Elizabeth J. Wood

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.

Drug delivery to the proximal colon.

The transits of a capsule and a multiparticulate pellet system have been monitored through the gastrointestinal tract in six healthy volunteers. Both preparations moved together through the stomach and small intestine, reaching the colon, on average, 4 h after dosing. Within the colon the pellets dispersed and moved at a slower rate than the capsule. There was considerable intersubject variability in the large bowel transit times. The findings are discussed in terms of drug delivery to the colon.

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.

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.

A Comparison of Manual Methods for Measuring Hearing Levels

A comparison was made of three manual methods for measuring pure-tone sensitivity; one method is proposed by the Education Committee of the British Society of Audiology (BSA), the second method is recommended by the American Speech and Hearing Association (ASHA) and the third is a shortened version of the ASHA method. 9 normally-hearing and 5 hearing-impaired subjects from differing educational backgrounds were tested at 1.0 kHz a total of fifteen times on each of the methods. False-positive responses were noted throughout the testing and also in a 20-second time-out period. Each threshold run was timed and the subjects were asked to rate each threshold run on a 10-point scale for ease of the task. No significant differences among the three methods were found in their threshold estimates, standard deviations, number of false-positive responses, or subject preferences. The ASHA method took longer and required more tone presentations to establish threshold. The number of successive tone presentations to which the subject did not respond was also counted. The BSA method produced more, and longer silent intervals than the other two methods.

A simple clinical measure of frequency resolution

A simple procedure for obtaining a 3-point approximation to a psychoacoustical tuning curve (PTC) using a clinical audiometer and tape recorder is described. Data from 45 normally-hearing subjects are presented in terms of distributions of scores amongst subjects and repeatability within subjects. The procedure has proven to be rapid and tractable and provides results which are comparable to more time-consuming methods.

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.