FM detection and F0 discrimination of complex tones

Abstract

Earlier experiments have shown that listeners are very poor at detecting frequency modulation (FM) imposed on the fundamental frequency (F0) of complex tones consisting only of unresolved harmonics. In the first experiment, the detection of 5 Hz FM was measured for a complex tone with a 62.5 Hz F0 and harmonics bandpass filtered between 1375 and 1875 Hz. These results were compared to performance on a task in which listeners were required to detect an F0 difference between two 50-ms bursts of the complex separated by 50 ms. It was shown that performance on the two tasks (measured in terms of maximum F0 deviation at threshold) was similar. A subsequent experiment showed that, in a two interval discrimination task, there was a dramatic deterioration in F0 discrimination for complexes composed of unresolved harmonics as the interstimulus interval was reduced from 500 to 100 ms. It seems, therefore, that poor performance on the FM detection task was due to difficulties in comparing F0s over short time intervals, rather than a difficulty in processing FM per se. The possibility that the auditory system uses a long temporal window when determining the pitch of these complexes will be discussed.