Journal of American Indian Education
Volume 25 Number 2
HEMISPHERIC DOMINANCE OF NATIVE AMERICAN INDIAN STUDENTS
John Stellern and Jim Collins
Native American Indians are presumed to be right-hemisphere dominant, and therefore need special teaching techniques. This study examined the language and spatial lateralization of American Indian students by means of the cognitive-manual dual task model as well as psychoeducational assessment techniques. The results indicated that the Indian students were lateralized to the left hemisphere for language, and some of those students were also lateralized to the left hemisphere for spatial function. Also, as scores went up on tests of right hemisphere dominance, behavior problems, and spatial function, scores went down on tests of reading, spelling, left hemisphere dominance, and being a good student. Two major conclusions are that the Indian students of this study were not right hemisphere dominant, and that right hemisphere dominance appears to be associated with a risk of learning and behavior problems.
CLINICAL AND LABORATORY EVIDENCE suggests that certain human cognitive functions depend predominately on either the left or right hemisphere of the brain (Galin and Ornstein, 1972). Each hemisphere is specialized for a particular type of information processing, for which it is, dominant. The left hemisphere of well-lateralized right-handed individuals is thought to be specialized for processing stimuli, especially oral language, in terms of left to right sequence, details, and step by step analysis, and thought to be cominant for speaking, reading, writing, and arithmetic. The right hemisphere is thought to be specialized for processing stimuli, especially visuospatial, according to simultaneous and holistic patterns and relationships (Bradshaw and Nettleton, 1981; Springer and Deutsch, 1981; Bogen, 1975).
The left brain is the preferred brain in school learning, but a large percentage of students failing school prefer right brain learning (Webb, 1983). Right hemisphere dominant subjects have been found to be disabled readers (Gordon, 1980); poor readers (Oexle and Zenhausern, 1981); more likely to dyslexic (Hier, et al., 1978); and have more learning/behavior problems (Stellern, Marlowe and Cossairt, 1984).
People usually cannot perform two concurrent tasks programmed in the same cerebral hemisphere as well as each task by itself. Dual-task performances will be inferior to those found when one activity is programmed on one side of the brain and one on the other side (Kinsbourne and McMurray, 1975). Speaking interferes more with concurrent right-hand than left-hand performance in normal right-handed adults and children. Conversely, spatial tasks interfere more with concurrent left-hand than right-hand performance in normal right-handed adults and children (Kinsbourne and Hiscock, 1983).
Asymmetric interference has been attributed to the specialization of the left cerebral hemisphere for both speaking and controlling the right limbs, and to the specialization of the right hemisphere for spatial tasks (Kinsbourne and Hiscock, 1983). Possible explanations are hemispheric competition (Kinsbourne and Hiscock, 1983), capacity limitation (Kahneman, 1973), and cortical inhibition (Kinsbourne and McMurray, 1975). Whatever the explanation, it appears that hemispheric time-sharing for two concurrent tasks results in the disruption of one or both of the tasks.
It is assumed that Native American Indians are right hemisphere dominant, regardless of handedness, and therefore special teaching techniques are necessary (Ross, 1982; Cattey, 1980; Wallis, 1983). If American Indian students are right hemisphere dominant, then dual-task performances with Indian students should result in a reversal of the usual left hemisphere verbal/ right hemisphere spatial lateralization, and yield left-hand task disruption while concurrently speaking and right-hand task disruption while concurrently performing spatial tasks.
The purpose of this study was to examine the language and spatial lateralization of American Indian students by means of the dual-task model as well as psychoeducational assessment techniques. The dual-task model is a non-invasive means of determining hemispheric specialization for various tasks (Hiscock, Antoniuk, Prisciak and Hessert, 1985).
Forty-nine Native American Indians were randomly selected from the fourth, fifth, and sixth grades at the St. Stephans Indian school located on the Wind River Indian Reservation near Riverton, Wyoming, during the spring of 1985. The Reservation is two million acres in size, and includes members of the Arapahoe and Shoshoni Indian tribes. St. Stephans is a K-12 Bureau of Indian Affairs contract school on the reservation. None of the 49 subjects had a known or suspected special education handicapping condition. Twenty-one were male and 28 were female; 43 subjects were right-handed, and six left-handed.
The dual-task experiments of this study involved reading and spatial problem solving while concurrently finger tapping. The tapping device consisted of a microswitch that was operated by depressing a knob at the end of a lever. The switch connected to an electromechanical counter, which registered incremental taps. The counter was positioned so that the subjects could not see the numbers.
The reading materials involved the Wide Range Achievement Test (WRAT) (Jastak, et al., 1978), by which to determine each subject's reading grade level and alternate forms of the Gray Oral Reading Test (Gray, 1963).
The spatial materials involved alternate forms of the Judgment of Line Orientation Test (JLOT) (Benton, Varney and Hamsher, 1975), which consists of 30 cards, each requiring the matching of visually presented lines with target lines that differ in length and slope - The JLOT is a test of visuospatial ability, and considered a right-hemisphere function (Benton, et al., 1978; Bradshaw and Nettleton, 1981).
The psychoeducational assessment instruments used in this study follow:
(1) The Adapted Children's Form of Your Style of Learning and Thinking (ACSOLAT) (Stellern, et al., 1983). The ACSOLAT is a 40-item paper-pencil self-report instrument which is thought to reveal hemispheric dominance, in the form of either left, right, or integrated cognitive mode. Hemispheric dominance and cognitive mode have been defined as the tendency of a person to rely more on one than the other cerebral hemisphere in processing information (Torrance, 1982).
(2) The Walker Problem Behavior Identification Checklist (WPBIC) (Walker, 1976) is a screening device designed for teachers to identify children with behavior problems. The WPBIC consists of 50 observable statements of classroom behavior, 14 of which relate to acting out (AO), five to withdrawal (W), 11 to distractibility (D), 10 to disturbed peer relations (DPR), and 10 to immaturity (1). The higher the score the more behavior problems exist.
(3) The Bender-Gestalt test (Bender, 1938) is a paper-pencil visual-motor integration test that involves copying geometric designs (Koppitz, 1975). Copying and drawing geometric designs is thought to be a right hemisphere function (Lezak, 1983).
Except for the WPBIC, each subject was tested individually by the authors, one of whom is a licensed psychologist, and two of whom are certified by the State Department of Education as educational diagnosticians. The WPBIC was administered by the teachers of the subjects.
There were four dual-task experiments: reading while concurrently tapping; solving spatial problems while concurrently tapping; tapping while concurrently reading as many words as possible; and tapping while concurrently solving as many spatial problems as possible.
Each subject was allowed a 10-second finger tapping practice trial. Handedness was determined by noting writing hand, and the hand used to perform such functions as unscrew a jar lid, strike a match, etc.
Each subject was asked to tap the key as rapidly as possible with the index finger of the preferred hand. Tapping frequency was recorded for 15 seconds. This formed the single-task baseline rate for that hand. The same procedure was used for the other hand. Then each subject was asked to read out loud at his/her grade level from the Gray Oral test while concurrently tapping with the index finger of the preferred hand as rapidly as possible (dual-task). Tapping frequency was recorded for 15 seconds. Same for the other hand. Similarly, each subject was asked to match look-alike lines from the JLOT, without speaking, while concurrently tapping (dual-task). Tapping frequency was recorded for 15 seconds. Same for the other hand.
Next, each subject was asked to tap as quickly as possible with the preferred hand while simultaneously reading out loud "to the best of your ability and as quickly as possible," from an alternate form of the Gray Oral test. This time the number of words read correctly was the dependent variable, and recorded for 15 seconds-same for the other hand. Similarly, each subject was presented with cards from an alternate form of the JLOT and asked to tap as quickly as possible with the preferred hand while simultaneously pointing to, without speaking, "as many correct look-alike lines as quickly as possible to the best of your ability." The number of lines correctly solved was the dependent variable, and recorded for 15 seconds. Same for the other hand.
Normal brain organization should result in oral language lateralized to the left hemisphere for most right handed subjects, and thus the contralateral right hand dual-task tapping rate should be disrupted more than the left hand rate. Conversely, normal brain organization should result in visuospatial functions lateralized to the right hemisphere for most right-handed subjects, and thus the contralateral left-hand dual-task tapping rate should be disrupted more than the right rate.
By determining an individual's right or left hand decrement regarding a dual-task oral language or visuospatial performance, it is possible to hypothesize language or spatial lateralization, and thus brain organization. Similarly, by comparing group mean scores regarding right and left hand decrements relative to dual-task language and visuospatial performance, it is possible to hypothesize language and spatial lateralization for groups of subjects, such as the Native American Indians of this study.
The results of dual-task experiments with children have found asymmetric interference in normal right-handed children, with right hand tapping rate being disrupted more than left hand tapping rate while concurrently speaking. This lateralized effect of speaking on tapping rate has been found in the youngest children tested (three years old) (Kinsbourne and Hiscock; 1983 Hiscock and Kinsbourne, 1978, 1980). Conversely, solving spatial tasks decreased left-hand tapping rate more than right-hand (Dalby and Dibson, 1981; McFarland and Ashton, 1975).
In this study the degree to which performance (e.g. tapping rate) was disrupted by a concurrent task (e.g. reading or spatial activity) is represented by the difference between the right hand tapping rate percentage decrement and the left hand tapping rate percentage decrement, which are derived from the following formula, for each hand: (P -B)/B X 100, where B is the single task tapping baseline rate, and P is the dual-task performance rate (e.g. tapping rate while concurrently reading) (Kinsbourne and Hiscock, 1977). This measure of percentage decrement has been found to be relatively independent of tapping baseline rate (Kinsbourne and Hiscock, 1983).
The Interference Index (U) is the percentage decrement for the right hand minus the percentage decrement for the left hand, and is a single figure which indicates whether an individual or group of individuals is lateralized to the left hemisphere for a specific task or to the right hemisphere for that task. For the dual-task part of this study, the scaling technique used to obtain the Interference Index resulted in minus (-) values representing left hemisphere lateralization, and plus (+) values representing right hemisphere lateralization, with higher numbers representing greater magnitude regarding that lateralization.
Left Handed Subjects
Six of the 49 subjects were left handed. The results of this study were analyzed both with and without the leffies. The results were essentially the same. Thus the data reported here are for all 49 subjects.
Good and Poor Students
The 49 subjects were divided into two groups, viz., good or poor students, by means of their WRAT achievement scores. Subjects who had standard scores of 95 or more on at least two of the three WRAT reading, spelling, and arithmetic subtests were considered "good" students (N = 27). Conversely, subjects with WRAT standard scores of less than 95 on at least two of the three subtests were considered "poor" students (N = 22).
As expected for right-handed subjects, the baseline tapping rate (single-task) was significantly greater with the right hand (M = 67.89) than left hand (M=62.10), which yielded a t test significance of p<.Ol.
The effect of concurrent reading on tapping rate (dual-task) resulted in an Interference Index mean score of -10.04, suggesting language lateralization in the left hemisphere. Similarly, the effect of concurrent visuospatial performance on tapping rate resulted in an II mean score of +3.53, suggesting spatial lateralization in the right hemisphere. The difference between the reading and spatial II means was significant at p<.001. (Note, again, that II minus values ( - ) represent left hemisphere lateralization whereas II plus values (+) represent right hemisphere lateralization).
The effect of concurrent tapping on the number of words read resulted in an II mean score of -13.53, again suggesting language lateralization in the left hemisphere. And, the effect of concurrent tapping on the number of correct lines solved resulted in an II mean score of + 3.00, suggesting spatial lateralization in the right hemisphere. The difference between these reading and spatial II means was significant at p<.01.
The psychoeducational assessment results follow, all in the form of Pearson correlation coefficients: the II mean score regarding the effect of concurrent reading on tapping rate correlated with SOLAT left hemisphere scores (-.31, p<.03), SOLAT right hemisphere scores (+.31, ;.03), Walker AO (+.38, p .01), and Walker Total score (+.32, p .04). The II mean score regarding the effect of concurrent spatial performance on tapping rate correlated with SOLAT left hemisphere scores (-.27, p .05), SOLAT right hemisphere scores (+.28, p .04), JLOT (.28, p .05), Walker AO (-.35, p .02), Walker DPR (-.50, p. 001), Walker Total scores (-.32, p. 04), WRAT reading scores (+.43, p .002), WRAT spelling scores (+.43, p .002), and good-poor student classification -.44, p .001).
The II mean score regarding the effect of concurrent tapping on the number of words read correlated with the Walker AO scores (+.32, p .04), and the Walker D scores (+.36, p .02).
The II mean score regarding the effect of concurrent tapping on the number of spatial problems solved correlated with the Walker Total scores (-.38, p .01), WRAT reading (+59, p .001), WRAT spelling (+.56, p .001), and good/poor student classification (-5, p .001).
SOLAT left hemisphere scores correlated with SOLAT right hemisphere scores (-.97, p .001), and SOLAT right hemisphere scores correlated with Bender-Gestalt scores (-.27, p .05).
The WRAT reading scores correlated with Walker AO scores (-.33, p .03), Walker D (-.33, p .03), Walker DPR (-.53, p .001), and Walker Total scores (-.46, p .002).
The WRAT spelling scores correlated with Walker AO (-.34, p .02), Walker D (-.48, p .001), Walker DPR (-.47, p .002), and Walker Total scores (-.42, p<.001).
WRAT arithmetic scores correlated with Walker AO (-35, p .02), and Walker Total scores (-.29, p .05). The good/poor student classification correlated with Walker AO (.30, p .05), Walker D (.38, p .03), Walker DPR (.42, p<.01), Walker Total (.41, p<.01). WRAT reading (-.80, p<.01), and WRAT spelling (-.79, p<.001). Neither age nor sex correlated significantly with any of the variables reported.
The results of these dual-task reading and spatial experiments indicate that the Native American Indian subjects of this study have language lateralized to the left hemisphere, and some of those subjects have spatial function also lateralized to the left hemisphere. As such, at least the Indians involved in this study are not right hemisphere dominant, and do not need right-minded teaching techniques (Stellern, Marlowe and Jacobs, 1983; Kaufman, Kaufman and Goldsmith, 1985; Hartlage and Telzrow, 1983).
As expected, SOLAT left- and right-hemisphere scales measured different variables (r = - .97, p. 001). The SOLAT left hemisphere (language) scores positively and significantly correlated with II mean reading scores (left hemisphere), whereas II mean reading scores correlated negatively and significantly with SOLAT right hemisphere scores. These results add to the validity of the SOLAT to discriminate between right and left hemisphere cognitive modes (Stellern, Marlowe, Jacobs and Cossairt, 1985; Stellern, Marlowe and Cossairt, 1983).
The SOLAT left hemisphere correlation of -.27 and SOLAT right hemisphere correlation of +.28 with II spatial scores indicates that subjects who had left hemisphere (right hand) intereference on the II spatial tasks tended to score high on the SOLAT left hemisphere scale. This is an unexpected reversal of the usual lateralization of spatial function to the right hemisphere. However, in a corollary study of these same Indian subjects, Stellern, Collins, Cossairt, and Gutierrez (1985) found that the Indian students not only had language lateralized to the left hemisphere, but one-third of the subjects also were lateralized to the left hemisphere for spatial function. This too is a reversal of the usual brain asymmetry, the cause of which could range from atypical brain organization to a sampling problem.
When only those subjects of this current study with normal left hemisphere language/right hemisphere spatial lateralization were included in the correlation analysis (N = 25), the SOLAT left hemisphere correlation with II spatial scores changed from -.27 to +.32, and the SOLAT right hemisphere correlation changed from +.28 to -.32. These correlation changes indicate that subjects who had left hemisphere interference on the II spatial tasks scored low on the SOLAT left hemisphere scale, which is normal lateralization for most right handers. The changes also suggest that the Indian subjects of this study are not only lateralized to the left hemisphere for language, but some subjects are also lateralized to the left hemisphere for spatial function, and as such are not right hemisphere dominant.
The two II reading (left hemisphere) scores are significantly associated with decreases in Walker behavior problem scores (fewer behavior problems), whereas the two II spatial (right hemisphere) mean scores are significantly associated with increases in Walker behavior problem scores (more problems), as well as being a poor student.
As expected good students were significantly associated with good WRAT reading and spelling achievement scores, whereas poor students were significantly associated with high Walker behavior problem scores. Also as expected, high WRAT achievement scores were associated with low Walker behavior problem scores; the II spatial mean scores were positively and significantly associated with the JLOT scores (spatial performance); and Bender scores were negatively and significantly associated with SOLAT right hemisphere scores.
The Indian subjects of this study are left hemisphere dominant and not right hemisphere dominant as has been assumed. If the Indians were right hemisphere dominant, then language would be lateralized to the right hemisphere, and/or information would be processed on a simultaneous and holistic manner, which is not supported by the II, SOLAT, and WRAT results of this study. This finding may be good, because as reported elsewhere (Stellern, Marlowe, Jacobs and Cossairt, 1985), right hemisphere dominance may be associated with a risk of learning/behavior problems. Such a risk factor is confirmed by this study, for as Walker behavior problem scores, SOLAT right hemisphere scores, and II mean spatial scores went up, good student scores, SOLAT left hemisphere scores, and achievement scores went down. Conversely, as scores on the WRAT achievement subtests, being a good student, II mean reading scores, and SOLAT left hemisphere scores went up, scores on the Walker behavior problem test and being a poor student went down. In other words, right hemisphere dominance appears to be associated with behavior problems and poor academic achievement.
The authors agree that right hemisphere dominant individuals seem to have a different neuropsychological method of processing information than left hemisphere dominant individuals, and that right-minded individuals may need special (or at least different) teaching techniques. However, at least on the basis of this study, American Indians appear to be left hemisphere dominant, for which right-minded instruction is not necessary. Nonetheless, instruction engaging the processing specialties of both sides of the brain into whole-brain education may be the best solution.
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DR. JOHN STELLERN is a Diplomate of the American Board of Professional Psychology in School Psychology, a licensed psychologist, and a certified school psychologist. He has taught regular and special education students, and has been a public school counselor, school psychologist, and clinical psychologist. Stellern is professor of special education at the University of Wyoming.
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