Relationship Between Cortical Handedness and Motor Function

In each analysis, we tested normality of the data by means of the Shapiro–Wilk test that did not confirm normality for some groups. For this reason, we chose non-parametric testing. Thus, for the CFT structures, for each dominant hand, we compared the signal intensities of the left and right CFT structures by Mann–Whitney U testing. We calculated peak signal intensity as the ratio of results of the left to right hemispheres (right/left). For hand motor function scores, grip and pinch strengths, and scores of speed and accuracy, we calculated test scores of TT as an asymmetry index ([right − left]/[left + right]). We did a second analysis to confirm whether every index reflected the effect of handedness, and we compared the right- and left-handed groups by Mann–Whitney U testing. The magnitude of the effect size (r) was named “small” at 0.1 or greater, “medium” at 0.3 or greater, and “large” at 0.5 or greater¹⁸ . To confirm the relationship between the signal intensity values of the CFT structures and the hand motor functions, we did a simple linear regression of the asymmetry indices of hand motor function against the signal intensity ratios of the CFT structures as the independent variables as a third analysis, and we did the same for each gender separately as a fourth analysis. We used SPSS Statistic 29.0 (IBM, Japan) for the analysis with the significance level set at less than 5%.