Meaning of “self-priming” in specific example

Question

I don't understand the term self-priming in the following sentence:

Illustrators may have a self-priming function, helping people put words together into reasonably coherent speech.

Just for the context, illustrators are gestures we do during the conversations.

Answer 1

It's a metaphor from engineering. A self-priming pump is one which doesn't need priming before it starts — that is, it can start from empty and doesn't need to be filled prior to starting to pump. It fills itself, ready to produce its output.

The gestures made in speech have a similar function of getting the brain “in gear” and ready to go, ready to produce something coherent and useful.