People gesture while they speak. They move their hands and arms in certain ways to accompany their speech. For example, in a route description as in (1)
- Then you will come by a church
the speaker can indicate the shape of the steeples with her hands. To do that, the stroke of the gesture will most naturally synchronize with speech in that it will align with the word that it modifies and the syllable that is stressed most (i.e. “CHURCH”). In this example, the co-speech gesture would be an iconic one, one that indicates the shape of the steeples. Interestingly, the speaker can convey information by means of this gesture that is not included in the speech signal, for example the fact that the church has two steeples, e.g. by indicating the two steeples with her two hands. After having heard (1) and having observed the co-speech gesture, the listener will know that she will pass a church and that this church has two steeples.