選擇性抑制係指當兩個動作同時進行時，停止其中之一，而讓另外一個動作繼續進行的能力。過去的研究通常只對一個動作參數來研究抑制機制，本論文想要探討不同動作參數對於選擇性抑制的影響。藉由一系列三個實驗，描繪出不同肢體配對以及不同動作方向的動作在行為上的差異。實驗一探討是否不同肢體所對應的動作控制皮質區之距離遠近，會影響其配對進行選擇性抑制之停止訊號反應時間。我們採用了Boucher et al. (2007)中修改過的停止訊號典範，以「右手食指與右手中指」或是「右手食指與右腳」的配對。受試者需要經過三種抑制階段的考驗：單獨抑制，同時抑制與交錯抑制，以比較停止訊號反應時間是否在不同肢體配對間會有差異。結果顯示選擇性抑制的停止訊號反應時間會顯著長於全面性抑制的停止訊號反應時間，而且右手跟右腳配對的停止訊號反應時間會顯著長於右手食指與右手中指配對的停止訊號反應時間。實驗二目標是去探討抑制機制是否會受「動作肢體」以及「動作方向」這兩個決定動作執行方式的參數。實驗二操弄了動作方向性(相同或相反)，結果顯示停止訊號反應時間在選擇方向的時候會比在選擇肢體的時候來的更長。為了澄清此種差異是否是來自於選擇方向時的選項，比選擇肢體的選項更多，而造成困難度差異，我們在實驗三中對於動作肢體以及動作方向設定了相同數量的可能反應選項。當困難度被控制的時候，停止訊號反應時間在比較肢體以及比較方向上就無顯著差異。 因此，「動作肢體」與「動作方向」兩個參數的選擇，對於選擇性抑制機制而言的困難度是相當的，抑制的歷程可能發生在決定動作肢體與方向之前，或是兩者的共同階段。The ability to selectively inhibit the execution of an action while performing other ones is crucial in humans’ multitasking daily life. Few studies have investigated the contributions of different motor parameters in inhibition. The current study aims to compare selective inhibition for choice reaction involving two effectors or response directions. We adopted a variation of the stop-signal paradigm to examine how selective inhibition is modulated by how potential motor responses are combined and inhibited. Experiment 1 investigated selective inhibition under different combinations of effectors, namely “index and middle fingers” versus “hand and foot”. The results showed that SSRT of the index finger was longer when the other response option was the foot than was the middle finger. Experiment 2 examined how selective inhibition differs between selective stopping of effectors and movement directions, and that for most of the situations SSRT is longer for stopping a response based on its direction than effector. After equating complexity of response mapping between direction and effector conditions in Experiment 2, Experiment 3 showed that SSRT is not different between selecting direction or effectors. To summarize, SSRT varies depending on the way response effectors are paired and selectively stopped. Selective inhibition is thus likely not amodal and may involve different inhibitory mechanisms depending on parameters specifying the motor response.
