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a narrow-band noise as the reference stimułus. The band wid th of thc narrow-hand noise used as test stimułus (NBN-150) was 150 Hz, and the bandwidth of the narrow-band reference stimułus (NBN-120) was 120 Hz. Both stimuli were arithmeticalły centered at 1 kHz. The loud-ness łevel functions for speech and for NBN-150 have slopes of approx-imately unity. However, the loudncss leve! function for the square wave has a slope of greater than unity below about 50 dB SL and the slope decreases above about 50 dB SL. Loudness predictions of two models are computcd and compared to the experimental measurements. ^ł,Work done as a consultant at AT&T Bell Laboratories, Acoustics Research Department.

SSP21. Humań frequency folłowing responses to vowel-like stimuli. A. K. Ananthanarayan (Dept. of Audiołogy and Speech Pathology, Univ. of Tennessee, 457 S. Stadium Hall, Knoxville, TN 37996) and H. S. Gopal (Univ. of Califomia, Santa Barbara, CA)

The frcquency folłowing responsc (FFR) reflects sustained neural actmty within the brain stem, phase łocked to the cycłes of the stimułus waveform. Auditory-nerve single unit responses have been shown to utilize the property of phase łocking to represent the stimułus spectrum of steady-state vowels. The purpose of this study was to determine if the scalp-recorded FFR would reveal similar neural representation of steady-state vowels. Scalp-recorded FFRs were obtained from six normal-hearing subjccts in response to fivc different synthesized steady-state vowels [/a/, /i/, /u/, /a:/, and /o/] presented binaurałly at 70, 50, and 30 dB nHL. Spcctral analyses of the FFRs indicated that, for each vowel, phase locking is robust at the fundamenlal frequency and the first three harmonics with phase locking to the fundamental preservcd even at stimułus levels close to response threshold. Spec trał peaks cor-responding to the first two formants were obscrved at only the higher intensities. These results, while not entirely consistcnt with the single-unit dala, seem to suggest that the FFRs reflect neural activity related to the processing of Iow pitch.

5SP22. A phase canccllation method for tinnitus. M. D. Judd and A. Unal (RTS, 3100 Central Expressway, Santa Clara, CA 95051)

Tinnitus is an intrinsic fcedback noise generated within the inner ear. Objective tinnitus is the kind in which a sound field does exist in thc outer ear canal. Rccent findings on the objective tinnitus problem strongly suggest that thc signal(s) emanate from damaged sensor hairs inside the cochlea. The ringing, or noise, that the patient “hcars” is most likely the firing of neighbor sensor hairs, duc to the damaged sensor. Thus these neighbors comprise somc signal bandwidth over which the patient detects the ringing. In the greater numbcr of patients, this phe-nomenon is diagnosed as due to a single tonę. Current signal methods used to mask the tonę, or noise, emanating from the cochlea typically employ wide bandwidth signals that overlap morę than the fuli band-width of the tonę (or noise). These methods inherently create noise in themselvcs and do litlle to remove the signals being generated from the inner ear. This papcr presents a simple viable method to cancel a single tonę, in the local region of the damagc sensor, in thc cochlea.

5SP23. Auditory-contrast sensitivity in normal and hearing-impaired listeners. David A. Hillier and James D. Miller (Central Inst. for the Deaf, 818 S. Euclid Ave., St. Louis, MO 63110)

The peak-to-valley ratio (depth of modulation in dB) of sinusoidal spectral envelopes nccessary to distinguish such modulated spectra from flat spectra was investigated in several experiments. In addition, several adaptation experiments were performed to test the hypothesis of enve-lope frequcncy channels in the auditory system similar to spatial fre-quency channels in the vi$ual system. Factors in hearing impairment that lead to contrast enhancement (recruitment) and contrast reduction (loudness saturation and loss of spectral resolving power) are discussed. Finally, auditory contrast sensitivity functions for two hearing-impaired subjects are presented.

1938 J. Acoust. Soc. Am.. Vol. 89, No. 4, Pt. 2, April 1991 5SP24. An automated test battery for assessing the auditory fitness of aviators. Gerald B. Thomas. Carl E. Williams, and And rew H. McCardie (Sensory Sci. Div., Naval Aerospace Med. Res. Lab., Pensacola, FL 32508-5700)

A microcomputer-bascd battery of tests has been developed to assess the performance of aviators on auditory tasks deemed important in the operation of aircraft. Included in thc test battery are measures of hearing threshold levels, speech perception in cockpit noise, speeded response to auditory signals. auditory attention management, and auditory short-tcrm memory. AU auditory stimuli are Computer synthesized or are digitized from analog sources, and all test administration and scoring proccdures are automated; test duration is approximately 30 min. The test battery was administcrcd to six aviator and nonaviator populations (Af= 120) and showed significant (p<0.05) performance differcnces among the populations on one or morę of the test battery elements. Test-retest reliabilities ranged from 0.71 to 0.88 (n = 64) within a rcstrictcd variance population (i.e., student naval aviators). Correlations between test battery scores and simulated “real world” performance are currcntly being determined.

5SP25. The effects of noise on the measurement of the 2f_t—f₂ otoacoustic emission. Richard W. Harrell, Law ren cc L. Fcth (Div. of Speech and Hearing Sci., Ohio State Univ., Columbus, OH 43210), and William Melnick (Ohio State Univ., Columbus. OH 43210)

The effects of noise exposure on the measurement of the cubic dis-tortion product emission (2/, — /₂) were measured. TTS was induced using white noise presented at four intensities, each for three different time periods, giving a total of twe!ve conditions. The subjecLs were normal-hearing adults. The trial conditions were randomized, with an appropriate rest period between each condition. The amount of tempo-rary threshold shift (TTS) in dB was obtained by comparing pre- and post-noise pure-tone thresholds for the 500-Hz to 8-kHz rangę by oc-tavc. The levcl of 2/, — /₂ was measured prior to and immediately folłowing the threshold testing. Changes in thc distortion product emission were determined by comparing pre- and post-noise emission measures. Preliminary results suggest that noise exposure may reduce the level of the distortion product emission. The degree to which this effect was seen appeared to be related to both intensity and duration of thc noise exposure.

5SP26. Importance and generality of various sound assess men t criteria. I. Naive listeners. Kim M. Smith and Tomasz Letowski (Dept. of Commun. Disord., Penn State Univ., 5 Moore Bldg., Univcrsity Park, PA 16802)

A series of criteria and their definitions has been developed describ-ing auditory image attributes that are felt to be important in sound quality assessment. These criteria were presented to two matching groups of 25 naive young listeners. Group 1 read the definitions for each criterion and then rated the attributes on two, five-point scales: (1) an importance scalę and (2) a generality scalę. Group II rated each criterion on the same scales, but they did not read any definitions. The same 50 listeners were retested under identical conditions. The folłowing results will be discussed: (1) importance and generality of various criteria, (2) differences between groups, (3) differences between test and retest data, and (4) application of results for futurę rescarch.

5SP27. Auditory processing of complex signals using the multichannel EWAIF. Jayanth Anantharaman (Dept. of Electrical Eng., Ohio State Univ., Columbus, OH 43210), Lawrence L. Feth,

121st Meeting: Acoustical Society of America 1938