Phase effects on the perceived elevation of complex tones

Abstract

Free-field source localization experiments with 30 source locations, symmetrically distributed in azimuth, elevation, and front-back location, were performed with periodic tones having different phase relationships among their components. Although the amplitude spectra were the same for these different kinds of stimuli, the tones with certain phase relationships were successfully localized while the tones with other phases led to large elevation errors and front-back reversals, normally growing with stimulus level. The results show that it is not enough to have a smooth, broadband, long-term signal spectrum for successful sagittal-plane localization. Instead, temporal factors are important. A model calculation investigates the idea that the tonotopic details that mediate localization need to be simultaneously, or almost simultaneously, accessible in the auditory system in order to achieve normal elevation perception. A qualitative model based on lateral inhibition seems capable in principle of accounting for both the phase effects and level effects.

Modeling sound-source localization in sagittal planes for human listeners

“…Several psychoacoustic studies have addressed the question of which monaural spectral features are relevant for sound localization. It is well known that the amplitude spectrum of HRTFs is most important for localization in sagittal planes (e.g., Kistler and Wightman, 1992), whereas the phase spectrum of HRTFs affects localization performance only for very specific stimuli with large spectral differences in group delay (Hartmann et al , 2010). Early investigations attempted to identify spectrally local features like specific peaks and/or notches as localization cues (e.g., Blauert, 1969; Hebrank and Wright, 1974).…”

Vertical-plane sound localization with distorted spectral cues

“…Increased scatter was also associated with reduced gain, which we take to be a hallmark of uncertainty. In Vliegen and Van Opstal (2004) and Hartmann et al (2010), however, the variability of head-pointing responses was not systematically related to reductions in vertical response gain, and in Hofman and Van Opstal (1998), although stimulus duration markedly affected the vertical gain and latency of eye-pointing responses, there was no associated change in response scatter. Based on those results with human listeners, on our own observation that in all but one subject reduced gain occurred without increased response scatter, and on doubts about how uncertainty might lead to such finely graded and stimulus-related reductions in gain, we prefer the explanation that reduced gain in our experiment and others is indeed a true perceptual effect.…”

“…That factor is the temporal fine structure of the stimulus waveform. Localization targets composed of wideband complexes of harmonics in cosine phase, sine phase, and positive or negative Schroeder phase (chirps) cause significant compression of perceived elevation even for long durations and moderate intensities, and are also subject to the Negative Level effect, whereas long-duration random-phase harmonic complexes and noise bursts are not subject to these effects (Brungart and Simpson, 2008; Hartmann et al, 2010). Hofman and Van Opstal (1998) also observed compression of elevation for targets consisting of 500-ms trains of frequency sweeps, all with long-term spectra flat up to 16 kHz, when the sweep period exceeded 5 ms. That is, it appeared necessary that the stimulus provide wideband energy within a 5-ms integration window for successful spectral cue processing.…”

Improving perceived elevation accuracy in sound reproduced via a loudspeaker ring by means of equalizing filters and side loudspeaker grouping

“…Hartmann et al [40] have associated similar elevationdependent degradation with temporal and intensity aspects of the signal. Authors in [39] suggest a possible ceiling/ flooring statistical effect in the computation of averages, whereas Kim et al suggested that this range compression was associated with discrepancies between assessors' HRTFs and the generic ones used for their spatialization: As a sound source moves from low to high elevations, notches above 5 kHz (related to pinna reflections) traverse the spectrum from low to high [9].…”