Spatial release from informational masking in speech recognition.

Three experiments were conducted to determine the extent to which perceived separation of speech and interference improves speech recognition in the free field. Target speech stimuli were 320 grammatically correct but nonmeaningful sentences spoken by a female talker. In the first experiment the interference was a recording of either one or two female talkers reciting a continuous stream of similar nonmeaningful sentences. The target talker was always presented from a loudspeaker directly in front (0 degrees). The interference was either presented from the front loudspeaker (the F-F condition) or from both a right loudspeaker (60 degrees) and the front loudspeaker, with the right leading the front by 4 ms (the F-RF condition). Due to the precedence effect, the interference in the F-RF condition was perceived to be well to the right, while the target talker was heard from the front. For both the single-talker and two-talker interference, there was a sizable improvement in speech recognition in the F-RF condition compared with the F-F condition. However, a second experiment showed that there was no F-RF advantage when the interference was noise modulated by the single- or multi-channel envelope of the two-talker masker. Results of the third experiment indicated that the advantage of perceived separation is not limited to conditions where the interfering speech is understandable.

Onset dominance in lateralization.

Saberi and Perrott [Acustica 81, 272-275 (1995)] found that the in-head lateralization of a relatively long-duration pulse train could be controlled by the interaural delay of the single pulse pair that occurs at onset. The present study examined this further, using an acoustic pointer measure of lateralization, with stimulus manipulations designed to determine conditions under which lateralization was consistent with the interaural onset delay. The present stimuli were wideband pulse trains, noise-burst trains, and inharmonic complexes, 250 ms in duration, chosen for the ease with which interaural delays and correlations of select temporal segments of the stimulus could be manipulated. The stimulus factors studied were the periodicity of the ongoing part of the signal as well as the multiplicity and ambiguity of interaural delays. The results, in general, showed that the interaural onset delay controlled lateralization when the steady state binaural cues were relatively weak, either because the spectral components were only sparsely distributed across frequency or because the interaural time delays were ambiguous. Onset dominance can be disrupted by sudden stimulus changes within the train, and several examples of such changes are described. Individual subjects showed strong left-right asymmetries in onset effectiveness. The results have implications for understanding how onset and ongoing interaural delay cues contribute to the location estimates formed by the binaural auditory system.

Consonant recognition for spectrally degraded speech as a function of consonant-vowel intensity ratio.

Normal-hearing subjects' recognition of spectrally degraded speech was evaluated under conditions in which the consonant-vowel (C-V) intensity ratio was modified. Subjects identified 22 consonants presented in an /a-Consonant-a/ format at suprathreshold and near threshold conditions. Prior to C-V ratio modification, the stimuli were processed to limit spectral information. In the suprathreshold experiment, stimuli were presented at the natural C-V ratio and at six modified C-V ratios. C-V ratio manipulations had dramatic effects on recognition scores for some groups of consonants. Scores for glides and sibilant fricatives increased with increasing C-V ratio, while scores for nasals and weak fricatives were best at low C-V ratios. Recognition scores for the stops and affricates were generally independent of C-V ratio. For nearly all consonants, changes in recognition scores as a function of C-V ratio were associated with changes in a general response bias toward those sounds. Performance was poor when the spectrally smeared VCVs were presented at low SN ratios in a second experiment. The influence of C-V ratio on percent correct scores was generally similar to the suprathreshold results, but consonant audibility, which was not a factor in the suprathreshold experiment, appeared to alter the effect of C-V ratio modification for some consonants.

An additional younger-age peak for cancer of the nasopharynx.

The age distribution of 666 masopharyngeal cancer patients attending the Tata Memorial Hospital, Bombay, during 1941-72 was found to show an additional younger-age peak in the age-group 13-22. The peak was found in both sexes, in different communnities, at two time periods and in histologically proved cases. One hundred cases of nasopharyngeal lymphosarcoma showed no deviation from a uniform age distribution. Pooled incidence data for 48 population groups showed the peak in the age-group 15-19 for males and in the age-group 10-14 for females. No such peak was observed for malignancies of the nose, sinuses, etc. (ICD NO:160)