I am not sure if it was the same work I was told about, but if it was, I
apologise for being mislead/ing.
I think the crucial point of the Lisa Duff paper was "...Research and
design initiatives intended to reduce cockpit noise should first consider
if there may be optimum decibel level for effective aviation instruction"
(Duff, L. 1997). Its the optimum level of noise that is crucial and a
simple example from outside aviation would perhaps be that of a car stereo
and its effect on the driver.
Stephen, I fall on my sword!
Best Wishes
Dr. Graham R. Braithwaite
Research Associate
Department of Aviation
University of New South Wales
Sydney 2052
Australia