Voicing judgements by chinchillas trained with a reward paradigm.

Experiments were performed to replicate and extend previous findings of similar categorization of voiced/voiceless consonant-vowel (CV) syllables by humans and chinchillas. A reward paradigm was applied to the question of how stimulus range affects the voice-onset-time (VOT) corresponding to the voiced/voiceless category boundary. Each of four adult chinchillas and four human subjects identified synthetic CV syllables as voiced (/ba/, /da/, /ga/) or voiceless (/pa/, /ta/, /ka/) using voiceless standards of either 80 or 120 ms. In both humans and animals, extending the VOT range from 80 to 120 ms shifted category boundaries to longer VOTs, but to a different extent across listeners. Control experiments suggested that listeners were attending to different phonetic cues in a manner that depended on the listener, rather than on species. The results are interpreted in terms of similar contextual effects and use of multiple phonetic cues to voicing in humans and animals.

Distortion product otoacoustic emissions in rhesus (Macaca mulatta) monkey ears: normative findings.

Distortion product otoacoustic emissions (DPOAEs) in rhesus monkeys were characterized and the optimal parameters for their generation were determined. Robust DPOAEs were readily measurable from the ear canals of six rhesus monkeys (n = 12 ears). The nonmonotonic behavior of the f2/f1 ratio functions in rhesus monkeys was found to be similar to other animals and humans. The optimal mean f2/f1 ratio of 1.21 and the effect of the primary frequency and level on the optimal f2/f1 ratios were also similar to human measurements. The contour of the rhesus monkey DPOAE 'audiograms' and their behavior were also comparable to human measurements with slight differences in peak frequencies. The rhesus monkey DPOAE input/output (I/O) functions were generally monotonic with a slope approaching unity with increasing frequency. Therefore, our study shows that many basic DPOAE characteristics are remarkably similar in the two species and emphasizes the appropriateness of the rhesus monkey as a model for DPOAE research. Detailed studies of the behavior of DPOAEs can be carried out in a model that is phylogenetically close to human both in hearing and in the gross structure and histology of the inner ear.

Spontaneous otoacoustic emissions in chinchilla ear canals: correlation with histopathology and suppression by external tones.

Two cases of spontaneous otoacoustic emissions (SOAEs) have been found among a sample of 28 chinchilla ears after noise exposure, and no cases of SOAEs have been found among 28 unexposed ears. Further observations of the characteristics of SOAEs recorded in the ear canals of two chinchillas after noise exposure are described. These signals were tonal, robust, and could be suppressed by presenting external tones to the ear. Histopathological evaluation of the cochlea of emitting ears revealed discrete basal-turn lesions near the positions corresponding to the frequencies of the emissions. Behavioral threshold shifts measured in one animal after noise exposure and acoustic intermodulation distortion product behavior in the other both suggest a region of increased vibratory response of the cochlear partition near the location of the SOAE. Results from these emitting ears support a hypothesis that a punctate loss of the organ of Corti (OC) may facilitate the occurrence of an SOAE. We further hypothesize that the following conditions are both necessary and sufficient for an SOAE to occur: (1) functional disruption of a normally present biomechanical control mechanism in a region of the OC; (2) presence of functionally active OC (especially outer hair cells) adjacent to the region. The observations from ears possessing SOAEs provide strong, though indirect support for active and nonlinear models in interpreting cochlear biomechanical phenomena.

Hearing levels of railroad trainmen.

The hearing sensitivity of 9427 railroad train crew members, determined during the first year of a company-wide hearing conservation program, was compared with hearing sensitivity in a control population not exposed to occupational noise. The hearing sensitivity of the trainmen did not differ significantly from that of the control population. Multiple regression analysis, which considered separately the effects of age and years of service, showed significant differences in hearing levels due to age, but no differences in hearing levels due to years of service. Evaluation of the data by risk categories developed by the National Institute for Occupational Safety and Health indicate that this group of trainmen had no risk of occupational noise-induced hearing loss. These analyses, combined with studies of locomotive cab noise, show clearly that trainmen are not typically exposed to hazardous occupational noise.

Acupuncture heroin detoxification: a single-blind clinical trial.

The increasing prevalence of HIV infection among injection drug users mandates the development of innovative treatments. While extensive clinical experience suggests that acupuncture detoxification is both safe and acceptable to those in withdrawal, little research has been conducted to assess its efficacy as a treatment modality. In this first controlled study of acupuncture heroin detoxification, 100 addicted persons were randomly assigned, in a single-blind design, to the standard auricular acupuncture treatment used for addiction or to a "sham" treatment that used points that were geographically close to the standard points. Attrition was high for both groups, but subjects assigned to the standard treatment attended the acupuncture clinic more days and stayed in treatment longer than those assigned to the sham condition. Additionally, attendance varied inversely with self-reports of frequency of drug use, suggesting that those with lighter habits found the treatment modality more helpful. Limitations of the study are discussed.

Predictors of HIV-related risk behaviors among heterosexuals in alcoholism treatment.

OBJECTIVE: To determine which measures of alcohol and drug use are associated with HIV-related sexual risk and protective behaviors. METHOD: Entrants (N = 743, 72% male) to alcoholism treatment clinics underwent a structured interview including an assessment of demographics, substance abuse characteristics and sexual behaviors. Associations were examined between alcohol- and drug-related behaviors, and demographic variables, with the prevalence of high-risk sexual behaviors. RESULTS: Those more likely to use alcohol or drugs when having sex, and those who expect to have high-risk sex when they drink alcohol, were more likely to engage in high-risk sexual behavior. Measures of severity of alcohol or drug problems alone were not consistently related to high-risk or protective behaviors. Several other concurrently used measures (such as the Addition Severity Index and alcohol expectancies) showed more consistent association with high-risk behaviors. There was no apparent reduction in the likelihood of practicing risk-reducing behaviors among those more severely addicted and those who combined alcohol and/or drugs with sex. CONCLUSIONS: This study suggests that sexual risk and protective behaviors are not consistently associated with severity of addiction problems. Some measures of alcohol and drug use (i.e., the ASI Drug Composite Score and the Enhanced Risk subscale of the alcohol expectancy measure) were more consistently related to the specific risk behaviors measured than were others (e.g., the ASI Alcohol Composite Score), while most measures showed little or no association with protective behaviors.

HIV infection and risk behaviors in two cross-sectional surveys of heterosexuals in alcoholism treatment.

OBJECTIVE: To measure the prevalence of human immunodeficiency virus (HIV) infection and high-risk behaviors among heterosexuals in alcoholism treatment, comparing two cross-sectional surveys completed 2 to 3 years apart. METHOD: Two groups of entrants to alcoholism treatment clinics were recruited, between October 1990 and December 1991 (n = 860; 639 men) and between January 1993 and March 1994 (n = 752; 520 men). Participants underwent a structured interview including an assessment of demographics. substance abuse characteristics and sexual behaviors, as well as serotesting for HIV antibodies. Associations were examined between HIV serostatus and several factors, including demographic variables, substance use and high-risk sexual behaviors. RESULTS: The overall HIV seroprevalence in the first and second samples was 5% (95% CI: 3-6%) and 5% (95% CI: 3-7%). When the two samples were compared, there were no significant differences in prevalence of HIV infection by categories of gender, race, income and most other demographic characteristics within either sample: history of injection drug use (IDU) was significantly related to HIV serostatus in both samples. Unsafe sexual practices were common in both samples. When samples were combined, those 30 years of age or older were more likely to be HIV infected, and men and women with no reported history of IDU still had an HIV prevalence of 3% and 2%, respectively. More than half of the respondents had two or more partners in the previous 6 months and reported a history of a sexually transmitted disease. CONCLUSIONS: There was no change in the substantial prevalence of HIV infection and high-risk behavior among heterosexual clients entering alcoholism treatment programs over the 3.5-year study period. The HIV prevalence among non-IDU clients remained several times higher than published estimates from similar community-based heterosexual samples. These data reinforce the concept that heterosexual noninjection drug users are at high risk for HIV and may benefit from intervention programs.

Hearing: the effects of noise.

We live in a noisy world. The clamor and din of modern society has increased in variety, if not in prevalence and intensity, in the past decades, making noise America's most widespread nuisance. Excessive noise exposure annoys individuals, produces stress, impairs the ability to communicate, interferes with work and play activities, and, in high enough doses, produces permanent damage to the auditory system, which leads to significant hearing loss. Noise exposure associated with the workplace has been known to produce hearing loss for centuries. More than 20 years ago the U.S. Department of Labor promulgated regulations designed to protect the hearing of employees who work in noisy environments. However, these regulations failed to consider noise exposures outside the workplace, and recent evidence suggests that these exposures are potentially hazardous for millions of Americans. The most important sources of nonoccupational noise exposure are hunting and target shooting, listening to amplified music through headphones, and attendance at rock concerts. For each source, an assessment of risk of hearing loss is made.

Effects of alcohol on the acoustic reflex threshold in the chinchilla.

The effect of ethanol on the acoustic reflex threshold was examined in a repeated measure design study in six chinchillas. Each subject was weighed and orally administered the control (water) at a dosage of 7.5 ml/kg. Commencing 1 h after alcohol ingestion, the acoustic middle ear reflex measures (AMRs) were taken every other hour, for a total of four recording sessions. Ascending and descending trials were alternated between each recording session. Two weeks later the same chinchillas were administered 35% alcohol by volume. AMRs were recorded under the same conditions and procedures as for the control. Alcohol produced AMRs that were significantly elevated over baseline values 1 h after alcohol ingestion and four of the five had AMRs that remained elevated 3 h after ingestion.

Animal model for the 4-kHz tonal dip.

In humans, noise exposures produce permanent hearing losses which usually begin at 4 kHz. In chinchillas, a similar pattern of hearing loss was observed following exposure for 9 or 18 days to an octave band of noise with a center frequency of 0.5 kHz. Histopathological observations of cellular degeneration showed that this exposure produced different types of damage in the basal and apical turns of the cochlea. Behavioral measures of auditory function showed that damage in the basal turn was associated with permanent threshold shifts for one to several of the high frequencies. However, moderate losses of outer hair cells commonly appeared in the apical turn without permanent threshold shifts for low-frequency tones. These findings indicate that the pure-tone audiogram may not accurately reflect the condition of the organ of Corti after noise exposure.

Encephalopathy in cattle experimentally infected with the scrapie agent.

Ten 8- to 10-month-old cattle were each inoculated intramuscularly, subcutaneously, intracerebrally, and orally with the scrapie agent to determine whether cattle are susceptible to it. Two inocula, both 10% homogenates of cerebrum, were used. One inoculum was from a sheep used for the second experimental ovine passage of the agent from 4 naturally affected Suffolk sheep. The other inoculum was from a goat used for the first experimental caprine passage of the agent from 2 naturally affected dairy goats living with the Suffolk sheep, the source of their infection. Between 27 and 48 months after inoculation, neurologic disease was observed in 1 of 5 cattle given the sheep brain homogenate and in 2 of 5 given the goat brain homogenate. In all 3 affected cattle, the disease was expressed clinically as increasing difficulty in rising from recumbency, stilted gait of the pelvic limbs, disorientation, and terminal recumbency during a 6- to 10-week course. Neurohistologic changes, though consistent with those of scrapie, were slight and subtle: moderate astrocytosis with sparse rod cells, some neuronal degeneration, a few vacuolated neurons, and scant spongiform change. Clinically and neurohistologically, the experimentally induced disease differed from bovine spongiform encephalopathy. The differences emphasize that such infections in cattle induce diverse responses, presumably depending largely on the strain of the agent. Pathologists should keep this variability in mind when looking for microscopic evidence of a scrapie-like encephalopathy in cattle.

Recent studies of temporary threshold shift (TTS) and permanent threshold shift (PTS) in animals.

It is well known that excessive exposure to noise results in temporary and/or permanent changes in hearing sensitivity in both human and animal subjects. The purpose of this review is to describe the major findings from laboratory studies of experimentally induced hearing losses, both temporary and permanent, resulting from exposure to noise in animal subjects which have been published since the report of Kryter et al. (1966). The data reviewed support the following general statements: (1) The chinchilla is the most widely used and most appropriate animal model for studies of noise-induced hearing loss; (2) with continuous exposures to moderate-level noise, thresholds reach asymptotic levels (ATS) within 18-24 h; (3) permanent threshold shifts, however, depend upon the level, frequency, and the duration of exposure; (4) below a "critical level" of about 115 dB, permanent threshold shift (PTS) and cell loss are generally related to the total energy in continuous exposures; (5) periodic rest periods inserted in an exposure schedule are protective and result in less hearing loss and cochlear damage than equal energy continuous exposures; and (6) under some schedules of periodic exposure, threshold shifts increase over the first few days of exposure, then recover as much as 30 dB as the exposure continues.

Noise exposure from leisure activities: a review.

Over the past two decades there has been increasing concern about the role of nonoccupational, or leisure noise on hearing. This paper reviews published studies that detail the noise levels and potential effects of some noisy leisure activities. Considered are the most common sources of leisure noise: exposure to live or amplified rock, classical, or jazz music; exposures from personal listening devices ("walkman" type); noise around the home, and hunting and target shooting. Although all activities listed above have the potential for dangerous levels of noise exposure, the most serious threat to hearing comes from recreational hunting or target shooting.

The effect of hand-held radio operation on audio dosimeters.

Six models of audio dosimeters from five manufacturers were tested to determine the effect of radio frequency (r-f) interference caused by the operation of hand-held radios near the dosimeters on the measured average sound pressure level in a controlled noise field. Exposures were in a reverberant chamber at levels of 36, 80, and 92 dBA to an octave of noise centered at 1 kHz. Two walkie-talkie type radios, one operating at 160 mHz and the other operating at 460 mHz were used to generate the r-f field. The radios were operated on two duty cycles (2 or 3 cycles/min) during the recording period. Reported measures, such as average sound pressure level and peak sound pressure level, were compared for each noise exposure condition with and without operation of the hand-held radio. The results indicate that all makes and models of the dosimeters that were tested gave false readings under some conditions. These values always exceeded the reading in the noise alone control condition and varied by as much as 45 dB above the "true" level. Because each dosimeter behaved differently--including different samples of identical models--it was not Rather, steps are recommended to help users identify potential r-f contamination on dosimeter performance in the field.

Attenuation and protection provided by ossicular removal.

Behavioral studies of hearing loss produced by exposure to ototraumatic agents in experimental animals, combined with the anatomical evaluation of end-organ pathology, have provided useful information about the relation between dysfunction and pathology. However, in order to attribute a given hearing loss to some pattern of cochlear damage, it is necessary to test each ear independently. The objective of the present study was to evaluate attenuation measured behaviorally and protection to the cochlea provided by removal of the malleus and incus in noise-exposed chinchillas. Results from one behaviorally trained chinchilla with ossicular removal indicated a conductive hearing loss that varied from 41 dB at 0.125 kHz to 81 dB at 4.8 kHz and averaged 60 dB. Counts of missing sensory cells in ears of seven chinchillas with unilateral ossicular removal and exposure to noise (octave band centered at 0.5 kHz, 95 dB SPL, for durations up to 216 days, or centered at 4.0 kHz, 108 dB SPL, for 1.75 h) showed no more cell loss on the protected side than in age-matched control ears. From these data it is concluded that ossicular removal provides enough attenuation to protect the chinchilla cochlea from damage during these noise exposures, and that it will insure monaural responses behaviorally as long as the hearing loss in the test ear does not exceed that in the ear with ossicular removal by approximately 50 dB at any frequency.

Detection of frequency and rate modulation by the chinchilla.

Thresholds for detection of frequency modulation were obtained from three chinchillas at seven frequencies between 320 Hz and 12.75 kHz and at three sensation levels (20, 40, 60, dB SL). These were compared with human thresholds at 40 dB SL obtained under the same conditions. Our data show no significant impact of sensation level and confirm Nelson and Kiester 's [J. Acoust. Soc. Am. 64, 114-126 (1978)] report that the chinchilla has much poorer frequency discrimination than man. In an attempt to assess separately the chinchilla's capacity for temporal coding of frequency, thresholds for detection of a change in the modulation rate of amplitude modulated noise were obtained for nine modulation frequencies between 10 and 320 Hz. The chinchillas needed a larger rate change for detection than most humans but the relative difference was less than that found for frequency modulation detection.

Effect of periodic rest on hearing loss and cochlear damage following exposure to noise.

Changes in hearing sensitivity and cochlear damage were determined in two groups of chinchillas exposed to an octave band of noise (OBN) centered at 0.5 kHz, 95 dB SPL on two different schedules: 6 h per day for 36 days, or 15 min/h for 144 days. Hearing sensitivity was measured behaviorally at 1/4-oct frequency intervals from 0.125 to 16.0 kHz before, during, and for a period of 1 to 2 months after the exposure, at which time the animals' cochleas were fixed and prepared for microscopic examination. Cochlear damage was determined by counts of missing sensory cells. Both exposures produced an initial shift of thresholds of 35-45 dB; however, after a few days of exposure, thresholds began to decline and eventually recovered to within 10-15 dB of original baseline values even though the exposure continued. Measures of recovery made after completion of the exposures indicated minimal permanent threshold shifts in all animals. The behavioral and anatomical data indicated that these intermittent exposures produced less temporary and permanent hearing loss and less cochlear damage than continuous exposures of equal energy.

Effects of periodic rest on physiological measures of auditory sensitivity following exposure to noise.

Whole nerve action potential (AP) and single auditory-nerve fiber thresholds were measured in chinchillas exposed to noise. The exposure stimulus was a 500-Hz octave band of noise presented at 95 dB SPL for 15 min/h, for 4 or 40 days. The AP thresholds were elevated by about 40 dB on day 4, between 0.5 kHz and approximately 8 kHz. On day 40, AP thresholds at the same frequencies were lower by 10-25 dB, even though the noise exposure had continued. Single fiber threshold tuning curves exhibited pathologies similar to those previously observed following noise exposure. Tuning curves measured on day 40 were more normal in appearance. These results confirm that similar recovery of threshold observed in psychophysical experiments [Clark et al., J. Acoust. Soc. Am. 82, 1253-1264 (1987)] can be understood in terms of the sensitivity of the peripheral auditory system.

The behavior of acoustic distortion products in the ear canals of chinchillas with normal or damaged ears.

Acoustic intermodulation distortion products were measured in 15 ear canals of chinchillas with normal or damaged ears. Pretreatment results showed that when two primary tones at frequencies f1 and f2, f1 less than f2, were presented at levels from 30 to 90 dB SPL, acoustic distortion products at 2f1-f2 and 2f2-f1 were 30 to 50 dB below primary-tone levels. Noise exposures that caused temporary or permanent hearing loss produced corresponding temporary or permanent reductions in distortion-product levels. Mechanical damage to the cochlea or middle ear reduced the distortion-product levels to below the noise floor of the measurement system. Comparisons of distortion-product level with behaviorally measured threshold shift and cochlear histopathology suggest that, in the absence of conductive impairment, the level of 2f1-f2 or 2f2-f1 can be used as a sensitive indicator of hearing sensitivity and the condition of the cochlea.