ASA 127th Meeting M.I.T. 1994 June 6-10

4aPP18. The effect of coherent frequency change on signal detectability.

Xiaofen Chen

Marion F. Cohen

Dept. of Commun. Sci. U-85, Univ. of Connecticut, Storrs, CT 06269

Coherent frequency change of a signal and masker can result in poorer detectability of the signal [M. F. Cohen and X. Chen, J. Acoust. Soc. Am. 92, 766--772 (1992)]. To further demonstrate the independence of this effect from the influences of spectral or harmonic factors, the following experiment was performed. Detectability of a 125-ms single component signal, of varying frequencies, was measured in the presence of three-component simultaneous masker. The signal and masker were either coherently frequency modulated (downglide), or were unmodulated (sinusoids), and were either harmonically related or not. The data show that the signal having coherent frequency change is the more difficult to detect for both harmonic and nonharmonic stimuli, even though the spectral and harmonic relationship between signal and masker are unchanged by the coherent modulation. In addition, this effect occurs even for signal frequencies spectrally distant from the masker. The experiment was repeated with signal modulating phase reversed to the masker modulator, i.e., an upward glide. The data show that the signal is easiest to detect in this condition. These results suggest that coherent frequency change among stimulus components can affect signal detectability. [Work supported by AFOSR.]