Academic talks are often given after lunch, which process diverts much of the circulatory system to the viscera at the expense of the head. I learned after a while that the younger members of the audience in the back three rows would open a book on whether the Bob the Oul'Feller in the front was, or was not, asleep. Dang! but it's hard to stay awake when the lights dim and the boring details start to be explained slide after slide after slzzzzzzzzz. At least I didn't fall extravagantly asleep like my Emeritus Professor of Genetics [R] at the TCD Quatercentenary symposium in 1992 . . . I started snoring 20 years later and 20 years younger.
We are desperate, consciously or unconsciously, for the approval of our peers. Gretchen McCulloch talks about taking one for the team by being conspicuously engaged when listening to talks. She knows, as a High Involvement conversationalist, that the speaker's equanimity depends on someone in the sea of faces looking like they're enjoying the event. This can <urban legend alert> be mobilised by co-ordinated crowd action. IF all the students in the room agree to look up and pay attention when The Prof moves left and look at their shoes when s/he drifts right THEN by the end of the lecture the poor speaker will be crammed into the left front corner between the bin and the fire-extinguisher. Ah go on try it.
And while we're on the judgmental front, I'll note that two of my colleagues, of full age, are in the habit of bringing their smart-phones to meetings and multitasking with the business at hand and the desperate demands of their social media. Well, really!