Of these 138 tonal trials, 90 were dichotic and 48 were monaural “catch” trials. These trials were included as a control for guessing and to reinforce the subjects discrimination ability on the dichotic trials. Results were calculated only from the 90 dichotic presentations.

RESULTS Gender differences Preliminary analyses of gender differences were computed using a 2 (Gender) x 2 (Handedness) x 2 (Stimuli) x 3 (Dichotic Condition) x 2 (Ear) analyses of variance (ANOVA) with repeated measures on the last three factors. The factor of reader type (good vs readingdisabled) was not included in this analysis because of unequal numbers of male and female subjects in each reader group. This ANOVA yielded a significant main effect for gender, F(1, 56)=4.07, P
I362

JOHU E. OHRLUT. PAMELA F. COSKAU and CAROL A. BOLIEK

stimuli across all groups and conditions. The main effect for Ear suggests that subjects produced more left ear (LE) than right ear (RE) reports overall, which is related to their better accuracy for tonal stimuli. Because of the central importance found for stimuli as a significant interacting factor in the preceding analyses, subsequent analyses were conducted separately by stimulus type. C‘V stimuli The mean percentage left and right ear correctly reported CV stimuli according to group and dichotic listening condition are reported in Table 2. A 2 Reader Group (good, readingTable 2. Mean percentage

of left and right ear correctly reported condition (N= 60)

Groups Right-handed good readers M SD Left-handed good readers M SD Right-handed reading disabled M SD Left-handed reading disabled M SD

Free recall Left Right

CV stimuli by group

and dichotic

Conditions Directed left Left Right

Directed Left

listening

right Right

29.07 6.94

49.60 9.96

31.33 6.61

43.69 6.42

26.67 7.42

49.27 IO.73

44.93 9.51

33.80 IO.17

46.67 9.93

30.47 X.36

37.20 9.00

39.80 I I.53

27.80 X.66

49.40 9.23

38.53 9.40

37.60

11.65

26.07 9.06

53.60 10.60

42.13 8.63

30.07 8.11

50.07 7.76

26.60 8.85

32.27 7.33

4 I .oo 8.12

disabled) x 2 Handedness (left, right) x 3 Dichotic Condition (free recall, directed left, directed right) x 2 Ear (left, right) ANOVA with repeated measures on the last two factors revealed one main effect, two two-way interactions, and two three-way interactions. The main effect for Ear, F (I, 56) = 7.20, PC 0.009, suggests the presence of a REA across reader groups, handedness, and dichotic conditions. The two-way interactions of Handedness x Ear, F (1, 56)= 63.89, P
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PROCESSING

the collapsed handedness factor) and a strong REA during the directed right condition [Critical Tukey HSD (12, 112) = 7.15, P < 0.011, there was a marked disparity between the reader groups during the directed left condition. In this condition, the good readers did not produce a significant left-right ear difference while the disabled readers produced a LEA (P< 0.01). The differences between the reader groups as a function of dichotic condition and ear report are illustrated in Fig. 1. As shown in this figure, LE report during the directed left Good Readers 65

60 55

m m

T

LeftEar RightEar

t t

II; t 45 z z ;

40 35 30 25 20 Free Recall

Directed Right Condition

Directed Left Condition

Condition

Poor

Readers Left Ear

65 60

m

RightEar

?

55 t;

50

: 2

45

E z & a

40 35 30 25 20 Free Recall

Condition Fig.

I. Mean percentage

Directed Left Condition

Directed Right Condition

correctly recalled CV stimuli from LE and RE for good and poor reader groups across dichotic conditions.

condition was significantly greater than LE report during the directed right condition for good readers (P< 0.05) and for disabled readers (P< 0.0 1). Conversely, RE report during the directed left condition was significantly less than RE report during the directed right condition for both reader groups (PcO.01). However, unlike good readers, the disabled readers produced significantly less LE report during the free recall condition than LE report

1364

JOHN E. OHK~UT, PAMELA F. CONRAD and CAKOL A. B~LIEK

during the directed left condition (P
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AND NONVERBAL

Left-handed

1365

PROCESSIYG

Subjects

65

m

Left Ear

m

Right Ear

60 55

2s 20

Recall Condition

Right-handed

Subjects

65 60

Directed Right Condition

Directed Left Condition

Free

m

Left Ear

@

Right Ear

T

25 20 Free

Recall

Condition Fig. 2. Mean percentage

correctly

brected Left Condition

brected Rlqht Condition

recalled CV stimuli from LE and RF_ for left- and right-handedness groups across dichotic conditions.

of free recall, directed left, and directed right (P < 0.0 1), left-handed good readers produced a LEA during the free recall and directed left conditions (P~0.01). with an absence of an eareffect noted for the directed right condition. Although these left-handed good readers did not show significant differences in RE report across the three conditions. their LE report was significantly greater during the directed left condition as compared to their performance during the directed right condition (P
JOHN E. OHRZLT, PAMFLA E‘. CONLW

1366

and CAROL A. B~LIEK

disabled produced a LEA during free recall and directed left conditions (PcO.01 ), whereas no significant ear-effect was noted in the direct right condition which parallels the findings for left-handed good readers. However, unlike their left-handed good reader counterparts, this group of children significantly increased their RE report from free recall to directed right (P< 0.05) and from directed left to directed right conditions (PC 0.01).

The mean percentage left and right ear correctly reported tonal stimuli according to group and dichotic listening condition are reported in Table 3. A 2 Reader Group (good, disabledreaders) x 2 Handedness (left, right) x 3 Dichotic Condition (free recall, directed left, direct right) x 2 Ear (left, right) ANOVA with repeated measures on the last two factors revealed one main effect, one two-way interaction, and one three-way interaction. The main effect for Ear, F (1, 56)=22.10, P
of left and right ear correctly condition

Groups Right-handed good readers M SD Left-handed good readers M SD Right-handed reading disabled M SD Left-handed reading disabled M SD

reported (N=60)

tonal stimuli by group

Free recall Left Right

Conditions Directed left Left Right

and dichotic

Directed Left

listening

right Right

6X.67 21.24

31.27 21.24

64.00 18.65

35.53 18.65

61.93 21.83

3x.00 21.83

48.80 18.91

51.20 18.91

56.87 24.40

43.13 24.40

53.21 19.16

46.13 19.16

61.67 9.10

38.33 9.10

63.20 13.14

36.80 13.14

54.87 16.61

45.13 16.61

59.53 II.19

40.47 Il.19

61.87 10.20

38.13 10.20

56.21 12.01

43.13 12.01

handedness, and dichotic conditions. The significant two-way interaction found between Condition and Ear, P (2, 112)=4.42, PcO.01, indicates that although LE report was significantly greater than RE report during all three conditions, Critical Tukey HSD (6, I 12) = 8.18, PC 0.01, the largest between-ear difference was found during the directed left condition (P
VEKBAL

AN,,

,iONVEKBAL

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1367

conditions. The significant two-way interaction found between condition and ear, F (2, ! 12) = 4.43, P < 0.01, suggests that the largest between-ear difference was found in the directed left condition [Critical Tukey HSD (6, 112)= 8.21, P
DISCUSSION In this study gender differences indicated that overall, males correctly reported more stimuli than did females regardless of dichotic condition or handedness group. However. while males outperformed females in the processing of CV stimuli, no differences were found in the processing of tonal stimuli. These findings are somewhat discrepant from those of ANDERSSON and HUGDAHL [l] for the processing of CV stimuli who reported that their boys showed a significant REA for CV stimuli at age 8, but not at age 9, while the girls showed neither a REA nor a LEA at eigher age, during a dichotic forced left condition. But similar to the present findings, ANDERSSONand HUGDAHL [l] found no gender differences during the free recall or directed right conditions. Based on overall analyses of the five factorial ANOVA for reader group. handedness, and stimuli differences, it was evident that children recalled more tonal stimuli than CV stimuli across all groups and conditions. Apparently these tonal stimuli were easier to process for all subjects and thus supports the hypothesis suggested earlier by OBRZUT ~‘t al. [35] that perceptual asymmetries can be strongly influenced by the type of stimulus material presented for processing. Based on the initial analyses of CV data, the two- and three-way interactions suggested that left- and right- ear reports were different for the reader and handedness groups and varied across the three conditions. However, the lack of a significant four-way interaction precluded the evaluation of left- and right-ear reports for reader and handedness groups as interacting factors independent and unconfounded of one another. Thus, with handedness as a unitary factor. the Reader Group x Condition x Ear interaction suggested that there was a marked disparity between good and disabled readers only during the directed left condition. While the disabled readers produced a LEA, good readers did not evidence a left-right ear difference. In addition, reading-disabled children produced less RE report during free recall than RE report during the directed right condition. In general more differences in LE and RE performances were evident for reading-disabled than for good readers across attentional conditions. On the other hand, with reader group as a unitary factor, the Handedness x Condition x Ear interaction suggested that right-handed children displayed the expected REA in all but the directed left condition, while left-handed children displayed the LEA in all but the directed right condition. These findings lend support to previous work 1361 which also found that when right-handers are directed rightward the effect of attention is greater than when they are directed leftward. Conversely, when left-handers are directed leftward the effect of attention is greater than when they are directed rightward. It appears that when the factors of reader group and handedness are evaluated separately as was the case with the two three-way interactions (see Figs 1 and 2), the handedness factor (less variability in performance) has a more robust effect than does the reader group factor (more variability in performance) in understanding the dynamic relationship between attention and its effect on perceptual asymmetries. However, conceptually, it is perhaps wiser to discuss in some detail the elrect

136X

JOHN E. OHKLUT.

PAMLLA

F. CO\KALI

and

CAROL

A.

BOLIEK

when reader group and handedness were logically combined. A very different picture then emerges. From this perspective, right-handed good readers exhibited a strong tendency to report the verbal stimuli in the right ear and this tendency was resistant to attentional manipulation. Directing attention produced no significant change in ear report which supports the overall RE bias in the processing of verbal stimuli and is consistent with previous dichotic studies using directed attention with children who are right-handed good readers (e.g. 137,381) (but see [18]). Therefore, right-handed good readers may have a strong underlying structure for processing language-based information in the left hemisphere. Left-handed good readers produced a consistent LEA for CV stimuli during the free recall and directed left conditions. However, they were able to increase their RE responses during the directed right condition, thus producing equivalent LE and RE performances. This increased RE report suggests that attentional manipulation may be responsible for the increased efficiency of the left hemisphere in the directed right condition. Unlike the righthanded good readers these findings suggest that left and right hemisphere processing varied significantly depending upon the attentional condition. Therefore, right hemisphere processing of language among left-handed good readers may be related to attentional strategies or manipulation [36]. As a group, the left-handers were able to attend to verbal stimuli received in their nondominant ear which was not found to the same degree in the right-handed good reader group. These results also support earlier studies which found that a large proportion of lcfthanded adults are either bilateral or right hemisphere dominant for language function [3, 411. Additionally, DEMARESTand DEMAREST[6] reported that left-handers having sinistral relatives exhibited this reversed laterality on dichotic words tasks. Thus. the data further suggest that right hemisphere dominance for language (LEA) may be related to degree of lefthandedness and familial sinistrality. For example. E. Warrington (INS, Atlanta, 1981) after studying individuals with speech dominance ascertained following ECT or by the sodium Amytal technique, has suggested that the dichotic ear advantage varies with handedness rather than speech lateralization. Thus, although these left-handed good readers appear to have reversed hemispheric dominance for verbal processing (right hemisphere), the LEA may be reflective more of their handedness. However, the data could also support the attentional theory of cerebral lateralization 124. 26,281. Although no strong theoretical position is proposed in the literature, this sensitivity to attentional strategies may be interpreted as resulting from the bilateral representation of language functioning in strongly left-handed subjects [ 14, 441. The right-handed reading-disabled group did not demonstrate a consistent REA across all experimental conditions as did their right-handed good reader counterparts. Left and right hemisphere processing varied depending on the attentional conditions. Previous studies of learning-disabled children have also found that this group is able to shift attention to the left car in verbal dichotic experiments 137. 381. Left-handed reading-disabled children produced a consistent LEA for CV stimuli during the free recall and directed left conditions. But like the left-handed good readers, the lefthanded reading-disabled group was able to shift their attention to the RE during the directed right condition, thus producing no ear differences. However, this shift in performance was greater than was found for the left-handed good reader group. The demonstrated ability to shift attention from the free recall to the directed attention condition more nearly parallels the results from the right-handed reading-disabled subjects, albeit in the opposite direction.

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Although the right hemisphere may be responsible for processing of verbal stimuli in strongly left-handed reading-disabled children, this group was more sensitive to attentional strategies, as were their right-handed reading-disabled counterparts. Thus, reading-disabled children, regardless of handedness in this context, appear to be more susceptible to attentional strategies which may suggest a lesser ability to suppress the nondominant hemisphere when required. The outcomes from this study provide theoretical implications in the neuropsychological functioning of the four groups of children. The results dramatically separate the right-handed good readers from the other groups in terms of their consistent ear report across directed attention conditions for CV stimuli. The findings from the remaining three groups (lefthanded good readers, left- and right-handed reading-disabled) suggest that their performances during the CV experiment were perhaps varied as a result ofeither their handedness or reading ability. The consistent LEA reported for nonverbal (tonal) stimuli across conditions by righthanded good readers is comparable to several previous dichotic pitch recognition studies using right-handed adults [7, 8, 12, 4.51. However, the overall percentages for this group (93% LEA and 7% REA) are much higher than those previously reported by GREGORY[ 121 where of 222 subjects, 75% were LE dominant and 20% were RE dominant. Directing attention during the tonal task produced no significant changes in ear report which supports the overall LE bias in the processing of dichotically presented tonal stimuli. The consistent LEA produced by these right-handed good readers supports the theoretical position that there may be anatomical and functional asymmetries in the primary and auditory association cortex which results in hemispheric specialization directed toward the right hemisphere when subjects are presented with a dichotic pitch recognition task. Individual subject differences which were evident in this study as well as in previous experiments may be related to what EFRON rt ul. [S]. call second- and third-order anatomical and functional brain asymmetries. When tonal stimuli were presented to left-handed good readers, there was a consistent LEA reported across conditions, similar to that found with previous studies of right-handed adults which utilized the tonal stimuli paradigm [S]. However, no studies have attempted to investigate handedness as a factor in nonverbal auditory processing. Response to dichotically presented tonal stimuli by the right-handed reading-disabled group was similar to that of the left- and right-handed good readers and thus did not differ in ear report of simple tones. Investigation into the nonverbal processing of left-handed reading-disabled children resulted in the same consistent LEA across conditions, which was also reported for the three previous groups. There are at least two theoretical views which may explain the results of the nonverbal data (i.e. tonal stimuli) in this study. One view would suggest that the right hemisphere is more efficient than the left in the processing of tonal stimuli in right- and lefthanded good and poor reader groups. However, an alternative view as to why subjects report the tonal sequence presented to the LE more often than they report the RE tonal sequence, regardless of focused attention condition, has been suggested by GREGORY et al. [ 131. These authors have presented evidence to show that if binaural fusion of acoustic information occurs at a brain stem level, then selective attention for input to one or the other ear could not possibly occur. Thus, the fact that directing attention did not produce significant changes in right/left performance asymmetries with these dichotic tonal stimuli which have relatively small values of frequency difference (i.e. 1650 vs 2750 Hz), may be expected.

1370

JOHN E. O~IKZU~. PAMELA F. CohRAt) and CAKOL A. BOLIEK

This study has provided initial findings on the nonverbal processing of anomalous groups of children. It is particularly important to stress the lack of significant differences between groups and the overall LEA for tonal stimuli. While previous dichotic studies have shown significant differences in the auditory processing of verbal information between good readers and reading-disabled children, this study hypothesizes that right hemisphere processing is generally unaffected by left hemisphere dysfunction and that neither handedness nor attentional manipulation affects these results for any of the groups. This strongly suggests that the source of the reading-disabled child’s difficulties may be primarily in the inability of either the left or the right hemisphere to assume a dominant role in the processing of only verbal information.

REFERENCES I. AYUEKSSO~, B. and HLGIIAHL, K. Effects of sex, age. and forced attention on dichotic listening in children: a longitudinal study. Der. ~Veuropsgcho/. 3, 19 I 206, 1987. 2. BLKLIN, C. I., Hu(;H~s, L. F., Lowt-BALL. S. S. and B~KLIN,H. L. Dichotic right ear advantage in children 5 to 13. Cortr% 9, 3Y3 401. 1973. 3. BKYI)IIN, M. P. Lateralif~: Functio,~u/ Asymmerry 111the In!trc/ Bruin.Academic Press, New York, IYXZ. 4. DIIE, H. L. Auditory asymmetry and strength of manual preference. Corlcu 7, 236 245, 1971. 5. DEMAKIX, L. and DI:MAKEST,J. Auditory asymmetry and strength of manual prcfcrcncc rc-cxamincd. Inr. J. Nwmwi. II, 121 124, 19X0. 6. D~MAKEST,L. and D~MAKEST.J. The interaction of handedness. familial sinistrality and sex on the performance of a dichotic listening task. ht. J. Nwrosci. 14, 7 13, 1981. 7. EPKON,R., CKANUALL, P. H., Koss, B., DIV~NYI, P. L. and YLNII. E. W. Central auditory processing. 111. The “cocktail party” effect and anterior temporal lobectomy. RrcCn Laru~. 19, 254- 263, 1983a. 8. E~KON, R., Koss. B. and YIJNII. E. W. Central auditory processing. Bruin Lany. 19, 264 2X2, lY83b. 9. E+RON, R. and YUNU, E. W. Dichotic competition of simultaneous tone bursts of different frequency I. Dissociation of pitch from lateralization and loudness. Nrurops?c,hologiu 12, 249 256, 1974. 10. E);KoN, R. and YUNL), E. W. A model for the relative salience of the pitch of pure tones presented dichotically. J. Auuisr. SIC. Am. 62, 607-617, 1977. Il. Gtbctu. G. The development bf the right ear advantage in dichotic listening with focused attention. (‘orfr.x 14, 169 177. 197x. 12. GKF.(;OKY, A. H. Ear dominance for pitch. Neurops~~holoyiu 20, 89 90. 1982. 13. GK~GOKY,A. H., E~KON. R.. DIVEI\;YI,P. L. and Yuri~). E. W. Central auditory processing: I. Ear dominance a perceptual or an attentional asymmetry’? Rririn Lump. 19, 225- 236, 1983. 14. H~~AEN. H. and SAUGLI~T.J. Ccrcbral dominance in left-handed subjects. Cortru 7, 19 4X. 1071. 15. HI(;C;FUHOTTAN, J. A. Relationships between sets of lateral and perceptual preference measures. Cor/uu 9, 402 409, 1973. 16. HU~;IIAHI., K. and A~UEKSSON. L. A dichotlc hstening study of differences in cerebral organization in dcxtral and sinistral subjects. C’orrez 20, 135 141, 1984. 17. HUC;I)AHI., K. and ANIXKSSON, B. The “forced-attention paradigm” m dlchotic listening to CV-syllables: a comparison between adults and children. C’orrrr 22, 417432, 1986. 18. HUGDAHI., K. and AYIIERSSO&,L. Dichotic listening and reading acquisition in children: a one-year follow-up. J. (,/in. ~Veurqycltol. 9, 631 649. 1987. 19. HYNI). G. W. and OHKZI:T, J. E. Effects of grade level and sex on the magnitude of the dichotic listening advantage. ,YPurops?.~ko/ogia 15, 6X9-692, 1977. 20. HYNI). G. W., OHKZLT, J. E.. WEED, W. and HYUII, C. R. Development of cerebral dominance: dichotic listening asymmetry in normal and learning-disabled children. J. ezp. Child Psycho/. 28, 445 454, 1979. 21. KIM\ KA, D. Cerebral dominance and the perception of verbal stimuli. Gun. J. Psychol. 15, I66 171, lY6la. 22. KIMLKA. D. Some effects of temporal lobe damage on auditory perception. Gun. J. P.sd~ol. 15, I56 165, I961 b. 23. KIM~ K~Z.D. Functional asymmetry of the brain in dichotic listening. C’orte.u 3, 163 178, 1967. 24. KINSBOLKSI:. M. The cerebral basis of lateral asymmetries in attention. Acttr f.sychokqin 33, 193 201. 1970. 25. KI~SBOLKSI:. M. The control ofattention by interaction between the hemispheres. In Afrenrion und Prrfmwxuwr II’, S. KORNBLUM(Editor). Academic Press, New York, 1973. 26. KINSHOLKNI:. M. Mechanisms of hemispheric interaction in man. In Hrwxsphuric~ Disconnrcrion und C‘errhrul Fmc/ion. M. KI~S~OLKNT and W E. SMITH(Editors). Thomas. Springfield, IL, 1974. 27. KINSHOUNL. M. The mechanism of hemispheric control of the lateral gradient of attention. In A~~L’II~~ou unrl prrfmwnntc~ C.. P. M. A. RABBITS and S. DOKYI~ (Editors). Academic Press, New York, 1975.

VERBAL AND NONVERBAL PROCESSlNG

1371

28. KINSBOURNE, M. and HISCOCK, M. Cerebral lateralization and cognitive development: conceptual and methodological issues. In Neuropsycholoyical Assessment and the School-age Child: I.ssues and Procedures, G. W. HYNU and J. F. OBRZUT (Editors), pp. 125 ~166. Grune & Stratton, Inc., New York, 1981. 29. KNOX, A. W. and BOONE, D. R. Auditory laterality and tested handedness. Cortex 6, 164 173. 1970. 30. KKASHEN. S. Lateralization. language learning and the critical period: some new evidence. Languczge Learning 23, 63-14, 1973. 31. LAKE, D. A. and BRYDEN, M. P. Handedness and sex differences in hemispheric asymmetry. Brain Lang. 3, 266~m282,1976. 32. LENNEBEKG, E. H. Biological Foundations of Language. John Wiley, New York, 1967. 33. LLSHMAK, W. A. and MTMEEKAN, E. R. L. Handedness in reaction to direction and degree of cerebral dominance for language. Cortrv 13, 30 43, 1977. 34. MOSTOVITCH, M. Information processing and the cerebral hemispheres. In Handbook qf 5rhariorul Neurobiology, M. S. GAZZAP;IGA (Editor). Plenum Press, New York, 1979. 35. OBKZUT, J. E., BOLIEK, C. A. and OBRZIX. A. The effect of stimulus type and directed attention on dichotic listening with children. J. cup. Child Psycho!. 41, 198- 209, 1986. 36. OIIKLUT, J. E., COYRAD, P. F., BKYDEN,M. P. and BOLIEK, C. A. Cued dichotic listening with right-handed. lefthanded, bilingual and learning-disabled children. Nruropsycholoyia 26, 119- 13 1, 1988. 37. OBRZUT, J. E.. HYNU. G. W., OBKZU~, A. and P~ROZ~OLO, F. J. Effect of directed attention on cerebral asymmetries in normal and learning disabled children. ner. Psycho!. 17, 118 125. 1981. 38. OHRZL~T, J. E., OBRZUT, A., BRYDEN. M. P. and BARTELS, S. G. Information processing and speech lateralization in learning-disabled children. Brain Long. 25, 87~-101, 1985. 39. OLDFIELD. R. C. The assessment and analysis of handedness: The Edinburgh Inventory. Neurops!,~holo~ia 9, 97 113,1971. 40. PIKIZZOLO. F. J. Language and brain: neuropsychological aspects of developmental reading disability. School Psychohqy Retiew IO, 35@-355. 1981. 41. RASMUSSEN, R. and MILNER, B. The role ofearly left-brain injury in determining lateraliaation ofcerebral speech functions. Arm/s. N. Y. Acad. Sci. 229, 355-369, 1977. 42. SATZ. P. ACHENBATH, K. and FENNELL. E. Correlations between assessed manual laterality and predicted speech laterality in a normal population. Neuropsychologia 5, 295 310, 1967. 43. SATZ, R., RARLXN, D. and ROSS, J. An evaluation of a theory of specific developmental dyslexia. Child Dec.. 42, 2009~ 2021, 1971. 44. SHECHAN. E. P. and %ITH, H. V. Cerebral laterahzation and handedness and their effects on verbal and spatial reasoning. Neuropsycho/ogia 24, 531 540, 1986. 45. SILXIS. J. J. The complex tone test: implications for assessment of auditory laterality effects. N~ump.s~~ho/o~~cr 19, 103-112, 1981. 46. WOOIXOCK, R. W. and JOHKSON, M. B. Woodcock -Johnson P.s~~hordur,atiorla/ Buttery. DLM Teaching Resources. Allen, Texas. 1977.