The experiment described was carried out to find the effect of the number of irrelevant lights on the human response time to light signals appearing amongst them. both the signal lights and the irrelevant lights could be made steady or flashing; this produced four conditions of eroding of the signal lights from the background, e.g. flashing signal with steady background and so on. It was found that the geometric mean response time increased to an unusually large extent. from 0-8 sec with no backgrounds lights up to nearly 2 sec with 21. A background of flashing lights was found to increase the response-time more than a background of steady lights, whether the signal was flashing or not: The shortest response times were obtained when flashing signals were seen against a steady background and the longest with flashing signals against a flashing background. Thus is is concluded that flashing signals should not be used in conditions where a number of them may appear together within the field of view.
Abstract