Reliability and validity of infant speech-sound discrimination-in-noise thresholds.

Infants were tested on a speech-sound discrimination-in-noise task using the visual reinforcement infant speech discrimination (VRISD) procedure with an adaptive (up-down) threshold protocol. An adult control group was tested using the same stimuli and apparatus. The speech sounds were synthetic magnitude of ba and magnitude of ga. The masker was band-passed presented continuously at 48 dB SPL. Test-retest reliability was good for both groups, although test-retest differences were smaller for adults. For infants the mean of the absolute values of the differences between tests was only 5.2 dB, and there was less than a 10-dB difference between the two tests of 14 (87.5%) of the 16 infants completing the study. The infant-adult difference in discrimination threshold in noise was 6.9 dB, which agrees well with detection-in-noise thresholds from earlier studies and with discrimination-in-noise thresholds obtained on a subset of subjects in our earlier work. Advantages of the adaptive threshold procedure and its possible applications both in research studies and in the clinic are discussed.

Infant-adult differences in unmasked thresholds for the discrimination of consonant-vowel syllable pairs.

Speech sound discrimination thresholds were obtained for two speech sound contrasts (/ba/ vs. /da/ and /ba/ vs. /ga/) for infant and adult subjects. The stimuli were computer-generated synthetic tokens. An adaptive (one-up, one-down) threshold procedure was used with the visual reinforcement infant speech discrimination procedure for the infant subjects. Adults were tested using the same apparatus and threshold-tracking protocol as the infants. There was a 28-dB difference in threshold for discrimination of /ba/ versus /da/ and a 25-dB difference in threshold for discrimination of /ba/versus/ga/ between the infants and the adults. The differences reveal that to reach a criterion level of performance on a simple speech perception task, infants require much greater stimulus intensity than do adults. This has implications for our understanding of normal auditory development, for our notions of hearing impairment in infants and for the role of intensity in research studies of infant speech perception.

Infant speech-sound discrimination in noise.

The effects of noise on 7- to 11-month-old infants' speech-sound discrimination (/ba/vs/ga/) were determined using a conditioned head-turn procedure. Variation in performance as a function of signal-to-noise ratio (S/N) was estimated by testing each infant at four S/N's (-8, 0, 8, and 16 dB). Adults were tested for comparison at four S/N's (-12, -8, -4, and 0 dB). The S/N's were chosen based on pilot data. Performance varied monotonically with S/N for both age groups, but infants required greater S/N than adults to achieve comparable levels of performance. Both groups were also tested using an adaptive (1-up, 1-down) threshold procedure with a 3-dB step size. There was a group mean difference in threshold of 5.8-dB S/N favoring the adults. Weighted group psychometric functions, derived from the responses obtained in the adaptive runs, showed good correspondence with the data points at the four S/N's. The slopes of these functions were the same (7.5%/dB) for infants and adults. The results suggest that infants are at a greater disadvantage than adults when processing speech in noise and that concern over the effects of a noisy environment on the acquisition of language is justified. In addition, the adaptive threshold procedure can be used as an efficient way to estimate the limits of discrimination ability as a function of S/N or intensity, both for individual subjects and for groups of subjects, in developmental research.

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.

Inter-interpreter agreement for ABR tracings. Results from 100 patients under otoneurologic investigation.

The auditory brainstem response (ABR) tracings of 100 patients under investigation for a neural lesion were examined independently by two audiologists. Each tracing for the ear under question was classified as normal or abnormal. There was 94% agreement. Suggestions are made as to how to establish quality control in audiology clinics.

Cerebellopontine angle lesions: an audiological test protocol.

Audiological test protocols were devised for use in patients suspected of having a cerebellopontine angle tumor. Data supporting the logic for inclusion of each test are presented. Protocol design was based on test results obtained in 45 tumor and 554 non-tumor patients. In summary, we found: 1) speech-in-noise results were of some value in those patients with normal hearing and of no value in those patients with hearing loss, 2) the acoustic reflex test gave misleading information in 25% of patients, and 3) the ABR test proved to be the most effective test in separating tumor and non-tumor patients. All individuals having cerebellopontine angle tumors and 11% of those without such lesions had abnormal ABR results in this series.

Diagnostic features of the auditory brainstem response in identifying cerebellopontine angle tumours.

This report concerns the diagnostic features of the ABR which are most effective in identifying patients with cerebellopontine angle tumours. The conclusions are based on the results of 40 normal subjects, 35 patients without a cerebellopontine angle tumour and 68 patients without a tumour. One hundred per cent of the tumour patients and ten per cent of the non-tumour patients had abnormal ABR results.

A comparison of three modes of hearing aid-telephone coupling.

The stray magnetic field emitted by telephone receivers has been used by hearing aid wearers to improve telephone communication. Recent technical advances by Bell Canada have eliminated the magnetic field. The company sponsored the design of a hearing aid modification to compensate for the loss of this magnetic field. This report concerns the evaluation of the modification. The results of two experiments indicated that it did not provide a satisfactory substitute for the magnetic field. A by-product of this project was the development of a device (audiometer-telephone interface) which permits simulation of telephone listening, thus allowing clinical assessment of a patient's telephone communication ability.