Volume 126, Issue 2, August 2009
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
126(2009); http://dx.doi.org/10.1121/1.3167842View Description Hide Description
Various physical aspects of room-acoustic simulation techniques have been extensively studied and refined, yet the perceptual attributes of the simulations have received relatively little attention. Here a method of evaluating the perceptual similarity between rooms is described and tested using 15 small-room simulations based on binaural room impulse responses(BRIRs) either measured from a real room or estimated using simple geometrical acoustic modeling techniques. Room size and surface absorption properties were varied, along with aspects of the virtual simulation including the use of individualized head-related transfer function (HRTF) measurements for spatial rendering. Although differences between BRIRs were evident in a variety of physical parameters, a multidimensional scaling analysis revealed that when at-the-ear signal levels were held constant, the rooms differed along just two perceptual dimensions: one related to reverberation time and one related to interaural coherence (IACC). Modeled rooms were found to differ from measured rooms in this perceptual space, but the differences were relatively small and should be easily correctable through adjustment of and IACC in the model outputs. Results further suggest that spatial rendering using individualized HRTFs offers little benefit over nonindividualized HRTF rendering for room simulation applications where source direction is fixed.
126(2009); http://dx.doi.org/10.1121/1.3158835View Description Hide Description
The choice of processing parameters for vocoded signals may have an important effect on the availability of various auditory features. Experiment 1 varied envelope cutoff frequency (30 and 300 Hz), carrier type (sine and noise), and number of bands (2–5) for vocoded speech presented to normal-hearing listeners. Performance was better with a high cutoff for sine-vocoding, with no effect of cutoff for noise-vocoding. With a low cutoff, performance was better for noise-vocoding than for sine-vocoding. With a high cutoff, performance was better for sine-vocoding. Experiment 2 measured perceptibility of cues to voice pitch variations. A noise carrier combined with a high cutoff allowed intonation to be perceived to some degree but performance was best in high-cutoff sine conditions. A low cutoff led to poorest performance, regardless of carrier. Experiment 3 tested the relative contributions of comodulation across bands and spectral density to improved performance with a sine carrier and high cutoff. Comodulation across bands had no effect so it appears that sidebands providing a denser spectrum improved performance. These results indicate that carrier type in combination with envelope cutoff can alter the available cues in vocoded speech, factors which must be considered in interpreting results with vocoded signals.
Sensitivity to interaural time difference with bilateral cochlear implants: Development over time and effect of interaural electrode spacing126(2009); http://dx.doi.org/10.1121/1.3158821View Description Hide Description
Sensitivity to interaural time difference(ITD) in constant-amplitude pulse trains was measured in four sequentially implanted bilateral cochlear implant(CI) subjects. The sensitivity measurements were made as a function of time beginning directly after the second ear was implanted, continued for periods of months before subjects began wearing bilateral sound processors, and extended for months while the subjects used bilateral sound processors in day-to-day listening. Measurements were also made as a function of the relative position of the left/right electrodes. The two subjects with the shortest duration of binaural deprivation before implantation demonstrated ITD sensitivity soon after second-ear implantation (before receiving the second sound processor), while the other two did not demonstrate sensitivity until after months of daily experience using bilateral processors. The interaural mismatch in electrode position required to decrease ITD sensitivity by a factor of 2 (half-width) for CI subjects was five times greater than the half-width for interaural carrier-frequency disparity in normal-hearing subjects listening to sinusoidally amplitude-modulated high-frequency tones. This large half-width is likely to contribute to poor binaural performance in CI users, especially in environments with multiple broadband sound sources.