Ewan A. Macpherson
Waisman Ctr., Univ. of Wisconsin--Madison, 1500 Highland Ave., Madison, WI 53705-2280
The directional filtering of sound by the pinnae is vital to localization, but distorts the spectrum of the signal reaching the eardrum. Sounds do not appear to change character dramatically as a function of direction, so listeners might have some ability to deconvolve pinna effects from the received signal. A three-interval profile analysis task measured listeners' ability to recover source spectra. The stimuli were wideband noise bursts in which the levels of 1/3-octave bands were adjusted to control spectral shape. They were filtered by listeners' measured head-related transfer functions (HRTFs) and delivered via headphones. Listeners discriminated between various nonflat spectra and perturbed versions of them. HRTFs were selected randomly for each interval, and localizability was controlled by varying the correspondence of the left and right HRTFs. Thresholds were highest when HRTFs were imposed diotically, and lowest in an unfiltered diotic baseline condition. Accurate spatialization improved recovery, but applying independent near-ear HRTFs dichotically was more effective. However, deconvolution was imperfect in both conditions. The results suggest that the ability to disregard HRTF filtering and achieve some timbre constancy over direction depends on having two independent, wideband ``looks'' at the source spectrum, rather than on accurate localization.