Auditory filter bandwidths were estimated in three experiments. The first experiment was a profile-analysis experiment. The stimuli were composed of sinusoidal components ranging in frequency from 200 to 5000 Hz. The standard stimulus was the sum of equal-amplitude tones, and the signal stimulus had a power spectrum that varied up-down ... up-down. The number of components ranged from four to 60. Interval-by-interval level randomization prevented the change in level of a single component from reliably indicating the change from standard to signal. The second experiment was a notched-noise experiment in which the 1000-Hz tone to be detected was added to a noise with a notch arithmetically centered at 1000 Hz. Detection thresholds were estimated both in the presence of and in the absence of level randomization. In the third, hybrid, experiment a 1000-Hz tone was to be detected, and the masker was composed of equal-amplitude sinusoidal components ranging in frequency from 200 to 5000 Hz. For this experiment, thresholds were estimated both in the presence and absence of level variation. For both the notched-noise and hybrid experiments, only modest effects of level randomization were obtained. A variant of Durlach et al.'s channel model ["Towards a model for discrimination of broadband signals," J. Acoust. Soc. Am. 80, 63-72 (1986)] was used to estimate auditory filter bandwidths for all three experiments. When a two-parameter roex(p,r) filter weighting function was used to fit the data, bandwidth estimates were approximately two to three times as large for the two detection tasks than for the profile-analysis task.
Relative weights for two profile analysis and one detection task were estimated. For the profile analysis ‘‘bump’’ task the standard was the sum of N equal-amplitude sinusoidal components ranging in frequency from 200 to 5000 Hz. The signal for this task was an increment in level to the 1000-Hz component of the standard. The number of components N ranged from 4 to 50. For the profile analysis ‘‘down–up’’ task the standard was composed of N equal amplitude tones ranging in frequency from 200 to 5000 Hz. The signal to be detected led to a spectrum that varied down–up...down–up. The detection task used the same standard as the profile analysis down–up task, but the signal to be detected was an added 1000-Hz tone. Comparisons of the relative weights revealed that profile analysis bump and the detection of a tone added to a notched masker rely on similar processing strategies. By contrast it was apparent that auditory processing in the profile analysis down–up task depended on a different strategy than the other two tasks. Finally, rough estimates of the auditory filter bandwidths suggest invariance with regard to task. [Work supported by NIH.]
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