The Role of Suppression in the Upward Spread of Masking

Abstract

The upward spread of masking refers to the higher growth rate of masking for maskers lower in frequency than the signal, compared to maskers at the signal frequency (Wegel RL, Lane CE. The auditory masking of one pure tone by another and its possible relation to the dynamics of the inner ear. Physics Rev. 23:266-285, 1924; Egan JP, Hake HW. On the masking pattern of a simple auditory stimulus. J. Acoust. Soc. Am. 22:622-630, 1950; Delgutte B. Physiological mechanisms of psychophysical masking: Observations from auditory-nerve fibres. J. Acoust. Soc. Am. 87:791-809, 1990a, Delgutte B. Two-tone rate suppression in auditory-nerve fibres: Dependence on suppressor frequency and level. Hear Res. 49:225-246, 1990b). The upward spread of simultaneous masking may arise from a combination of excitatory and suppressive effects. In this study, growth of masking functions were obtained for a 4-kHz signal masked by an on-frequency (4 kHz) or offfrequency (2.4 kHz), simultaneous or forward masker, in the presence of a notched noise with a center frequency of 4 kHz presented to restrict off-frequency listening. Compression was estimated from the slopes of the off-frequency growth of masking functions. Suppression was estimated by comparing the offfrequency simultaneous-and forward-masked growth of masking functions. Results showed that, for midlevel signals (35-60 dB SPL), the compression exponent estimated from simultaneous and forward masking averaged 0.31 and 0.26, respectively. The maximum amount of suppression (defined as the decrease in the basilar-membrane response to the signal) was variable, ranging from about 6 to 17 dB across subjects. Despite the substantial reduction in the response to the signal, the results suggest that suppression has a minimal effect on the slope of the masking function at mid levels. Rather, upward spread of masking seems to be mainly determined by the compressive basilar-membrane response to the signal in relation to the linear response to the lowerfrequency masker.

Simultaneous masking additivity for short Gaussian-shaped tones: Spectral effects

“…With respect to the MOCR, there is at least one reason why simultaneous masking additivity for the Gaussian stimuli used in the present study may differ from that observed in the cited studies of masking additivity (Humes et al, 1992) and USSM (Oxenham and Plack, 1998;Bacon et al, 1999;Yasin and Plack, 2005). All those studies involved relatively long maskers and presented the target at the temporal center of the masker, while the Gaussians used in the present study had a very short duration (<10 ms).…”

“…For target-masker frequency ratios and target levels approximately comparable to our condition M2M3, masking growth rates of about 2.0 (Oxenham and Plack, 1998;Bacon et al, 1999) to 2.5 dB/dB (Yasin and Plack, 2005) have been reported. Considering the average rate of 2.2 dB/dB across these studies and assuming intensity summation of the individual masker excitations would lead to excess masking for a masker pair of (3 Â 2.2) À 3 ¼ 3.6 dB.…”

“…As estimates of the function f, we used the I/O functions derived in Laback et al (2011) for nonsimultaneous Gaussian maskers assuming that (1) BM compression of the target is similar in nonsimultaneous and simultaneous masking, as suggested in Yasin and Plack (2005), and (2) The dashed lines in the panels of Fig. 1 show the model predictions.…”

“…Another well-known effect related to the additivity of simultaneous masking is the so-called "upward spread of simultaneous masking" (USSM, Egan and Hake, 1950;Oxenham and Plack, 1998;Bacon et al, 1999;Yasin and Plack, 2005). The USSM refers to the nonlinear (excessive) growth of masking for maskers lower in frequency than the target, compared to maskers close to the CF of the target.…”

Computational Modeling of Individual Differences in Behavioral Estimates of Cochlear Nonlinearities

“…Behavioral measures often infer cochlear compression by estimating the cochlear input/ output (I/O) function, which exhibits linear growth at low levels and compressive growth at mid to high levels (e.g., Ruggero and Rich 1991). Compression can be estimated from masking data by calculating the minimum slope of the derived I/O function (Yasin and Plack 2005) or by fitting a linear function to the data above the breakpoint that separates the linear and compressive regions (Yasin and Plack 2003). Temporal masking curves (TMCs) have gained acceptance as a behavioral measure for estimating cochlear compression in adults with normal and impaired hearing (Nelson et al 2001).…”