A critical evaluation of models of gesture and speech production for understanding gesture in aphasia

Abstract

Background: The background to this study is that aphasiologists have increasingly started to pay attention not only to the speech that people with aphasia produce, but also to their gestures. As there are a number of competing models about the production of gesture and speech in healthy subjects, it is important to evaluate whether, and if so how, these models could be used to guide the research into gesture and speech, and the relationship between these, in speakers with aphasia.

Aims: The aims and objectives of this study are to see how existing models of gesture and speech are able to accommodate the findings regarding the gesture and speech behaviour of speakers with aphasia, in the hope that (1) these models could shed light on the use of gesture in aphasic speakers, and potentially suggest new approaches to therapy for people with aphasia and (2) the aphasia gesture data might help fundamental psycholinguistics to evaluate the adequacy of existing gesture and speech models.

Methods & Procedures: The methodology here was theoretical. Four models of gesture and speech interaction were critiqued and we reviewed their ability to explain some of the central empirical findings in the area of gesture and speech in aphasia.

Outcomes & Results: The outcomes and results of this theoretical analysis were that, with respect to the relationship between gesture and speech in aphasia, (1) the four models under investigation could be reduced to two models, because three of the investigated models were based on the same core assumptions and (2) both of these models adequately explain these findings, but the Growth Point/Sketch/Interface Model is more satisfactory than the Lexical Access Model, because of the better fit with the experimental results on the use of gesture for facilitating word finding, and because it is more compatible with the finding that gestures are also used to enhance communicative efficiency by replacing speech.

Conclusions: The two main conclusions from this study were that both the Growth Point/Sketch/Interface Model and the Lexical Access Model are compatible with data on gesture and speech in aphasia, and that the former appears to be preferable on the basis of the evidence available so far.

Keywords:

• Gesture
• Speech
• Adaptation
• Broca
• Models

Notes

¹For instance, Bühler’s (1934) famous “Organon” model.

²This is also very clear from looking at the model by Krauss et al. (2000, Figure 1)

Figure 1. The sketch model.

³In the Sketch Model, there is no distinction made between metaphoric and iconic gestures, because for processing in a production model it is not relevant whether the imagistic representation underlying a gesture is of a metaphoric or a concrete origin.

⁴Assumptions three to five are not addressed in GP theory, as they are concerned with computational implementation, an aspect that lies outside the scope of GP theory.

⁵An intriguing proposal for a faster and therefore arguably more plausible self-monitoring architecture based on forward modelling can be found in Pickering and Garrod (in Press).