Is it only possible to pay attention to one thing at a time?

I once was at a (theravada) mini-retreat where the teacher insisted that if one really watched carefully, one would recognize that it is not possible for the mind to pay attention to more than one thing at a time. I commented that in my experience it is possible to experience a lot of stimuli simultaneously. to see "whole picture" in one glimpse, just like listening to many instruments at the same time, but he kept insisting that this was due to the fact that attention shifted at a very fast pace between objects. And that if I kept practicing I would realize this. Is what he said in accordance with buddhist teaching? I have never heard it mentioned from any teacher other than him (but I remember it from some old perception psychology which I don't know if is out dated), and it really interferes with my mindfulness when I come to think of what he said.