雙語人之感知磁吸效應:腦事件相關電位研究

Abstract

從語音範疇內部結構的研究中，我們知道Kuhl(1991)所提出的感知磁吸效應很令人深思，人們會就其音類範疇的典型音展現出類化能力。也就是說，人在音類的感知上是以一個典型音為基準，與它相鄰近的音都會被視作是同一個音，儘管聲學物理性有其差異性，但人的感知是會去忽略的。然而，前人的研究著重在單語，操弄兩種語言系統的雙語人的感知研究付之闕如。我們的研究發現，國台雙語人在相似音[i,u,a]皆展現感知磁吸效應。相似音的語音感知並不會受到語音生成類化的侷限。

更近一步以腦事件相關電位研究探討之，從鄰界面國語[a]與鄰界面台語[a]的MMN腦波反應來看，證據顯示支持了雙語人的感知磁吸效應，並且雙語人的兩種語言間相似音的感知是不會有所干擾。最外軌的刺激音(如圈軌3跟圈軌4)引發最大的MMN振幅，相對地，這些圈軌音觸發較早的時間潛伏期。這意謂著，國台雙語人可以察覺比之圈軌1和圈軌2這些鄰近中心典型音還外軌的刺激項。即便處在國台[a]兩個相似音鄰界面中，雙語人仍舊可以區辨各自音類範疇的刺激音項，而不混淆。此為雙語人能在兩種語言系統下各自展現感知磁吸效應的有力證據。

The perceptual magnet effect proposed by Kuhl (1991) is well considerable through the studies of the internal structures of phonetic categories, indicating that humans show a similarity adoption for the prototypes of speech categories. That is, the surrounding referent sounds would be regarded perceptually as the same with the center perceptual prototype in each category; however, previous studies just focus on monolinguals and the perception of bilinguals is unknown. In our findings, bilingual speakers of Mandarin and Taiwanese show the perceptual magnet effect respectively on similar vowels of [i,u,a] on Mandarin and Taiwanese. Perception of two similar vowels is not confined by the bilinguals’ assimilation of production.

Furthermore, speaking of ERPs study, evidence of MMN activation on both Mandarin and Taiwanese Interface dimension of [a] not only supports the perceptual magnet effect but also demonstrates that there is no interference on perception of two similar vowels for bilinguals. The Outer Orbit stimuli (Orbit 3 and Orbit 4) evoke larger MMN amplitude whereas they took earlier MMN latency. That is to say, Mandarin-Taiwanese bilinguals can detect the more deviant stimuli in the outer than Orbit 1 and Orbit 2, which are adjacent to the prototype. Even on the interface of Mandarin [a] and Taiwanese [a], bilinguals get no trouble in discriminating stimuli within each interface of a language. It is hard evidence that the perceptual magnet effect functions both on Mandarin and Taiwanese.