Perceplual and Motor Skills, 1975, 40, 263-266. @ Perceptual and Motor Skills 1975
HANDEDNESS AS A FUNCTION OF TEST COMPLEXITY H. J. STEINGRUEBER University of Di~erseldorf,West Germany Summary.-Handedness as a function of test complexity was investigated with two tests, Dotting and Tapping-on-squares. For each one three levels of complexity were established by varying radius (Dotting) and square sides (Tapping-on-squares). Administration of the different complexity levels to a total of 310 third and fourth grade boys and girls showed that the rare of lefthandedness increased from 6% "00 16% with decreasing level of test complexity. It is concluded that optimal classi€ication of handedness is only made possible by maximal levels of test complexity, which have to be established empirically for different populations.
Development of a hand-dominance-test (Steingrueber, 1971) showed that the three scales with highest retest reliabilities were Dotting (marking pencil dots into irregularly aligned circles), Tapping-on-squares (marking pencil dots into aligned squares), and Tracing (drawing a pencil line into an irregular parallel track without touching the borders). Right and left hands were tested successively with these three subscales, and scoring was based on the achievement difference of both hands and not on hand preference. The scales identified different proportions of left-handers out of the same population, namely, 2% (Dotting), 11% (Tapping-on-squares) , and 35 % (Tracing). This considerable variation was obtained although a factor analysis of intercorrelations, still including other tests, showed all three criteria to be highly correlated with the first factor. Therefore, the different proportions of left-handers were not related to the fact that different dimensions of handedness were measured with each scale; rather it could only be a matter of positional change. In other words, the positions of Ss in relation to each other were maintained and only a shift of the zero point of the scale (defined as "equal achievement of both hands" or "ambidexterity") occurred. The consequences are of special importance for applications in this field because all research work in clinical and educational problems of handedness (cf. Hecaen & de Ajuriaguerra, 1964; Sovak, 1968) is invalidated when one test classifies only 2% and another test 35% as left-handed Ss. The following study intends to clarify the conditions of varying classifications of left- and right-handedness by analyzing the shift of the zero point of the scale. Blau (1946, p. 36 ff.) intends to explain this shift by presupposing that a test of handedness must demand a certain amount of psychomotor complexity in order to show the dominance of one hand over the other. It can therefore be assumed that in extremely simple tests both hands are equally competent. Under these conditions two not completely independent hypotheses on
264
H.J. STEINGRUEBER
the effect of variation of test complexity on the distribution of handedness can be formulated for empirical investigation: ( 1) With a decreasing level of test complexity the distribution of handedness approaches a chance distribution. That is, the zero p i n t of the scale ("ambidexterity") which in our right-hand oriented culture lies to the left of the mean, shifts further to the right of the scale. This shift can be seen in the numerical change of the mean score. In extreme cases zero point and mean score coincide. ( 2 ) Range and standard deviation of the distribution of handedness decrease with a decreasing level of test complexity because of decreasing difference in achievement between right and left hands.
METHOD With two tests of hand-dominance, Dotting and Tapping-on-squares, different levels of complexity were established by varying radius length (Dotting) and square side length (Tapping-on-squares) . Three complexity levels were tried in prior investigations and turned out to be convenient: 2 rnrn (Level I ) , 6 mm (Level 11), and 9 mm (Level 111) of radius and square side length, respectively. The subscale Tracing was omitted because preliminary testings had shown ceiling effects with variations in complexity levels comparable to those complexity levels employed in Dotting and Tapping-on-squares. Ss were 310 third and fourth grade boys and girls ( 8 to 10 yr.) and were group tested in their school classes with one level of complexity in each group test session. Due to differing class sizes different sample sizes were obtained (see Table 1). The dominance of one hand was calculated according to the following index (Buxton, 1937) : Dominance
right-hand-achievement - left-hand-achievement = right-hand-achievement + left-hand-achievement . 100
This quantity which is analogous to Fechner's correlation coefficient (cf. Biometrisches Woerterbuch, 1968) can vary between minus 100 (extreme lefthandedness) and plus 100 (extreme right-handedness) ; a positive score indicates right-handedness, a negative score left-handedness, and a zero score "ambidexterity." The dominance scores of Dotting and Tapping-on-squares were added for each level of complexity resulting in increased scale length and thereby in an increased reliability. This procedure was justified because the important condition of factoral homogeneity of the scales had been checked before.
RESULTS Means
The shift of the zero point of the scale in the direction of the mean score with decreasing test complexity was statistically significant (one-way analysis
HANDEDNESS AND TEST COMPLEXITY
265
TABLE I
MEASUREMENT OF HANDEDNESS AS A FUNCTION OF LEVELOF TESTCOMPLEXITY (DOTTINGAND TAPPING-ON-SQUARES COMBINED) Treatment group Sample size M SD Range
Level I
Level I1
108 40.77 26.69 -49-+98
127 38.08 24.78 -46+101
Level I11
75 17.76 17.85 - 32--t 59
of variance, Model I: Fixed effects, F = 23.25, p < 0.01). This significance results from the differences in scores between Level II/III and Level I/III; however, differences in scores between Level 1/11 did not reach statistical significance (Duncan test, protection level: 0.98, p = 0.01).
Dispersion Ranges and standard deviations of the scores, i.e., differences in competency between left and right hands, decreased with decreasing levels of test complexity. However, the difference between Level I and Level I1 was smaller than that between Level I1 and Level 111.
DISCUSSION The definition of handedness is obviously a function of test complexity. The dominance of one hand diminishes with a decrease in test complexity. Since in our culture generally the right hand is the dominant one in the performance of more complex tasks the mean score of the distribution of handedness decreases, roo. Our limited treatment variation, however, cannot achieve the theoretical extreme situation of coincidence of the zero point of the scale ("ambidexterity") and mean score. Yet the results of this study show that with Levels I and I1 only about 6% of the sample can be defined as left-handed, whereas Level 111 identifies 16%. Together with the decrease of the mean score a decrease of dispersion is found in test complexity, underlining the decreasing efficiency of the test to differentiate handedness. On the other hand, there is obviously a limit of differentiation with increasing level of complexity because only minor differences in mean and dispersion between Level I and Level I1 were obtained. Possibly the absence of significant differences can be interpreted as ceiling effect which indicates maximal competence of test differentiation. For the classification of left- and right-handedness this means a maximal polarization and thereby an optimal classification. Such a maximal limit of differentiation is desirable in the construction of handdominance-tests because it can be assumed that in cases of less complex test levels there is an increasing importance of transfer bias from one hand to the other. In such cases it is not the difference in skill before measurement which determines
266
H. J. STEINGRUEBER
final classification of right- or left-handedness but rather transfer effects during measurement, since the-hand tesced second can profit decisively from the hand tested first. Another problem is posed from developmental aspects. If handedness is an expression of intra-individual differentiation (Palmer, 1964) making people more capable to cope with the environmental demands for skilled performance, tests of handedness have to be adapted to different stages of motor and brain development, respectively. An empirical adaptation may be as useful for different age groups as for different groups of brain pathology. Only if considerations of this kind are sufficiently taken into account, can reliable statements be made on the differentiation of motor development in terms of handedness. REFERENCES
BLAU,A. The master hand. American Orthopsychiatric Association, Research Mono-
graphs, 1946, No. 5 . BUXTON. C. F. A comparison of preference and motor learning measures of handedness. Journal of Experimental Psychology, 1937, 21, 463-469. DEUrSCH-UNGAR~SCH-POLNISCHESAUTORENKoLLEKTlV. Biome)risches Woerterbrrch. Berlin: VEB Deutscher Landwi rtschaftsverlag, 1968. HECAEN, H., & DE AJURIAGUERRA, J. Left-handedness, manual superiority and cerebrnl dominance. New York: Grune & Stratton, 1964. PALMER, R. D. Development of a differentiated handedness. Psychological Bullerin, 1964, 62, 257-272. SOVAK, M. Paedagogische Probleme der Lateralitaet. Berlin: VEB Volk und Gesundheit, 1968. STEINGRUEBER, H. J. Zur Messung der Haendigkeit. Zeitschrift fuer experimentelle und angewandte Psychodogie, 1971, 18, 337-357. Accepted November 18, 1974.
HANDEDNESS AS A FUNCTION OF TEST COMPLEXITY H. J. STEINGRUEBER University of Di~erseldorf,West Germany Summary.-Handedness as a function of test complexity was investigated with two tests, Dotting and Tapping-on-squares. For each one three levels of complexity were established by varying radius (Dotting) and square sides (Tapping-on-squares). Administration of the different complexity levels to a total of 310 third and fourth grade boys and girls showed that the rare of lefthandedness increased from 6% "00 16% with decreasing level of test complexity. It is concluded that optimal classi€ication of handedness is only made possible by maximal levels of test complexity, which have to be established empirically for different populations.
Development of a hand-dominance-test (Steingrueber, 1971) showed that the three scales with highest retest reliabilities were Dotting (marking pencil dots into irregularly aligned circles), Tapping-on-squares (marking pencil dots into aligned squares), and Tracing (drawing a pencil line into an irregular parallel track without touching the borders). Right and left hands were tested successively with these three subscales, and scoring was based on the achievement difference of both hands and not on hand preference. The scales identified different proportions of left-handers out of the same population, namely, 2% (Dotting), 11% (Tapping-on-squares) , and 35 % (Tracing). This considerable variation was obtained although a factor analysis of intercorrelations, still including other tests, showed all three criteria to be highly correlated with the first factor. Therefore, the different proportions of left-handers were not related to the fact that different dimensions of handedness were measured with each scale; rather it could only be a matter of positional change. In other words, the positions of Ss in relation to each other were maintained and only a shift of the zero point of the scale (defined as "equal achievement of both hands" or "ambidexterity") occurred. The consequences are of special importance for applications in this field because all research work in clinical and educational problems of handedness (cf. Hecaen & de Ajuriaguerra, 1964; Sovak, 1968) is invalidated when one test classifies only 2% and another test 35% as left-handed Ss. The following study intends to clarify the conditions of varying classifications of left- and right-handedness by analyzing the shift of the zero point of the scale. Blau (1946, p. 36 ff.) intends to explain this shift by presupposing that a test of handedness must demand a certain amount of psychomotor complexity in order to show the dominance of one hand over the other. It can therefore be assumed that in extremely simple tests both hands are equally competent. Under these conditions two not completely independent hypotheses on
264
H.J. STEINGRUEBER
the effect of variation of test complexity on the distribution of handedness can be formulated for empirical investigation: ( 1) With a decreasing level of test complexity the distribution of handedness approaches a chance distribution. That is, the zero p i n t of the scale ("ambidexterity") which in our right-hand oriented culture lies to the left of the mean, shifts further to the right of the scale. This shift can be seen in the numerical change of the mean score. In extreme cases zero point and mean score coincide. ( 2 ) Range and standard deviation of the distribution of handedness decrease with a decreasing level of test complexity because of decreasing difference in achievement between right and left hands.
METHOD With two tests of hand-dominance, Dotting and Tapping-on-squares, different levels of complexity were established by varying radius length (Dotting) and square side length (Tapping-on-squares) . Three complexity levels were tried in prior investigations and turned out to be convenient: 2 rnrn (Level I ) , 6 mm (Level 11), and 9 mm (Level 111) of radius and square side length, respectively. The subscale Tracing was omitted because preliminary testings had shown ceiling effects with variations in complexity levels comparable to those complexity levels employed in Dotting and Tapping-on-squares. Ss were 310 third and fourth grade boys and girls ( 8 to 10 yr.) and were group tested in their school classes with one level of complexity in each group test session. Due to differing class sizes different sample sizes were obtained (see Table 1). The dominance of one hand was calculated according to the following index (Buxton, 1937) : Dominance
right-hand-achievement - left-hand-achievement = right-hand-achievement + left-hand-achievement . 100
This quantity which is analogous to Fechner's correlation coefficient (cf. Biometrisches Woerterbuch, 1968) can vary between minus 100 (extreme lefthandedness) and plus 100 (extreme right-handedness) ; a positive score indicates right-handedness, a negative score left-handedness, and a zero score "ambidexterity." The dominance scores of Dotting and Tapping-on-squares were added for each level of complexity resulting in increased scale length and thereby in an increased reliability. This procedure was justified because the important condition of factoral homogeneity of the scales had been checked before.
RESULTS Means
The shift of the zero point of the scale in the direction of the mean score with decreasing test complexity was statistically significant (one-way analysis
HANDEDNESS AND TEST COMPLEXITY
265
TABLE I
MEASUREMENT OF HANDEDNESS AS A FUNCTION OF LEVELOF TESTCOMPLEXITY (DOTTINGAND TAPPING-ON-SQUARES COMBINED) Treatment group Sample size M SD Range
Level I
Level I1
108 40.77 26.69 -49-+98
127 38.08 24.78 -46+101
Level I11
75 17.76 17.85 - 32--t 59
of variance, Model I: Fixed effects, F = 23.25, p < 0.01). This significance results from the differences in scores between Level II/III and Level I/III; however, differences in scores between Level 1/11 did not reach statistical significance (Duncan test, protection level: 0.98, p = 0.01).
Dispersion Ranges and standard deviations of the scores, i.e., differences in competency between left and right hands, decreased with decreasing levels of test complexity. However, the difference between Level I and Level I1 was smaller than that between Level I1 and Level 111.
DISCUSSION The definition of handedness is obviously a function of test complexity. The dominance of one hand diminishes with a decrease in test complexity. Since in our culture generally the right hand is the dominant one in the performance of more complex tasks the mean score of the distribution of handedness decreases, roo. Our limited treatment variation, however, cannot achieve the theoretical extreme situation of coincidence of the zero point of the scale ("ambidexterity") and mean score. Yet the results of this study show that with Levels I and I1 only about 6% of the sample can be defined as left-handed, whereas Level 111 identifies 16%. Together with the decrease of the mean score a decrease of dispersion is found in test complexity, underlining the decreasing efficiency of the test to differentiate handedness. On the other hand, there is obviously a limit of differentiation with increasing level of complexity because only minor differences in mean and dispersion between Level I and Level I1 were obtained. Possibly the absence of significant differences can be interpreted as ceiling effect which indicates maximal competence of test differentiation. For the classification of left- and right-handedness this means a maximal polarization and thereby an optimal classification. Such a maximal limit of differentiation is desirable in the construction of handdominance-tests because it can be assumed that in cases of less complex test levels there is an increasing importance of transfer bias from one hand to the other. In such cases it is not the difference in skill before measurement which determines
266
H. J. STEINGRUEBER
final classification of right- or left-handedness but rather transfer effects during measurement, since the-hand tesced second can profit decisively from the hand tested first. Another problem is posed from developmental aspects. If handedness is an expression of intra-individual differentiation (Palmer, 1964) making people more capable to cope with the environmental demands for skilled performance, tests of handedness have to be adapted to different stages of motor and brain development, respectively. An empirical adaptation may be as useful for different age groups as for different groups of brain pathology. Only if considerations of this kind are sufficiently taken into account, can reliable statements be made on the differentiation of motor development in terms of handedness. REFERENCES
BLAU,A. The master hand. American Orthopsychiatric Association, Research Mono-
graphs, 1946, No. 5 . BUXTON. C. F. A comparison of preference and motor learning measures of handedness. Journal of Experimental Psychology, 1937, 21, 463-469. DEUrSCH-UNGAR~SCH-POLNISCHESAUTORENKoLLEKTlV. Biome)risches Woerterbrrch. Berlin: VEB Deutscher Landwi rtschaftsverlag, 1968. HECAEN, H., & DE AJURIAGUERRA, J. Left-handedness, manual superiority and cerebrnl dominance. New York: Grune & Stratton, 1964. PALMER, R. D. Development of a differentiated handedness. Psychological Bullerin, 1964, 62, 257-272. SOVAK, M. Paedagogische Probleme der Lateralitaet. Berlin: VEB Volk und Gesundheit, 1968. STEINGRUEBER, H. J. Zur Messung der Haendigkeit. Zeitschrift fuer experimentelle und angewandte Psychodogie, 1971, 18, 337-357. Accepted November 18, 1974.
