Effects of signal duration and temporal position on physiological measures of the growth of masking

Abstract

Psychoacoustic studies have shown that the growth of masking for pure-tone signals in broadband noise is linear when the signal onset is delayed relative to the masker but is nonlinear when signal and masker onsets are synchronous [e.g., Strickland (2001)]. Curiously, for very short duration signals (10 ms), nonlinear effects have been observed for some delayed-onset conditions (Oxenham et al., 1997). While nonlinear effects may result from peripheral compression, it is unclear if other physiological mechanisms might be responsible for the influence of signal temporal parameters on the growth of masking. To address this issue, the growth of masking was studied using evoked-potential responses recorded from the chinchilla inferior colliculus (IC). Quiet and masked thresholds were obtained for 1.0-, 4.0-, and 6.5-kHz signals as a function of signal duration (2–100 ms) and temporal position (delayed or nondelayed) within a 400-ms broadband noise masker. Masker spectrum levels ranged from −10 to 20 dB. Consistent with Stricklands data, physiological growth of masking was linear under delayed conditions and nonlinear under nondelayed conditions. Specifically, for nondelayed conditions, the degree of nonlinearity was greatest for high-frequency signals but did not vary with signal duration. [Work supported by NSF IBN-9996379.]