Level dependence of critical bandwidth: notched-noise masking paradigm

The effect of increased stimulus level on critical bandwidth was investigated. Noise-masked, pulsed-tone thresholds were obtained by a Bekesy tracking procedure from 4 practiced normal-hearing adults at .5, 1, 2, and 4 kc/s. Tones were placed symmetrically within a band-reject region. Critical bandwidth was taken as the frequency separation between noise bands at which masked tonal threshold began to change and was found to increase fairly regularly as the spectrum level of the noise increased from 30-60 db SPL. However, the data at 60 db SPL may have been influenced a 2 and 4 kc/s by the detection of aural distortion products. The suggestion was made that when signal frequency is outside the spectral limits of the masker, critical bandwidth widens as masker level is raised; however, when signal frequency is within the spectral limits of the masker (as with a continuous noise wit no notches), critical bandwidth remains unchanged up to 80 bd SPL.