Effect of a suppressor on slopes of psychometric functions for forward-masked tones

The compressive nonlinearity defined by the basilar membrane (BM) input-output (I/O) function is evident in the slopes of psychometric functions for forward-masked tones [Schairer et al., 2003]. A suppressor tone may affect the BM I/O function by either i) reducing compression by linearizing the compressive portion of the BM I/O function, or ii) reducing the cochlear gain without affecting the value of maximum compression. The aim of the present study was to compare slopes of psychometric functions for a fixed low-level signal in the presence of a variable masker with or without a suppressor gated with the masker. Thresholds and psychometric functions were obtained for four normal-hearing listeners using a 2I-AFC task. The sinusoidal signal was a low-level 4-kHz tone (0-ms steady state, 2-ms cos2 ramps) masked by a sinusoidal masker (100-ms steady state, 2-ms cos2 ramps). The masker was either on frequency (4 kHz) or off frequency (2.2-kHz). The on- and off-frequency maskers were presented at masker-signal intervals of between 20 and 100 ms. Initial analyses suggest that the slopes of psychometric functions in the presence of an on-frequency masker become increasingly shallow as the masker level falls within the compressive region of the BM I/O function whilst the slopes of psychometric functions in the presence of an off-frequency masker remained relatively steep across masker levels. Slopes of psychometric functions in the presence of a suppressor are increased. Acknowledgement Work supported by the ESRC