Detecting a tone of one frequency when a tone of a different frequency is amplitude modulated.

Abstract

It is assumed in many of the recent studies of cross-frequency effects of temporal processing that the effects are not occurring within any one frequency channel. This study was an attempt to investigate that assumption. A 500-ms carrier (the masker tone) of one frequency (e.g., 4000 Hz) was sinusoidally amplitude modulated at a slow rate (4, 8, or 16 Hz) and listeners were asked to detect a brief (10 ms) tone (the probe tone) presented at another frequency (e.g., 1000 Hz) and at different times relative to the phase of the masker modulator. Masker level was 75 dB SPL. If probe threshold varies as a function of the probe’s temporal relation to the phase of the masker modulator, then masker modulation might be preserved in the frequency channel of the probe indicating a within-channel interaction between the masker and the probe. There was a small (3–5 dB) variation of probe threshold when the probe was presented at different times relative to the phase of the masker modulator when the masker was modulated at 4 Hz and with 100% modulation depth. A similar change in threshold occurred when the masker was either higher or lower in frequency than the probe (mask is 4000 Hz, probe is 1000 Hz or mask is 1000 Hz, probe is 4000 Hz). No threshold changes were obtained at the higher modulation rates or at 4-Hz modulation when the depth of modulation was less than 100%. Thus there might be a small within-channel interaction, but only when the modulation rate is slow (i.e., 4 Hz). [Work supported by grants from the NIDCD and the AFOSR.]