Intrahemispheric competition between vocal and unimanual performance in right-handed, left-handed and inverted left-handed subjects

Abstract

Levy and Reid (1976, 1978) propose that inverted left handers, that is, those left-handers who write with the tip of their pen pointed towards the bottom of the page, demonstrate ipsilateral hemispheric control over distal musculature responding. This theory of cerebral organization has not been well supported by empirical evidence, partly because of the failure of many studies to examine the complete musculature system involved in writing. The present study was proposed to study more of the musculature system involved in writing in the context of performing a dual task. Kinsbourne and Cooke’s (1971) model of intrahemispheric competition states that dual task performance, compared to single task performance, will decrease (1) as the two competitive functions share the same cerebral space, and (2) as the concurrent activity increases in complexity. The theory further states that dual task performance will increase with practice. Controlling for Familial Sinistrality, the present study compared the performance of right handed (n=20), left handed (n=20) and inverted left handed (n=20) male subjects during a Pursuit Rotor Test, which was hypothesized to parallel some of the motor behaviors involved in writing. Subjects completed this task while remaining silent or while repeating either a four word phrase or a four word alliteration. Considering Levy and Reid’s (1976, 1978) theory it was hypothesized that (I) the performance of inverted left handers (ILH) without a history of Familial Sinistrality would show decrements in responding with their left hand under both interference conditions. ILH subjects with a history of Familial Sinstrality were predicted to demonstrate right hand response decrements during both interference conditions. (II) Left handed (LH) subjects without a history of Familial Sinistrality were predicted to demonstrate a right hand response decrement under both levels of the interference conditions, whereas LH with a history of Familial Sinistrality were expected to show decreased left hand responding under both interference conditions. (III) Both right handed (RH) groups of subjects were proposed to demonstrate right hand decrements in responding under both interference conditions. The RH group with a history of Familiar Sinistrality was also predicted to demonstrate a smaller left hand decrement under both the interference conditions. Based upon Kinsbourne and Cooke’s (1971) dual-code theory, both interference conditions were hypothesized to interfere with and decrease the motor performance of subjects under the conditions listed in I, II and III above. It was hypothesized that the alliteration condition would decrease the performance more than the simple phrase condition. Overall, the results did not support the predictions based upon Levy and Reid (1976, 1978) hypothesis. Neither group of left handed subjects (LH & ILH) showed any significant response decrements under concurrent verbal interference. The overall performance of RH subjects demonstrated some support for the dual-task theory posited by Kinsbourne and Cooke. Two out of a possible five groups of RH subjects demonstrated significant right hand response decrements under concurrent verbal interference. However, no difference in responding was found between simple and complex verbal interference. Some qualitative results imply that some subtle differences do exist between LH and ILH subjects. Some limitations of the experiment are discussed as well as some future research topics.