Coverbal gestures: Between communication and speech production

Some of the gestures that normally accompany continuous speech (coverbal gestures) seem to be related to the content of speech and have a form that is related to this content (iconic gestures). They have a low semantic specificity, they are physically complex, they have systematic timing relations with the parts of speech to which they relate and they tend to occur in the neighborhood of speech dysfluencies in both normal and pathological speech. The present chapter reviews the evidence concerning iconic gestures and suggests that they reflect the facilitation of lexical processing by recourse to secondary, imagistic information. Other coverbal gestures may be more variable in their form and timing in relation to speech. These include pointing to a particular direction (deictics), pantomiming an action (pantomimes), indicating measures (quantifiers) or performing a gesture with a specific, well-known meaning (emblems). These gestures have primarily communicative functions that act like words or specify the meanings of the accompanying speech. I present a model (after Hadar and Butterworth 1997) in which I suggest that the function of most iconic gestures is to facilitate word retrieval. To enhance retrieval, the cognitive system elicits imagistic information from two distinct stages in the speech production system: pre-verbally, from the processes of conceptualization, and post-semantically, initiated in the lexicon. Imagistic information assists or facilitates lexical retrieval in three ways: first, by defining the conceptual input to the semantic lexicon; second, by maintaining a set of core features while reselecting a lexical entry and, third, by directly activating phonological word-forms. The model offers an account of a range of detailed gestural phenomena, including the semantic specificity of gestures, their timing in relation to speech and aspects of their selective breakdown in aphasia.