Prediction of speech intelligibility in spatial noise and reverberation for normal-hearing and hearing-impaired listeners

Speech segregation in rooms: effects of reverberation on both target and interferer

Speech reception thresholds were measured to investigate the influence of a room on speech segregation between a spatially separated target and interferer. The listening tests were realized under headphones. A room simulation allowed selected positioning of the interferer and target, as well as varying the absorption coefficient of the room internal surfaces. The measurements involved target sentences and speech-shaped noise or 2-voice interferers. Four experiments revealed that speech segregation in rooms was not only dependent on the azimuth separation of sound sources, but also on their direct-to-reverberant energy ratio at the listening position. This parameter was varied for interferer and target independently. Speech intelligibility decreased as the direct-to-reverberant ratio of sources was degraded by sound reflections in the room. The influence of the direct-to-reverberant ratio of the interferer was in agreement with binaural unmasking theories, through its effect on interaural coherence. The effect on the target occurred at higher levels of reverberation and was explained by the intrinsic degradation of speech intelligibility in reverberation.

Infant Auditory Sensitivity to Pure Tones and Frequency-Modulated Tones

It has been suggested that infants respond preferentially to infant-directed speech because their auditory sensitivity to sounds with extensive frequency modulation (FM) is better than their sensitivity to less modulated sounds. In this experiment, auditory thresholds for FM tones and for unmodulated, or pure, tones in a background of noise were measured for 4-month-old infants using a conditioned response procedure. The FM tones swept from 150 to 275 Hz or from 150 to 550 Hz. The frequency of the pure tone was either 275 or 550 Hz. The results showed that infants were slightly, but significantly, more sensitive to the sounds that included 550 Hz than they were to the lower frequency sounds, whether or not the sound was frequency modulated. It appears that infants could be somewhat more sensitive to infant-directed than to adult-directed speech, not because of FM per se, but because the fundamental frequency excursions in infant-directed speech extend into a higher frequency range than those in adult-directed speech.