We explained that conceptual pacing has to do with how fast you go through difficult and easy content. Attentional pacing is related to that, but has to do with how much change you introduce into your speaking. It’s not a measurable thing, but a conceptual one.
When you introduce a lot of change in the audience’s environment as you speak we call that a high attentional pace because it makes it easier for the audience to pay attention. For example, you may vary your tone and loudness, move around, use gestures, shift attention to an audio-visual aid, and so on. The more of these you use, the higher the attentional pace.
Attentional pacing and conceptual pacing interact. When you have a difficult concept to convey (conceptual pacing), you lower your attentional pace so that people have more time to process the difficult concept. When your concepts and material are simpler, you use more attentional pacing to keep attention.