本文針對在進行句內代碼轉換時雙語腦詞匯的活動與性質加以研究。文章著重提出所謂的腦詞匯不僅僅包含詞位而且包含「詞義素」。詞義素是存在於腦詞匯中的抽象條目。正是這種抽象條目支撐著實際詞位的表象實體。其原因在於這種抽象條目包含對詞位有關的語義、句法、語用以及詞法方面的信息。文章並提出在腦詞匯中的詞義素是各種語言特定的，而各語言特定的詞義素在進行含有句內代碼轉換的談話過程中相接觸。這種詞義素的相接觸出現在抽象的詞匯結構的三個層次：詞匯概念結構、謂語組合結構以及詞法實現形式。各語言特定的詞義素在抽象的詞匯結構中任何一個層次上的激活便會激發句內代碼轉換的產生。本文中討論到的句內代碼轉換的例子證明參與句內代碼轉換的語言的激活程度是不同的。它們的不同激活程度表現在語言特定的詞義素對詞素及詞素句法程序的激活。句內代碼轉換的例子並且證明為使句內代碼轉換的實現有可能，從內嵌語（EL）那裡激活的詞義素必須與母體語（ML）中相應的詞義素等合 (Myers-Scotton 1993a [1997])。

This paper studies intrasentential codeswitching (ICS) in terms of the nature and activity of the bilingual mental lexicon. It claims that the mental lexicon does not simply contain lexemes but also “lemmas”, which are abstract entries in the mental lexicon that support the surface realization of actual lexemes because they contain semantic, syntactic, pragmatic, and morphological information about lexemes. It further claims that lemmas in the bilingual mental lexicon are language-specific and are in contact during a discourse involving ICS at three levels of abstract lexical structure: lexical-conceptual structure, predicate-argument structure, and morphological realization patterns. Activation of such lemmas at any level of abstract lexical structure motivates ICS. The ICS instances provide evidence that there is differential activation of participating languages in terms of language-specific lemma activation for morphemes and morphosyntactic procedures, and activated lemmas from the Embedded Language (EL) must be congruent with the counterparts of the Matrix Language (ML) (Myers-Scotton 1993a [1997]) for permissible ICS realizations.