Information processing and speech lateralization in learning-disabled children

BRAIN

AND

LANGUAGE

25, 87-101 (1985)

Information Processing and Speech Lateralization in Learning-Disabled Children JOHN E. OBRZUT University

of Arizona

ANN OBRZUT Greeley

School

District

Six

M. P. BRYDEN University

of Waterloo

AND

SHARONG. BARTELS University

of Northern

Colorado

The relationship between information processing and speech lateralization was investigated in learning-disabled children. The Kaufman Assessment Battery for Children (K-ABC) assessed simultaneous and successive processing while a dichotic listening paradigm with free recall and directed attention conditions assessed speech lateralization. A three-factor ANOVA design conducted on the dichotic data revealed that normal children demonstrated stronger right ear advantage (REA); whereas learning-disabled showed weaker right ear advantage. Further, A analyses conducted on individual subjects revealed that the learning-disabled did not demonstrate the REA, were not biased attenders, and did not get more right ear than left ear items when attention was directed to one ear. Multipleregression analysis was used to predict sequential processing from the dichotic data for both groups. Learning-disabled children demonstrated a substantial deficit in sequential processing as compared to normal children. These results indicate that learning-disabled children may not have adequate cerebral laterahzation of The authors thank the children and teachers of the Greeley Public Schools for their participation and cooperation in the study. Requests for reprints should be addressed to John E. Obrzut, Department of Educational Psychology, University of Arizona, Tucson, AZ 85721. 87 0093-934X184 $3.00 Copyright 8 1985 by Academic Press. Inc. All rights of reproduction in any form reserved.

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receptive speech processes, shift their attention more readily, and are more inadequate in sequential processing that presumably subserves language functioning. Perhaps learning-disabled children have deficiencies of processor capacity of salient areas of the left (language) hemisphere. o 1985 Academic PRSS, IW.

Since Kimura’s (1961) initial work, the dichotic technique has been employed in many experiments as a measure of speech lateralization for both adults and children. In children, however, findings are often inconsistent. While the right ear advantage (REA) has been found for groups of normal children (e.g., Hiscock & Kinsbourne, 1980; Hynd & Obrzut, 1977), mixed results are often found for clinical groups of children. For example, Zurif and Carson (1970) found that their poor readers did not demonstrate the REA whereas Sparrow and Satz (1970) reported evidence that dyslexic children do demonstrate a right-ear (RE) superiority in recall. Carefully selected groups of learning-disabled children also seem to demonstrate the REA but to lesser extent than that reported for normals (Corballis, 1983; Hynd, Obrzut, Weed, & Hynd, 1979; Naylor, 1980; Obrzut, Hynd, Obrzut, & Leitgeb, 1980; Obrzut, Hynd, Obrzut, & Pirozzolo, 1981). These discrepant findings have led researchers to alter and refine the dichotic listening methodology in an attempt to control the variance in the observed REA (e.g., Bryden, Munhall, & Allard, 1983). In the recent past the role of directed or focused attention in children’s dichotic listening performance has been investigated (Geffen, 1978; Hiscock & Kinsbourne, 1980; Obrzut et al., 1981; Obrzut, Hynd, & Obrzut, 1983). Directed attention procedures in particular allow the experimenter to study the factor of attentional bias on the observed right ear effect. While learning-disabled children have been found to increase correct recognition of left and right ear presentations upon cue from the examiner, normal children produced a REA independent of cued instructions (Obrzut et al., 1981). These results can be interpreted as indicating that learningdisabled children are lateralized for lower order speech representation but are more susceptible to attentional bias than normal controls. Similar to the findings with normal control children, Dean and Hua (1982) found that cued attention had little effect on the observed REA for right-handed adults. However, subjects in the left-handed and mixed groups significantly improved their report of stimuli presented to the directed ear. Thus it appears that children and adults who display less consistent patterns of lateral preference may be more affected by attentional instructions. It is not entirely clear whether the observed laterality effects are primarily due to attentional bias or to an asymmetry of perceptual discrimination. Further, learning-disabled children are more likely to be bilateralized for language, which, in turn, may affect their style of information processing. In the past, researchers have used various paradigms of sensory integration to study information processing in learning-disabled and retarded

INFORMATION

PROCESSING

89

readers (Birch & Belmont, 1964, 1965; Muehl & Kremenak, 1966; Sterritt & Rudnick, 1966). In general, these studies have demonstrated the irrelevance of sensory modality or cross-modal transfer and emphasized the importance of translation of information from space to time or vice versa (Bauserman & Obrzut, 1981; Blank, Weider, & Bridger, 1968; Bryden, 1972; Goodnow, 1971; Obrzut, 1979; Rude1 & Denckla, 1976; Sterritt & Rudnick, 1966). In fact, Luria (1973) has suggested that information is processed in a sequential (temporal) or simultaneous (spatial) manner and that there is a diminishing specificity of sensory modality in the hierarchical structure of the brain. As the previous findings suggested, it is the stimulus characteristics (spatial or temporal) that determine whether information is processed in a simultaneous or sequential manner. Furthermore, empirical evidence from studies has suggested a continuum of difficulty level depending upon whether the task is spatial, temporal, or both (Rudnick, Martin, & Sterritt, 1972; Sterritt, Martin, & Rudnick, 1971). These studies and others have indicated that the factor of integration appears to be of little significance in determining test difficulty for children but that the sheer addition of temporal stimuli heightens the difficulty level of task demands (Bauserman & Obrzut, 1981; Bryden, 1972). For example, Bauserman & Obrzut (1981) studied subtypes of reading disabled classified on the basis of Boder’s (1973) criteria and found that dysphonetic and alexic readers had most difficulty when matching purely temporal information. These authors concluded that matching abilities were less related to integration ability than to an ability to sequence temporal information. This study attempted to test the hypotheses that learning-disabled children are more susceptible to attentional bias and use differential information-processing styles. The investigation employed a dichotic listening paradigm with free recall and directed attention conditions and assessed simultaneous and sequential processing (Das, Kirby, & Jarman, 1975; Luria, 1966) via the new Kaufman Assessment Battery for Children (K-ABC) (Kaufman & Kaufman, 1983). According to the K-ABC “simultaneous processing” measures the ability to integrate and synthesize information that is spatial while “sequential processing” measures the ability for ordering stimuli in a sequential or serial order.’ It was also hypothesized that learning-disabled children would vary from normal children on simultaneous and sequential processing tasks. METHOD

Subjects A sample of 32 middle-class students ranging in age from 7 years, 8 months to 12 years, 1 month participated in the study. Sixteen subjects (14 male, 2 female) officially placed in ’ The authors are aware that the K-ABC is a new measure and that the construct validity of the processing scales has not yet been firmly established.

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learning-disabled programs were matched with normal subjects on the basis of chronological age and gender. The learning-disabled children were classified on the basis of an extensive psychoeducational assessment. They demonstrated at least average intellectual potential on the Wechsler Intelligence Scale for Children-Revised (WISC-R); the mean IQ quotients were Verbal x = 88.19 (SD = 13.34); Performance x = 99.81 (SD = 13.91); Full ScaleX = 93.06 (SD = 12.12). All of these subjects demonstrated a significant discrepancy (3 2-year delay) in school achievement. In addition, the learning-disabled children demonstrated a significant discrepancy between their verbal and performance IQs with a mean difference (x = 15.75) in favor of performance abilities. This sample also experienced specific reading disability and could be characterized as the auditory-linguistic dyslexic, as described by Pirozzolo (1979). The normal subjects were selected on the basis of teacher recommendation, achievement scores, and WISC-R scores. All normal children scored above the 50th percentile on the Metropolitan Achievement Test. They were described by teachers as above average readers. Mean IQ quotients on the WISC-R were Verbal x = 115.69 (SD = 8.52); Performance x = 119.88 (SD = 12.40); Full Scale x = 119.81 (SD = 8.88). In order to verify a priori group selection, a discriminant analysis was conducted utilizing the experimental data. All subjects were correctly classified into the learning-disabled or normal groups with no misclassifications present. Handedness was established by observing the hand each child used in eight activities selected from the Edinburgh Handedness Inventory (Oldfield, 1971): writing, cutting with scissors, drawing, using a spoon, using a knife, brushing teeth, throwing a ball, and removing the lid from a box. All subjects preferred the right hand, using a cutoff of five out of eight activities being performed by the right hand. Mean laterality quotients (LQ) were as follows: learning-disabled students LQ = 93.75 (SD = 11.18); normal students LQ = 98.44 (SD = 6.25). All subjects were required to pass a pure-tone audiometric screening test conducted at 20 dB (A) at 5000-4000 Hz.

Materials

and Apparatus

A dichotic tape prepared at Kresge Hearing Research Laboratory, New Orleans, Louisiana, was used in the dichotic listening task. Thirty pairs of synthesized consonant-vowel (CV) syllables (ba/ka/da/pa/ga/ta) were presented through a TEAC A-2300SX two-channel tape recorder. The test stimuli were received through KOSS K-6 stereophonic headphones at a hearing amplitude of 55 dB. A calibration tone on the tape recorder was used to monitor each channel. The ambient noise level was 40 dB. The presentation of the CV syllables represented all possible nonidentical pairings of the dichotic stimuli, with an interpair interval of 6 sec. The K-ABC (Kaufman & Kaufman, 1983) was administered to all subjects. This is an individually administered measure of intelligence and achievement based on theories researched by neuropsychologists, cognitive psychologists, and cerebral specialization researchers (Bogen, 1969; Gazzaniga, 1975) suggesting that the left hemisphere is lateralized for analytic, sequential, and logic processing; whereas the right hemisphere is lateralized for gestalt or holistic processing. The K-ABC uses normalized standard scores with a mean of 100 and a standard deviation of 15 on the global scales. Four global scales are computed: Sequential Processing, Simultaneous Processing, Mental Processing Composite, and Achievement. This new scale purports to measure mental or information processing with the sequential and simultaneous processing scales. The work of Luria (1973) and the factor analytic studies of Das et al. (1975) underlie the development of the processing scales. Sequential processing involves sequencing or temporal ordering of information; whereas, simultaneous processing refers to the synthesis of separate elements into groups or gestalts (Das et al., 1975).

INFORMATION

91

PROCESSING

Procedure A certified school psychologist administered all the procedures (dichotic listening, WISCR, K-ABC). Each subject was examined individually in a quiet room free from external noise and distraction. Each child was presented a strip of tagboard on which the CV syllables were presented for the dichotic task. The examiner then pronounced each CV syllable with the subject repeating it orally, All subjects received the following instructions: “You will hear a word in one ear (right) and another in the opposite ear (left), and it will sound like two people are talking to you at the same time.” Three practice trials were given to confirm comprehension of directions. In an attempt to assess each subject’s ability to direct attention, three sets of the 30 trials were given. One condition involved free recall (FR), another involved a directed right ear report (DR), and a third condition reflected the directed left ear report (DL). The order of trial presentation 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). An example of the directed conditions involved instructing the child to report what was heard only in the right ear, then this ear was touched. In addition, hemispatial body field (i.e., hemispace) was controlled for by having each subject maintain their lateral gaze to the external space to the right of body midline (Bowers & Heilman, 1980). In the event the children did not maintain their lateral gaze, they were visually signaled to redirect their gaze to the directed side. After the entire 30 trials were completed, the tape was rewound and the same directions were used for the directed left condition with appropriate control for left hemispatial body field. In the case of free recall, the child was instructed to listen very carefully and report only one response per trial.

RESULTS

Table 1 presents the mean number of correctly reported CV syllables according to diagnostic group and dichotic listening condition. A 2 group (normal vs. learning disabled) x 3 dichotic condition (free recall x directed right x directed left) x 2 ear presentation (right vs. left) ANOVA with repeated measures on the last factor was conducted. Results of the ANOVA revealed two main effects and two interactions. There was a significant group difference, F(1, 60) = 4.70, p < .05, with the normal children demonstrating an overall greater dichotic recall than the learning-disabled group. The main effect for ear, F( 1, 60) = 8.98, p TABLE MEANS

AND

STANDARD

DEVIATIONS DIAGNOSTIC

GROUP

Free recall Group Normal x SD

Learning disabled B SD

1

OF CORRECTLY AND

REPORTED

DIRECTED

CV

SYLLABLES

FOR EAR

BY

CONDITION

Directed left

Directed right

LE

RE

LE

RE

LE

RE

9.88 2.80

13.81 2.37

9.81 2.10

12.75 2.11

8.63 3.61

15.31 4.69

10.38 3.16

11.62 3.14

11.50

9.63 3.03

10.19 3.15

Il.56 3.05

3.32

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ET AL.

< .Ol, suggests the presence of a REA although the foregoing needs to be interpreted in light of the significant group x ear interaction, F(1, 60) = 7.20, p < .Ol. An analysis of simple effects, F(1, 60) = 4.06, p < .05, reflected the REA in the normal group, suggesting the presence of left hemisphere lateralization for language with this group. In contrast, the learning-disabled group did not demonstrate a consistent REA under all dichotic conditions, as they reported more CV syllables from the left ear (LEA) under the directed left condition. The significant condition x ear interaction, F(1) 90) = 7.01, p < .Ol, suggests that the stability of the REA is affected by the condition of directing attention. An analysis of simple effects with this interaction, F(2, 90) = 4.09, p < .05, indicates that the REA was apparent under all three dichotic conditions for the normal group, but not under the directed left condition for the learningdisabled group. The learning-disabled group’s inability to maintain the REA under this condition accounted for the interaction. The fact that the normal subjects demonstrated the REA under the directed conditions appears to support the structural hypothesis of cerebral asymmetry. In contrast, the learning-disabled children’s performance may suggest a susceptibility to attentional bias and perhaps poorer lateralization of receptive speech processes. The data were also analyzed using the recently developed laterality index (A) by Bryden and Sprott (1981). This index makes use of the data from each trial and provides a test of significance on each subject as well as on the group as a whole. The laterality question is simply whether more correct responses are given from the right ear than the left ear. Each subject in the free recall condition received 30 trials and were required to give one response per trial. Thus, the appropriate A index is defined as A = ln(R/L). Using the mean A coefficient, normal children demonstrated a right ear superiority (x = 0.358), whereas the learning disabled did not (x = 0.126). The two groups, however, were not significantly different, t(30) = 1.38, n.s. Although the limited number of trials precludes the individuals from reaching strong significance levels, five normals showed significant REAs while two learning-disabled children showed significance in each direction, given a criterion of ? 1 SD (z score). These data summarized in Table 2. The second analysis can be viewed as a signal detection task and determined whether or not normal and learning-disabled children were more effective when attending to one ear than to the other; did they get more items correct that were actually presented when attending right as opposed to attending left? In this analysis, any item reported that had actually been presented was scored a “hit.” Thus, the laterality index is defined as A = ln(hits R/misses R) - ln(hits L/misses L) or A = (hits R x misses L)/(hits L x misses R). A “miss” was considered to be any incorrect response: thus both omissions and incorrect responses were classified as misses.

INFORMATION TABLE PERFORMANCE

OF NORMAL

AND

93

PROCESSING 2

LEARNING-DISABLED

CHILDREN

ON DICHOTIC

FREE

RECALL

Correct responses Group Normal

x Learning disabled

x

Left ear

Right ear

x

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

7 12 12 13 11 7 9 14 9 I 12 I 9 14 10 5 9.88

14 11 14 13 15 14 14 11 15 15 8 15 14 14 15 19 13.81

0.693** - 0.087 0.154 0.000 0.310 0.693** 0.442 -0.241 0.470 0.762** - 0.405 0.762** 0.442 0.000 0.405 1.335** 0.358

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

8 10 8 12 11 5 8 14 9 10 13 17 13 9 6 13 10.38

13 13 11 13 9 19 16 7 13 9 8 8 12 12 10 13 11.62

0.486 0.262 0.318 0.080 -0.201 1.335** 0.693** -0.693* 0.367 -0.105 - 0.486 -0.753* - 0.080 0.287 0.511 0.000 0.126

Subject

* Significant LEA. ** Significant REA.

This might best be termed a “detection” A. Table 3 shows the data for individual subjects with corresponding mean A values for groups. From this table, it appears that although some subjects seemed to do better when attending to one ear, (normals: 3 REA and 1 LEA; learning disabled: 2 REA and 1 LEA), a significant overall bias did not appear to be present. Mean A coefficients indicated that normal children (x = 0.457) did not

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TABLE PERFORMANCE

OF NORMAL

AND LEARNING-DISABLED STIMULI WITH DIRECTED

3 CHILDREN ATTENTION

ON DETECTION

Correct responses

Group Normal

Intrusions

Directed left both ears

Directed right both ears

A

Directed left both ears

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

23 22 23 23 25 26 21 24 22 21 23 17 27 23 18 23 22.56

22 21 16 29 29 24 26 23 22 25 25 17 25 29 26 24 29.93

-0.178 -0.164 - 1.056* 2.178** 1.758 - 0.486 1.025 -0.197 0.000 0.762 0.420 0.000 - 0.588 2.178** 1.466** 0.197 0.457

7 8 7 7 5 4 9 6 8 9 7 13 3 7 12 7 7.43

8 9 14 1 1 6 4 7 8 5 5 13 5 1 4 6 6.06

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

22 23 17 13 20 21 26 21 21 20 20 25 26 21 18 24 21.12

20 22 24 21 19 21 20 19 18 20 21 26 29 25 17 26 21.75

0.318 - 0.178 2.094** 1.116** -0.147 0.000 - 1.179* - 0.300 -0.442 0.000 0.154 0.262 1.495 0.762 -0.137 0.486 0.229

8 7 13 17 10 9 4 9 9 10 10 5 4 9 12 6 8.87

10 8 6 9 11 9 10 11 12 10 9 4 1 5 13 4 8.25

Subject

x Learning disabled

OF DICHOTIC

x * Significant LEA. ** Significant REA.

-

Directed right both ears

INFORMATION

PROCESSING

95

differ from learning-disabled (x = 0.229), t(30) = 0.71, n.s., children. However, there was a slight trend for children to do better when attending to the RE that when attending to the LE, as evidenced by the overall positive mean A. The final analysis determined whether or not normal and learningdisabled children demonstrated an overall asymmetry in the directed attention conditions. That is, of the items they identified in these conditions, did they get more from the LE or the RE? For this, the RE A ratio is ln(RR/RL), the LE h is ln(LL/LR). Thus the laterality index is defined as A = ln(RR x LR/LL x RL). It is perhaps best termed a “localization” A. Table 4 shows the mean A values for normal (x = 0.937) and learningdisabled (X = 0.028) groups. As with the more conventional analyses, normal children showed a clear REA, while learning disabled did not, t(30) = 2.57, p < .05. Inspection of the data for individuals indicated that six of the normal children showed significant REAs, while two learning-disabled children showed a REA and one showed a LEA. In effect, this suggests that of the items that were identified correctly, the majority came from the RE in normals, but this pattern was not found to be as strong in learning disabled. To examine the potential relationships between the criterion variable of (K-ABC) processing style and the predictor variables of dichotic report two multiple regression analyses were conducted. The first regression analysis compared the dichotic report (FR-LE, FR-RE, DR-LE, DRRE, DL-LE, DL-RE) data to the K-ABC simultaneous scores for all subjects and revealed nonsignificant findings, F(6, 25) = .27, p < .95, R2 = .06. This suggests that the dichotic data does not explain or predict variance in the simultaneous processing style. These results are consistent with theoretical expectations in that one would not anticipate association between lateralization of speech processes (left hemisphere and simultaneous processing thought to be associated with the right hemisphere). The second regression analysis compared the dichotic performance for all subjects to the sequential processing scores. A significant R* = .40, F(6, 25) = 2.73, p < .05, revealed a relationship between sequential processing and various dichotic report conditions. A forward selection procedure was utilized to develop a model that maximized the unique contribution of the dichotic predictor variables. The best three variable model included DL-RE report, R2 = .32, F(1, 30) = 13.66, p < .Ol; DR-RE report, R2 = .35, F(2, 29) = 5.15, p < .Ol; and DR-LE, R2 = .37, F(3, 28) = 5.55, p < .Ol. The RE report under the DL condition explained more variance in sequential processing than any other dichotic variable. The RE and LE reports, respectively, under the DR condition were second and third in predicting sequential processing. The remaining dichotic report conditions did not offer any further information in explaining

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TABLE PERFORMANCE

Group Normal

Subject 1 2 4 5 6

x

4

OF NORMAL AND LEARNING-DISABLED DICHOTIC STIMULI WITH DIRECTED

8 9 10 11 12 13 14 15 16

Learning disabled

8 9 10 11 12 13 14 15 16 x * Significant LEA. ** Significant REA.

CHILDREN ON LOCALIZATION ATTENTION

OF

Correct responses directed left ear

Correct responses directed right ear

LE

RE

LE

RE

h

12 11 10 11 10 9 7 8 10 9 12 7 15 10 8 8 9.81

11 11 13 12 15 17 14 16 12 12 11 10 12 13 10 15 12.75

9 11 7 16 7 7 1 9 11 10 12 7 9 13 5 4 8.63

13 10 9 13 22 17 25 14 11 15 13 10 16 16 21 20 15.31

0.281 -0.096 0.514 0.121 1.551** 1.523** 3.912** 1.135** 0.182 0.693 - 0.007 0.713 0.352 01470 1.658** 2.238** 0.937

13 15 11 3 14 5 11 15 11 10 12 14 14 11 12 13 11.50

9 8 6 10 6 16 15 6 10 10 8 11 12 10 6 11 9.63

5 10 11 9 10 5 7 15 8 9 11 14 16 11 10 12 10.19

15 12 13 12 9 16 13 4 10 11 10 12 13 14 7 14 11.56

0.731 -0.446 -0.439 1.492** 0.953 2.326** 0.929 - 2.238* 0.128 0.201 - 0.501 - 0.395 - 0.362 0.146 - 1.050 -0.013 - 0.028

INFORMATION

97

PROCESSING

variance in this processing style. The finding of a strong RE report under the DL condition supports the structural hypothesis of cerebral lateralization for speech processes. In effect, the REA is directly related to sequential processing but not to simultaneous processing. Sequential processing has been associated with the left hemisphere as has the REA with dichotic speech stimuli. The fact that the relationship in this data was strongest between sequential processing and the REA, even under a DL condition, offers construct validity for the K-ABC Sequential Processing scale and supports the invariance of cerebral lateralization for linguistic processes. To further explore the variable of K-ABC processing style, a 2 group (normal vs. learning disabled) x 2 processing style (simultaneous vs. sequential) ANOVA was conducted. Table 5 shows the means for the K-ABC processing scales x group. Main effects for group, F(l, 30) = 31.51, p < .OOOl, and processing style, F(1, 30) = 38.46, p < .OOOl, were found. A Scheffe post hoc analysis, F(1, 60) = 4.00, p < .05, revealed that the learning-disabled group had a significantly poorer performance on both processing scales than did the normal group. A second Scheffe post hoc analysis, F(1, 60) = 4.00, p < .05’, revealed that the results of the sequential processing scale were lower for both groups than the simultaneous processing scale. The learning-disabled group’s poorer performance on the processing scales in general and the sequential processing scale specifically is supportive of the dichotic findings suggesting a deficiency in this group’s sequential information processing. DISCUSSION

The present study examined the relation between laterality effects as measured by dichotic report under free recall or directed attention and information-processing styles as measured by the K-ABC with normal and learning-disabled children. Results of the free recall data replicate those of earlier studies demonstrating that normal children show a strong REA (Hynd et al., 1979; Obrzut et al., 1980, 1981) whereas the learning disabled demonstrate a weaker REA. One explanation for these differences TABLE MEANS

AND

STANDARD

PROCESSING

Group Normal x SD

Learning disabled x SD

5

DEVIATIONS SCALES

FOR K-ABC

BY GROUP

Simultaneous

Sequential

133.563 9.061

117.375 19.083

120.188 22.250

77.0625 21.103

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ET AL.

is the structural theory of cerebral lateralization for language processes (Kimura, 1961). This theory predicts that the left hemisphere is prewired for language and that weakness may lead to poorer asymmetry of perceptual discrimination as found in the learning disabled. Another hypothesis may be that learning disabled function with inadequate suppression of the nondominant hemisphere. Kinsbourne’s (1970, 1973) model of selective attention for hemisphere specialization states that activation of one hemisphere turns attention toward the opposite side and, at the same time, decreases activation of the other hemisphere (Leong, 1980). Results of the dichotic directed attention indicated that while normal children demonstrate the REA in both the directed left and directed right conditions, learning-disabled children appear to be more affected by attentional instructions. Upon cuing, these subjects shifted attention to the left or right ear and demonstrated improved recognition of the directed stimuli. Rather than showing the strong REA under free recall and directed conditions as do normal children, learning-disabled children displayed weaker REAs in both dichotic conditions. Since the dichotic task has been considered an index of cerebral lateralization for language, these findings support the conclusion that the learning disabled may have poorer lateralization of receptive speech processes. The A indices were employed as a means of examining the data for each individual subject as well as the group data. These analyses allow the experimenter to ask additional questions regarding laterality effects. As with the more conventional analysis of free recall, normal children demonstrated the REA while learning-disabled children did not consistently display the REA, and the groups were not significantly different, although the general pattern for the REA is present. On an individual basis, five normals showed significant REAs, while two learning disabled showed significance in each direction (see Table 2). These results indicate that when attention is focused by instruction or when a detection procedure is employed, major individual differences in dichotic performance are observed. Thus the data seem to have both pragmatic and theoretical implications. The directed attention data were also used to classify individual subjects as biased or unbiased attenders. A biased attender is one who makes many more intrusion errors from one ear than from the other, while an unbiased attender is one who has approximately the same intrusion rate when attending to the left ear as when attending to the right (Bryden et al., 1983). Although some subjects (see Table 3) seem to do better when attending to one ear, there was no significant overall difference in bias between normal and learning-disabled children. However, there was a slight trend for children to do better when attending to the RE than when attending to the LE. The results also provided information about left-right differences in

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99

normal and learning-disabled children when these subjects were asked to identify items from the attended and unattended ears. As a group, normal children recalled more RE items than learning-disabled children. On an individual basis, six normal children showed the REA while only two learning-disabled demonstrated the REA and one a LEA (see Table 4). Since the majority came from the RE in normals but not in the learning disabled, this may be evidence for a perceptual primacy effect for the RE in normals and not in the learning disabled. Perhaps learning-disabled children evidence poorer lateralization of receptive speech processes. Rather than being a spatial bias in attention as Kinsboume (1975) described, such an effect may be indicative of a consistent right ear superiority in the normal group but not in the learning-disabled group. Overall, inspection of the data reveals that while the normal children show a much larger REA than the learning disabled, the attention instructions have a different effect on performance of the two groups. In learning-disabled children, the directed right and free recall data yield the same results, suggesting that in free recall these children are already devoting as much attention to the right as possible. In the normal group, the free recall data are similar to the directed left data and there is a switch to the stronger REA as shown in the directed right data. This suggests that the normal children have an inherent REA and can improve it, while the learning disabled do not have the REA and have difficulty creating one. Bryden et al. (1983) found evidence that attentional factors were a major contributor to the laterality effect observed in dichotic listening of normal subjects. The present study further provides evidence that learning-disabled children are more susceptible to attentional factors, which in turn may cause these children to perform cognitive type tasks in an inefficient manner. The considerable variability of the learningdisabled children on these tasks may also be related to inefficient information processing. The K-ABC data provided some evidence as to how normal and learningdisabled children process information on a cognitive level. A comparison of group differences points out that the learning disabled were less proficient in both simultaneous and sequential information processing than normal children. Furthermore, they were specifically inadequate in the sequential processing of information. Analysis exploring potential relationships between dichotic performance and sequential processing revealed that the normal group’s invariant right ear report and the directed right conditions with both groups explained this processing style. The primary conclusions from these data suggest that learning-disabled subjects may not be as lateralized for speech discrimination processes as are normal children. Also, learning-disabled children were susceptible to attentional bias and were inadequate in sequential processing that

100

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ET AL.

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