Volume 118, Issue 3, September 2005
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
Contribution of harmonicity and location to auditory object formation in free field: Evidence from event-related brain potentials118(2005); http://dx.doi.org/10.1121/1.2000747View Description Hide Description
The contribution of location and harmonicity cues in sound segregation was investigated using behavioral reports and source waveforms derived from the scalp-recorded evoked potentials. Participants were presented with sounds composed of multiple harmonics in a free-field environment. The third harmonic was either tuned or mistuned and could be presented from the same or different location from the remaining harmonics. Presenting the third harmonic at a different location than the remaining harmonics increased the likelihood of hearing the tuned or slightly (i.e., 2%) mistuned harmonic as a separate object. Partials mistuned by 16% of their original value “pop out” of the complex and were paralleled by an object-related negativity (ORN) that superimposed the N1 and P2 components. For the 2% mistuned stimuli, the ORN was present only when the mistuned harmonic was presented at a different location than the remaining harmonics. Presenting the tuned harmonic at a different location also yielded changes in neural activity between 150 and after sound onset. The behavioral and electrophysiological results indicate that listeners can segregate sounds based on harmonicity or location alone. The results also indicate that a conjunction of harmonicity and location cues contribute to sound segregation primarily when harmonicity is ambiguous.
118(2005); http://dx.doi.org/10.1121/1.1992675View Description Hide Description
This study assessed informational masking and utilization of cues to reduce that masking in children aged and in adults. The signal was a train of eight consecutive tone bursts, each at and in duration. Maskers were comprised of a pair of synchronous tone-burst trains, with randomly chosen frequencies spanning , with a protected region . In the reference condition, maskers were eight bursts in duration, with a fixed frequency within intervals. Experiment 1 tested two monotic masking release conditions: within-interval randomization of masker burst frequency and the introduction of leading masker bursts. Experiment 2 examined masking release in which the signal was presented to one ear and masking components were presented to both ears (masker components in the contralateral ear were higher than those in the ipsilateral ear). Both adults and children demonstrated a significant informational masking effect, with children showing a larger effect on average. Both groups also showed significant release from masking in the two monotic conditions, although children received somewhat less benefit from the masking release cues. The binaural condition supported a moderate release from informational masking in adults, but resulted in increased informational masking in children.
118(2005); http://dx.doi.org/10.1121/1.1984876View Description Hide Description
Binaural release from informational masking (IM) was examined in a speech identification task. Target and masker sentences were processed into mutually exclusive frequency bands, thus limiting energetic masking (EM), and presented over headphones. In a baseline condition, both were presented monotically to the same ear . Despite minimal frequency overlap between target and masker, the presence of the masker resulted in reduced performance, or IM. Presenting the target monotically and the masker diotically resulted in a release from IM. Release was also obtained by imposing interaural differences in level (ILDs) and in time (ITDs) on the maskers . Any masker with a perceived lateral position that differed from that of a truly monaural stimulus resulted in a similar amount of release from IM relative to . For binaural targets and maskers , release was seen whenever ITDs or ILDs differed between target and masker. These results suggest that binaural cues can be very effective in reducing IM. Because mechanisms based on differences in perceived location make predictions that are similar to those of nonlocation-based binaural mechanisms, a variant of the equalization-cancellation model is also considered.
Measures of extents of laterality for high-frequency “transposed” stimuli under conditions of binaural interference118(2005); http://dx.doi.org/10.1121/1.1984827View Description Hide Description
Our purpose in this study was to determine whether across-frequency binaural interference would occur if ITD-based extents of laterality were measured using high-frequency transposed stimuli as targets. The results of an earlier study [L. R. Bernstein and C. Trahiotis, J. Acoust. Soc. Am.116, 3062–3069 (2004)], which focused on threshold-ITDs, rather than extents of laterality, suggested that high-frequency transposed stimuli might be “immune” to binaural interference effects resulting from the addition of a spectrally remote, low-frequency interferer. In contrast to the earlier findings, the data from this study indicate that high-frequency transposed targets are susceptible to binaural interference. Nevertheless, high-frequency transposed targets, even when presented along with an interferer, yielded greater extents of ITD-based laterality than did high-frequency Gaussian noise targets presented in isolation. That is, the “enhanced potency” of ITDs conveyed by transposed stimuli persisted, even in the presence of a low-frequency interferer. Predictions made using an extension of the model of Heller and Trahiotis [L. M. Heller and C. Trahiotis, J. Acoust. Soc. Am.99, 3632–3637 (1996)] accounted well for across-frequency binaural interference obtained with conventional Gaussian noise targets but, in all but one case, overpredicted the amounts of interference found with the transposed targets.