Attending to dual-screen presentations

Large classrooms now often have not one, but two, screens onto which slide shows are presented. The idea (presumably) is that people on the left hand side of the room will find it easier to look at the left hand screen and those on the right will look at the right hand screen. But before implementing this design, did anyone do any research into how audience and speakers will actually behave?

Whilst at a conference yesterday, I noticed that the speaker spent the whole time standing to the left of the left-hand screen (as viewed by the audience). Every now and again I glanced at the audience, the vast majority of whom were also looking at the left hand screen. Even those in the front-most rows on the right were mainly looking at the left-hand screen. I myself found it very difficult to watch the screen on the right whilst listening to a speaker on the far left of the room. Perhaps this is because every now and again you want to switch attention from screen to speaker and vice versa, and this is easier if you are looking at the screen closest to the speaker.

More than this, however, the head and hand movements of the speaker him/herself are also a guide for the audience. When the speaker shifts his/her gaze from the audience to the screen, or waves a hand towards something on the screen, this is a cue for the audience to direct their own attention to the same thing. And if the speaker is using a laser pointer, that of course will only be pointed at one screen.

I began to wonder whether the learning experience may actually be slightly harder for the audience on the far side of the room from the speaker. Could the screen in front of you be a distraction? You glance at it occasionally, but then it feels uncomfortable so you switch your attention to the other screen or the speaker? This may be an idle worry, but has anyone researched this?

Obviously, the way the speaker positions him/herself may matter. What happens if the speaker stands in the centre of the room, between the two screens? In a different talk yesterday, I noticed that a centrally-positioned speaker still seemed to only look at the screen to his right (the audience's left), and consequently this was where the audience mostly looked. However, this may have been partly determined by the positioning of the computer screen on the desk in front of the speaker. From the speaker's viewpoint, this was positioned to the right of the desk and also with a tilt such that the speaker would have naturally looked rightwards to see the computer screen.

If the majority of an audience only look at one of the two screens, then surely having two is actually a waste of money. This is even worse if the non-focal screen is actually a distraction. However, I don't know of any research and would be interested to know if there is any.