轉換慣用手孩童執行冗餘任務之行為表現與其兩半球溝通特質

The Performance and Inter-Hemispheric Communication During Redundant Task in Children with Switched Left-Handedness

先前研究顯示部分「轉換慣用手者」（“switched” left-handers）之大腦活化模式與未轉換之慣用左手與右手者不同，偏向雙側活化。為進一步釐清轉換慣用手者之兩大腦溝通是否亦受到轉換過程影響，本研究收取未轉換之慣用左手、慣用右手與轉換慣用手者等三組（每組各14 位，平均年齡7.42 歲，SD=0.79歲）執行常被用來探討兩大腦溝通表現之冗餘任務（redundant task）──在參與者視野左側、右側或雙側隨機呈現刺激，全程皆以雙手食指按鍵反應；並評估三組基本能力表現，來了解強迫轉換慣用手對行為與大腦溝通機轉之影響。過程會紀錄參與者之反應時間、反應時間差與錯誤率等行為資料。結果顯示慣用左手與右手者雙側視野反應時間明顯快於單側，出現明顯的冗餘增益（redundancy gain）；而轉換慣用手者則否。如與會出現較強冗餘增益之缺胼胝體族群比較，可推論轉換慣用手者之兩大腦聯繫比未轉換者強，可能也包括大腦半球間抑制訊息（inter-hemispheric inhibition, IHI）之傳遞，亦可合理使用「競爭模式」（race model）、「大腦半球間抑制假說」（inter-hemispheric inhibition hypothesis）與「共同活化模式」（co-activation model）來解釋，而為了解何種理論較符合轉換慣用手者之行為表現，未來需要蒐集更多資料來釐清。而前述大腦溝通特質的改變並未使轉換者的任務表現與基本能力有所提升，顯示轉換歷程對慣用左手孩童而言並不會有明顯效益產生，轉換孩童慣用手可能帶來的影響仍待有系統的後續研究。

Previous studies showed that the pattern of brain activation might vary between switched left-handers and consistent left-/right-handers. The switched left-handers were found to display a more bilaterally symmetrical pattern. However, the communication between the two brain hemispheres in this switched population has not been studied. The present study used redundant task combined with redundancy gain to investigate the influence of converting children’ handedness. Fourteen switched left-handers and twenty-eight consistent left-/right-handers (average age 7.42 years) performed a redundant task; whatever the visual stimuli were presented in the left, right, or bilateral visual field, they had to press the buttons with both index fingers. Behavioral data (reaction time [RT], redundancy gain, and error rate) and basic evaluations were collected for analysis and exploration. The results revealed that left-/right-handers had significant redundancy gain, their manual RTs to bilateral stimuli were faster than those to unilateral stimuli; but this phenomenon did not occur in switched left-handers who showed weaker redundancy gain than the consistent left-/right-handers. Compared with split-brain individuals that showed larger redundancy gain, we used “race model,” “inter-hemispheric competition hypothesis,” and “co-activation model” to infer that the switched left-handers showed stronger hemispheric communication than non-switched ones (probably exhibiting inter-hemispheric inhibition, IHI). The above-mentioned changes in switched left-handers did not enhance their behavioral performance or showed any obvious benefits. The impact of switched handedness in children requires further investigation.