Dynamic perception of tones simultaneously modulated in both frequency and amplitude

Abstract

Auditory processing in the dynamic perception of tones with simultaneous frequency modulation (FM) and amplitude modulation (AM) was investigated. Thresholds for the detection of target modulation (FM or AM) were measured with the respective nontarget modulation (AM or FM) kept well above threshold. The carrier frequencies of tones below 1 kHz were used. For FM and AM having the same sinusoidal modulation frequencies below 20 Hz, the thresholds of the target modulation changed as a function of the phase difference between the target and nontarget modulations. When the frequencies of the FM and AM were different from each other, the thresholds of the target modulation were nearly the same as those obtained for a tone with the target modulation alone. When the frequency and amplitude continuously increased or decreased in a short tonal duration, there was little difference in the threshold of the target modulation between the cases for increase and decrease in nontarget modulation. These results suggest the existence of channels selectively tuned to the periodicity of FM and AM in the auditory pathways. [Work supported by a Grant in Aid for Scientific Research (No. 62510059) from the Ministry of Education.]