Index of content:
Volume 122, Issue 5, November 2007
- PSYCHOLOGICAL ACOUSTICS 
122(2007); http://dx.doi.org/10.1121/1.2785035View Description Hide Description
Three experiments investigated the roles of interaural correlation and of the monaural power spectrum in the detection and discrimination of narrow-band-noise signals in broadband maskers . The power and of the target band were independently controlled, while the flanking noise was fixed and diotic.Experiments 1 and 2 involved and power values that would be produced by specific values of signal-to-noise ratio (SNR) in the binaural configuration. Listeners were required to discriminate different SNRs via a 2I-FC loudness-discrimination task. At low reference SNRs, changes in fully accounted for listeners’ performance, but as reference SNR increased, additional energy in the target band played an increasing role. Experiment 2 showed that at these higher SNRs the combination of information from the power spectrum and was superadditive and could not be explained by simple signal-detection models. The equalization-cancellation (EC) theory would explain these data using the output from interaural cancellation, , rather than . Experiment 3 attempted to foil binaural processing, by fixing either or across intervals. Consistent with EC theory, when was fixed, the contribution of the binaural system appeared negligible, while fixing did not have this effect.
122(2007); http://dx.doi.org/10.1121/1.2780143View Description Hide Description
In three experiments, listeners identified speech processed into narrow bands and presented to the right (“target”) ear. The ability of listeners to ignore (or even use) conflicting contralateral stimulation was examined by presenting various maskers to the target ear (“ipsilateral”) and nontarget ear (“contralateral”). Theoretically, an absence of contralateral interference would imply selectively attending to only the target ear; the presence of interference from the contralateral stimulus would imply that listeners were unable to treat the stimuli at the two ears independently; and improved performance in the presence of informative contralateral stimulation would imply that listeners can process the signals at both ears and keep them separate rather than combining them. Experiments showed evidence of the ability to selectively process (or respond to) only the target ear in some, but not all, conditions. No evidence was found for improved performance due to contralateral stimulation. The pattern of interference found across experiments supports an interaction of stimulus-based factors (auditory grouping) and task-based factors (demand for processing resources) and suggests that listeners may not always be able to listen to the “better” ear even when it would be beneficial to do so.
122(2007); http://dx.doi.org/10.1121/1.2783130View Description Hide Description
The interaural level difference (ILD) is an important cue for the localization of sound sources. Just noticeable differences (JND) in ILD were measured in 12 normal hearing subjects for uncorrelated noise bands with a bandwidth of octave and a different center frequency in both ears. In one ear the center frequency was either 250, 500, 1000, or . In the other ear, a frequency shift of 0, , , or 1 octave was introduced. JNDs in ILD for unshifted, uncorrelated noise bands of octave width were 2.6, 2.6, 2.5, and for 250, 500, 1000, and , respectively. Averaged over all shifts, JNDs decreased significantly with increasing frequency. For the shifted conditions, JNDs increased significantly with increasing shift. Performance on average worsened by 0.5, 0.9, and for shifts of , , and 1 octave. Though performance decreases, the just noticeable ILDs for the shifted conditions were still in a range usable for lateralization. This has implications for signal processing algorithms for bilateral bimodal hearing instruments and the fitting of bilateral cochlear implants.
Estimation of interaural level difference based on anthropometry and its effect on sound localization122(2007); http://dx.doi.org/10.1121/1.2785039View Description Hide Description
Individualization of head-related transfer functions (HRTFs) is important for highly accurate sound localization systems such as virtual auditory displays. A method to estimate interaural level differences (ILDs) from a listener’s anthropometry is presented in this paper to avoid the burden of direct measurement of HRTFs. The main result presented in this paper is that localization is improved with nonindividualized HRTF if ILD is fitted to the listener. First, the relationship between ILDs and the anthropometric parameters was analyzed using multiple regression analysis. The azimuthal variation of the ILDs in each 1/3-octave band was then estimated from the listener’s anthropometric parameters. A psychoacoustical experiment was carried out to evaluate its effectiveness. The experimental results show that the adjustment of the frequency characteristics of ILDs for a listener with the proposed method is effective for localization accuracy.