Effects on Sleep

It is common knowledge that noise can disturb sleep (that's why we use alarm clocks). In fact, a study published in 1963 by McKennell reported that 40 percent of the London residents who were interviewed had been awakened by aircraft noise at least "occasionally," and since the volume of air traffic has certainly increased substantially since then, it is likely that even more people are affected now. Additionally, Knipschild and Oudshoorn (1977) found that increased levels of noise from aircraft were associated with an increased use of sedatives by people in a village near an airport, further indicating that aircraft noise disrupts sleep. And air traffic is not the only culprit; Thiessen and Olson (1968) found that most of their subjects were awakened by 70 dB truck noises, which Bugliarello et al. (1976) consider "a comparatively modest intensity" (p. 44). Further, Abel (1990) describes several studies, including laboratory studies and home studies, and found that in almost all cases increased levels of noise were associated with sleep disturbances, including shorter sleep duration, more frequent awakenings, downward shifts in sleep stages, and increased sleep latency (i.e. difficulty in falling asleep).

Bugliarello et al. (1976) describe several factors that affect sleep disturbance: factors involving the stimulus itself (e.g. type of noise, repetition, duration, intensity, etc.), the stage of sleep at which the stimulus occurs, and individual variables (e.g. state of health, motivation to wake, etc.).

First, sleep disturbance by noise is affected by characteristics of the noise itself. For example, stimulus intensity is related to sleep disturbance, with more intense stimuli awakening people more often. However, disturbance thresholds vary widely among people, with some people being disturbed by levels as low as 35 dB and others being able to sleep through 90 dB levels. And a person's threshold depends on the type of stimulus, as well. For example, it appears that most people can sleep through 60 dB of aircraft noise, but only 40 dB of street traffic noise (Bugliarello et al., 1976).

Another factor affecting sleep disturbance is the stage of sleep during which a noise occurs. In general, it requires greater intensity stimuli to awaken people in the deeper stages of sleep, and REM sleep appears to be particularly easy to disturb (Berry and Thiessen, 1970). However, this can sometimes be avoided by incorporating the stimulus into dreams, which occurs most often in REM sleep.

Individual variables also affect noise's ability to awaken a person. For example, lower intensities of noise are generally required to awaken people as they grow progressively older. Thus, an elderly person is more likely to be awakened by a given stimulus than a young adult in a similar situation. Additionally, motivation to wake must also be considered, as must a person's state of health, since certain disorders (e.g. depression) are known to affect sleep behavior. Further, people have been shown to be capable of habituating to various stimuli that they encounter repeatedly (i.e. they "get used to it"), especially stimuli that are lower in frequency and that are similar to stimuli encountered during the waking day. However, according to Bugliarello et al. (1976) "adaptation to noise during sleep is at best very limited" (p. 62).

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