Detection of a Pulsed Sinusoid of Uncertain Frequency

Abstract

Two conditions were used in the experiments. In one condition the observer knew that a particular signal frequency would be used on all the trials of a sequence. In the other condition the observer knew only that the signal would always be some frequency in a given range. In this second condition the particular signal frequency used on any trial of the sequence was determined by a random process. The observer was therefore uncertain as to the signal frequency on any one trial but did know the range of possible signal frequencies. In both conditions the signals were adjusted in amplitude so that their detectability would be the same at all frequencies. The effect of frequency uncertainty was very small. In the most extreme condition, in which the signal ranged from 500 to 4000 cps, the decrement in detectability was approximately 3 db when compared with the condition where the signal frequency was fixed. The results are inconsistent with several models which have been proposed to explain the effects of signal uncertainty. The data also raise questions about the interpretation of the “critical-band” experiments.