Intermanual differences on neuropsychological motor tasks in a Japanese university student sample 1

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1 bs_bs_banner Japanese Psychological Research 2014, Volume 56, No. 2, doi: /jpr Intermanual differences on neuropsychological motor tasks in a Japanese university student sample 1 HIKARI YAMASHITA 2 * Ehime University Abstract: We explored the intermanual difference scores of 128 Japanese university students for five typical neuropsychological motor tasks (grip strength, finger tapping, two versions of the grooved pegboard, and the dot-filling test) and examined the relation between hand preference and intermanual difference in motor proficiency. Using the Edinburgh Handedness Inventory, 18 and 110 participants were identified as left- and right-handed, respectively. Although the right hand performed better than the left for right-handed participants, and vice versa, in all five tasks, the degree of intermanual difference varied between tasks. A discriminant function analysis using the laterality quotients of the five motor tasks as independent variables indicated that hand preference was predictable from the task performances with an accuracy of 90% or more. The dot-filling test and finger tapping had stronger canonical loadings than the other tasks. Key words: laterality, handedness, hand preferences, hand performances. The human brain s left and right hemispheres are functionally asymmetric. The most obvious human behavioral asymmetry is handedness, which is important for understanding structural and functional asymmetry in the human brain. Since Paul Broca described left-hemisphere language regions in his right-handed patients in the middle of the 19th century, handedness has been associated with cerebral dominance for language processing (Annett, 2002; Hatta, 1996; McManus, 2002). Although it is indispensable to clinical practice and research in neuroscience, the optimum method by which to classify individuals as rightor left-handed remains controversial; traditionally, both hand preference and performance measures have been used. Preference measures are subjective and have usually been measured through handedness inventories quantifying hand preference for the performance of various unimanual tasks (Annett, 1970; Chapman & Chapman, 1987; Oldfield, 1971; Steenhuis & Bryden, 1989). Although this method requires no time and effort to divide individuals into handedness groups, its reliability has been questioned because of its subjectivity. The problem is more serious for very young children with underdeveloped verbal ability. In contrast, performance measures (proficiency) are objective but require a greater amount of both time and effort to administer. Despite the advantage of objectivity, the degree of manual asymmetry is generally assumed to vary with different tasks. On most manual tasks, the preferred hand is used more than the non-preferred hand. However, variations in task performance depend on different aspects of motor proficiency (e.g., strength, speed, and accuracy), which may have differential importance in determining hand preference (Bronstein, 1986; *Correspondence concerning this article should be sent to: Hikari Yamashita, Faculty of Education, Ehime University, Bunkyo-cho, Matsuyama , Japan. ( yamabcd@ed.ehime-u.ac.jp) 1 This research was supported by a Grant-in-Aid for Scientific Research (C) from JPSP (No ). 2 I would like to thank Fumi Yamashita, Ayumi Ichida, and Masaru Kanamori for their technical assistance Japanese Psychological Association. Published by Wiley Publishing Asia Pty Ltd.

2 104 H. Yamashita Brown, Roy, Rohr, & Bryden, 2006; Bryden, Bulman-Fleming, & MacDonald, 1996; Corey, Hurley, & Foundas, 2001; Thompson, Heaton, & Matthews, 1987). Furthermore, the results are partially influenced by age, sex, experience with the task, health conditions, and the effort needed to perform the task (Bronstein, 1986; Dodrill, 1979; Thompson et al., 1987). Preference measures of handedness are strongly lateralized and yield a bimodal distribution (two distinct handedness groups), whereas performance measures yield a unimodal distribution and no clear division between groups (Corey et al., 2001). To improve the validity and reliability of research, the subjective and objective preference measures must be linked by developing predictive models of handedness. Recently, many studies, mainly conducted by North American researchers, have examined the relation between preference and performance measures (Brown et al., 2006; Brown, Roy, Rohr, Snider, & Bryden, 2004; Corey et al., 2001). In Japan, the division of experimental and clinical samples into handedness groups for the purpose of neuropsychological studies has been accomplished almost exclusively using hand preference measures, the H. N. Handedness Inventory (HNI), which was developed in Japan (Hatta & Nakatsuka, 1974), and the Japanese translation of the Edinburgh Handedness Inventory (EHI) (Hatta, 1996; Hatta & Hotta, 2008). However, detailed studies of laterality in upper limb motor functions have hardly been reported since the pioneering study among primary school children conducted before World War II by Megumi Imada, the founder of the Psychology Department of Kwansei Gakuin University (Imada, 1935). He studied the laterality of performances in five motor tasks (grip strength, tapping, pegboard, tracing by pencil, and cutting by scissors) among more than 700 children across all six school years. In addition, he examined the relation between intermanual differences on each task and hand preference in daily life on the basis of teachers observations. He reported that performance differences between the preferred and nonpreferred hand varied considerably between tasks. He also suggested that there was a close relationship between observed hand preference and laterality of task performances. This is one of the oldest neuropsychological studies in Japan, and it used sophisticated research methods for its time. From a clinical viewpoint, the degree of intermanual difference in motor tasks is an important clue in identifying the possibility of hemispheric damage. Although few specific guidelines for interpreting the differences have been offered, the most frequently reported guideline for simple motor tasks such as grip strength, finger tapping, and the pegboard task has been that the preferred hand should perform approximately 10% better than the non-preferred hand (Bronstein, 1986; Thompson et al., 1987). On the basis of normative studies of the Halstead-Reitan Neuropsychological Battery, Golden (1978) claimed that the performance of the preferred hand being worse than that of the non-preferred hand is a strong indication of dominant hemisphere damage, whereas the performance of the preferred hand being at least 20% better is a strong sign of non-dominant hemisphere damage. Although deviations occur in the normal population for a single motor task, consistency across performances on several tasks is rare and more suggestive of dysfunctions of the contralateral hemisphere (Bronstein, 1986; Thompson et al., 1987). However, most of the available normative data on the laterality of neuropsychological motor tasks have been reported from outside Japan. The present study had two aims: (a) to examine the performance differences between the right and left hand in five typical unimanual motor tasks (grip strength, finger tapping, two versions of the grooved pegboard, and the dot-filling test) in relation to the handedness assessed using subjective questionnaires among young Japanese participants; and (b) to examine the relation between hand preference and asymmetries in motor proficiency. In previous studies, handedness inventories were used to match the number of left- and right-handed participants (Brown et al., 2006; Corey et al., 2001). We aimed to study the

3 Neuropsychological motor tasks: Intermanual difference 105 natural distribution of handedness in Japan from a clinical perspective and recruited participants without any bias. According to the data of previous large-scale inventory surveys in Japan (Hatta, 1996; Hatta & Hotta, 2008), it was estimated that 90 95% of participants would be determined as right-handed using the present experiment design. However, there could be considerable differences in the laterality of the motor tasks in participants classified as right-handed (or left-handed) by the handedness inventory. Methods Participants One hundred and twenty-eight undergraduate students, aged years (M = 21.2, SD = 1.1) participated voluntarily in the experiment. There were 64 women and 64 men, all with no history of neurological or psychiatric illness. All procedures conformed to the Japanese Psychological Association s code of ethics and conduct. All participants provided informed written consent. Apparatus and procedure Each participant was required to complete the EHI (Oldfield, 1971) to determine hand preference. To assess hand performance asymmetries, five performance-based measures were examined: grip strength, finger tapping, two versions (place and remove tasks) of the grooved pegboard, and the dot-filling test. The first three tasks are used routinely in North America as basic motor tasks in neuropsychological assessment. The grooved pegboard remove task was introduced recently by Bryden and Roy (2005) as a purer measure of the motor speed of two hands than the standard grooved pegboard task (place task). The dot-filling test was developed as a task to judge handedness because there are large differences between the dominant and non-dominant hand performances (Tapley & Bryden, 1985). Edinburgh Handedness Inventory Studies of cognitive laterality in Japan have primarily used the HNI for cultural compatibility (Hatta, 1996; Hatta & Hotta, 2008). However, in the present study, we adopted the EHI for the following reasons: (a) for clinically oriented research such as the present study, the EHI, which simply dichotomizes participants into left- and right-handed, is more practical than the HNI, which classifies them into three groups, left-handed, right-handed, and ambidextrous; (b) we wanted to use the laterality quotient (LQ) of the EHI as a quantitative index of hand preference; and (c) use of the EHI facilitates comparison with previous studies in other countries. The EHI requires preference for ten types of manual activities and an indication of a strong or weak preference. The activities are writing, drawing, throwing, using a pair of scissors, using a toothbrush, using a knife without a fork, using a spoon, using a broom, striking a match, and opening a box. A laterality quotient (LQ) is calculated on the basis of the provided answers. The range of quotients is 100, for extreme left-handedness, to +100, for extreme righthandedness. In this study, the criterion LQ < 0 was taken to indicate left-handedness. Grip strength (GS) An electric hand dynamometer (Takei Scientific Instruments) was used. Participants were required to hold the dynamometer at their side with a straight arm and squeeze its handle using maximum power. They were randomly assigned to begin with either the left or right hand, and performed three trials with each hand used alternately. Performances were measured in kilograms and averaged across all trials. Finger tapping (FT) Finger tapping was counted using a mechanical tapper (Takei Scientific Instruments). After a short practice, each participant was required to tap the key of the device with their right index finger as fast as possible for 60 s. After a short rest, a similar procedure was performed with the left index finger. The number of taps in 60 s was measured, and the average of each 10-s period was adopted as a performance index.

4 106 H. Yamashita Grooved pegboard (GP) The enforcement method of the grooved pegboard (Lafayette Instruments) was based on the method of Bryden and Roy (2005). In the first part (place task), participants were instructed to place 25 pegs, one at a time, into keyholes in a prescribed order as quickly as possible. They were also instructed to position each peg from left to right on the pegboard when using their right hand and vice versa. In the second part (remove task), the participants were instructed to remove the 25 pegs, one at a time, and return them to the receptacle as quickly as possible. The participants were timed for both the place and remove tasks.they completed one trial of the place and remove tasks with the assigned hand and another with the opposite hand. This was repeated for a second trial. The participants were randomly assigned to begin with either the left or the right hand. In each phase, the average time across the two trials was used as a performance index. Dot-filling test (DFT) This task involves using a pencil to make a dot in a small circle as quickly as possible (Tapley & Bryden, 1985). The participants were presented with a single sheet of A4 landscape paper, on which 110 circles were printed in four rows that were linked at the top and bottom in a W shape. There were four such stimulus arrays on a sheet. Participants were asked to make a dot in each circle following the pattern as quickly as they could. It was emphasized that the dot must be completely inside the circle and that dots made on the edge of or outside the circle would not be scored. Twenty seconds were allotted for each trial. The participants began with their writing hand (A) and performed four trials in the order ABBA. In the case of a right-handed writer, the participant performed in the order of a right-hand start at the top left, a left-hand start at the top right, a left-hand start at the bottom left, and a right-hand start at the bottom right. The number of correctly filled circles was counted for each trial, and the average of two trials with each hand was used as a performance index. Data analysis For each of the five tasks (GS, FT, GP-P, GP-R, and DFT), performance was expressed using two different measures. The percentage difference score ((preferred hand performance non-preferred hand performance/ preferred hand performance) 100) is often used clinically to evaluate the performance difference between the preferred and nonpreferred hands. The laterality quotient (LQ) of performance ((right hand performance left hand performance)/(right hand performance + left hand performance) 100) is used to evaluate the performance difference between the left and right hands (negative LQ scores reflected superior performance of the left hand and positive LQ scores reflected superior performance of the right hand). To maintain consistency, the signs were reversed on the pegboard tasks. The performance difference between the preferred and non-preferred hands in each task was tested using a three-way (sex handedness hand used) analysis of variance (ANOVA). Similarly, the laterality quotients of the five performance tasks were tested using another three-way (sex handedness tasks) ANOVA. The relation between hand performance and preference was analyzed using the Spearman s rank correlation coefficients and a discriminant function analysis. These analyses were performed using SPSS for windows (version 15.0J) and js-star 2012 (Freeware, programming by Tanaka and Nappa). Results Hand preference Eight women (12.5%) and 10 men (15.6%) were identified as left-handed using the EHI. No significant difference was found between the proportions of left-handed women and men (χ 2 = 0.26, df =1,p =.61).The frequency of lefthandedness was higher than in previous Japanese studies (Hatta, 1996; Hatta & Hotta, 2008) even though there was no recruitment bias.

5 Neuropsychological motor tasks: Intermanual difference 107 Figure 1 shows the relative frequency of LQs on the EHI. The distribution deviates to the right (J shaped), which means that the majority of participants had a strong right-hand preference, and a Kolmogorov-Smirnov test indicated that it was not normally distributed ( p <.01). No significant differences in the LQ on the EHI were found between women (Mdn = 100, M = 73.7, SD = 56.1) and men (Mdn =100, M = 67.1, SD = 60.9) (U = , p =.21). In 18 left-handed participants, eight participants (4 women and 4 men) answered that writing was performed with the right hand (corrected left-handed persons). Performance data Table 1 presents the means and standard deviations of the performance with each hand on the five tasks, shown according to hand preference and sex. In most tasks, performances by both women and men were superior with the preferred than with the non-preferred hand. The percentage difference scores are also presented in Table 1. We analyzed performance on each task using a 2 (sex) 2 (handedness) 2 (hand used) ANOVA. The main effect of sex was significant only in two tasks: GS, F(1, 124) = , p <.01, η p2 =.63, and FT, F(1, 124) = 15.78, p <.01, η p2 =.11. In all five tasks, the interaction between handedness and hand used was significant: GS, F(1, 124) = 25.57, p <.01, η p2 =.17; FT, F(1, 124) = 86.71, p <.01, η p2 =.41; GP-P, F(1, 124) = 24.68, p <.01, η p2 =.17; GP-R, F(1, 124) = 7.14, p <.01, η p2 =.05; and DFT, F(1, 124) = , p <.01, η p2 =.46. Simple main effects analysis of the interaction revealed that, for all five tasks, the right handed participants performed better than the left hand: GS, F(1, 124) = 16.30, p <.01, η p2 =.12; FT, F(1, 124) = 67.37, p <.01, η p2 =.35; GP-P, F(1, 124) = 12.39, p <.01, η p2 =.09; GP-R, F(1, 124) = 4.03, p <.01, η p2 =.03; and DFT, F(1, 124) = , p <.01, η p2 =.53. Hence, the left hand performed better than the right hand for GS, F(1, 124) = 9.70, p <.01, η p2 =.07; FT F(1, 124) = 24.61, p <.01, η p2 =.17; GP-P, F(1, 124) = 12.28, p <.01, η p2 =.09; and DFT, F(1, 124) = 7.41, p <.01, η p2 =.06, in left-handed participants. Figure 2 shows box plots of the distribution of the performance LQ in each motor task. There did not appear to be a systematic deviation in one direction except for in the DFT. Kolmogorov-Smirnov tests indicated that, Figure 1 Relative frequency of the laterality quotient (LQ) of the Edinburgh Handedness Inventory.

6 108 H. Yamashita Table 1 Means and standard deviations for each hand performance on the five tasks according to hand preference and sex Sex Task Left-handed Right-handed Left hand Right hand Difference (%) Left hand Right hand Difference (%) M SD M SD M SD M SD M SD M SD Women GS FT GP-P GP-R DFT (n =8) (n = 56) Men GS FT GP-P GP-R DFT (n = 10) (n = 54) Composite GS FT GP-P GP-R DFT (n = 18) (n = 110) Note. DFT = Dot Filling Test (number of dots); Difference (%) = Percentage difference score; FT = Finger Tapping (tapping per 10 s); GP-P = Grooved Pegboard Place task (speed; seconds); GP-R = Grooved Pegboard Remove task (speed; seconds); GS = Grip Strength (kg). among the five motor tasks, only the DFT was not normally distributed (p <.01). Table 2 shows the LQs for the five performance tasks according to hand preference and sex. A 2 (sex) 2 (handedness) 5 (tasks) ANOVA indicated significant main effects of handedness, F(1, 124) = , p <.01, η p2 =.50, tasks, F(4, 496) = 26.03, p <.01, η p2 =.17, and their interaction, F(4, 496) = 39.99, p <.01, η p2 =.24. The simple main effects of handedness were significant in all five tasks: GS, F(1, 124) = 30.07, p <.001, η p2 =.20; FT, F(1, 124) = 87.09, p <.01, η p2 =.41; GP-P, F(1, 124) = 26.73, p <.01, η p2 =.18; GP-R, F(1, 124) = 6.76, p <.05, η p2 =.05; and DFT, F(1, 124) = , p <.01, η p2 =.47. These results indicated that right-handed participants showed higher LQs than left-handed participants on all five tasks. The simple main effect of task was significant in the right-handed participants, F(4, 496) = 64.40, p <.01, η p2 =.34. In contrast, it was not significant in the lefthanded participants. To be sure, the differences of LQ between tasks were large in the righthanded participants, but the DFT was definitely extreme. Bonferroni-corrected t-tests at p =.05 showed significant differences between all tasks except for only two pairs (GS vs. GP-P and GP-P vs. GP-R). Table 3 shows the frequencies and ratio of participants who deviated from the provisional criteria proposed by Golden (1978). The results showed considerable variability in the frequencies with which preferred and non-preferred hand differences were observed on individual tasks in these participants. Thompson et al. (1987) reported that by combining the percentages of participants having an intermanual difference implicating either hemisphere, between one-quarter and more than one-third of their sample was classified as abnormal using the criteria. The present results almost accord with their findings from the American sample. Only the DFT had a unique characteristic. Among the righthanded participants, only one had a nonpreferred hand performance that was superior to that of the preferred hand. Moreover, 87.3% of the participants showed a preferred hand performance that was at least 20% better than that of the non-preferred hand. The DFT appears to be the best task by which

7 Neuropsychological motor tasks: Intermanual difference 109 to judge handedness if we focus only on this aspect of performance. However, among the left-handed participants, 38.9% (seven people) showed non-preferred hand performance that was superior to that of the preferred hand. All of these participants were so-called corrected left-handed persons, who used the right hand for writing despite using the left hand for other everyday tasks. Thus, performance on the DFT may simply reflect which hand is used for writing. Relation between hand performance and preference The present study also determined the extent of the relation between motor performance and hand preference assessed using questionnaires. The correlation matrix of Spearman s rank correlation coefficients indicates that the LQs of all performance measures were significantly correlated with the LQ of the EHI (Table 4).The LQ of the DFT had the highest correlation with that of the EHI. Although intercorrelations among hand performance tasks are significant, the correlations themselves are relatively weak. A similar tendency has been reported in a previous study (Brown et al., 2006). They interpreted these results as follows. As each performance task evaluates a different aspect of motor control, these different aspects of motor control may not be strongly correlated with one another. Because the intercorrelations among hand performance tasks are weak, it is difficult to predict hand preference only from the performance of a single task.a combination of performance tasks is required. A discriminant functional analysis was conducted using the LQs of the five performance tasks as independent variables. A significant relation between preference and performance Figure 2 Box plot of the distribution of the performance laterality quotient (LQ). The box represents the interquartile range that contains 50% of values of the LQ in each task; the median is indicated by a heavy line. The whiskers are lines that extend from the box to the highest and lowest values, excluding outliers. Outliers (o) are cases with values between 1.5 and 3 box lengths from the upper edge of the box. DFT = Dot Filling Test; FT = Finger Tapping; GP-P = Grooved Pegboard Place task; GP-R = Grooved Pegboard Remove task; GS = Grip Strength.

8 110 H. Yamashita Table 2 Means and standard deviations for the laterality quotients of the five performance tasks according to hand preference and sex Sex Task Left-handed Right-handed Composite M SD M SD M SD Women GS FT GP-P GP-R DFT (n =8) (n = 56) (n = 64) Men GS FT GP-P GP-R DFT (n = 10) (n = 54) (n = 64) Composite GS FT GP-P GP-R DFT (n = 18) (n = 110) (n = 128) Note. DFT = Dot Filling Test; FT = Finger Tapping; GP-P = Grooved Pegboard Place task; GP-R = Grooved Pegboard Remove task; GS = Grip Strength. Table 3 Frequencies and the ratio of participant that deviated from the provisional criteria by Golden (1978) Groups GS FT GP-P GP-R DFT Non-preferred hand performance superior to preferred hand performance Left-handed (n = 18) 2 (11.1) 3 (16.7) 3 (16.7) 4 (22.2) 7 (38.9) Right-handed (n = 110) 20 (18.2) 4 (3.6) 26 (23.6) 37 (33.6) 1 (.9) Composite (n = 128) 22 (17.2) 7 (5.5) 29 (22.7) 41 (32.0) 8 (6.3) Preferred hand performance at least 20% better than non-preferred hand performance Left-handed (n = 18) 1 (5.6) 1 (5.6) 1 (5.6) 1 (5.6) 9 (50.0) Right-handed (n = 110) 12 (10.9) 23 (20.9) 18 (16.4) 4 (3.6) 96 (87.3) Composite (n = 128) 13 (10.2) 24 (18.8) 19 (14.8) 5 (3.9) 105 (82.0) Note. DFT = Dot Filling Test; FT = Finger Tapping; GP-P = Grooved Pegboard Place task; GP-R = Grooved Pegboard Remove task; GS = Grip Strength. was found (Wilks lambda = 0.41,χ 2 (5) = , p <.001). The model was df = (GS), (FT), (GP-P), (GP- R), and (DFT). The DFT and FT had comparatively strong canonical loading: GS = 0.156, FT = 0.539, GP-P = 0.254, GP-R = 0.257, and DFT = Participants could be correctly classified into two hand-preference

9 Neuropsychological motor tasks: Intermanual difference 111 Table 4 Spearman s rank correlation coefficients (laterality quotients of the Edinburgh Handedness Inventory and the five performance tasks) EHI GS FT GP-P GP-R DFT EHI.339**.425**.437**.214*.510** GS.401**.363**.264**.461** FT.188*.230**.484** GP-P.452**.483** GP-R.438** DFT Note. DFT = Dot-Filling Test; EHI = Edinburgh Handedness Inventory; FT = Finger Tapping; GP-P = Grooved Pegboard Place task; GP-R = Grooved Pegboard Remove task; GS = Grip Strength. *p <.05, **p <.01. groups with 95.3% overall accuracy. Lefthanded participants were classified with 83.3% accuracy (15/18), while right-handed participants were classified with 97.3% accuracy (107/ 110). Discussion The present study evaluated performance differences between the right and left hands among normal Japanese young adults on five typical unimanual tasks. Previous studies in other countries have examined the influence of sex on the laterality of motor control. The present data indicated that for two tasks (GS and FT), the performance of men for both hands was significantly stronger and faster than that of the women. Sex differences on these two tasks, which have a strong relation with the factor of simple strength or speed, are consistent with those reported in previous studies (Bronstein, 1986; Dodrill, 1979; Thompson et al., 1987). However, no sex difference was observed on the performance ratio scores of the dominant and non-dominant hands. These results are also in agreement with previous studies. The present results confirm the findings of Bronstein (1986) that considerable variability in preferred and non-preferred hand differences is frequently observed on individual tasks among normal participants. Therefore, cortical dysfunction should not be suggested based on the results of a single motor task. However, as Thompson et al. (1987) indicated, a consistent discrepancy across several tasks is extremely rare. In three tasks that are typically used in neuropsychological assessment in North America (GS, FT, and the GP-P), only one right-handed person deviated from the provisional criteria of Golden (1978) on all the tasks. In addition, this individual showed a left-hand predominance on the other two tasks (the GP-R and DFT). Nevertheless, she considered herself as right-handed, and the EHI also classified her as right-handed (her LQ was 68.4). She showed a strong preference for the left hand only when writing but not in other everyday unimanual activities. She had no medical history of neurological or orthopedic problems. A detailed analysis of such a unique case may enhance the understanding of cortical asymmetry and laterality of motor control. The present study also examined the relation between hand preference and asymmetries in motor proficiency. A discriminant function analysis showed that hand preference was predictable from the task performance data with an accuracy of 90% or greater. Among the five motor tasks, the DFT had the strongest canonical loading. With the exception of only one lefthanded woman, the patterns of the right- and left-hand difference of the DFT were in agreement with the hand used for writing. Writing is a special action performed only by one hand of the two, and it is thought that it has a character different from other tasks. However, the present results also highlight problems with the DFT. Because performance on this task is highly associated with writing, it is more likely to be mistakenly judged as right-handed in the case of corrected left-handed persons who use

10 112 H. Yamashita their right hand for writing. It is well known that the Japanese population shows a low frequency of left-hand preference. The main cause is cultural pressures against left-handedness within Japanese society. Although this tendency has weakened after World War II, the custom of forcibly correcting a left-handed child to righthandedness has not completely disappeared (Hatta, 1996). It is thus believed that there are many corrected left-handed persons in Japan who use the right hand for specific movements such as writing. This creates a technical problem in the determination of handedness using the DFT, which is particularly serious in Japan. In four tasks, except the DFT, the best predictor of hand preference was the FT. The present findings that a combination of performance measures was able to predict hand preference supports the study by Brown et al. (2006), suggesting that handedness is not a unidimensional trait and should be defined using multiple measures of both preference and performance. The present study has several limitations. As results in university students may differ from those in children or an older population, generalization of the present findings is limited to educated young Japanese adults. Furthermore, since recruitment was randomly performed except for sex, the sample of left-handed participants was smaller than that of right-handed participants. Further studies covering a wider age range and including more left-handed participants should be conducted to substantiate the findings of the present research. Moreover, the present study did not include tasks that assessed the sensitivity of touch and the skill of performance without a speed requirement (time restriction). It may be necessary to examine those factors in future. Despite these limitations in the data, the present study contributes to a better understanding of the laterality of motor control and handedness. References Annett, M. (1970). A classification of hand preference by association analysis. British Journal of Psychology, 61, Annett, M. (2002). Handedness and brain asymmetry: The right shift theory. Hove, UK: Psychology Press. Bronstein, R. (1986). Normative data on intermanual differences on three tests of motor performance. Journal of Clinical and Experimental Neuropsychology, 8, Brown, S. G., Roy, E. A., Rohr, L. E., & Bryden, P. J. (2006). Using hand performance measures to predict handedness. Laterality, 11, Brown, S. G., Roy, E. A., Rohr, L. E., Snider, B. R., & Bryden, P. J. (2004). Preference and performance measures of handedness. Brain and Cognition, 55, Bryden, M. P., Bulman-Fleming, M. B., & MacDonald, V. (1996). The measurement of handedness and its relation to neuropsychological issues. In D. Elliott & E. A. Roy (Eds.), Manual asymmetries in motor performance (pp ). Boca Raton, FL: CRC Press. Bryden, P. J., & Roy, E. A. (2005). A new method of administering the Grooved Pegboard Test: Performance as a function of handedness and sex. Brain and Cognition, 58, Chapman, L. J., & Chapman, J. P. (1987). The measurement of handedness. Brain and Cognition, 6, Corey, D. M., Hurley, M. M., & Foundas, A. L. (2001). Right and left handedness defined: A multivariate approach using hand preference and hand performance measures. Neuropsychiatry, Neuropsychology and Behavioural Neurology, 14, Dodrill, C. B. (1979). Sex differences on the Halstead- Reitan Neuropsychological Battery and on other neuropsychological measures. Journal of Clinical Psychology, 35, Golden, C. J. (1978). Diagnosis and rehabilitation in clinical neuropsychology. Springfield, IL: Charles C. Thomas. Hatta, T. (1996). Neuropsychology of the lefthandedness. Tokyo, Japan: Ishiyaku-Syuppan. (In Japanese.) Hatta, T., & Hotta, C. (2008). Which inventory should be used to assess Japanese handedness? Journal of Human Environmental Studies, 6, Hatta, T., & Nakatsuka, Z. (1974). H.N. Handedness inventory. In S. Ohno (Ed.), Papers for celebration of the 63rd birthday of Prof. Ohnishi. (pp ). Osaka: Osaka City University Press. (In Japanese.) Imada, M. (1935). Experimental study of handedness. Japanese Journal of Psychology, 10, (In Japanese.)

11 Neuropsychological motor tasks: Intermanual difference 113 McManus, I. C. (2002). Right hand, left hand: The origins of asymmetry in brains, bodies, atoms and cultures. London, UK: Weidenfeld and Nicolson. Oldfield, R. C. (1971). The assessment and analysis of handedness: The Edinburgh Inventory. Neuropsychologia, 9, Steenhuis, R. E., & Bryden, M. P. (1989). Different dimensions of hand preference that relate to skilled and unskilled activities. Cortex, 25, Tapley, S. M., & Bryden, M. P. (1985). A group test for the assessment of performance between the hands. Neuropsychologia, 23, Thompson, L. L., Heaton, R. K., & Matthews, C. G. (1987). Comparison of preferred and nonpreferred hand performance on four neuropsychological motor tasks. Clinical Neuropsychologist, 11, (Received November 2, 2012; accepted September 7, 2013)