Two-tone suppression in forward masking as a function of probe frequency and suppressor frequency

Abstract

Masking functions (probe threshold vs probe frequency) in forward masking were measured for a tonal masker at 2 kHz with and without a suppressing tone. An adaptive 2IFC procedure was used with 300-ms maskers (10 ms rise/fall), 20-ms probe tones (10 ms rise/fall, no steady state), and no silent interval between masker and probe. The frequency of the suppressing tone was varied in the range 2025 to 2800 Hz. The suppression, measured as the reduction in probe threshold produced by adding the suppressing tone, was found to have two components. One component was limited to a narrow range of probe frequencies around 2 kHz, while the other component shifted in frequency region as the frequency of the suppressing tone was altered. In some cases there were two distinct peaks in the functions relating amount of suppression to probe frequency. The suppression around 2 kHz probably reflects a qualitative change in the cues available to the observer when a suppressing tone is added to the masker, while the suppression which shifts with the frequency of the suppressor may reflect a reduction in level of only part of the excitation pattern of the masking tone.