885095966

1:45

9PP4. Inaudible stimulus may causc threshold shift. I. M. Young and L. D. Lowry (Dept. of Otolaryngol., Jefferson Med. College of Thomas Jefferson Univ., Philadelphia, PA 19107)

Interrupled pure-tone threshold measurements were madę monau-rally by Bekesy audiometry with and without presentation of inaudible identical continuous stimulus and white noise on subjects with bilateral normal hearing and unilateral sensonneural hearing loss with and without abnormal auditory threshold adaptation. Thresholds were com-pared for interrupted stimulus only and both interrupted stimulus and inaudible stimulus presentation. Subjects with norma! hearing and sen-sorineural hearing loss without abnormal adaptation showed no differ-cnce with and without presentation of the inaudible continuous stimulus. Subjects with sensorineural hearing loss demonstrating marked abnormal adaptation revealcd observable threshold shift for the interrupted stimulus by adding inaudible stimulus. It is assumed that the inaudible stimulus affecting partially damaged nerve fibers produce widespread abnormal adaptation that the threshold for another signal is inaudible until an abnormally high intensity is reached. A stimulus incapabłe of evoking a response may cause adaptation in such fibers.

2:00

9PP5. Auditory factors in obscure auditory dysfunction. Susan R. Mahanes and Robert Peters (Speech and Hearing Sci., Dept. of Med. Allied Health Professions, Univ. of North Carolina, Chapel Hill, NC 27599-7190)

Obscure auditory dysfunction (OAD), defined as a self-reported difficulty in understanding speech in noise by persons with normal audiograms and no other obvious causes, is commonly seen in clinical settings [G. H. Saunders and M. P. Haggard, Ear Hear. 10, 200-208). In an attempt to characterize the hearing difticulties expericnccd by this population, measures of frequency selectivity, complex and pure-tone discrimination and gap detection were obtained, as well as speech, au-diometric, and case history data. Results indicatcd impaired frequency selectivity at Iow frequencies, especially at 100 Hz and higher than normal thresholds for complcx- and pure-tone pitch and gap detection also at the lower freąucncies. Speech reception thresholds in noise were not consistently higher than for normal lisleners. [Research supported by the American Speech-Language-Hearing Foundation, NC Regional Chapter of the Acoustical Society of America, and the Andrus Foundation.]

2:15

9PP6. Monaural detection witb a contralateral cue in normal-hearing and hearing-impaired Hsteners. J. Koehnke and J. Besing (Univ. of Connecticut, Dept. of Commun. Sci., Box U-85, Storrs, CT 06260, and MIT, Cambridge, MA 02139)

Monaural detection with and without a contralateral cue (MDCC) in normal-hearing and hearing-impaired listeners is investigated. The signals and cues are l/3-octave noise bands centered at 500 and 4000 Hz, and the masker is a 4500-Hz low-pass noise. The Ievcl of the ntasker is 77 dB SPL for the normal-hearing listeners and 25 dB SL for the hearing-impaired listeners; when present, the cue is at — 7 dB relativc to the masker. Psychometrie functions for threc normal-hearing subjects and three subjects with moderate-to-sevcre, bilateral sensorineural hearing losses have been measured. The normal-hearing listeners show a 2-8 dB cued advantage at 500 Hz and a 1-11 dB cued disadvantage at 4000 Hz. Like the normal-hearing listeners, the hearing-impaired subjects have poorer performance at 4000 Hz when the cue is present. At 500 Hz, however, one of the hearing-impaired listeners shows a 5 dB cued advantage, comparable to normal, while the other hearing-impaired subjects have poorer detection when the cue is present. Results of these MDCC measurements will be compared with the performance of thcsc hearing-impaired listeners on other tests of binaural detection and discrimination. [Work supported by DRF.]

FRIDAY AFTERNOON, 3 MAY 1991

INTERNATIONAL B, 1:00 TO 4:45 P M.

Session 9SP

Speech Communication: Word and Sentence Effects

H. Timothy Bunnelł, Chair

Speech Processing Laboratory, Alfred /. du Pont Institute, Wilmington, Delaware 19899

Contributed Papers

IKK)

9SP1. Underwater audioingicai testing of a diver communicator. Richard W. Ranlet (Raytheon SSD, Box 360, Portsmouth, RI 02871)

An underwater communicator was developed to evaluate the suit-ability of direct audio voice transmission as a practical means to enable close-range Communications between divcrs using opcn-circuit SCUBA. A communicator that transmits speech directly inlo the water was de-signed and human engineered to yield a practical workmg prototype suitable for normal open-water dive conditions. lntelligibility testing of the device entailed underwater audiological testing that attempted to match in-air standards and practices. Measurements of hearing thresholds, speech reception thresholds, and speech discrimination/ recognition were performed using accepłed ASHA practices. Intełligi-bilily of sentences deemed rclevant to the diving environmcnt was also tested. In-water intelligibility testing levels were correlated with ac-cepted in-air standards using measured hearing and speech reception thresholds as common rcference points between the two media. Binaural intelligibility tests were performed in a pool using Auditec and Campbell PB50 word lists. Based on averaged results from two underwater listeners, intelligibility for the finished communicator measured 82% correct responses (5-m distance between transmitting and receiving divers). Similar tests for sentence intelligibility yieldcd near 100% correct responses for the same conditions.

2009

J. Acoust. Soc. Am., Vol. 89. No. 4, PI 2, Apnl 1991

121 sl Meeting: Acoustical Society of America

2009