Index of content:
Volume 124, Issue 2, August 2008
- PSYCHOLOGICAL ACOUSTICS 
124(2008); http://dx.doi.org/10.1121/1.2940582View Description Hide Description
This investigation examined whether listeners with mild–moderate sensorineural hearing impairment have a deficit in the ability to integrate synchronous spectral information in the perception of speech. In stage 1, the bandwidth of filtered speech centered either on 500 or was varied adaptively to determine the width required for approximately 15%–25% correct recognition. In stage 2, these criterion bandwidths were presented simultaneously and percent correct performance was determined in fixed block trials. Experiment 1 tested normal-hearing listeners in quiet and in masking noise. The main findings were (1) there was no correlation between the criterion bandwidths at 500 and ; (2) listeners achieved a high percent correct in stage 2 (approximately 80%); and (3) performance in quiet and noise was similar. Experiment 2 tested listeners with mild–moderate sensorineural hearing impairment. The main findings were (1) the impaired listeners showed high variability in stage 1, with some listeners requiring narrower and others requiring wider bandwidths than normal, and (2) hearing-impaired listeners achieved percent correct performance in stage 2 that was comparable to normal. The results indicate that listeners with mild–moderate sensorineural hearing loss do not have an essential deficit in the ability to integrate across-frequency speechinformation.
124(2008); http://dx.doi.org/10.1121/1.2945117View Description Hide Description
Three studies demonstrate listeners’ ability to use the rate of a sound’s frequency change (velocity) to predict how the spectral path of the sound is likely to evolve, even in the event of an occlusion. Experiments 1 and 2 use a modified probe-signal method to measure attentional filters and demonstrate increased detection to sounds falling along implied paths of constant-linear velocity. Experiment 3 shows listeners perceive a suprathreshold tone as falling along a trajectory of constant velocity when the frequency is near to the region of greatest detection as measured in Experiments 1 and 2. Further, results show greater accuracy and decreased bias in the use of velocity information with increased exposure to a constant-velocity sound. As the duration of occlusion lengthens, results also show a downward shift (relative to a trajectory of constant velocity) in the frequency at which listeners’ detection and experience of a continuous trajectory are greatest. A preliminary model of velocity processing is proposed to account for this downward shift. Results show listeners’ use of velocity in extrapolating sounds with dynamically changing spectral and temporal properties and provide evidence for its role in perceptual auditory continuity within a noisy acoustic environment.
124(2008); http://dx.doi.org/10.1121/1.2945159View Description Hide Description
The ability to segregate two spectrally and temporally overlapping signals based on differences in temporal envelope structure and binaural cues was investigated. Signals were a harmonic tone complex (HTC) with fundamental frequency and a bandpass noise (BPN). Both signals had interaural differences of the same absolute value, but with opposite signs to establish lateralization to different sides of the medial plane, such that their combination yielded two different spatial configurations. As an indication for segregation ability, threshold interaural time and level differences were measured for discrimination between these spatial configurations. Discrimination based on interaural level differences was good, although absolute thresholds depended on signal bandwidth and center frequency. Discrimination based on interaural time differences required the signals’ temporal envelope structures to be sufficiently different. Long-term interaural cross-correlation patterns or long-term averaged patterns after equalization-cancellation of the combined signals did not provide information for the discrimination. The binaural system must, therefore, have been capable of processing changes in interaural time differences within the period of the harmonic tone complex, suggesting that monaural information from the temporal envelopes influences the use of binauralinformation in the perceptual organization of signal components.
124(2008); http://dx.doi.org/10.1121/1.2945710View Description Hide Description
Spatial release from masking was studied in a three-talker soundfield listening experiment. The target talker was presented at 0° azimuth and the maskers were either colocated or symmetrically positioned around the target, with a different masker talker on each side. The symmetric placement greatly reduced any “better ear” listening advantage. When the maskers were separated from the target by , the average spatial release from masking was . Wider separations increased the release to more than . This large effect was eliminated when binaural cues and perceived spatial separation were degraded by covering one ear with an earplug and earmuff. Increasing reverberation in the room increased the target-to-masker ratio for the separated, but not colocated, conditions reducing the release from masking, although a significant advantage of spatial separation remained. Time reversing the masker speech improved performance in both the colocated and spatially separated cases but lowered the most for the colocated condition, also resulting in a reduction in the spatial release from masking. Overall, the spatial tuning observed appears to depend on the presence of interaural differences that improve the perceptual segregation of sources and facilitate the focus of attention at a point in space.
Spectrogram denoising and automated extraction of the fundamental frequency variation of dolphin whistles124(2008); http://dx.doi.org/10.1121/1.2945711View Description Hide Description
Marine mammal vocalizations are often analyzed using time-frequency representations (TFRs) which highlight their nonstationarities. One commonly used TFR is the spectrogram. The characteristic spectrogram time-frequency (TF) contours of marine mammal vocalizations play a significant role in whistle classification and individual or group identification. A major hurdle in the robust automated extraction of TF contours from spectrograms is underwater noise. An image-based algorithm has been developed for denoising and extraction of TF contours from noisy underwater recordings. An objective procedure for measuring the accuracy of extracted spectrogram contours is also proposed. This method is shown to perform well when dealing with the challenging problem of denoising broadband transients commonly encountered in warm shallow waters inhabited by snapping shrimp. Furthermore, it would also be useful with other types of broadband transient noise.