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Psychophysical tuning curves for very low centre Frequencies

Abstract:

Noise with energy in the low-frequency range (i.e. below 200 Hz) is known to produce problems with annoyance and represents an environmental problem (Leventhall, 2004). Attempts to understand and pbkp_redict problems produced by low-frequency noise require information about human frequency selectivity in the low-frequency range. However, there are few data on frequency selectivity for centre frequencies below 100 Hz. To estimate the characteristics of auditory tuning for very low frequencies, in this study psychophysical tuning curves (PTCs) were obtained for tonal and narrow-band noise maskers at centre frequencies (CFs) of 31.5, 40, 50, 63, and 80 Hz. For the tonal maskers, pairs of tones designed to produce modulation-detection-interference (MDI) were added to the masker, as a way to evaluate and reduce the effects of beats. For each subject, an equal-loudness-level contour was also obtained using closely spaced frequencies. This was used as a rough estimate of the shape of the individual middle-ear transfer function (METF) in the frequency range below 100 Hz. Preliminary results obtained using 9 subjects are described. Sharp tips were observed for some of the PTCs derived with the tonal maskers, probably reflecting the influence of beats. Addition of the MDI tones produced more regular and broad tips for cases where beating was evident. The PTCs obtained with the noise maskers were generally more regular around their tips. For both masker types, the overall shapes of the PTCs were broad, indicating that frequency selectivity at very low frequencies is relatively poor. Also, the PTCs were generally asymmetrical, with steeper lower skirts than upper skirts, an effect that became more pronounced as the CF was decreased. For the CFs of 31.5 and 40 Hz, the tips of the tuning curve did not occur at the CF, but at a higher frequency. The overall shapes of the tuning curves, and the degree to which tuning was affected at the lowest CFs, appear to be influenced by the shape of the (estimated) METF. Copyright © (2010) by the International Congress on Acoustics.