Closed-set effects in consonant confusion patterns.

Invariance of error patterns in confusion matrices of varying dimensions were examined. Normal-hearing young adults were presented closed-set arrangements of digitized syllable tokens, spoken by 1 male and 1 female talker, and selected from a set of 14 consonants (stops and fricatives). Each consonant was paired with the vowel/a/ in a vowel-consonant format and presented at three intensity levels. Patterns of errors among voiceless stops and among voiced fricatives were dependent on the set of alternatives. Voiceless fricatives and voiced stops were not significantly affected by the number of response alternatives. Speaker differences, individual differences among listeners, and implications relating to the generalization of confusion data collected in small closed-set arrangements are discussed.

Basic acoustic considerations of ear canal probe measurements.

This publication contains a review of several acoustic investigations in which the effects of probe location on real-ear gain were examined through theoretical models based on acoustic properties of the average human ear and ear simulator studies. The results of these investigations are used to demonstrate the effect of standing waves and eardrum impedance on probe measurements made in the ear canal. Investigations were also conducted in the sound field with a KEMAR manikin. A commercial probe microphone system was used to measure the SPL and real-ear gain at various locations with the KEMAR ear canal. The results emphasize the critical effect of probe location on absolute or relative ear canal measurements and indicate the necessity to establish clinical procedures for probe measurements based on relevant acoustic principles.

Recognition of nonsense syllables by hearing-impaired listeners and by noise-masked normal hearers.

In the present study, speech-recognition performance was measured in four hearing-impaired subjects and twelve normal hearers. The normal hearers were divided into four groups of three subjects each. Speech-recognition testing for the normal hearers was accomplished in a background of spectrally shaped noise in which the noise was shaped to produce masked thresholds identical to the quiet thresholds of one of the hearing-impaired subjects. The question addressed in this study is whether normal hearers with a hearing loss simulated through a shaped masking noise demonstrate speech-recognition difficulties similar to those of listeners with actual hearing impairment. Regarding overall percent-correct scores, the results indicated that two of the four hearing-impaired subjects performed better than their corresponding subgroup of noise-masked normal hearers, whereas the other two impaired listeners performed like the noise-masked normal listeners. A gross analysis of the types of errors made suggested that subjects with actual and simulated losses frequently made different types of errors.

Application of the Articulation Index and the Speech Transmission Index to the recognition of speech by normal-hearing and hearing-impaired listeners.

The present article is divided into four major sections dealing with the application of acoustical indices to the prediction of speech recognition performance. In the first section, two acoustical indices, the Articulation Index (AI) and the Speech Transmission Index (STI), are described. In the next section, the effectiveness of the AI and the STI in describing the performance of normal-hearing and hearing-impaired subjects listening to spectrally distorted (filtered) and temporarily distorted (reverberant) speech is examined retrospectively. In the third section, the results of a prospective investigation that examined the recognition of nonsense syllables under conditions of babble competition, filtering and reverberation are described. Finally, in the fourth section, the ability of the acoustical indices to describe the performance of 10 hearing-impaired listeners, 5 listening in quiet and 5 in babble, is examined. It is concluded that both the AI and the STI have significant shortcomings. A hybrid index, designated mSTI, which takes the best features from each procedure, is described and demonstrated to be the best alternative presently available.

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.