Noise, Stress and Annoyance
NVWW June 2006-final 20/6/06 5:05 pm Page 9
NOISE, STRESS AND ANNOYANCE
Noise, stress and annoyance
Ragnar Rylander Professor emeritus, BioFact Environmental Health Research Center, Bjorkasvagen 21, 443 91 Lerum, Sweden [email protected]
(independent) nervous system and the neuro- Summary endocrine system. This wide dispersion of the The effects of sound on man are reviewed sound stimulus carries a message of the with emphasis on the physiological reaction character of the sound to different defence and mechanisms and the ultimate stress adaptation systems, including muscular reaction. It is seen that energy related noise functions, and many of these systems are levels are poor predictors for the reactions in preparing the individual to escape. The man as noise is always interpreted in the secretion of different hormones induced by the central nervous system, generating reflexes generated by the sound will affect secondary and tertiary reactions that are not different functions of the body but will also controlled by the brain cortex. The influence emotional reactions. A hymn in the stimulation of these reaction pathways in church during a funeral can make us cry; a acute situations lead to involuntary reflexes melancholy song on the beach will fill us with and feelings of fright and despair. In chronic happiness. exposure situations a give-up stage may There is a large variation between develop with reduced corporal and mental individuals how these central nervous functions. In the acoustical panorama peak reactions are initiated and how strong they level noises usually cause the most become. Some of these differences depend pronounced effects as they stimulate upon genetic factors but previous experiences reactions of fear and flight. The practical of the sounds, the simultaneous presence of consequences of these reaction patterns in other environmental stimuli and the health terms of prevention are discussed. state of the individual also play important roles. Air displays by the air force at festivities might make the ordinary citizen proud but 1. Introduction they will evoke deep emotions and fear Sound is an important part of man’s contact reactions among those who have experienced with the environment and has served as a these sounds during wars and personal critical means for survival in evolution. sufferings. Persons with fever or who are Sounds around us can arouse reactions of fear under great stress for social or work related or delight, influence our nervous system and reasons have an augmented reaction to sounds also serve as a source of enjoyment. This that they would normally tolerate or even review will highlight some of the appreciate. characteristics of sounds and the human reaction with the emphasis on our 3. Acute effects of sounds interpretation and reactions after exposure to The acute effects of sound exposure are an different sounds. As the effects discussed in orienting response, a startle reflex and a the following mostly refer to sounds that are defence/flight reaction. The orienting response generally considered as pollution by the comprises a mental and physical orientation individual, the term noise will be used towards the source of the noise. The startle although that term in reality includes an reflex is an involuntary contraction of the interpretation that has taken place after the muscles around the eyes, in the abdomen and stimulation of the auditory system. the legs, designed to turn the person in a position that protects the most vulnerable 2. Sounds and central nervous parts of the body. The defence/flight reaction, system reactions finally, involves the muscles in the legs and the Sounds stimulate the hearing nerve through arms, preparing the person to flee away. All the mechanical function of the middle ear. The these effects become particularly pronounced ensuing nerve impulses go both to the brain when the sound is sudden and unexpected; for cortex for conscious interpretation and to some sounds there is a habituation but for centres in the deep parts of the brain with others not. Even among policemen who further connections to the autonomous regularly train with gun shooting and are
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accustomed to the sound, the muscular The ability to relax and to sleep is of great contractions appear, particularly around the importance for the normal functioning of eyes. man. The auditory system, however, continues The reflexes described above are for the to function and sounds can thus interfere with protection of the individual – alertness against sleep and recreation. An unknown sound at the source of sound and a readiness to escape night might, even if the sound level is very if the sound is interpreted as dangerous. The low, cause an intensive reaction of fright. Even nervous system reactions also incorporate a if there is no awakening, such sounds may temporary increase in blood pressure and disturb the normal sleep rhythm and cause pulse rate – sudden deaths from heart failure long term fatigue and possibly depression. have been described after intense exposure to The different reactions to sounds also unfamiliar sounds. determine our judgement of the sounds. The automatic focus on the source and Unwanted or disturbing sounds are usually location of the sound may interfere with an referred to as noise. This is a subjective ongoing task because of over-saturation of the classification as exemplified by music where capacity of the central nervous system. Is has one kind of music can be a noise to some been shown that persons engaged in a persons and not to others. The owner of a demanding visual task temporarily interrupt transportation company is pleased by the this if they are exposed to a sudden, intensive sound of his trucks passing by, a sound that and unknown sound. Disruption of reading or most of us would characterise as noise. thinking when exposed to sounds in the environment is an experience common to all of us. 4. Chronic effects of sounds The character of the sound is of great importance. An illustrative example is a family A repeated exposure to sounds over longer that lived closed to a newly erected water time periods may lead to the development of a tower in a rural area. The tower was placed number of different effects. A common on pillars and the bottom had a dome shaped reaction is a feeling of disturbance of ongoing form. Soon the population discovered that activities or interference with the quality of sounds emitted under the tower became the environment. This feeling is usually grossly amplified and reverberated, making it referred to as “annoyance” and has to be a local tourist attraction. The farming family determined using questionnaires. In these the was thus almost continuously exposed to subjects grade their annoyance in quantitative screams, whistles and cries from the sightseers, terms such as “none/a little/rather much/very implying danger or cries for help which much”. The subjective nature of annoyance severely disrupted their normal lives. means that there are large differences between
%veryannoyed 60 50 40 30 20 10 0 50 55 60 65 70 75 80 85 LAEq
Figure 1. Relation between extent of annoyance and noise exposure from road traffic
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individuals – some will be annoyed by a sound The exposure to sound is measured using that others accept or even like. To overcome equipment that records the acoustical energy this variation, studies usually report the (sound pressure). The sound pressure is average annoyance in a group of persons. This transformed into a logarithmic scale that measure of the proportion of the population ranges from the acoustical energy at the expressing that they are “very annoyed” is hearing threshold to the levels which cause related to the sound level and dose-response damage to the ear. The units in this arbitrary relationships for transportation noises have scale are Bels, divided into tenths (deciBel). been reported in many publications. An Humans are less sensitive to the lower example is given in Figure 1. frequencies of sounds so these are adjusted by The repeated exposure to a noise over inserting a filter (the A-filter) to make the longer time periods may also cause effects on measured value better adapted to the human health. These can derive from the acute effects reaction pattern. The ensuing unit is the dBA such as increased blood pressure, disturbances value. At very low frequencies, however, the of hormonal secretion or from reactions in an sensitivity to the sound increases and the dBA exhausted central nervous system in terms of unit is no longer a useful measure of exposure. the defeat reaction. When repeated sounds with different A long-term exposure to unwanted or intensities such as road traffic noise are disturbing sounds might lead to a reaction of measured, the principle commonly used is to exhaustion or defeat. This is a stage when the determine an average sound intensity over a individual gives up mentally – there is no way specific time period eg 24 hours. This is to influence the source of the sound and there against the physiological principles of sound is no way to escape from it. The ensuing reception where the highest noise level and the effects are decreased muscular movements, a noisiest event determine the reaction. Several decreased secretion of hormones, possibly studies have studied the importance of peak followed by a decreased function of the levels and found good relationships to the immune system and a mood change into extent of annoyance as illustrated in figure 2. apathy and decreased social contacts. Such The implication of the peak level is reactions have been observed in populations important for understanding the results from living near airports or close to heavily studies on the effects of sounds in the trafficked roads. environment. In some investigations the Regarding the transformation of acute erection of barriers along heavily trafficked effects into persistent or chronic ones, the roads has resulted in an increased extent of effect on blood pressure is of particular annoyance instead of the expected interest. A number of studies from industry improvement in the environmental conditions. have shown that a continuous exposure to high While barriers can be very efficient, in this levels of noise at the workplace may cause an case the construction shielded the populations increased blood pressure over time. From a from the low level sound from the traffic but physiological point of view this reaction is easy did not reduce the peak levels enough. With to understand and it is likely that it exists also the barrier the acoustical environment thus among persons exposed to noise in the general transformed from a steady murmur of sound environment although only a few studies have to periods of relative silence with sudden been made. An increased blood pressure peaks of sound that were experienced as more depends on many other factors such as diet, annoying. In a study on school children in smoking and heredity and the relation to and noisy areas it was found that the reading relative importance of noise exposure is thus comprehension was decreased at higher levels difficult to ascertain. of aircraft noise but episodic memory was increased after exposure to road traffic noise. 5. Prevention and control As road traffic noise is a more or less Sounds are an unavoidable part of the modern continuous noise, the improvement in episodic society and a large segment of the population memory could reflect a more intense attention is exposed to high levels of noise, particularly on the test, shielding the noise in the from the transportation apparatus. From a environment, whereas aircraft noise with public health point of view there is a need for distinctive and irregular noise peaks would be improved control to decrease the risk for more difficult to shield. annoyance and health effects. A control From a public health point of view, control system is highly dependent on the methods to of environmental sound exposure with the determine the exposure which will be used to goal to decrease sleep disturbances and severe set exposure limits. annoyance has a high priority. The goals can
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%veryannoyed 60 50 40 30 20 10 0 75 80 85 90 95 100 105 110 max dBA
Figure 2. Relation between extent of annoyance and maximum noise level exposure from road traffic
only be achieved in long term programs where soundscapes are background music in public town planning, banning of vehicles with high meeting places, the sound of birds singing in noise levels and shielding of noise sources are toilette facilities and modulation of sound the main tools. Restriction from building in characteristics at the workplace. So far the areas where noise levels are high is another knowledge of such optimal soundscapes and important preventive measure. Individual criteria for their application has not been actions are also important to decrease the extensively studied but merits more attention extent of annoyance due to noise. Lower levels in parallel to efforts to control unwanted on radios and TV-sets, lower voices when sounds in the environment. talking in mobile phones and less aggressive So in conclusion, sounds in the driving habits are examples of such actions. environment represent a multifaceted problem in terms of exposure, reactions and control. 6. Soundscapes There is a need for a multidisciplinary When dealing with sounds in the environment approach to improve the present noisy the emphasis has by tradition been on its environment and it is important that all such negative effects. In a larger perspective it is actions are be based on an understanding of necessary to consider the positive effects as the physiological reactions that occur in man well. Sound is an agent where the dose- after exposure to sounds. response relationship is of a hormesis nature as illustrated in Figure 3. Further reading The concept of the hormesis dose-response Gold PW, Chrousos GP. Organisation of the is that a small amount of the agent is stress system and its dysregulation in beneficial and that negative effects develop at melancholic and atypical depression; high vs higher dose levels. This relationship is valid low CRH/NE states. Mol Psyciatr 2002; for a number of agents such as vitamin D, 7:254-275. various stimuli such as alcohol and even substances generally considered as very toxic Namba S, Kuwano S, Okamoto T. Sleep such as arsenic. It is very applicable to sounds disturbance caused by meaningful sounds and in the environment. Staying for a longer time the effect of background noise. J Sound Vibr period in an environment where sounds are 2004; 277: 445-452. completely absent causes a feeling of isolation, insecurity and in some circumstances Rosenlund M, Beglind N, Pershagen G, Järup pathological reactions from the brain and the G, Bluhm G. Increased prevalence of nervous system. Man requires a background hypertension in a population exposed to of sounds for normal functioning and also for aircraft noise. Occ Env Med 2001; 58: 769- satisfaction. Examples of efforts to improve 773.
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Beneficicial effects
No effect
Adverse effects
dose
Figure 3. Hormesis dose-response relationship
Rylander R. Physiological aspects of noise- Timio M, Saronio P, Verdura C, Schiaroli M, induced stress and annoyance. J Sound Vibr Timio F, Monarca C. A link between 2004; 277:471-478 psycosocial factors and blood pressure trend in women. Physiol Behav 2001; 732:359-363. Sato T, Yano T, Björkman M, Rylander R. Road traffic noise in relation to average noise levels, number of events and maximum noise level. J Sound Vibr 1999; 223:775-784.
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