It is easy to label the students as superficial, but double speed replay has a perfectly valid though slightly embarrassing, for us the teachers, justification. When I was trained in public speaking, I was taught this basic technique for preparing a time-framed lecture:
- make up your mind and prepare visual aids if required,
- talk about the subject twice the time you are allocated and record yourself,
- transcribe your recorded speech and read it aloud, at a slow pace.
- talk about the subject the second time, consulting the transcript if needed.
The result is that you normally get a smooth talk with the correct duration (half of the original time) the second time around. This is because that when we speak about a subject freely, even if we are well familiar with the subject, we spend as much time thinking about what we are going to say next as actually speaking (and conceal this by slowing down the overall speaking pace).
Let’s admit that we do not do the full rehearsal of every lecture we deliver. Because of that, we put the time burden of thinking about what we are going to say on our students. And students are smart enough to compensate for that by replaying at 2x speed — actually at the normal lecture speed if we came prepared.