Self-Assessment Questions

This section provides a review. Mark each statement on the Answer Sheet according to the factual materials contained in this issue and the opinions of the authors.

Article One (pp. 226–227) Overview

1. Which of the following is not an example of continuous noise, which remains constant and stable over time?

   • Boilers in power plants

   • Weaving machine in a textile plant

   • Nail guns on a construction site

   • Newspaper printing press

2. Which of the following statements best describes intermittent noise?

   • Intermittent noise refers to noise levels that are interrupted by intervals of relatively low sound levels. Intermittent noise will have relatively large fluctuations in level within the period of observation.

   • Intermittent noise exposure refers specifically to occupational environments in which broadband noise from machinery is either present or absent.

   • Intermittent noise refers to acoustic environments with fluctuating frequency components and peak sound pressure levels ranging from 85 dBA to 115 dBA.

   • Intermittent noise exposures are characterized by spectral fluctuations in the noise signal.

3. Why has intermittent noise been considered less hazardous to hearing than continuous noise?

   • The exchange rate is different for intermittent versus continuous noise.

   • The ear may have a chance to recover during quiet periods.

   • Inner hair cells are not sensitive to intermittent noise exposures.

   • Intermittent noise does not contain impulsive noise components.

4. The exchange rate

   • is the ratio between A-weighted noise exposures and C-weighted noise exposures

   • is used to determine the ratio between peak sound pressure levels and 8-hour time-weighted average noise exposures

   • is the relationship between a noise level and the halving or doubling of the amount of time a person can be exposed at that noise level

   • has also been referred to as the “time-intensity tradeoff,” the “trading relation,” or the “doubling rate”

   • Both C and D

5. Auditory synaptopathy is

   • a condition that is easily identified with standard audiometric testing

   • unlikely to be caused by noise exposure

   • the destruction of synaptic connections between hair cells and auditory nerve fibers

   • the construction of synaptic connections between hair cells and auditory nerve fibers

   Article Two (pp. 227–229) Attempts to Define Non-Gaussian Noise

6. Effective quiet has been defined as

   • the lowest level of noise that does not lead to permanent threshold shifts in otologically normal young adults

   • the highest level of noise that will not interfere with temporary threshold shift recovery

   • the level of noise necessary to successfully complete a quantitative task

   • the maximum noise level regulated for public libraries

   • average noise levels that do not exceed 45 dBA over an 8-hour period

7. The beginning of an impulse noise–from the time the noise starts until the noise level first returns to the baseline level–is termed the

   • A-duration

   • B-duration

   • C-duration

   • Friedlander wave

8. The classic waveform of an impulse or impact noise can change considerably when the sound is measured in an indoor versus an outdoor environment due to

   • reverberation and reflection from walls and other interior surfaces

   • limitations of sound measuring equipment

   • the effects of temperature and humidity on sound transmission

   • increased background noise

9. Which of the following is an example of impact noise?

   • Rifle shots

   • A burst of compressed air

   • Fireworks

   • Hammering

   • A chemical explosion

10. All other factors remaining constant, which of the following noise environments may be presumed to pose the greatest hazard to hearing?

    • Continuous noise averaging 90 dBA

    • Intermittent noise averaging 90 dBA

    • Impulsive noise superimposed on continuous noise averaging 90 dBA

    • Varying noise averaging 90 dBA

    Article Three (pp. 229–234) Summary of the Previous Report to the National Institute forOccupational Safety and Health on the Exchange Rate (1992)

11. Which exchange rate is most commonly used worldwide?

    • 3 dB

    • 4 dB

    • 5 dB

    • 6 dB

12. In the 1960s, the National Academy of Sciences Committee on Hearing and Bioacoustics (CHABA) based its noise exposure criteria on which of the following?

    • Temporary threshold shift measured 2 minutes after cessation of exposure (TTS₂) is a consistent measure of the effects of a single day's exposure.

    • All exposures producing a given TTS₂ will be equally hazardous.

    • Noise-induced permanent threshold shift produced after many years of habitual exposure will be the same as the TTS₂ produced in normal ears by an 8-hour exposure to the same noise.

    • All of the above.

13. Why might using a 5-dB exchange rate be underprotective against noise-induced hearing loss?

    • Research has shown that a higher exchange rate is more protective than a lower exchange rate.

    • Animal models indicate exactly which exchange rate should be used.

    • Many of the assumptions on which the 5-dB exchange rate is founded have been called into question.

    • Studies involving human subjects have shown that the exchange rate is irrelevant when the ambient noise level is over 100 dBA.

14. Which occupation could receive a benefit (i.e., potentially less risk of hearing loss) from intermittent noise exposures?

    • Power plant boiler operator

    • Forklift driver in a noisy warehouse

    • Assembly line worker

    • Lumberjack

15. According to Passchier-Vermeer's analysis for the 3000-Hz frequency after 15 years of noise exposure:

    • The data points for intermittent and varying noise show less hearing loss than those for continuous noise.

    • The data points for intermittent and varying noise show roughly the same hearing loss as the curve for continuous noise exposure.

    • The data points for intermittent noise show less hearing loss than the continuous noise curve predicts.

    • The varying noise data points show significantly more hearing loss than the intermittent noise data.

    Article Four (pp. 234–237) Laboratory Investigations Since the 1992 Report

16. The findings from Ward's 1991 report on the role of intermittence in permanent threshold shift support which of the following concepts?

    • The equal energy hypothesis (i.e., 3-dB exchange rate) is suitable for some noise exposure conditions, but higher exchange rates are more appropriate for several others.

    • The equal energy theory was based on uninterrupted exposures for indefinite time periods, such as weeks or months.

    • Shorter pauses and shorter durations did not show ameliorative benefits.

    • Controlling the duration of noise bursts and pauses were not important in predicting auditory damage.

17. In 2004, Harding and Bohne analyzed several studies that show, at least under certain laboratory conditions, that

    • rest periods between exposures do not provide significant benefits in terms of cochlear cell loss

    • rest periods between exposures can provide significant benefits in terms of cochlear cell loss

    • rest periods between exposures demonstrate a simple relationship to the location of damage along the basilar membrane

    • rest periods between exposures demonstrate a simple relationship to the time of damage assessment

18. An improvement in hearing threshold levels as the noise exposure continues has been referred to as

    • threshold shift

    • minimal auditory damage

    • intermittency

    • toughening

19. Delayed recovery from temporary threshold shift could have a negative effect on the ear's ability to recuperate between exposures; this would help to explain

    • the increase in the damaging potential of impulse/impact noise documented in many investigations

    • the increase in linear recovery patterns generated by impulse noise

    • the decrease in the damaging potential of impulse/impact noise documented in many investigations

    • the decrease in linear recovery patterns generated by impulse noise

20. Which of the following is not a reason the chinchilla is often considered as an excellent model for studying the effects of noise on humans?

    • Its audibility curve is similar to that of humans in the frequencies at which both species are maximally sensitive.

    • The patterns and progression of noise-induced damage appear to be very similar to humans.

    • The chinchilla has a long life span, which is convenient for assessing the effects of long exposures.

    • Its middle and inner ears are surgically accessible so that it may be rendered monaural.

    • The chinchilla appears to be somewhat more sensitive to noise than humans.

    Article Five (pp. 237–239) Impulse Noise

21. Which of the following statements is true regarding the main difference between impact and impulse noise?

    • Impulse noise refers to a sudden reduction in noise levels, and impact noise refers to the high spike in sound levels generated from explosions.

    • Impulse noise does not occur under normal atmospheric conditions, and impact noise refers to the high-level energy released in the atmosphere.

    • Impulse noise refers to the sudden high-level transient energy released in the atmosphere, and impact noise refers to the collision of two more solid objects.

    • Impulse noise is generally above 120-dB sound pressure level, and impact noise is generally less than 120-dB sound pressure level.

22. In general, research on both animals and humans has found that noise exposures that contain impact or impulse sounds

    • produce an auditory hazard equivalent to broadband continuous noise when broadband noises are measured using A-weighting and impulse or impact sounds are measured using peak sound pressure levels

    • usually produce greater damage to the auditory system than exposure to continuous noise

    • produce less hearing damage than continuous noise because of their very short durations

    • produce a hearing damage risk that is equal to the risk of a continuous noise with an exposure duration long enough to produce an asymptotic threshold shift

    • typically produce threshold shifts that, because of the short duration of impulse and impact sounds, recover more quickly than exposures to continuous noise of equivalent sound pressure levels

23. What are the main damage-risk metrics used to characterize exposure to impulsive sounds?

    • Time-weighted average and noise dose

    • Peak sound pressure level and A/B duration as specified by MIL-STD-1474D

    • The auditory hazard units as specified in the auditory hazard algorithms for humans model

    • An energy-based metric such as the A-weighted equivalent sound level (LA_eq) or the LA_eq100msec

    • A and B are true

    • C and D are true

24. Impulsive sounds can typically be measured using

    • any sound level meter or noise dosimeter

    • type 1 sound level meter or type 2 noise dosimeter

    • specialized equipment capable of capturing high-level transients

    • all of the above

25. The importance of the critical level concept in the development of damage-risk criteria is:

    • The critical level may vary according to species.

    • Delayed recovery is more likely to occur from high levels of intermittent noise than from varying or continuous noise.

    • Any adjustment to the exchange rate needs to take into account sound levels that appear to shift the damage mechanism from metabolic to mechanical.

    • The critical level in both animals and humans is independent of waveform, spectrum, duration, and repetition rate.

    Article Six (pp. 239–249) Complex Noise

26. Non-Gaussian (or complex noise) refers to

    • noise with an average 8-hour exposure level less than 85 dBA

    • occupational noise exposures whose levels have not been filtered to exclude potential electromagnetic interferences

    • noise with asymmetrical spectral distribution dominated by frequency components below 1,000 Hz

    • noise environments in which the temporal distribution of the noise is not normally distributed or “Gaussian”

    • that portion of a 24-hour timeweighted average exposure that includes both recreational and environmental noise but that excludes work-related noise exposures

27. Recent animal experiments by Hamernik, Qiu, and others at SUNY Plattsburgh showed that:

    • Breaks during the work shift tended to reduce the damaging effects on hearing as long as the LA_eq and kurtosis values were the same.

    • There was an inverse relationship between hearing damage and kurtosis above β = 50.

    • There was no toughening effect with the intermittent pattern the experimenters chose.

    • Both cell loss and PTS were independent of the temporal structure of the complex noise so long as the spectral energy and kurtosis values were the same.

28. What parameter can be used as a descriptor of noise environments with levels and temporal characteristics that are non-Gaussian?

    • Hoarseness

    • Timbre

    • Squeakiness

    • Peakedness

    • Repetitiveness

29. It is difficult to conduct demographic studies of complex noise in the U.S. mainly because:

    • It is difficult to find worker populations that are exposed only to complex noise and not to other kinds of noise.

    • Worker populations that have rarely or never used hearing protection devices are very hard to find.

    • The exchange rate used by most American companies is the 5-dB, OSHA exchange rate

    • It is difficult to find workers exposed primarily to continuous noise to use as control populations.

30. The principal finding from the studies by the U.S./China team was:

    • The same prevalence of hearing loss occurred among workers exposed to continuous noise and complex noise so long as the complex noise was adjusted for kurtosis.

    • The textile workers exposed to continuous noise had more hearing loss because they had more years of exposure.

    • The metal fabrication workers benefited from the intermittencies characteristic of their type of work.

    • The fact that the Chinese population had been carefully screened reduced the differences between the two types of exposures.

    Article Seven (pp. 249–256) Neurological Investigations of the Auditory System

31. The term synaptopathy as applied to the ear can be associated with

    • pathogenic lesions on the external auditory meatus

    • fusion of the stapes to the cochlear wall

    • loss of spiral ganglion neurons and their synapses

    • loss of inner hair cells while outer hair cells remain intact

32. The term hidden hearing loss is used to describe

    • malingering

    • hearing thresholds of 20 dB hearing loss

    • a gap between the air conduction and bone conduction thresholds of less than 10 dB

    • disorders that affect suprathreshold perception without loss of threshold sensitivity.

33. Based upon recent studies of auditory synaptopathy resulting from noise exposure, which of the following is thought to be true?

    • Damage to hearing appears to continue after the cessation of noise exposure.

    • Noise exposure appears to exacerbate the effects of aging.

    • Normal hearing threshold levels do not signify an absence of damage to the auditory system.

    • Current noise exposure guidelines and diagnostic procedures for identifying noise-related damage may need to be re-evaluated.

    • All of the above are true.

34. Why have the adverse effects of auditory synaptopathy not been investigated until this decade?

    • Spiral ganglion cells can survive for years despite the loss of their connection with hair cells.

    • The synaptic terminals of these nerve fibers are unmyelinated and are therefore difficult to see with traditional microscopy and staining techniques.

    • Neuronal degeneration is selective for cochlear nerve fibers with high thresholds.

    • All of the above are true.

35. Which of the following recent scientific developments may be relevant in considering future noise standards?

    • New instrumentation capable of integrated noise measurements

    • New metrics for the characterization of non-Gaussian noise

    • New imaging for quantifying changes to inner hair cells and spiral ganglion synapses

    • New audiological tests for the evaluation of central auditory function

    • All of the above