Background Babble Research Articles

The effect of amplitude modulation on the intelligibility of sentences in noise

Previous work has demonstrated that amplitude‐modulated time‐varying sinusoidal (AMTVS) replicas of natural sentences were more intelligible than simple time‐varying sinusoidal (TVS) sentences [T. D. Carrell, J. Acoust. Soc. Am. Suppl. 1 84, S158 (1988)]. More recent work indicated that this improvement was very likely based on the grouping effects of comodulation masking release [T. D. Carrell, J. Acoust. Soc. Am. Suppl. 1 86, S102 (1989)]. It was further proposed that amplitude modulation, which is often found in natural signals such as voiced speech, comodulates the components of a sound from a single source and may be used to help separate an auditory figure from its background in natural listening environments. The present experiment tested this claim directly. Eight TVS sentences and eight AMTVS sentences were presented in a background of multispeaker babble at a signal to noise ratio of + 6 dB. Listeners perceived only 36.9% of the phonemes in the unmodulated TVS sentences correctly, whereas they perceived 72.3% of the phonemes in the AMTVS sentences correctly. These results suggest that the amplitude comodulation of the components of a speech sound allow them to be grouped together and segregated from simultaneous sounds from other sources. This grouping and segregation is claimed to account for the improved intelligibility that was found.

Consonant recognition and confusion patterns among elderly hearing-impaired subjects.

This study investigated whether unique consonant recognition and confusion patterns are associated with hearing loss among elderly listeners. Subjects were all greater than 65 years, and had normal hearing, or gradually or sharply sloping sensorineural hearing losses. Recognition of 19 consonants, paired with each of three vowels in a CV format, was assessed at two speech levels in a background of babble (+6 dB signal-to-babble ratio). Analyses of percent correct scores for overall nonsense syllable performance and for consonants according to place, manner, and voicing categories generally revealed better performance by the normal-hearing subjects than by the hearing-impaired subjects. However, individual differences scaling analysis of consonant confusions failed to retrieve speech perception patterns that were unique to listener group. These results tentatively suggest that the presence and configuration of hearing loss among elderly listeners may affect the level of performance but not the specific pattern of performance.

Articulation index predictions of contextually dependent words.

Three investigations were conducted to determine the application of the articulation index (AI) to the prediction of speech performance of hearing-impaired subjects as well as of normal-hearing listeners. Speech performance was measured in quiet and in the presence of two interfering signals for items from the Speech Perception in Noise test in which target words are either highly predictable from contextual cues in the sentence or essentially contextually neutral. As expected, transfer functions relating the AI to speech performance were different depending on the type of contextual speech material. The AI transfer function for probability-high items rises steeply, much as for sentence materials, while the function for probability-low items rises more slowly, as for monosyllabic words. Different transfer functions were also found for tests conducted in quiet or white noise rather than in a babble background. A majority of the AI predictions for ten individuals with moderate sensorineural loss fell within +/- 2 standard deviations of normal listener performance for both quiet and babble conditions.

Effects of aging on response criteria in speech-recognition tasks.

This study examined whether young and elderly listeners exhibit different response criteria on speech-recognition tasks. Young and elderly listeners with normal hearing and with matched mild hearing losses were evaluated on Northwestern University Test No. 6 (Tillman & Carhart, 1966) and the California Consonant Test (Owens & Schubert, 1977) presented at 80 dB SPL and 95 dB SPL. The level of the multitalker babble background was adjusted individually to the signal-to-babble ratio at which the listener achieved 50% criterion performance. Significant differences between the performances of young and elderly listeners were observed on the response bias measure (B) but not on the percent-correct or sensitivity [P(A)] measures. Elderly listeners exhibited less cautious response criteria than did younger listeners. The implications of these results to communication strategies of elderly listeners are discussed.