Effector independence and practice: specific left hand gains in right-handers

Ulysses Araujo
Escola de Educa??o F?sica e Esporte - USP

*Jaqueline Neiva
Escola de Educa??o F?sica e Esporte - USP

*Miriam Umeki
Escola de Educa??o F?sica e Esporte - USP

*C?ssio Meira Jr.
Escola de Educa??o F?sica e Esporte - USP

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     Last modified: February 27, 2007

Abstract
The aim of this study was to investigate the effector specificity hypothesis (through bilateral transfer of learning) after a moderate practice period with the non-dominant left hand. In studies focusing the dominant right hand, an effector independent improvement is usually found after a short period of practice, which is followed by effector dependent gains after more widespread practice. However, it?s questionable if the same would hold true for the non-dominant left hand despite the lateralization of cortical motor function. Eighteen right-handed subjects completed five practice trials with the non-dominant hand (inserting 25 pins per trial) after a pre-test (PT) with both hands in the Grooved Pegboard task. After a retention test (RT1), participants performed five additional trials, followed, two days later, by ten trials and another retention test (RT2). The task goal was to insert all pins as quickly as possible; knowledge of results was given on all trials and withheld on all tests. A two-way ANOVA (side X test blocks) with repeated measures on the second factor was performed on pre-test and both retention tests' scores for both hands (ND: non-dominant hand; D: dominant hand). The Bonferroni post-hoc test was used to locate the differences. Results showed main effects for ?side? [F(1, 32) = 6.80, p<0.05], ?tests? [F(2, 64) = 53.16, p<0.001] and in the interaction ?side? X ?tests? [F(2, 64) = 6.47, p<0.05]. Differences throughout practice were detected for the non-dominant hand in all tests: RT1/ND and RT2/ND were both better than PT/ND (p<0,001 in both cases), and RT2/ND was better than RT1/ND (p<0,05). However, only an initial improvement was evident on the dominant hand: despite RT1/D and RT2/D were both better than PT/D (respectively, p<0,007 and p<0,001), no statistical differences were verified between RT1/D and RT2/D. Comparisons between non-dominant and dominant hands showed that subjects had dissimilar performances with different hands in the beginning of practice, with PT/ND worse than PT/D (p<0,001). However, no statistical differences were detected in the other retention tests. This result might be related to the halt in the dominant hand improvement after retention test 1. Results suggest a confirmation of the effector independent/effector dependent sequence of learning achievements found in studies focusing the dominant right hand. Our findings are in line with the notion of functional integration between specialized brain areas and the dynamic characteristics of motor function lateralization.