Psychophysical tuning curves and filter shapes sharpen over time

Abstract

Psychophysical tuning curves (PTCs) measured in simultaneous masking usually sharpen as a short signal is moved from the onset to the temporal center of a longer duration masker. Filter shapes derived from notched-noise maskers have not consistently shown this effect. One possible explanation for this difference is that the PTC paradigm uses a fixed signal level, whereas filter shapes typically have been derived from results where the noise masker was fixed in level. In the present study, PTCs and filter shapes were measured with a signal fixed in level at 10 dB SL. The masker was either a pure tone (PTCs) or a noise with a spectral notch placed symmetrically or asymmetricaly about the 2-kHz signal frequency (filter shapes). The 20-ms signal was presented at the onset or temporal center of the 400-ms masker. For a given signal delay, the PTCs were substantially sharper than the filter shapes. Importantly, however, for all four subjects, the PTCs and the filter shapes sharpened on both the low- and high-frequency sides as the signal moved from the beginning to the temporal center of the masker. This sharpening was considerably greater for the filter shapes. [Work supported by NIDCD.]