Volume 103, Issue 3, March 1998
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.421292View Description Hide Description
Release of masking for a sinusoidal signal of 5 kHz masked by a 25-Hz-wide noise band centered around 5 kHz was measured. The masking release was provided by a second noise band that was comodulated with the on-frequency masker band. For CMR configurations the second noise band was centered at 3 kHz and presented to the ipsi-lateral or to the contra-lateral ear. For BMLD configurations the second band was centered at 5 kHz and presented to the contra-lateral ear. In another condition the second noise band also contained the signal presented with such a phase that maximal differences in the envelope resulted. For both the CMR and the BMLD paradigm, the masking release for the latter condition was larger than for the former condition. To assess further the similarity between monaural and binaural masking release, a sinusoidal masker and either a noise or a sinusoidal signal were used. The data indicate that, at high frequencies, envelope correlation may be a valuable cue for CMR as well as for the BMLD.
103(1998); http://dx.doi.org/10.1121/1.421293View Description Hide Description
Sequences composed of alternating bursts of different levels with no silences separating them can give rise to a perception of a continuous sound upon which is superimposed an intermittent stream. These experiments sought to determine how the perceived loudness of the intermittent stream depends on the level difference between higher-level and lower-level bursts in the sequence in cases in which continuity is either heard or not heard. In the main experiment, listeners were asked to adjust the level of continuous or intermittent comparison sequences to match the loudness of components that appeared to be either continuous or intermittent in an alternating-level reference sequence, thus urging them to focus on the two-stream percept. Loudness matches of the continuous comparison stimulus were close to physical levels of the lower-level bursts, whereas matches of the intermittent comparison stimulus were well below the physical levels of higher-level bursts. These results are discussed in terms of Bregman’s [Auditory Scene Analysis (MIT, Cambridge, MA, 1990)] “old-plus-new” hypothesis: The loudness of the intermittent stream should result from the subtraction of the lower level from the higher level under the assumption that the higher-level burst represents a simultaneous mixture of sounds including the continuation of the lower-level burst. Additional experiments verified that, in the absence of the continuity phenomenon, matched levels were very close to the physical levels and that matches to fixed-level continuous and intermittent sequences were precise. The matching results from the main experiment support predictions of neither classical loudnessmodels that do not take auditory organization processes into account nor schema-based models that presume a selection of information from the higher-level burst that does not affect the perceptual content of this burst. The matched levels fell between predictions of models based on subtraction of acoustic pressure and acoustic power, but were very different from subtraction of loudness measured in sones, suggesting that loudness is computed subsequent to auditory organization processes.
103(1998); http://dx.doi.org/10.1121/1.421304View Description Hide Description
The detection advantage associated with masker envelope coherence across frequency has typically been described in terms of comparisons of information across auditory channels. More recently it has been suggested that analysis of the output of a wider initial filter, similar to that suggested for the TMTF, can account for the data [B. G. Berg, J. Acoust. Soc. Am. 100, 1013–1023 (1996)]. This approach suggests that a change in envelope beats could serve as the cue to the addition of a pure-tone signal. Data are presented here for the detection of a tone added to multiple maskers with coherent envelopes. In one condition a change in envelope beats was an accurate potential cue, whereas in others the change was too unreliable to serve as an indicator of the presence of the signal. All conditions employing maskers with coherent envelopes produced very similar thresholds, and all showed improved sensitivity over the case of detecting a signal added to a single masker centered on the signal frequency. Results are interpreted as evidence that a change in envelope beats does not form the basis of detection in CMR.
103(1998); http://dx.doi.org/10.1121/1.421294View Description Hide Description
Forward masking growth functions were measured for pure-tone maskers and signals at 2 and 6 kHz as a function of the silent interval between the masker and signal. The inclusion of conditions involving short signals and short masker-signal intervals ensured that a wide range of signal thresholds were recorded. A consistent pattern was seen across all the results. When the signal level was below about 35 dB SPL the growth of masking was shallow, so that signal threshold increased at a much slower rate than masker level. When the signal level exceeded this value, the masking function steepened, approaching unity (linear growth) at the highest masker and signal levels. The results are inconsistent with an explanation for forward-masking growth in terms of saturating neural adaptation. Instead the data are well described by a model incorporating a simulation of the basilar-membrane response at characteristic frequency (which is almost linear at low levels and compressive at higher levels) followed by a sliding intensity integrator or temporal window. Taken together with previous results, the findings suggest that the principle nonlinearity in temporal masking may be the basilar membrane response function, and that subsequent to this the auditory system behaves as if it were linear in the intensity domain.
Binaural detection as a function of interaural correlation and bandwidth of masking noise: Implications for estimates of spectral resolution103(1998); http://dx.doi.org/10.1121/1.421295View Description Hide Description
Detection thresholds were measured for an antiphasic (Sπ) 500-Hz tone masked by a binaural noise, as a function of the bandwidth of the noise. Several values of interaural correlation of the masking noise were used, ranging from to The bandwidth dependence of the thresholds showed a pattern consistent with a 100-Hz-wide critical band for most values of interaural correlation, even for those values which resulted in a considerable binaural release of masking. Only when the interaural correlation of the masking noise was very close to, or equal to, unity was the bandwidth dependence of the thresholds in accord with an approximately 300-Hz-wide “binaural” critical band measured in previous studies. Our analysis of the data calls into question the commonly stated notion that binaural processing is characterized by a wider critical band than is monaural processing.