3.2: Potential Effects of Noise on Health
Shaw (SHAW 96) emphasises the importance of a thorough understanding of all effects of noise on people to assist in bringing community noise exposure under control in the most consistent and effective way. These effects include; psycho-social effects such as annoyance and other subjective assessments of general well-being and quality of life; effects on mental health; effects on sleep which can be both psychological and physical effects; effects on physical health such as hearing loss; and stress-related health effects which can be psychological, behavioural, somatic and physical. Possible indicators of these different effects cover a very broad range.
Annoyance
Annoyance has been defined as "a feeling of displeasure evoked by a noise" (WHO 80) and "any feeling of resentment, displeasure, discomfort and irritation occurring when a noise intrudes into someone's thoughts and moods or interferes with activity". It is the most common and most researched effect of noise on people and can often be related to the potentially disruptive effects of intrusive noise on a broad range of activities, although people can be annoyed by noise simply because they feel it to be inappropriate to the situation in which it is heard. It can only be measured by a subjective report, although techniques have been investigated based on observing behaviour assumed to be related to annoyance. Noise annoyance is simple in concept, but since it can only be defined subjectively, comparative studies are often defeated to some extent by the problems of comparing annoyance scales using different verbal or numeric descriptors. The extent of noise annoyance, however described or reported, is clearly influenced by numerous non-acoustic factors such as personal, attitudinal, and situational factors in addition to the amount of noise per se.
Noise annoyance is usually attributed to a specific source of noise, yet the underlying causal mechanisms are not always clear (PORTER 1997). Research studies can often be surprisingly vague in terms of whether specific or general effects are being described. For example, reported annoyance to a specific noise source can often considerably exceed aggregate or total annoyance to the overall noise environment. Many researchers have concentrated on the role of specific interferences with speech, communication, sleep, concentration, or task performance in mediating reported annoyance, but the underlying relationships found vary from one study to another. Figure 1 shows one of many possible interpretations of the various underlying relationships between noise and reported annoyance showing both direct and indirect routes from stimulus to effect.
Figure 1: Noise annoyance in a community setting (from NELSON 87)
Speech interference
Human society depends on communication by speech, which is subject to masking by noise. The precise degree of interference with speech communication can be measured either subjectively by using rating scales, or objectively by measuring the percentage of words or sentences correctly understood (true speech intelligibility measures). Physical measures of so-called speech intelligibility such as the Speech Transmission Index and the Articulation Index are only proxies for direct measurement using subjective reports or proper behavioural tests, and can give erroneous results.
Environmental noise, especially varying and intermittent noise, can interfere with many activities involving speech. The extent to which any particular degree of speech interference can be overcome or contribute to stress in different situations is not well understood.
Performance - concentration and task interference
Noise can contribute to increased arousal; can require changes of mental strategy; can impair social performance; can distract attention from relevant social cues; can mask wanted signals in tasks involving auditory cues; and can contribute to what has been described as unwanted aversive changes in affective state. Interference of this type can contribute to the creation of less desirable living environments and might therefore lead to increased annoyance and stress or to a decreased state of well-being or general health.
Mental Health
A variety of mental health effects due to noise have been suggested by research. Indicators which have been studied in the past include mental hospital admission rates, headaches, susceptibility to minor accidents, and increased reliance on sedative and sleeping pills.
Hearing loss
Noise can contribute to both temporary and permanent hearing loss, although current evidence suggests that the risks at the typical exposure levels associated with environmental noise are very low. Noise induced hearing loss often occurs at higher frequencies first, at around 4000 Hz. Hearing damage can then extend to lower frequencies and become relatively more severe after increasing exposure at higher levels. Temporary hearing loss after short term exposure may be associated with permanent hearing loss even though the physiological mechanisms may be quite different. Noise induced hearing loss can directly contribute to increased stress and annoyance, particularly in respect of speech communication and tasks requiring auditory cues. There are of course many other potential or contributory causes of hearing loss in any particular case including illness, ototoxic drugs, hereditary factors and inflammation of the middle ear.
Noise induced stress related effects
As the Dutch Health Council recognised (NETHERLANDS 97), individual reactions to a stressor can be of a psychological, behavioural or somatic nature. It is not clear precisely what is meant by the concept of stress in this situation. Not all effects of noise exposure are necessarily negative. It is clear that a certain amount of noise can contribute to beneficial arousal, and that individuals differ in the their ability to adapt. Increased arousal can assist with task motivation and thereby improve performance, depending on the individual concerned. On the other hand, excessive stress is by definition 'excessive' and there are a number of possible stress-related adverse effects of excessive environmental noise reported in the literature. Psychological effects concern feelings of fear, depression, frustration, irritation, anger, helplessness, sorrow and disappointment. Examples of behavioural reactions to a stressor are social isolation, aggression, and resort to excessive use of alcohol, tobacco, drugs or food. Psychological and behavioural stress could have direct or indirect effects on physiological processes in the body. In the absence of any more definitive results, many studies have implicitly assumed that noise could be considered as an unspecified stressor leading to over-stimulation of the central nervous and endocrine systems. Potential indicators of health impact due to stress-related effects and appearing in the literature include changes in blood pressure, abnormalities in the electrocardiogram, rates of diagnosing clinical hypertension, occurrence rates of ischaemic heart disease and other cardiovascular disorders, biochemical effects, changes in the immune system, and effects on the unborn child such as birthweight effects and incidence rates for various congenital defects.
Sleep disturbance
Sleep patterns vary considerably between different individuals and sleep disturbance can arise from a large number of different causes. Disturbance can be measured subjectively using morning after questionnaires, or objectively, using a wide range of physiological indicators. The problem with objective measurements using instruments is that they can be intrusive, particularly when used in the laboratory, and there is often a significant difference between results obtained in sleep laboratories and in own-home experiments. Laboratory studies can be extremely well controlled, particularly in terms of the stimuli used, but on the other hand, it may take some considerable time for subjects to get used to the laboratory. Field studies are difficult in terms of instrumentation, and might not be at all well controlled in terms of the pattern of stimuli that actually occur on instrumented nights. An additional problem is that the clinical or social significance of any particular increment of sleep disturbance associated with additional noise events is not at all clear.
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Published 12 September 2000
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