Volume 115, Issue 6, June 2004
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
115(2004); http://dx.doi.org/10.1121/1.1738839View Description Hide Description
Buus and Florentine [J. Assoc. Res. Otolaryngol. 3, 120–139 (2002)] have proposed that loudness recruitment in cases of cochlear hearing loss is caused partly by an abnormally large loudness at absolute threshold. This has been called “softness imperception.” To evaluate this idea, loudness-matching functions were obtained using tones at very low sensation levels. For subjects with asymmetrical hearing loss, matches were obtained for a single frequency across ears. For subjects with sloping hearing loss, matches were obtained between tones at two frequencies, one where the absolute threshold was nearly normal and one where there was a moderate hearing loss. Loudness matching was possible for sensation levels (SLs) as low as 2 dB. When the fixed tone was presented at a very low SL in an ear (or at a frequency) where there was hearing impairment, it was matched by a tone with approximately the same SL in an ear (or at a frequency) where hearing was normal (e.g., 2 dB SL matched 2 dB SL). This relationship held for SLs up to 4–10 dB, depending on the subject. These results are not consistent with the concept of softness imperception.
115(2004); http://dx.doi.org/10.1121/1.1687834View Description Hide Description
The present work investigated the temporal tuning of the auditory motion aftereffect (aMAE) by measuring the time course of adaptation and recovery to auditory motion exposure. On every trial, listeners were first exposed to a broadband, horizontally moving sound source for either 1 or 5 seconds, then presented moving test stimuli after delays of 0, or All stimuli were synthesized from head related transfer functions recorded for each participant. One second of motion exposure (i.e., a single pass of the moving source) produced clearly measurable aMAEs which generally decayed monotonically after adaptation ended, while five seconds exposure produced stronger aftereffects that remained largely unattenuated across test delays. These differences may imply two components to the aMAE: a short time-constant motion illusion and a longer time-constant response bias. Finally, aftereffects were produced only by adaptor movement toward but not away from listener midline. This aftereffect asymmetry may also be a consequence of brief adaptation times and reflect initial neural response to auditory motion in primate auditory cortex.
115(2004); http://dx.doi.org/10.1121/1.1736649View Description Hide Description
A human psychoacoustical experiment is described that investigates the role of the monaural and interaural spectral cues in human sound localization. In particular, it focuses on the relative contribution of the monaural versus the interaural spectral cues towards resolving directions within a cone of confusion (i.e., directions with similar interaural time and level difference cues) in the auditory localization process. Broadband stimuli were presented in virtual space from 76 roughly equidistant locations around the listener. In the experimental conditions, a “false” flat spectrum was presented at the left eardrum. The sound spectrum at the right eardrum was then adjusted so that either the true right monaural spectrum or the true interaural spectrum was preserved. In both cases, the overall interaural time difference and overall interaural level difference were maintained at their natural values. With these virtual sound stimuli, the sound localization performance of four human subjects was examined. The localization performance results indicate that neither the preserved interaural spectral difference cue nor the preserved right monaural spectral cue was sufficient to maintain accurate elevation judgments in the presence of a flat monaural spectrum at the left eardrum. An explanation for the localization results is given in terms of the relative spectral information available for resolving directions within a cone of confusion.
115(2004); http://dx.doi.org/10.1121/1.1738687View Description Hide Description
Localization dominance is an aspect of the precedence effect (PE) in which the leading source dominates the perceived location of a simulated echo (lagging source). It is known to be robust in the horizontal/azimuthal dimension, where binaural cues dominate localization. However, little is known about localization dominance in conditions that minimize binaural cues, and most models of precedence treat the phenomena as “belonging” to the binaural system. Here, localization dominance in the median-sagittal plane was studied where binaural cues are greatly reduced, and monaural spectral/level cues are thought to be the primary cues used for localization. Lead–lag pairs of noise bursts were presented from locations spaced in 15° increments in the frontal, median-sagittal plane, with a 2-ms delay in their onsets, for source durations of 1, 10, 25, and 50-ms. Intermixed with these trials were single-speaker trials, in which lead and lag were summed and presented from one speaker. Listeners identified the speaker that was nearest to the perceived source location. With single-speaker stimuli, localization improves as signal duration is increased. Furthermore, evidence of elevation compression was found with a dependence on duration. With lead–lag pairs, localization dominance occurs in the median plane, and becomes more robust with increased signal duration. These results suggest that accurate localization of a co-located lead–lag pair is necessary for localization dominance to occur when the lag is spatially separated from the lead.
115(2004); http://dx.doi.org/10.1121/1.1719025View Description Hide Description
Thresholds for interaural intensitive disparities (IIDs) for a 500-Hz tone were measured in several stimulus conditions including those in which the use of intracranial position as a cue was effectively eliminated by roving the interaural temporal disparity of the stimuli. Removing position as a cue resulted in substantial degradation of sensitivity to IID. The overall patterning of the data suggests that threshold-IIDs measured in standard binaural paradigms that yield fused intracranial images reflect the use of changes in intracranial position. That is, comparisons among the data suggest that listeners’ judgments depend upon binaural spatial cues and not on comparisons of the concomitant monaural increments and decrements in level, per se, that inevitably result from the imposition of IIDs.