Validity of Arm Extension as a Measure of Dominance

Abstract

LYELLE L. PALMER Winona (Minnesota) State University' An arm extension test, proposed and studied as a quick index of the language hemisphere of the brain ( 2 , 3, 4, 5 ) , requires that an individual stand erect with his arms at the side. Wi th eyes closed, he is required to raise his arms with the fingers extended until they feel level, i.e., parallel to each other and to the floor. H e must hold them in that position. Alternate testing involves lowering of the arms from above the head until they are level or raising the outstretched arms sideways (5 , pp. 168f). The higher arm/hand is considered dominant. Abnormal arm-extension dominance has been reported for 69 to 78% of pupils with reading problems in contrast to 12% in normal readers ( 5 ) . T o test the validiry of the arm-extension technique, composite scores for manual, tactile, pedal, eye, and ear lateraliry were gathered from 2 0 ma!es and 2 0 females randomly selected from each of Grades 4, 8, and 12 in dichotomous samples of high and low achievers in a suburban Texas school district ( 1 ) . High achievers scored in the upper 10% on achievement and IQ tests, while low achievers comprised the lowest quartile on achievement tests and IQ above the first standard deviation below the mean on a group measure. The arm lowering alternative of the extension test was administered and compared to a composite lateraliry from all other measures to test for significance of agreement. Comparisons of arm extension to composite sidedness showed agreement ranging from 35% to 70% among the 120 high achievers, with an average of 52.5%. Agreement among the 120 low achievers ranged from 30% to 75%. with an avercge of 58.3%. Among the 224 rightand 16 left-sided subjects, the test m~sidentified 97 leftand 10 mixedor right-dominant subjects, resulting in a phi coefficient of only .10 for all subjects. Contrary to expectation, low achievers showed slightly higher agreement between rneasurm than high achievers in this sample. All differences were statistically nonsignificant. Agreements of 6O%, 50%, and 57% were found for combined groups at Grades 4, 8 , and 12, respectively. In conclusion, validicy of the arm-extension test as an index of cerebral language dominance, insofar as such dominance may be inferred from a composite of sidedness , measures, is questionable. Arm extension may, however, have validity as a criterionreferenced measure of differences in upper torso muscle tonus but without reference to language dominance of the brain.