Rapid psychophysical calibration using bisection scaling for individualized control of source elevation in auditory display
Martens, W. L.
MetadataShow full item record
In an effort to reduce problems stemming from individual differences in spatial hearing, a rapid method for customizing an interactive spatial auditory display for individual users was developed and tested. This paper describes how new users of a DSP-based spatial auditory display system perform a short series of psychophysical calibration tasks via realtime manipulation of the elevation of a virtual sound source removed from the median plane by a constant angle (on a ``cone of confusion'' centered on the interaural axis). The user first produces five settings indicating the point at which the perceived elevation of a virtual source matches their own internal standard for ``ear-level'' incidence. The median of these settings provides an anchoring stimulus for creating an individualized psychophysical scale for controlling source elevation as perceived by the user of the display system. The experimentally-derived anchoring stimulus is regarded as the origin for an angular bisection session that enables the rapid construction of a look up table (LUT) for the full range of elevations produced by the display for each individual user. In contrast to systems that base source elevation control upon individualized head-related transfer functions (HRTFs), the tested system uses a generic set of HRTFs, and manipulates only the values in the LUT for the elevations produced by each HRTF. The method does not attempt to find for each individual listener a single best frequency scaling for the generic set of HRTFs, but attempts to map the useful range of elevations produced by them. Though such a LUT for perceived elevation can be based upon angular estimates made for virtual sources created using each of many HRTFs, the bisection task presented here requires users to complete only a short listening session in which they adjust the elevation of a comparison stimulus to bisect the angle subtended by a pair of reference stimuli. In contrast to other rapid methods of customization, such as those based upon a user's subjective preferences, the current method is based upon active spatial manipulation of a virtual source. The adjustments are referenced to the user's internal standard for ``ear-level'' incidence, which is tangibly defined and quite easily explained to new users.