Lateral preference in six to nine year old children: Relationships to language lateralization and cognitive ability

LATERAL PREFERENCE IN SIX TO NINE YEAR OLD CHILDREN: RELATIONSHIPS TO LANGUAGE LATERALIZATION AND COGNITIVE ABILITY JOHN KERSHNERAND MARTA CHYCZIJ UNIVERSITY OF TORONTO

ABSTRACT: Lateral preferences in hand, foot, eye, and ear are known to undergo significant increases in dextrality sometime between six and 15 years of age. The study investigated the age range horn six to nine for evidence of such changes and tested whether individual differences in lateral preference were related either to hemispheric specialization for language or to cognitive ability. Measures of lateral preference, dichotic listening, verbal reasoning, and school grades were obtained in 227 normally achieving children. Increased dextrality was found between eight and nine years in foot preference and in hand and foot congruency. Except for a weak relationship to handedness, age-invariant language lateralization was psychometrically independent of (1) lateral preference and (2) all cross-preference coordinations, i.e., hand-eye. Superior cognitive ability was found in right handed males with right ear and left eye preference but in right handed females with left ear and right eye preference. The results (1) demonstrate an important link between motor development and cognitive ability and (2) suggest cautiously that the linkage may be mediated by gender differences in the cortical organization of the output pathways controlling lateral head turn, handedness, and eye preference.

Children in the first several years of school are exposed to a complex network of formal educational demands requiring the elaboration of new intellectual, social, and physical skills. Children first become aware of their learning potential as well as their educational weaknesses relative to their peers. Coincidentally, morphometric studies of human cerebral cortex during early development have shown that synaptic density (area 17) undergoes prolonged postnatal developDimd all correspondence to: John Kershner, Ontario Institute for Studies in Education, University of Toronto, 252 Bloor St. West. Tomnto, Ontario, Canada M5S 1V6. Leaminp and Individual DWemnces, Volume 4, Number 4, 1992, pages 347-367. All riohtiof

raomduction in anv form reserved.

Copyright 0 1992 by JAI Press, Inc. ISSN: 1041-6060

348

LEARNING

AND INDIVIDUAL

DIFFERENCES

MLUME

4, NUMBER

4.1992

mental pruning, not reaching a decrease to the adult level (50-60s of maximum) until eleven years of age (Huttenlocher 1990). Pruning or per-unit-volume, synapse reduction occurs during brain maturation as neurons compete for finer and finer interneuronal connectivity. It seems reasonable to assume that the dynamic socio-biological period between six and nine years of age may involve increased asymmetrical responses from the paired sense organs and limbs and increases in cross-modal coordinations. For instance, one could speculate that the fine-motor and intellectual requirements of written language may produce greater asymmetrical reliance on the preferred hand and increased ipsilateral hand and eye preference. Participation in organized sports may result in greater sided alignment for hand and foot, or eye and ear use, and so on. In addition, as Kinsbourne (1988) has pointed out, much faith has been placed in the “classical” Ortonian (1937) thesis that the more lateralized (usually the right) pattern of coordination is the more competent intellectually. Moreover, it is common in current practice for any deviation from dextrality, especially in hand and eye preference, to be taken as evidence of a developmental abnormality (Croft & Yeo 1990; Whittington & Richards 1987). However, only a few studies in this formative age range have investigated aspects of sensory-motor lateralization in relationship to cognitive growth. Comparing preschool children with young adults, Coren, Porac, and Duncan (1981) reported developmental increases in the lateral concordance (consistency or agreement across modes in the direction of lateralization) of hand, foot, eye, and ear and increased dextrality in hand, eye, and ear. Unfortunately, no six to nine year olds were in the sample, leaving the question unanswered as to whether the observed changes may have occurred in grades one through four. Cognitive measurements also were not a part of the study. Handedness experiments including six to nine year olds do indicate that no significant relationship exists in this period between manual preference and cognitive ability (Fennel, Satz, & Morris 1983; Hardyck, Petrinovich, & Goldman 1976; Kaufman, Zalma, & Kaufman 1978; McManus, Sik, Cole, Mellon, Wong, & Kloss 1988). Nevertheless, more complex sidedness-cognition relationships may be found in handedness coordinations with other modalities. Although Ullman (1977) was unable to find a relationship between lateral concordance (hand, foot, eye) and cognitive skills, the study did not look at cognitive performance relative to the congruence between specific pair-wise modalities, i.e., hand-foot; hand-ear; hand-eye; etc. And, finally, none of the lateral concordance studies included measures of cerebral dominance for language; thus, we have no information on possible correlations between multi-mode sensory-motor asymmetries and hemispheric asymmetries for speech. It is apparent that we have very little scientific knowledge of the potential importance of individual differences in sensory-motor preferences during the early school years. The purposes of the present study were to: (1) examine age trends in sensorymotor lateralization in children from six to nine years of age; (2) test for correlations between sensory-motor lateralization and hemispheric lateralization for receptive speech; and (3) test for relationships between sensory-motor lateraliza-

LATERALPREFERENCE/NSIXTO NINEYEAR OLD CHILDREN

349

tion patterns and cognitive ability. The relationship of language iateralization to cognitive ability is the subject of a separate paper (Kershner & Chyczij 1991) and will not be addressed .here in any detail. Our main conclusion was that the children’s cognitive level was related to their efficiency in laterally controlling the direction of attention. Cognitive ability was unrelated to language lateralization.

METHODS

Principals and teachers in three urban schools selected 227 children from grades one, two, three, and four as representative of a normal population. All children were included except those perceived to be in need of, or receiving, special education. The children were Caucasian and represented a cross-section of socioeconomic levels. English was the main language spoken at home in all cases. The sample was comprised of 54 six year olds (M = 79.24 months, SD = 3.38); 55 seven year olds (M = 90.22 months, SD = 3.52); 60 eight year olds (M = 102.17 months, SD = 2.99); and 58 nine year olds (M = 115.55 months, SD = 3.33). There were 110 males and 117 females who were distributed about equally within each grade.

MEASURESAND PROCEDURES Sensory-Motor Lateralization. The D-K Scale of Lateral Dominance (Dusewicz & Kershner 1969)‘ a seventeen item scale consisting of five behavioral measures of hand, foot, and eye preference and two measures of ear preference, was used in individual testing. Each hand, foot, and eye task is given twice and the ear tasks are given three times to a total of 36 test observations. During standardization, the tasks were selected on the basis of high point-biserial correlations and task variability from an original 54-item list. Based on 109 elementary pupils from grades two to six, a split-half reliability coefficient, corrected according to the Spea~an-Brown prophecy formula, of 0.98 was obtained. The Scale assessed the magnitude and direction of lateral usage in each modality. Hand, foot, and auditory preference (HP, FP, AI’) were measured through simple behavioral tasks that typically require a choice in sidedness. The lateral preference measures are summarized in Table 1. The order of the tasks was randomized on an individual basis and the same order was followed in the repeat administrations. Each child’s score in each modality was calculated in percentage, (R - L/R + L) x 100, where R and L = right and left. Scores range from -100 to +lOO, with negative scores indicating left preference and positive scores indicating right preference.

350

LEARNING AND lNDlVlDUAL

Performance

Foot

Eye

4. 1992

Behavioral Observation 1. 2. 3. 4. 5.

Picks up comb to comb hair. Picks up scissors and cuts paper. Picks up pencil and writes name Picks up ball and throws overhand. Rapidly writes columns of numbers

1. 2. 3. 4. 5.

Kicks ball placed on the floor. Stamps out imaginary fire with foot. Stands on one foot. Stands on toes of one foot with eyes closed. Hops on one foot across room.

1.

Looks Looks Looks Looks Sights

2. 3. 4. 5. Ear

VOLUME 4. NUMBER

TABLE 1 Measures of Lateral Preference

Modality Hand

DIFFERENCES

I. 2.

through a hole in through a hole in through telescope through telescope along index finger

simultaneously

with both hands.

card to identify far-point object. card to identify near-point object. to identify far-point object. to identify near-point object. toward the experimenter.

Sits at desk with a watch placed face down on the desk-top and selects one ear for placement close to the watch to count the number of ticks. The above task is repeated with the experimenter tapping the underside of the desk.

Language Lateralization. For language lateralization, a standard, selective listening dichotic procedure was used with triad strings of digit pairs as stimuli (Kershner & Morton 1990). With ear order counterbalanced by age and gender, each child received twenty trials (ten trials per ear) presented dichotically for immediate recall from the attended ear. In individual testing, the triad pairs were presented at the rate of two pairs per set with a twelve set interval between trials. Dichotic raw scores were transformed using the natural log lambda coefficient recommended by Bryden and Sprott (1981). The lambda ratio of correct responses (C) and intrusions (I) from the left ear (LE) and the right ear (RE) reflects each subject’s overall linguistic lateralization, (A) = Ln [(RC)(RI)/ (LC)(LI)] in a single score. A positive score indicates an RE advantage (REA) and by inference a left hemisphere verbal advantage. A negative score indicates an LE advantage (LEA) and by inference a right hemisphere linguistic superiority. COGNITIVE ABILITY Two measures of cognitive ability were obtained. The first, a measure of abstract intelligence, consisted of the Verbal battery from the Canadian Cognitive Abilities Test (CCAT) (Thorndike & Hagen 1974) which evolved from the Lorge-Thorndike Intelligence Tests series, modified and standardized in Canada. Factor analysis has shown that the Verbal scale contains an abstract reasoning factor and a word knowledge factor. The CCAT is group-administered and yields verbal intelligence scores with a M of 100 and a SD of 16.

lATERAL PREFERENCE IN SIX TO NINE YEAR Oil? CtNDREN

351

Based on the CaT$ the children were divided into three ability levels: VerbafIow (M = 79X, SD = 7.81); Verbal-average fM = 101.80, SD = 5.06); and Verbaihigh (M = 122.13, SD = 9.48). Teacher grades (TRG) were used as the second estimate of cognitive ability. A TRG was obtained for each child in January of the school year for Reading, Oral language, and Math. Teachers gave each child a grade-level rating to the nearest quartile (i.e., .OO,25, .50, .?5) which were then converted to a grade difference score by subtracting the actual grade placement from the earned grade. Thus .OO indicates average perfarmance; a negative sign indicates below grade-level performance; and a positive sign indicates above grade-level performance. Preliminary analyses showed that there were no differences according to subject area; so the TRG scores for each child were averaged into one TRG, representing the child’s overall academic achievement in Ianguage and math. The children were divided into three TRG achievement levels: TRG-low (M = -42, SD = -31); TRGaverage (M = -00, SD = .04); TRG-high (M = .35, SD = .23).

RESULTS LATERAL PREFERENCE AS A CONTINUOUS MEASURE (feneraf ~~~~rl~~~ RW&S. The lateral preference battery theoretically gives approximations to continuous measures for Hand (HP), Foot (FP), Eye (VP)l and Ear (AP), The MS and SDS for the preference indices and dichotic listening index as a function of age and gender are reported in Table 2. Visual inspection shows a rightward bias on each measure, especially handedness among the lateral preference indices. Unfortunately, ~lmogorov-~rni~ov Goodness of Fit Tests disclosed sig~~~n~y non-normal ~s~bu~ons in each lateral preference measure, Zs = 3.05 to 7.25, all ps < .OOOl.The distributian of scores was skewed to the extremes, particularly to the right and less so to the left, in HP, FP, and VP, In AP, a majority of children either selected one ear (left or right) consistently or they alternated auditory preference systematically between tasks. Consequently, the AI? index produced three categorical outcomes: 100% left; 100% right; or undecided. These data characteristics precluded the application of correlational and multiple regression analyses. Hence, we were restricted in the examination of lateral preference as a quasi-continuous measure to the use of the fixed-effect model of analysis of variance (ANOVA& which is not heavily dependent upon the assumption of normal distributions (Hays 1963). Latent! Ptefwence ~la~~u~h~~s to Diehtiic Listening and Cognitive AMitya Analyses with lateral preference as a continuous dependent measure failed to detect any relationships either to dichotic listening or to cognitive ability.

352

LEARNING AND INDIVIDUAL

Lateral Preference Group

DIFFERENCES

VOIJJME 4. NUMBER 4. 1992

TABLE 2 and Dichotic Listening Indices by Age and Gender Hand

Foot

Eye

M SD

73.85 60.87

29.23 74.45

9.23 97.69

Female N = 28

M SD

74.29 63.68

25.00 58.53

7 year Olds Male N = 28

M

SD

90.71 30.54

M SD

8 year Olds Male N = 31

Ear

Dichotic

50.00

81.24

1.17 1.05

29.29 92.29

30.36 80.90

0.53 1.37

40.71 52.03

39.29 89.03

17.86 90.49

0.67 0.93

84.44 45.18

17.78 60.34

33.33 92.15

33.33 78.45

0.62 1.05

M SD

63.87 70.32

16.77 66.15

-03.87 90.98

35.48 83.86

1.12 1.22

Female N = 29

M SD

80.69 53.05

31.72 58.44

31.03 96.75

27.59 88.22

0.31 I .58

9 year Olds Male N = 25

M SD

73.60 59.08

55.20 52.05

45.60 86.32

24.00 83.07

0.82 1.27

Female N = 33

M SD

91.52 21.23

61.21 49.48

14.55 90.59

15.15 79.54

0.60 1.16

Total Male N = 110

M SD

75.27 57.53

34.55 62.83

21.46 92.22

31.82 84.52

0.95 1.13

Female N = 117

M SD

83.08 47.39

35.21 58.35

26.50 92.02

26.07 81.10

0.52 1.29

6 year Olds Male N = 26

Female N = 27

Age Trends. An Age (6, 7, 8, 9) by Gender (Male, Female) ANOVA on the dichotic listening lambda index showed only a main effect for Gender, F (1,225) = 7.23, p < .Ol. This effect was produced by an age invariant greater REA in the males. However, an Age (6, 7, 8, 9) by Gender (Male, Female) by Verbal ability (Low, Medium, High) MANOVA with HP, FP, VP, and AI’ as dependent variables resulted in a significant multivariate Age effect, Wilks F (12,529) = 2.13, p < .05. Follow-up univariate tests revealed a significant Age effect for FP, F (3,203) = 3.53, p < .05, and a Tukey post-hoc comparison showed that a significant increase in right FP occurred between eight and nine years of age. There were no significant interaction effects. The sample’s average developmental trends on all four preference measures are displayed in Fig. 1. To summarize, all analyses with lateral preference as a continuous measure were compromised to some extent by skewed, non-normal distributions of lateral preference. With due caution for the high probability of Type II errors, the

353

LATERAL PREFERENCEIN SIX TO NINE YEAR OLLJCHILDREN

FIGURE 1 Mean age trends in lateral preference as a continuous

measure.

lone significant effect of importance, which does appear to be reliable, was a developmental (cross-sectional) increase in dextrality in foot preference at nine years of age. Thus, it appears that a more sensitive approach to data analysis may be to treat lateral preference as a categorical measure.

LATERAL PREFERENCE AS A CATEGORICAL MEASURE General Descriptive Results. Table 3 shows the number of children with left preference and right preference, split at .OO, and also divided at -90 to -1 and + 1 to +90. Chi square comparisons, with Yates correction, in each modality between the number with right preference compared to all others showed a statistically significant dextral bias in HP, x2 (1) = 136.46, p < .OOl; in FP, x2 (1) = 20.37, p < .OOl; and in VP, x2 (1) = 12.85, p < .OOl. In Al’, the proportion with right preference was just above half of the sample and included a comparatively high number of children in the undecided category. Such results suggest that the

354

LEARNING

Number of Children Categorically

Modalities Hand Foot Eye EaI

AND INDMDUAL

DIFFERENCES

TABLE 3 Showing Left, Undecided,

MLIJME 4, NUMBER

4.1992

and Right Lateral Preference

_

*

+

Proportion Left

100% Left

90 to I Left

00

1 to 90 Right

100% Right

Proportion Right

.II .34 .31 .24

II 06 72 54

13 71 13 00

01 02 01 54

14 70 18 00

188 78 123 119

.89 .65 .62 .52

auditory modality may involve more complex neurological mechanisms and more dynamic decision processes in comparison to the purer motor systems subserving hand, foot, and eye performance. There were 24 children who to some degree were left handed, which is consistent with the 11% left handedness reported by McManus, et al. (1988) with a sample of 314 children aged three to nine. Also, with the exception of FP, the percentage demonstrating right preference was almost identical to the prevalence figures reported by (a) Coren, et al. (1981) in West coast Canadian children, aged three to five years old, and (b) Longini and Orsini (1988) in a sample of four to six year olds in Italy. Table 4 contains a comparison of these distributions across studies. Congruent and crossed preferences between modality pairs were assessed by placing a child (a) in the congruent (same side) category if both indices were O and (b) in the crossed category if the two indices failed to agree or were on different sides. Because of the rightward skewness of the lateral preference distributions the chance prevalence of congruence between any two modalities exceeds 50%. Hence, to evaluate the significance of congruent and crossed preferences, as suggested by Coren, et al. (1981), the observed frequencies were compared to theoretically expected values, calculated on the assumption that side preferences for any pair of modalities are independent events. Comparisons of the obtained vs. expected congruence values, presented in Table 5, failed to indicate any significant deviations from chance (all Zs = ~1.96, ps > .05). Such TABLE 4 Comparison of the Present Percentage Distributions of Right Handedness with Cohen, et al. (1981) and Longini and Orsini (1988)

Modality Hand Foot Eye Ear

Present Study 6 to 9 yr. olds N = 227

Cohen, et al. (1981) 3 to 5 y. olds N = 384

Longini & Orsini (1988) 4 to 6 y. olds N = 271

.89 .65 .62 .52

.94 .77 .61 .52

.91 .87 .60 .60

355

bITERAL PREFERENCE IN SIX TON/NE YEAR OLD CHILDREN

TABLE 5 Percentage of Congruency of Lateral Preference

Modality

Obtained Rate of Congruency

Theorefical Expectation of Congruency

Hand-foot Hand-eye Hand-ear Foot-eye Foot-ear Eye-ear

65.7 63.9 49.8 58.6 45.8 45.8

61.6 59.4 51.6 53.6 50.6 50.4

negative results also are consistent with Coren, et al. (1981) and Longini and Orsini (1988), with the exception of the higher than expected congruency rate for eye-ear that was reported in both previous studies but not replicated here. Table 6 contains a further breakdown of the congruent and crossed categories. This sub-categorization shows (a) a greater frequency of consistent dextrality in the congruent groups (b) relatively greater right, left vs. left, right combinations in Hand-foot, Hand-eye, and Hand-ear and (c) nearly equal numbers of right, left vs. left, right in the Foot-eye, Foot-ear, and Eye-ear combinations. None of these sub-categories deviated from chance. Finally, the large number (n = 54) of undecided children in Al’ was examined separately to determine whether they should constitute a third category. In AI’, Laterality Group (~0, 0, >O) by Age (6, 7, 8, 9) by Gender (Male, Female) ANOVAs on Verbal ability, TRG, and dichotic listening failed to produce any significant effects. Thus, the undecided in Al’ were not treated as a unique group. And, this justifies their inclusion in the crossed pair-wise combinations.

Lateral Preference and Dichotic Listening. In each lateral preference modality, the children were divided into two groups of those demonstrating right sidedness (>O) and those who were sinistral or undecided (50). Lateral Preference Group (SO, >O) by Gender (Male, Female) ANOVAs were performed for HP, FP, VP,

Percentage of Congruent

TABLE 6 and Crossed Sub-categories

of Lateral Preference

Modalities

RightRight

LeftLeft

RightLeft

LeftRight

Either one Undecided

Hand-foot Hand-eye Hand-ear Foot-eye Foot-ear Eye-ear

60 58 48 43 37 37

05 06 02 15 09 12

29 31 21 22 14 16

05 04 05 19 16 11

01 01 24 01 24 24

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LEARNING AND INDIVIDUAL

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VOLUME 4. NUMBER

4, 1992

and Al’ with the dichotic lambda scores as the dependent measure. No significant Laterality Group main effects or interactions were found. The only effect to approach significance was for HP, F (1,223) = 2.36, p = .12, produced by a marginally greater REA in the right handed children. Speech lateralization is known to be more strongly represented in the left hemisphere in right handers (Kinsbourne 1988); therefore we can assume that the HP effect would have reached significance had we included a larger number of left handers. The relationship between pair-wise congruence in preference and dichotic listening was evaluated by computing Laterality Group (Congruent, Crossed) by Gender (Male, Female) ANOVAs for hand-foot, hand-eye, hand-ear, foot-eye, foot-ear, and eye-ear pairs with dichotic listening as the dependent measure. The results failed to show any significant Lateral@ Group main effects or interactions.

Age Trends. In each modality,

Lateral Preference (5, >O) by Age (6, 7, 8, 9) comparisons showed no significant variation in preference categories across ages, x2(3) = all ps >.05, for any of the indices. To assess gender differences, Age (6, 7, 8, 9) by Gender (Male, Female) comparisons on the proportion who were dextral showed no significant variation between genders, x2(3) = all ps > .05. However, to follow-up the eight to nine year old increase in the strength of right FP (as a continuous measure) a comparison between the combined six, seven, and eight year olds vs. the nine year olds in FP, with Yates correction, demonstrated a higher proportion of right footed children in the nine year olds, x2(1) = 6.03, p = .Ol. In the younger subjects, n = 102 > 0 and n = 67 5 0; while the nine year olds had n = 46 > 0 and n = 12 1. Thus, excluding FP, Table 3 represents the distribution of lateral preference categories at each age and in each gender. In FP, the percentage right shifted from 60% at six, seven, and eight to 79% at age nine. The possibility of finding developmental changes in the laterality congruency rates in Table 5 is limited to those pairs involving FP because FP was the only single modality to undergo an age effect. Laterality Group (Congruent, Crossed) by Age (6, 7, 8, 9) comparisons in hand-foot, foot-eye, and foot-ear revealed an increase in hand-foot congruency at age nine, x2(1), with Yates correction, = 4.48, p = .03. Comparison of the obtained rate of hand-foot congruency at age nine (74.1) with the expected sample frequency (61.6) produced a statistically significant difference, Z = 4.08, p, .OOl. There were no gender effects. Moreover, this increased hand-foot congruency could only have come about by a decrease in the right hand-left foot sub-category and not by a decrease in the left handright foot sub-category.

lateral Preference Relationship to Cognitive Ability. Preliminary evidence modality, computed variables.

analyses showed no for age interactions; so the data were collapsed over years. In each Laterality Group (50, >O) by Gender (Male, Female) MANOVAs were for HP, FP, VP, and AI’ with Verbal ability and TRG as the dependent MS and SDS are presented in Table 7. No significant effects emerged

357

LATERAL PREFERENCE IN SIX TO NINE YEAR OLLI CHILDREN

TABLE 7 MS and SDS for Verbal Ability a and Teacher Grade@ in Right Sided and Nonright Sided Children Teacher Grades

Verbal Ability GrOUpS

Hand

Foot

Eye

Ear

Hand

Foot

Eye

105.2

106.7

104.2

106.8

-.02

-.02

-.08

16.2

17.4

16.9

17.9

94

73

66

61

105.6

105.5

107.6

103.4

14.9

15.7

15.1

16.2

75

75

58

108.5

103.7

107.9

104.3

.06

.oo

.08

16.9

14.0

15.3

14.1

.37

.37

.38

16

37

44

49

107.4

106.1

Ear

Males (R)=

M SD N

.39

.39 73

94

.04

.37 66

.35 61

Females (R)c

M SD N

108

.oo

-.02

.42 108

.03

.46 75

- .03

.43 75

.38 58

Males (NR)d

M SD N

16

37

44

-.07 .42 49

Females (NR)’

M SD N

18.7 9

102.3

107.9

14.23

14.9

13.9

42

42

59

“Canadian Cognitive Abilities Test (Tbomdike & Hagen 1974). bA discrepancy score based on the eanne&grade minus actual-grades, ‘(R) = Right Sided. “(NR) = Nonright Sided.

.06

.04 .44 9

-.04

42

.04

.40

.35 42

.46 59

in quartiles. where .oO = average.

for HP, FP, or Al’. Significant effects were found in VP. The VP by Gender multivariate effect was significant, Wilks F (2,222) = 3.08, p < .05. Both univariate effects were significant: Verbal ability, F (1,223) = 4.38, p < .05; and TRG, F (1,223) = 4.39, p < .05. However, a Visual Laterality Group (50, >O) by Gender ANOVA on TRG with the Verbal scores as covariates showed that the two effects were not independent, F (1,222) = 1.77, p = .18. The disordinal VP by Verbal interaction is depicted in Fig. 2. Superior Verbal ability (and academic achievement) was shown by males who preferred their left eye and by females with right eye preference [Critical Tukey HSD (4,222) = 2.141. To examine congruency among index pairs, Laterality Group (Congruent, Crossed) by Gender MANOVAs were computed for hand-foot, hand-eye, handear, foot-eye, foot-ear, and eye-ear with Verbal ability and TRG as dependent variables. MS and SDS are shown in Tables 8 and 9. The only significant multivariate effect occurred in hand-ear, Wilks F (2,222) = 3.14, p < .05. Both univariate effects were significant: Verbal ability, F (1,223) = 4.41, p < .05, and TRG, F (2,222) = 4.37, p = c.05. Again, however, with the Verbal scores as covariates TRG was no longer significant, F (1,222) = 1.86, p = .17. The disordinal hand-ear congruence by Verbal interaction is shown in Fig. 3. Superior Verbal ability (and academic grades) was shown by males with congruent hand-ear preference and

LEARNING AND INDIVIDUAL

350

DIFFERENCES

FIGURE 2 Mean verbal scores by eye preference

WLUME

4. NUMBER 4,1992

and gender.

1081

107-

106-

106-

104-

103-

102

*

Female

1

by females with crossed hand-ear preference [Critical Tukey HSD (4,222) = 2.091. Notably, the congruent subjects were almost exclusively dextral and the crossed subjects were almost exclusively right handed and left eared. To assess whether the hand-ear congruency effect was related to the strength of preference in HP or Al’, both indices were used as covariates in repeat, Group by Gender ANOVAs. The significant interactions were maintained even with HP and Al’ controlled: TRG, F (1,221) = 4.09, p < .05; Verbal ability, F (1,221) = 4.26, p < .05. Two important questions are whether the eye preference and hand-ear effects on cognitive ability were (1) independent and (2) additive? To test for independence, the observed frequencies of co-occurance were compared to theoretically expected values. For males and females separately, the observed frequencies did not deviate from chance (Zs = < 1.92, ps > .05). Thus, one cannot predict eye preference from hand-ear congruency or vise-versa; the two effects are independent. To test for additivity, four male and female groups depicted in Figures 4 and 5 were created. Because it appears that males benefit from left visual preference and hand-ear congruence while females benefit from right visual preference and hand-ear incongruence, orthogonal 2 x 2 matrices were created of all possible combinations for each gender. For each gender, one-way ANOVAs com-

359

LATERAL PREFERENCE IN SIX TO NINE YEAR OLLI CHILLG?EN

MS and SDS for Verbal

Ability”

TABLE 8 in Children with Congruent

and Crossed Lateral

Preference

Hand Foot

Hand Eye

Hand Ear

Foot

Groups

Eye

Foot Ear

Eye Ear

Males (C)b M SD N

107.0 16.5 74

104.6 16.6 70

107.7 17.2 60

104.7 16.9 65

106.9 16.8 61

106.2 15.9 52

Females (C)b M SD N

106.3 16.5 74

107.2 16.1 75

103.3 16.6 53

107.7 16.3 68

102.9 17.4 43

103.5 16.1 59

Males (CR)= M SD N

102.9 16.1 38

107.5 15.8 43

103.3 15.0 50

107.2 15.6 47

104.2 15.8 49

105.3 16.83 58

Females (CR)= M SD N

105.5 12.4 41

103.2 13.4 42

107.7 15.7 64

103.5 12.9 47

107.3 13.6 74

107.9 14.0 58

“Canadian Cognitive Abilities Test (Thomdike & Hagen 1974). b(C) = Congruent Preference. ‘(CR) = Crossed Preference.

TABLE 9 MS and SDS for Teacher Grades0 in Children with Congruent

Groups Males (C)b M SD N Females M SD N

Hand Foot

Hand

.Ol .41

-.05 .39 70

74

Eye

and Crossed Lateral Preference

Hand Ear

Foot

.06 .36

-.06 .40 65

60

Eye

Foot Ear

Eye Ear

.02 .34

.02 .32 52

61

(C)b

Males (CR)’ M SD N Females (CR)= M SD N

.oo

.03 .43

.44 74

75

-.06 .32 38 .06 .33 41

.05 .35 43 -.02 .37 42

-.04 .39 53 -.09 .40 50

.04 .45 64

.05 .47 68

.03 .41

-.02 .39 59

-.05 .43 49

-.04 .43

43 .07 .34

47 -.07 .33 47

.oo

.03 .46

.43 74

“A discrepancy score based on the earned-grade minus actual-grade, in quartiles, where .OO = average. W) = Congruent Preference. ‘(CR) = Crossed Preference.

58

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FIGURE 3 Mean verbal scores by hand-ear congruence

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and gender.

log-

107-

106-

105-

104-

108-

102-

101-

-

Male

-

Female

$ 0

1 congnunt

C-d

Hand-Ear

pared the four groups on TRG and on Verbal ability. For the males, the group TRG effect was significant, F (3,106) = 3.10, p < .05. As shown in Figure 5, males without either attributes were significantly below average in achievement; those with one or the other attribute were average with no difference between them; and those who were congruent and left eyed were significantly above average [Critical Tukey HSD (4, 106) = .073]. A test for practical significance recommended by Borg (1987) produced I’ = .86, well above the practical significance level of .50. For the females, the group Verbal ability effect was significant, F (3,113) = 2.70, p < .05. As shown in Figure 4, females without either attribute were average in verbal ability; those with one or the other attribute were significantly higher with no difference between them; and those who were crossed and right eyed attribute were significantly superior [Critical Tukey HSD (4,113) = 3.07, p < .05]. The test for practical significance (Borg 1987) produced I’ = .99, well above the critical level of .50. Hence, the gender differentiated hand-ear congruency and eye preference effects on cognition were shown to be independent as well as additive. For both genders, similar trends were found in verbal ability and teacher grades. Finally, with the dichotic scores as the dependent measure, no differences were found for either gender among the four congruence-preference groups.

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LATERAL PREFERENCE IN SIX TO NINE YEAR OLD CHIDREN

FIGURE 4

Mean verbal scores by hand-ear (congruent, crossed) and eye preference (left, right) groups. 112lllllO108MB107Pt

106-

% m 1

105104-

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102lM101” 10088_Q

02

I

I

Femde:Crossd

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Male: Congnmt

Male: IeffEyed * N&XI

I

Female:

I

Female: Cthen N=l2

Male: others N=30

To summarize: (1) because 89% of the sample was right handed, the results can only be generalized safely to other presumably normal samples with similar handedness frequencies; (2) with the exception of footedness, the lateral preference indices were inappropriate psychometrically for analysis as continuous measures; (3) with the exception of a marginally higher REA among the right handed children compared to the left handed children, no relationships were found between any of the lateral preference measures and dichotic listening; (4) the only age effects were increased dextrality at age nine in foot preference and consequently in hand-foot congruence; (4) in males, congruent hand-ear preference (mainly right hand-right ear) and left eye dominance were found to have independent and additive beneficial effects on verbal reasoning and school achievement; whereas (5) in females, crossed hand-ear preference (mainly right hand - left ear) and right eye dominance were found to have independent and additive effects on verbal reasoning and school achievement.

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FIGURE 5 Mean teacher rated grades by hand-ear (congruent, (left, right) groups.

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crossed) and eye preference

0.141 0.120.100.08 Osx0.048

O&?-

g

O.oo-

3

-0.02 -

I3

-0.04 -

I

-0.08 -

$

-0.08 -O.lO-0.12-0.14-0.16-

-“‘18 Female: Crossed g&ed Male: Congruent anl Le&w t&s?4

Female: Right Eyed MY N=4l

Female: Crowd MY NS30

Female: othrs N&?

Male: MEyed only N*

MaleI Congruent w Nz16

Male: others N=30

DISCUSSION Whether one assumes that lateral preference is a continuous or a discontinuous dimension of human behaviour, the unmistakable right bias in hand, foot, eye, and ear preference is consistent with other large samples of three to six year old children from the Canadian West coast (Coren, et al. 1981) and from the central West coast of Italy (Longini & Orsini 1988). The concordance of the results of these three studies across such a wide geographical area supports the view that sensory-motor lateralization, not unlike language lateralization, has a large biological component (Corballis 1983). Similarly, the absence in all three studies of above-chance congruence in the majority of bimodality coordinations in children

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aged from three to nine years suggests the absence of significant early cultural influences. These common null findings are somewhat surprising in that our data extend these findings upward and through the first four years of school, a formative period where such development might be expected to be highly susceptible to environmental influence. In the Coren, et al. (1981) study, preschool children were compared to young adults, aged from 15 to 19 years. The older children demonstrated either continuous or categorical evidence for increased dextrality in hand, foot, ear, and eye preference, and beyond-chance congruence in hand-foot, hand-eye, and eye-ear combinations. Unfortunately, we have no way of untangling the relative weight of biology as opposed to culture in this presumed (cross-sectional) development. However, these results do raise the easier question of the age at which such changes might occur. We know that they occur sometime between six and fifteen. Our data directly test whether these proposed changes take place in the more restricted period from six to nine years of age. The present results showed an increase in right foot preference and increased hand-foot congruence at nine years of age. This cross-sectional shift was produced by a change at age nine in the incidence of left to right foot preference among the right handed children in the sample. Thus, both effects reflect increased dextrality. Our developmental findings, in the context of previous research, suggest that the additional shifts in lateral preference that were observed by Coren et al. (1981) may occur between nine and fifteen years of age. Moreover, future cross-cultural studies of foot preference at age nine can capitalize on the present results to answer the naturenurture question. For instance, converging cross-cultural evidence for increased foot dextrality at age nine would argue for its basis in biological constraints. Alternatively, the introduction of a sporting activity at age nine that required dominant hand-foot congruence, e.g., soccer, might also be expected to produce such results. We were unable to obtain reliable data regarding this question from the schools who participated in the present study. Two findings are at odds with popular assumptions. From at least as far back as the seminal work of Orton (1937) a relationship has often been implied between cerebral specialization for language and hand, foot, eye, and ear preference. The link between language lateralization and handedness is well established (Hellige 1990) and consistent with our results. However, to the extent that dichotic listening is a valid measure of linguistic lateralization (Bryden 1988), the findings disconfirm any connection between cerebral specialization for language and (a) foot, eye, or ear preference, and (b) congruence between any two of the four lateral preference modalities, including handedness. In particular, a systematic association has been assumed between hand and eye preference and between hand-eye preference and linguistic lateralization (Delacato 1966). In contrast, the present findings concur with VanCamp and Bixby (1977), showing chance hand-eye associations. Ad~tionally, they provide the first suggestive evidence that crossed hand-eye patterns may have no relationship to hemispheric asymmetries for speech. These findings are consistent with Rausch, Boone, and Ary (1991) who found that in right handers, fine bilateral manual

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control suffered as a result of left temporal seizures regardless of whether language was primarily -localized in the left or right hemisphere. It appears that language specialization may also exist independently of the unilateral motor control for foot, eye, and ear preferences. Second, the results provide no support for the “classical” notion that “right is better.” On the contrary, the findings suggest behavioral advantages in association with both dextrality and sinistrality. And such behavioral consequences or correlates are complexly linked to gender and to specific combinations of sensory-motor bias in sidedness. The congruency of children’s hand and ear preference and, independently, their eye preference were shown to be related to their abstract verbal reasoning ability and to have a practical impact on their teacher-rated academic progress in language and math. However, prominent contradictory gender differences were found. Males with superior cognitive talent were congruent in hand-ear preference; while cognitively advanced females were crossed in hand-ear preference. Furthermore, these hand-ear effects on cognition were unrelated to the direction and degree of their preferences in either hand or ear. Thus, the effect appears to be a gender differentiated result of having established an ipsilateral or a contralateral pattern per se without regard for the directional bias of either hand or ear separately. In eye preference, a cognitive advantage was found in left eyed males and in right eyed females. Once again, however, the eye effect was unrelated to the hand, foot, or ear preference measures. Thus, the hand-ear and eye preference effects were found to be independent of the other, to have additive effects on cognitive ability, and to be independent of other laterality measures. Such results are consistent with Longini and Orsini (1988) in suggesting different underlying neurological mechanisms for hand, foot, eye, and ear preference in this age range. Our results, in addition, suggest that gender differences in brain organization will need to be considered in attempts to explain the contradictory cognitive implications of what are quite similar gender lateral preference patterns. Among the children with a congruent hand-ear pattern, only four were left sided and among the crossed children, only eleven were left handed. Therefore, for males, the cognitive advantage involves mainly the right side in hand and ear; whereas for females the cognitive advantage involves primarily the right side in hand and the left side in ear. But, before any attempt at interpretation, we need to acknowledge theoretical and methodological difficulties with measures of ear preference. For instance, Longini and Orsini (1988) reported low test, retest reliability for their ear preference measures. Porac, Coren, and Duncan (1980) with a sample ranging in age from eight to one-hundred years, reported linear increases in dextrality with increasing age in hand, foot, and eye preference; but they reported inexplicably a linear reduction with age in the incidence It is apparent that the ear preference measures, i.e., of right ear preference. placing an ear near a radio, pose difficulties not encountered with the other measures. One observation with clear theoretical implications is that ear preference is totally confounded with lateral head turn. Right becomes left and left becomes right. Indeed, if we assume that the ear index is actually a measure of

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head turn, the cognitive results are consistent with at least one theoretical position on gender differences in brain organization that has been advanced by Galaburda, Rosen, and Sherman (1990). Briefly, the model proposes that the male brain compared to the female brain is less anatomically symmetrical and possesses more contralateral connections but fewer ipsilateral connections. The female brain is more dependent on intrahemispheric processes while the male brain is more dependent on interhemispheric processes. In the context of the present study, the model predicts a more efficient brain organization (a) in right handed males with a leftward head turning bias and left eye preference and (b) in right handed females with a rightward head turning bias and right eye preference. Thus, the cognitive effects in the present study may be due to gender differences in the cortical organization of the controlling pathways for handedness, postural head movements, and eye preference. Verbal reasoning may be accelerated in males when receptive speech and hand preference are controlled contralaterally to the hemispheric control of postural head orientation and eye preference. Females, in contrast, may gain an advantage in verbal reasoning when receptive speech, handedness, head turn, and eye preference are controlled by the same cerebral hemisphere. In considering the plausibility of this hypothesis a key question is whether there is any evidence that linguistic processing may share common neuronal pathways with the lateral expression of motor output? We assume that putative performance constraints between any two behavioral domains, i.e., motor and verbal, must be due to underlying neurological constraints imposed by the proximity of processing demands in the brain (Kinsbourne & Hicks 1978). Indeed, in a series of early studies with humans, Penfield and Welch (1951) demonstrated behavioral interference effects between involuntary asymmetrical motor movements and language as a result of mild electrical stimulation of the supplementary motor area (SMA). Typically, the same point of medial frontal lobe stimulation produced an arrest of language that was accompanied by contralateral head and eye rotation and movement of the contralateral arm and leg. Eye preference, of course, is not easily observed and was not of concern. Thus the SMA contains overlapping boundaries in the descending cortical pathways controlling language, lateral postural movements, and lateral preferences in hand and foot. This early research established a connection between motor lateralization (implicating the corticospinal, ventromedial brain stem, and lateral brain stem systems) and language and, also, identified the SMA as one neuronal location for interference effects during development. Therefore, the tentative explanation given for the present cognitive results does have a reasonable empirical basis and warrants further study. Finally, three limitations need to be emphasized. Our failure to find a relationship between dichotic listening and lateral preference may be related to the use of digit strings as stimuli or to our specific testing procedures. Although, in our own work (using the directed-attention paradigm rather than free-recall) we obtain somewhat higher test-retest correlations with digits compared to conso-

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nant-vowel syllables, other dichotic listening tests may be more sensitive to lateral preference effects. Second, Coren et al. (1981) suggest that lateral preferences undergo significant developmental changes. Our results pertain only to children in the six to nine age range and cannot be generalized safely to other ages. Lastly, while our interpretation of the cognitive findings does provide a cohesive theoretical account, admittedly, it is post-hoc and speculative. Gender differences in research are notorious for showing up unexpectedly and for their elusiveness in attempts at replication. Firm conclusions will necessarily have to wait for converging evidence and for studies that can test these ideas a priori. ACKNOWLEDGMENTS: Supported by grants from the Hospital for Sick Children Foundation, Toronto, and from OISE. We gratefully acknowledge the participation of the students, parents and staffs of the Halton and Peel School Boards, Ontario. We thank Sonia DePasqua for her expertise in preparing the manuscript and Dr. Evelyne Corcos for assistance with the statistical analysis.

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the motor coordination, mental ability, and right-left awareness of young normal children.” Child Development, 49, 885-888. Kershner, J. & L. Morton. (1990). “Directed attention dichotic listening in reading disabled children: A test of four models of maladaptive lateralization.” Neuropsychologia, 28, 181-198. Kershner, J. & M. Chyczij. (1991, July). The development of lateralized attention and ifs relationship to intellectual ability and school achievement. Paper presented at the International Neuropsychological Society, Queensland, Australia. Kinsbourne, M. (1988). “Sinistrality, brain organization, and cognitive deficits.” Pp. 259279 in Brain lateralixation in children, edited by D. Molfese & S. Segalowitz. New York: Guilford Press. Kinsboume, M. & H. Hicks. (1978). “Functional cerebral space: A model for overflow, transfer and interference effects in human performance.” Pp. 345-363 in Attention and performance VII, edited by J. Requin. New York: Wiley. Longini, A. & L. Orsini. (1988). “Lateral preference in preschool children: A research note.” Journal of Child Psychology and Psychiaty, 29, 533-539. McManus, I., G. Sik, D. Cole, A. Mellon, J. Wong &J. Kloss. (1988). “The development of handedness in children.” Journal of Developmental Psychology, 6, 257-273. Ortonian, S. (1937). Reading, writing and speech problems in children. New York: Norton. Penfield, W. & K. Welch. (1951). “The supplementary motor area of the cerebral cortex.” Archives of Neurology and Psychiaty, 66, 289-317. Porac, C., S. Coren, & I’. Duncan. (1980). “Life-span age trends in lateral@.” Journal of Gerontology, 35, 715-721. Rausch, R., K. Boone, & C. Ary. (1991). “Right hemisphere language dominance in temporal lobe epilepsy: Clinical and neuropsychological correlates.” Journal of Clinical and Experimental Neuropsychology, 13, 217-231. Thomdike, R., & E. Hagen. (1974). Canadian cognitive abilities test, edited by E. Wright. Toronto: Thomas Nelson & Sons. Ullman, D. (1977). “Children’s lateral preference patterns: Frequency and relationships with achievement and intelligence.” journal of School Psychology, 15, 36-43. Van Camp, S. & M. Bixby. (1977) “Eye and hand dominance in kindergarten and firstgrade children.“ Merrill-Palmer Quarterly, 23, 129-139. Whittington, J. & P. Richards. (1987). “The stability of children’s lateral@ prevalences and their relationship to measures of performance.” British Journal of Educational Psychology, 57, 45-55.