Evaluating Models of Gesture and Speech Production for People With Aphasia.

People with aphasia use gestures not only to communicate relevant content but also to compensate for their verbal limitations. The Sketch Model (De Ruiter, 2000) assumes a flexible relationship between gesture and speech with the possibility of a compensatory use of the two modalities. In the successor of the Sketch Model, the AR-Sketch Model (De Ruiter, 2017), the relationship between iconic gestures and speech is no longer assumed to be flexible and compensatory, but instead iconic gestures are assumed to express information that is redundant to speech. In this study, we evaluated the contradictory predictions of the Sketch Model and the AR-Sketch Model using data collected from people with aphasia as well as a group of people without language impairment. We only found compensatory use of gesture in the people with aphasia, whereas the people without language impairments made very little compensatory use of gestures. Hence, the people with aphasia gestured according to the prediction of the Sketch Model, whereas the people without language impairment did not. We conclude that aphasia fundamentally changes the relationship of gesture and speech.