Mariano A. Fernandes

Psychoacoustic and phonetic temporal processing in normal and hearing‐impaired listeners

Four measures of auditory temporal processing were obtained from 16 normals and 16 individuals with a hearing loss of heterogeneous origin. These measures were: (1) temporal integration—the difference in detection thresholds between signals of 10‐ and 1000‐ms duration (which was determined to provide an estimate of the ability to integrate energy over time), (2) gap detection—the shortest duration of silence between two noise bursts that can be discriminated from an uninterrupted noise, (3) temporal difference limen—the increment in duration necessary to detect a difference in the duration of a noise burst, (4) gap difference limen—the increment in duration necessary to detect a difference in the duration of a silent interval between two noise bursts. Each measure was obtained for stimuli centered both at 500 and at 4000 Hz using a three‐alternative forced‐choice procedure. In addition, measures of identification and discrimination were obtained for two sets of synthetic speech syllables varying chiefly in a temporal parameter, voice‐onset‐time, from /ba/ to /pa/ and from /bi/ to /pi/. Finally, speech identification in noise was measured with the FAAF test. Most of the hearing‐impaired listeners displayed poorer temporal analysis than the normals on all of the psychoacoustical tasks, regardless of whether the two groups were compared at similar sound pressure levels or at similar sensation levels. Although the hearing‐impaired listeners displayed a reduction in the ability to discriminate subphonemic cues for the voiced–voiceless distinction, their identification of that distinction in stop consonants appeared to be normal. The hearing‐impaired group made about twice as many errors as did the normals on each of the consonant features of place, manner, and voicing when identifying speech in noise. Increased temporal difference limen and longer gap‐detection thresholds were found to correlate significantly with reduced speech intelligibility in noise, even when the effects of the pure‐tone threshold loss were partialed out.

Frequency resolution and discrimination of constant and dynamic tones in normal and hearing‐impaired listeners

Frequency resolution and three tasks of frequency discrimination were measured at 500 and 4000 Hz in 12 normal and 12 hearing-impaired listeners. A three-interval, two-alternative forced-choice procedure was used. Frequency resolution was measured with an abbreviated psychoacoustical tuning curve. Frequency discrimination was measured for (1) a fixed-frequency standard and target, (2) a fixed-frequency standard and a frequency-transition target, and (3) frequency-transition standard and a frequency-transition target. The 50-ms frequency transitions had the same final frequency as the standards, but the initial frequency was lowered to obtain about 79% discrimination performance. There was a strong relationship between poor frequency resolution and elevated pure-tone thresholds, but only a very weak relationship between poor frequency discrimination and elevated pure-tone thresholds. Several hearing-impaired listeners had normal discrimination performance together with pure-tone thresholds of 80-90 dB HL. A slight correlation was found between word recognition and frequency discrimination, but a detailed comparison of the phonetic errors and either the frequency-discrimination or frequency-resolution tasks failed to suggest any consistent interdependencies. These results are consistent with previous work that has suggested that frequency resolution and frequency discrimination are independent processes.

Monaural and binaural auditory frequency resolution measured using bandlimited noise and notched‐noise masking

Several studies using bandlimited masking noise have indicated that NOSO frequency resolution is better than that for NOS pi. The present study examined NOSO and NOS pi frequency resolution with two different masking methods: bandlimited noise and notched noise. Noise spectrum levels of 10, 30, and 50 dB/Hz were used. Thresholds were determined for a 500-Hz signal, using a three-alternative forced-choice adaptive procedure, as a function of masker bandwidth and notchwidth. For NOSO presentation, 3-dB down points were comparable for the notched-noise and bandlimiting methods. For NOS pi presentation, 3-dB down points were generally greater for the bandlimiting method than the notched noise method. Furthermore, for NOS pi presentation, the 3-dB down estimate increased as noise level increased for the bandlimiting method, but stayed constant for the notched-noise method. It is suggested that the two masking methods measured different aspects of binaural processing.

Frequency Resolution and Hearing Loss

Future scientific and diagnostic interest in frequency resolution requires an evaluation of the different methods that are available to measure it. We compared three methods: (1) pure-tone thresholds in broadband noise, (2) pure-tone thresholds in the presence of a fixed pure-tone masker and (3) psychoacoustical tuning curves. We additionally obtained estimates of temporal integration and of speech intelligibility in noise. Three subject groups were tested: 10 normals, 13 subjects with a noise-induced hearing loss and 18 subjects with a cochlear hearing loss but no history of noise exposure. Generally the three measures of frequency resolution show moderate agreement with each other. Poor frequency resolution is invariably associated with a pure-tone threshold loss. Temporal integration appears unrelated either to the pure-tone threshold loss or frequency resolution. Some of the measures of frequency resolution display significant correlation with speech intelligibility in noise. However, since both variables are correlated with pure-tone threshold loss the exact relationship between frequency resolution and speech intelligibility cannot be clearly established.

Temporal integration, frequency resolution, and off‐frequency listening in normal‐hearing and cochlear‐impaired listeners

Temporal integration for a 1000-Hz signal was determined for normal-hearing and cochlear hearing-impaired listeners in quiet and in masking noise of variable bandwidth. Critical ratio and 3-dB critical band measures of frequency resolution were derived from the masking data. Temporal integration for the normal-hearing listeners was markedly reduced in narrow-band noise, when contrasted with temporal integration in quiet or in wideband noise. The effect of noise bandwidth on temporal integration was smaller for the hearing-impaired group. Hearing-impaired subjects showed both reduced temporal integration and reduced frequency resolution for the 200-ms signal. However, a direct relation between temporal integration and frequency resolution was not indicated. Frequency resolution for the normal-hearing listeners did not differ from that of the hearing-impaired listeners for the 20-ms signal. It was suggested that some of the frequency resolution and temporal integration differences between normal-hearing and hearing-impaired listeners could be accounted for by off-frequency listening.

Monaural and Binaural Intensity Discrimination in Normal and Cochlear-Impaired Listeners

Monaural and binaural intensity difference limens for 75-dB SPL pure tones were determined for 6 normal subjects and for 6 subjects with cochlear hearing loss. The magnitude of binaural masking level difference (BMLD) was also determined. Both normal and hearing-impaired subjects showed a 0.45-dB binaural advantage for intensity discrimination. In contrast, the BMLD was appreciably reduced with hearing impairment. Results are discussed in terms of specific effects of hearing loss on binaural hearing.

The role of monaural frequency selectivity in binaural analysis

The relation between the monaural critical band and binaural analysis was examined using an NoSm MLD paradigm, in order to resolve ambiguities about the width of the masking spectrum important for binaural detection. A 500-Hz pure-tone signal was presented with a 600-Hz-wide band of masking noise to the signal ear. Bands of noise ranging in width from 25 to 600 Hz, or noise notches (imposed on a 600-Hz-wide band centered on the signal frequency) ranging in width from 0 to 600 Hz were presented to the nonsignal ear. All noise bands and notches were centered on 500 Hz, the frequency of the signal. The effects of varying bandwidth were radically different from those of varying notchwidth: the MLD changed from zero to approximately 8 dB over a bandwidth range of 400 Hz; for notchwidths, however, the MLD changed 8 dB over a range of only 50 Hz. The results support an interpretation that the fine frequency selectivity of monaural analysis is preserved in peripheral binaural interaction, but that a relatively wide frequency range of critical bands is scanned at a later stage of binaural processing. It was suggested that the wide spectral range of binaural analysis may provide a background against which binaural differences due to the signal are detected.

The effect of random intensity fluctuation on monaural and binaural detection

Two experiments were performed to determine the effects of random intensity fluctuation on NoSo and NoS pi performance. Noise was used as both signal and masker, and stimuli were bands of noise from either 0-2.0 or 2.0-4.0kHz. Signal and masker were either coherent (from the same source) or noncoherent (from independent sources). In the first experiment, noise fluctuation was achieved by modulating a wide band of noise. In the second experiment, fluctuation was achieved by narrowing the noise bandwidth. Results from both experiments indicated that NoSo performance was adversely affected by fluctuation and by noncoherent relation between signal and masker. NoS pi detection was not adversely affected by fluctuation at low frequency, and was affected less adversely than was NoSo detection at high frequency. This difference between NoSo and NoS pi performance is an important consideration when making inferences about monaural and binaural processing when the stimuli are fluctuating rather than temporally steady.

Masking, temporal integration and speech intelligibility in subjects with noise‐induced hearing loss

Three psychoacoustical measures of frequency analysis were obtained from ten normal‐hearing subjects and twelve subjects with noise‐induced hearing loss. First, thresholds of pulsed 500‐ and 4000‐Hz pure tones were measured in the presence of a continuous, 60 dB/Hz spectrum level white‐noise masker. Second, thresholds of pulsed, pure tones were measured in the presence of a continuous, 85‐dB SPL tonal masker of 500 and 4000 Hz. Third, the intensity required to mask pulsed, 500‐ and 4000‐Hz test signals at 10‐dB sensation level was measured with sinusoidal masker of five adjacent frequencies [psychoacoustical tuning curves]. We also measured thresholds for 10‐ and 1000‐ms duration signals of 500 and 4000 Hz as an indication of temporal integration. Two tests of speech intelligibility, one in a speech‐spectrum shaped noise and one in a speech‐babble background, were presented at a fixed intensity. Some hearing‐impaired subjects clearly display increased thresholds in white noise (larger critical ratios), pr...

Validation of a screening oto- admittance instrument.

A within-subject comparison between an American Electromedics 85R screening tympanometer and a Grason-Stadler 1723 clinical otoadmittance meter indicated equivalent results for middle-ear pressure. Tympanometer admittance readings needed to be rescaled to concur with the oto-admittance meter. Screening by acoustic reflex response using the single-intensity stimulus of the tympanometer was problematic and gave many misleading results.