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on digital signal processing of received signals. the Doppler system may be uscd to examine blood vessels of variable size and sliape. Measure-ments of beam profiles in a wave-guided system are compared with theoretical predictions. Preliininary design of a waveguide for a probe to measure the blood flow vęlocily at different points through the aorta is presented. [Work supported by NSF.)

FRIDAY AFTERNOON, 3 MAY 1991

INTERNATIONAL C, 1:00 TO 2:30 P.M.

Session 9PP

Psychological and Physiological Acoustics: Auditory Perception in Hearing-Impaired Listeners

Janet Koehnke, Chair

Department of Communication Sciences, University of Connecticut, Box U-85, Storn, Connecticut 06269

Contributed Papers

1:00

9PPI. Temporal resolution of frequency-modulatcd signals by hearing-impaired listeners. John P. Madden (Dept. of Speech and Hearing, Cleveland State Univ., Cleveland, OH 44115) and Lawrence L. Feth (Ohio State Univ., Columbus, OH 43210)

Hearing-impaired and normally hearing subjects werc asked to dis-criminate between two sinusoidal signaLs. One signal, the glide, movcd from its initial frequency over a linear path to its finał frequency. The other, the step signal, was the same except that its trajectory followed a series of discrete steps in freąuency. As the number of steps inereased, the duration of the individua! steps decreased, and the signal morę closely resembled the glide. The center frequencies of the signals were 0.5, 1.0, 2.0, and 4.0 kHz. The signals were presented to the two groups at equal SLs and at equal SPLs. The impaired subjects exhibited signif-icantly pooreT discrimination than the normally hearing subjects, indi-cating a reduccd ability to temporally resolve the step modulation. A frequcncy effect was cvident in both groups, with much poorer rcsolu-tion at 4.0 kHz. A level effect was noted in the normal subjects, who exhibited poorer resolution at higher SPLs. The results from the normally hearing subjects were very similar to temporal resolution values obtaincd in previous studies using amplitude-modulated (gapped) sinu-soids. [Work supported by a grant from AFOSR.]

1:15

9PP2. Freąuency selectivity and pitch discrimination in young and elderly subjects with cochlear hearing loss. Robert Peters (Speech and Hearing Sci., Dept. of Med. Allied Health Professions, Univ. of North Carolina, Chapel Hill, NC 27514) and Brian C. J. Moore (Dept. of Experimcntal Psychol., Univ. of Cambridge, Cambridge CB2 3EB, England)

Pure and complex tonę pitch discrimination data were obtained for two groups of hearing-impaired subjects, young and elderly, and for normally hearing subjects. Auditory filtcr shapcs were also estimated for center frequencies of 100, 200, 400, and 800 Hz using a modified notched-noise method [B. J. Glasberg and B. C. J. Moore, Hear. Rcs. 47, 103-138 (1990)]. Freąuency DLs for pulsed tones were measured for frequenries from 50-4000 Hz. DLs for the fundamental freąuency (F₀) of complex tones were measured for FqS of 50, 100, 200, and 400

2008 J. Acoust Soc. Am., Vol. 89, No. 4, Pt. 2. April 1991

Hz, for complcxes containing harmonics 1-12,6-12,4-12, and 1-5. The components were added in either cosine phase or in altemating sine-cosine phase. Auditory filters for the young and elderly impaired subjects were similar, both groups had broader filters than the normal subjects. Complex tonę DLs were larger for the impaired subjects. Com-plex tonę DLs were cspecially large for the tones with harmonics 1-5 and 1-12 at F₀s of 50 and 100 Hz. Thcse DLs were reduced (i.c., performances improved) when the lower harmonics were removed. Complex tonę DLs were alfected by the relative phases of the components for some but not all of the hearing-impaired subjects. The impli-cations of the results for pitch theories will be discusscd. (Research supported by the Andrus Foundation.]

1:30

9PP3. Modulation detection as an index of residual auditory function. C. Formby (Dept. of Otolaryngol., Johns Hopkins Univ. School of Medicine, Camegie 442, Baltimore, MD 21205), L. Morgan, J. Burton (Univ. of Florida, Gainesville, FL 32611), and T. G. Forrest (Univ. of Mississippi, University, MS 38677)

Indirect tests of residual auditory function often assume that the temporal envelope is the primary cue in the acoustic signal for pro-foundly hearing-impaired persons who are without auditory function. In contrast, for hearing-impaired persons who retain residual auditory function, both temporal envelope and spectral cues are available. This hypothesis was evaluated directly by studying simultaneously temporal envclopc and spectral resolution in scvcn profoundly hearing-impaired subjects (ten ears). Amplitudę modulation (AM) detection thresholds were measured with a 250-Hz carrier, modulated at rates of 40 and 150 Hz, presented by headphones and by hand vibration. At 40 Hz, where the AM sidebattds fell within the same critical band as the carrier and could not be resolved, all subjects yielded similar headphone and vibra-lor results. At 150 Hz, headphone thresholds for six ears were better than the vibrotactile threshold, while four ears yielded little or no dif-ference in performance between the two transducers. The lattcr results reflect differenccs in resolution between ears with and without func-tional critical band mechanisms and, hence, inherent differenccs between auditory and vibrotactile processing. [Research supported by NIH.]

121st Meeting: Acoustical Sodę ty of America 2008