2 Car talk , car listen

Among age-old speculations about the origins of human language is a suggestion that use of the oral channel evolved to leave the hands and the rest of the body free for other activities. Whether this is true or not, there are few human activities that proceed unaccompanied by talking or listening. With the scope of everyday activities expanding to include some that are life-threatening unless performed with sufficient care, questions about the demands of language use on attention to other things have assumed new priority. This new priority runs up against an old, unresolved, but theoretically central psycholinguistic debate over how language production and language comprehension are related to each other. The terms of this relationship involve shared or divided components of linguistic knowledge and shared or divided resources of perceptual, motor, and cognitive skill. Our question in this chapter is how production and comprehension differ in their demands on attention or working memory (Baddeley, 2003), as reflected in how much production and comprehension interfere with other tasks. At bottom, we are interested in whether talking is harder than listening. The automatic answer to this question seems to be " of course ". Talking involves retrieving linguistic information from memory and assembling utterances in working memory, using only information from the intended meaning; listening benefits from specific form cues and accompanying recognition processes. The retrieval challenges for speakers are imposing: The estimated vocabulary of an educated English speaker is over 45,000 words. Failures of retrieval are common enough to have inspired a famous observation of William James (1890) about tip-of-the-tongue states and a large research literature on the phenomenon, beginning with Brown and McNeill (1966). Assembling utterances entails structuring and ordering the words into one of the infinite number of possible phrases or sentences of English, drawing on the 12,000-or-more syllables of which English words are composed , and articulating the syllables at a rate of three or four per second, using more muscle fibres than any other mechanical performance of the human body (Fink, 1986). It is ability to speak a foreign language, not ability to understand one, that constitutes the commonplace standard of bilingual competence: Every word uttered, indeed every sound, is on display for