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Sonic boom exposure effects II.2: Sleep effects
SONIC BOOM EXFO!JURE EFFECTS: II.2
511
SONIC BOOM EXPOSURE EFFECTS 11.2: SLEEP EFFECTS C. G. RICE Institute of Sound and Vibration Research, University of Southpton, Southampton So9 SNH, Enghd
1. INTRODUCTION Undisturbed sleep is essential for bodily relaxation, for sustained and efficient attention to daily tasks, and for the general well-being of man. Any interference with sleep is therefore undesirable. In an attempt to understand basic relationships more fully, resort has increasingly been made to the systematic study of sleep interference effects under laboratory conditions. These, and social surveys, have provided pertinent information concerning the general problems of sonic boom induced sleep interference. However, quantitative data on the actual effects in the community, especially in terms of exposure of selected population sub-groups, are insufficient for the establishment of predictive criteria. The following report reviews the quantitative data which express sleep interference in terms of certain aspects of sleep patterns (sleep stage and accumulated sleep time), individual differences (age, sex, temperament, responsiveness), and stimulus variables (type of sound and intensity). The effects of such interference on performance, health and attitudes are also briefly commented upon. The findings of laboratory studies and their relationship to the real life situation are discussed, together with suggestions for standardization of some of the experimental techniques used in different laboratories, in order to receive the maximum information from research efforts on sleep disturbance due to the sonic boom. Annoyance responses which are heavily influenced by sleep disturbances are discussed by Borsky (see paper 11.4). 2. REVIEW OF DATA 2.1.
RISK GROUPS
Social survey data indicate clearly that sleep interference is an important human response element in community reaction following exposure to sonic booms [I]. The population subgroups at risk by day appear to be, apart from the ill and hospitalized, those people who work during night hours. Whilst it has been shown that such people sleep erratically and spend long periods in sleep stages in which awakening is easier [2], other research has indicated that postawakening subjective evaluations of sleep pattern and sleep quality by night-shift and day-time workers are similar [3]. One estimate suggests that about 10 % of the working population sleep during the day [4] but it is important to obtain additional data to decide whether the group is large enough to warrant a special research effort. 2.2.
INTERRELATIONSHIP
OF SURVEY AND LABORATORY STUDIES
It is important to realize that the laboratory experimenter does not gain as much from the social survey as he would like, possibly because the problem is more complicated from his viewpoint. For example the term “sleep interference”, as reported in surveys, could be subdivided to reveal more clearly to the experimenter the major cause of the expression: is it
512
C. Ci. RICE
awakening, subjective feelings of having slept poorly, fatigue during work, or reflections of a generally negative attitude or other subjective responses? The exposure situation is also different. Survey data describe the real-life situation in which people give composite reactions acquired by experiencing sonic booms and other noises over long periods of time together with a variety of stimuli. Laboratory experimentation gives only information on small population samples which bear limited relationships to real-life situations. Nevertheless, certain findings from laboratory studies can significantly influence the collection of data in surveys. Detailed social surveys concentrating on specific aspects of sleep interference initially studied in the laboratory will be a feasible way of increasing pertinent knowledge, particularly if sub-groups identified in surveys as being particularly sensitive could be subsequently incorporated into laboratory studies. Only this systematic pooling of data is likely to enable formulation of predictive criteria. 2.3.
SLEEP DISTURBANCE DETERMINATORS
The important variables associated with sleep disturbance by ordinary noise and the sonic boom are discussed in this section. A more detailed discussion on the effects of noise on sleep can be found in certain review articles [5-71, whereas others contain definitive descriptions of the terminology and scoring techniques for the assessment of human sleep stages and the effects of aircraft noise thereon [8-l 11. By necessity the major part of the findings discussed in the following section was derived from laboratory studies. 2.3.1. Sleep stage and accumulated sleep time Two variables associated with patterns of human sleep which may determine whether or not awakening to a stimulus will occur are accumulated sleep time and sleep stages. Awakening in response to a stimulus appears more likely to occur with accumulated sleep time, regardless of sleep stages [12-l 51. Although the relationship is not clearcut, awakening thresholds appear to be lower in Stages REM and 2, than in Stages 3 and 4 both for ordinary noise and sonic booms [lo, 12, 16, 171. It is important to know the percentage distribution of sleep stages throughout the dayand night-time exposure periods for certain subgroups and some data are available [18]. For example, if this distribution for a particular group were known, experimental laboratory information would only be needed on a relatively few selected subjects to predict the behavioural awakening effects for that part of the community. Besides behavioural awakening, the rates of change between sleep stages and, in particular, changes to Stage 1 or Stage “Awake” as seen in the EEG are also considered important by some workers [19-211. 2.3.2. Individual subject diferences A major factor contributing towards differences in awakening thresholds from ordinary noise or boom exposure is age, older people being more easily awakened [lo, 171. Assessed by questionnaires and subjective tests, the quality of sleep appears to depend, in part, upon temperament, health and responsiveness to sound during sleep [ 151,the distribution of which in the population has not clearly been specified. The evidence of both laboratory and field studies on aircraft noise and sonic boom suggests that women are more easily awakened than men [20,22-251. 2.3.3. Stimulus variables The auditory stimulus itself plays a role in the awakening reaction. Stimuli with little or no information content for the sleeper are less likely to induce a response than a stimulus having some significance: e.g., his name [5,6,20,26]. However, the significance of a stimulus,
SONIC BOOM EXPOSURE EFFECTS : II.2
513
particularly one having no inherent meaning such as a name, may vary. With repeated exposures habituation to sounds which initially interfered with sleep may occur, particularly when sounds are regular, frequent and not temporarily associated with any subsequent noxious event [5, 121. Experimental data suggest that adaptation to the laboratory environment is still present after several consecutive nights of exposure to sonic booms [14, 15, 241. This indicates that sleep experiments have to be conducted over periods of at least two to three weeks. Additional research is required on adaptation and spontaneous awakening rates in particular sub-groups. 2.3.4. Intensity efects As discussed previously, the intensity of a sound which will awaken a sleeper varies with sleep stage, accumulated sleep time, individual subject differences, as well as the type of sound. Recent experiments also indicate that awakening rates are intensity dependent, and that certain predictions may be made with respect to threshold values for behavioural awakening [lo, 11, 15, 17, 24, 27-301. In the range 25-300 N/m2 (as measured outdoors) children are relatively insensitive to simulated sonic booms whilst middle-aged people awaken to about 30 % of the stimuli [25]. Young men are awakened by 10-30x of stimuli depending upon the experimental conditions and techniques [14, 15, 17, 301. 2.3.5. Psycho-physiological variables
Biochemical and physiological effects have been reported following prolonged sleep deprivation, and behavioural activity of subjects may be affected also during the deprivation period [31, 321. Performance tests sufficiently sensitive to detect the effects of reduced sleep ration and possible sleep interference have been described to some extent [33-351 but results from such tests although important [6,36] are not considered to be sufficient to form criteria at this stage. From the medical point of view and the risk to health in the wider sense, transitory physiological changes do occur, but their importance is unknown [5,37]. There is insufficient evidence available to judge the effect which existing environmental noises have on sleep patterns and health in the population. Little is known of the subjective effects of noise induced sleep interference although techniques to assess the effects are being currently used in laboratory studies on sonic booms [IO, 14, 151. Preliminary results suggest that such subjective scales merit attention when relating laboratory work to field situations, and they may be as valid a measure of sleep disturbance as is behavioural awakening [15]. 2.4.
FIELD EXPOSURE DATA
Very few field experiments have involved study of the awakening effect of real sonic booms. In the Oklahoma study (see paper II.4 by Borsky) around 15 % of the respondents reported sleep disturbance, but the boom exposures took place during the day-time only. A limited study was performed in Sweden where a community was exposed to 7 sonic booms of around 60 N/m2 at 04.25 on irregular days during a three month period [30]. The reaction was evaluated by using a postal questionnaire on 220 persons. More than 20 % of this random sample of the population had heard all the booms and about 40% indicated difficulties in returning to normal sleep. 2.5.
FACTORS TO CONSIDER IN LABORATORY EXPERIMENTATION
In order to concentrate research efforts on sleep disturbance due to the sonic boom, standardization of experimental techniques among laboratories is necessary. Workers in the field have felt this need for some time [6], and the following factors are particularly relevant. 33
514
C. G. RICE
2.5.1. Sonic boom simulators Simulators for sonic boom sleep research should ideally take account of both the acoustic and the vibratory responses of typical bedrooms. Literature surveys [38,39] of field measurements of sonic boom induced building vibrations show that vibration levels extend from those below man’s threshold of perception to levels sufficient to cause whole body vibration, and to even higher levels which may cause feelings of physical unpleasantness or unease. The vibratory response of the room and bed may therefore be of importance especially to certain subgroups of people (e.g., the light sleeper, the elderly or people with hearing defects). Consonant with the above, measures of vibration induced in the room and bed should be provided in research reports. It is suggested that peak acceleration (in g units) and the predominant frequency in the 2 (vertical)-axis measured in the centre of the test room be reported. In the case of the bed, if possible, the peak vibration acceleration of a mass of about 60 kg located in the centre of the bed should be obtained. The acoustic response characteristics of the indoor boom produced by the simulator should be specified and measured as follows: (i) at the head positions, but in the absence of the sleepers; (ii) in terms of “short term root mean square overpressures”, preferably in one-third octave band spectral values integrated over 0.5 s intervals; (iii) in terms of the indoor and equivalent outdoor boom signatures; the time taken to reach peak overpressure as measured indoors, regardless of discontinuities in the leading edge, is acceptable as a definition of rise time; the outdoor boom signature will be specified as measured at ground level; (iv) in addition to the above methods of specifying the sonic boom or other standard noises used in sleep experimentation, and in order to compare data more easily among laboratories, measurements on the dBA (fast) scale using a precision sound meter should also be reported. 2.5.2. Equipment In addition to simple behavioural awakening response indicators (button pressing, bed movement indicators), it is recommended that certain EEG measures of sleep stage be obtained. A distinction between light (stages REM, 1 and 2) and deep (stages 3 and 4) sleep has to be accepted in the absence of details concerning the relative importance of the different sleep stages for the quality of sleep. In the experiment, response frequencies to stimuli occurring in these stages should be described, and if possible, the time for returning to sleep following an awakening by noise. 2.5.3. Experimental methods Techniques will vary among different experiments, but it is proposed that at least one standard noise be used during each experiment. This will facilitate comparison of data obtained in different laboratories, and enable some comparison of subjects’ particular response patterns to a relatively neutral stimulus. It is proposed that the standard noise be a one-half second of pink noise (100 Hz-l 1 kHz) at a standard intensity of 90 dBA (fast). For boom experiments the times of presentation of this standard stimuli could be made to correspond to estimated flight schedules, in order to provide useful information regarding real-life situations. 2.5.4. Subjects It is imperative that as much personal information as possible be obtained for each subject. Individual sensitivities to noise, attitudinal factors, personality variables, personal problems at time of experimentation, normal sleeping habits, motivation, hearing acuity, etc., are all factors which need careful definition. Sleep questionnaires and subjective tests to assess fatigue, stress, etc., are felt to be very good indicators of sleep disturbance, although their interpretation with small numbers of subjects can sometimes be uncertain [15].
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Subgroups of particular importance are thought to be those most easily disturbed during sleep. For example, it appears more useful to study subjects over 50 years of age rather than college students. 2.6.
CONCLUSIONS
It is not yet possible in terms of sonic boom variables and subject responses to ascertain the factors of greatest importance in predicting sleep disruption and its physiological and psychological significance. For reasons described above, more information is necessary. However, to assume that specification of these factors alone will permit accurate prediction of the community response seems unwarranted since sonic booms may be only a small part of total noise in the environment. Existing information [40] indicates that the behavioural and attitudinal reaction of a community to noise may be predicted with reasonable accuracy only by combining the annoyance due to the noise in question with the total human reactions to other noises in the environment. There is no reason to suppose that the sonic boom should be treated any differently. 3. SUMMARY
OF RECOMMENDATIONS
A close co-operation should exist between scientists engaged in field and laboratory experiments concerning the use of similar techniques as well as the exchange of results. A better specification of the subgroups of the population at risk of sleep interference is required. The extent of day sleepers in a population must be ascertained if the relative importance of the day-night problem is to be resolved. A knowledge of the distribution of sleep stages through day- and night-time exposure periods for selected subgroups is important, if predictions concerning the awakening effects of sonic booms are to be made with a reasonable research effort. Studies investigating the intensity dependent relationships of sex and age by selected subgroup should be continued. The question of adaptation to a sonic boom environment during sleep is very important. Little data are yet available on this phenomenon because of the long term nature of the research involvement. It is felt that such studies ought to be encouraged. Serious consideration should be given to the use of subjective testing procedures, which appear to be as least as reliable an indicator of sleep disturbance as is behavioural awakening. Sonic boom simulators need to be carefully designed and constructed in order to reproduce the correct acoustic and vibratory environment. The characteristics of such environments also require standardization of specification and measurement. REFERENCES
1. P. N. BOR~KY 1965AMRLTR-6.5-67, AD 613 620, Wright-Patterson AFB. Community reactions to sonic booms in the Oklahoma City area. 2. D. F. KRIPKE, B. &JK and 0. F. LEWIS1971Psychophysiology 7, 377. Sleep of night workers: EEG recordings. 3. G. S. TUNE1968 Ergonomics 11,183. A note on the sleep of shift workers. 4. C. M. O’CONNOR 1970 Monthly Labour Review-November 1970, 37. Late shift employment in manufacturing industries. 5. K. S. -y-I-RR 1970 Tire E&cts of Noise on Man. New York and London: Academic Press. See pp 516-526. 6. M. E. DOBBS 1972Journal of Soundand Vibration 20,467-476. Behavioural responses to auditory stimulation during sleep. 7. P. A. MORGAN 1970 Institute of Sound and Vibration Research, University of Southampton, Technical Report No. 40. Effects of noise upon deep.
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C. ‘3. RICE
A. RECHTSCHAFFEN and A. KALES(eds.) 1968 NationaZZnstituteofpublic Health, U.S. Department of Health, Education and Welfare, Washington, Publication No. 204. A manual of standardized
terminology, techniques and scoring system for sleep stages of human subjects. 9. J. S. LUKAS and K. D. KRYTER 1968 National Aeronautics and Space Administration, Report No. CR-1193. A preliminary study of the awakening and startle effects of simulated sonicbooms. 10. J. S. LUKAS,M. E. DOBBSand K. D. KRYTER1971 National Aeronautics andSpace Administration, Report No. CR-1780. Disturbance of human sleep by subsonic jet aircraft noise and simulated sonic booms. 11. R. W. BECKER,J. S. LUKAS, M. E. DOBBSand F. POZA 1971 National Aeronautics and Space Administration, Report No. CR-1840. A technique for automatic real-time scoring of several simultaneous sleep electroencephalograms. 12. A. RECHTSCHAFFEN, P. HAURI and M. ZEITLIN 1966 Perceptual Motor Skills 22, 927. Auditory awakening thresholds in REM and NREM sleep stages. 13. A. SHAPIRO, D. R. G~~DENOUGH and R. B. GRYLER 1963 Psychosomatic Medicine 25, 174. Dream recall as a function and method of awakening. 14. P. A. MORGAN and C. G. RICE 1970 Znstitute of Sound and Vibration Research, University of Southampton, Technical Report No. 41. Behavioural awakening in response to indoor sonic booms. 15. J. LUDLOW 1971 Institute of Sound and Vibration Research, University of Southampton. Unpublished data (report in preparation). 16. H. L. WILLIAMS,J. T. HAMMACK,R. L. DALY, W. C. DEMENTand A. LUBIN 1964 Electroencephalography and Clinical Neurophysiology 16,269. Responses to auditory stimulation, sleep loss and the EEG stages of sleep. 17. J. S. LUKASand K. D. KRYTER 1970 National Aeronautics and Space Administration, Report No. CR-1599. Awakening effects of simulated sonic booms and subsonic aircraft noise on six subjects, 7 to 72 years of age. 18. A. KALES(ed.) 1969 Sleep: Physiology andPathology. A Symposium. Philadelphia and Toronto: Lippincott. See pp. 17-205. 19. I. OSWALD 1971 Proceedings NATO Advanced Study Institute, Basic Sleep Mechanisms, Bruges, Belgium, 24-30 June 1971. Influence of drugs on sleep and correlations with behaviour. 20. W. P. WILSONand W. M. K. ZUNG 1966 Archives of General Psychiatry 15 Nov., 253. Attention, discrimination and arousal during sleep. 21. G. GLOBUS,E. PHOEBUS,R. BOYD, R. DRURY and T. LEVENTHAL1971 Proceedings First Znternational Congress of the Association for the Psychophysiological Study of Sleep. Bruges, Belgium, June 19-23. The effect of a tranquilizer on the temporal organization of sleep. 22. A. MCGHIE and S. M. RUSSELL1962 Journal of Mental Science 108,642. The subjective assess-
ment of normal sleep patterns. 23. G. S. TUNE 1969 British Journal of Psychology 60,43 1. The influence of age and temperament on the adult human sleepwakefulness pattern, 24. J. S. LUKAS 1972 Journal of Sound and Vibration 20,457-466. Awakening effects of simulated sonic booms and aircraft noise on men and women. 25. Second Survey of Aircraft Noise Annoyance Around London (Heathrow) Airport. London: H.M.S.O. 26. I. OSWALD, A. M. TAYLORand M. TREISMAN1960 Bruin 83, 440. Discriminative responses to stimulation during human sleep. 27. G. J. THIE~SENand N. OLSON 1968 Sound and Vibration 2, 10. Community noise-surface transportation. 28. M. KRAMER 1970 CPE-69-132, Veterans Administration, Ohio. Interim report: Noise-sleep study. 29. B. BERRY and G. J. THIE~~EN1970 National Research Council, Canada, Division of Physics, Report APS-478. The effects of impulse noise on sleep. 30. R. RYLANDER,S. SORENSENand K. BERGLUND 1972. Sonic boom effects on sleep-a field experiment on military and civilian population (to be published). 31. R. T. WILKINSON1966 In Sleep in Physiology of Survival (0. G. Edholm and A. L. Bacharach, eds.). London: Academic Press. Sleep deprivation. 32. W. B. WEBB 1969 In Sleep in Physiology and Pathology, A Symposium (A. Kales, ed.). Philadelphia: Lippincott. Partial and differential sleep deprivation (pp. 221-231). 33. R. T. WILKINSON,R. S. EDWARDSand E. HAINES1966 Psychonomic Science 5,471. Performance following a night of reduced sleep.
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34. R. T. WILKINSON1968 Progress in Clinical Psychology 8, 28. Sleep deprivation: performance tests for partial and selective sleep deprivation. 35. T. ROTH, M. KRAMERand J. TRINDER 1971 Proceedings 124th Annual Meeting of the American Psychiatric Association, Washington D.C. Noise-sleep, and post sleep behaviour. 36. A. COHEN 1969 Noise as a public health hazard: The American Speech and Hearing Association, Washington, Report No. 4, 74. Effects of noise on psychological state. 37. G. JANSEN1969 Noise as a public health hazard: The American Speech and Hearing Association, Washington, Report No. 4, 89. Effects of noise on physiological state. 38. J. C. GUIGNARDand E. G~JIGNARD1970 Institute of Sound and Vibration Research, University of Southampton, Memorandum No. 373. Human response to vibration-a critical survey of published work. 39. J. R. MCKAY 1971 Institute of Sound and Vibration Research, University of Southampton, Memorandum No. 435. Human perception of whole body vibration. 40. K. S. KRYTER 1970 The Eficts of Noise on Man. New York and London: Academic Press. See pp. 443444.
511
SONIC BOOM EXPOSURE EFFECTS 11.2: SLEEP EFFECTS C. G. RICE Institute of Sound and Vibration Research, University of Southpton, Southampton So9 SNH, Enghd
1. INTRODUCTION Undisturbed sleep is essential for bodily relaxation, for sustained and efficient attention to daily tasks, and for the general well-being of man. Any interference with sleep is therefore undesirable. In an attempt to understand basic relationships more fully, resort has increasingly been made to the systematic study of sleep interference effects under laboratory conditions. These, and social surveys, have provided pertinent information concerning the general problems of sonic boom induced sleep interference. However, quantitative data on the actual effects in the community, especially in terms of exposure of selected population sub-groups, are insufficient for the establishment of predictive criteria. The following report reviews the quantitative data which express sleep interference in terms of certain aspects of sleep patterns (sleep stage and accumulated sleep time), individual differences (age, sex, temperament, responsiveness), and stimulus variables (type of sound and intensity). The effects of such interference on performance, health and attitudes are also briefly commented upon. The findings of laboratory studies and their relationship to the real life situation are discussed, together with suggestions for standardization of some of the experimental techniques used in different laboratories, in order to receive the maximum information from research efforts on sleep disturbance due to the sonic boom. Annoyance responses which are heavily influenced by sleep disturbances are discussed by Borsky (see paper 11.4). 2. REVIEW OF DATA 2.1.
RISK GROUPS
Social survey data indicate clearly that sleep interference is an important human response element in community reaction following exposure to sonic booms [I]. The population subgroups at risk by day appear to be, apart from the ill and hospitalized, those people who work during night hours. Whilst it has been shown that such people sleep erratically and spend long periods in sleep stages in which awakening is easier [2], other research has indicated that postawakening subjective evaluations of sleep pattern and sleep quality by night-shift and day-time workers are similar [3]. One estimate suggests that about 10 % of the working population sleep during the day [4] but it is important to obtain additional data to decide whether the group is large enough to warrant a special research effort. 2.2.
INTERRELATIONSHIP
OF SURVEY AND LABORATORY STUDIES
It is important to realize that the laboratory experimenter does not gain as much from the social survey as he would like, possibly because the problem is more complicated from his viewpoint. For example the term “sleep interference”, as reported in surveys, could be subdivided to reveal more clearly to the experimenter the major cause of the expression: is it
512
C. Ci. RICE
awakening, subjective feelings of having slept poorly, fatigue during work, or reflections of a generally negative attitude or other subjective responses? The exposure situation is also different. Survey data describe the real-life situation in which people give composite reactions acquired by experiencing sonic booms and other noises over long periods of time together with a variety of stimuli. Laboratory experimentation gives only information on small population samples which bear limited relationships to real-life situations. Nevertheless, certain findings from laboratory studies can significantly influence the collection of data in surveys. Detailed social surveys concentrating on specific aspects of sleep interference initially studied in the laboratory will be a feasible way of increasing pertinent knowledge, particularly if sub-groups identified in surveys as being particularly sensitive could be subsequently incorporated into laboratory studies. Only this systematic pooling of data is likely to enable formulation of predictive criteria. 2.3.
SLEEP DISTURBANCE DETERMINATORS
The important variables associated with sleep disturbance by ordinary noise and the sonic boom are discussed in this section. A more detailed discussion on the effects of noise on sleep can be found in certain review articles [5-71, whereas others contain definitive descriptions of the terminology and scoring techniques for the assessment of human sleep stages and the effects of aircraft noise thereon [8-l 11. By necessity the major part of the findings discussed in the following section was derived from laboratory studies. 2.3.1. Sleep stage and accumulated sleep time Two variables associated with patterns of human sleep which may determine whether or not awakening to a stimulus will occur are accumulated sleep time and sleep stages. Awakening in response to a stimulus appears more likely to occur with accumulated sleep time, regardless of sleep stages [12-l 51. Although the relationship is not clearcut, awakening thresholds appear to be lower in Stages REM and 2, than in Stages 3 and 4 both for ordinary noise and sonic booms [lo, 12, 16, 171. It is important to know the percentage distribution of sleep stages throughout the dayand night-time exposure periods for certain subgroups and some data are available [18]. For example, if this distribution for a particular group were known, experimental laboratory information would only be needed on a relatively few selected subjects to predict the behavioural awakening effects for that part of the community. Besides behavioural awakening, the rates of change between sleep stages and, in particular, changes to Stage 1 or Stage “Awake” as seen in the EEG are also considered important by some workers [19-211. 2.3.2. Individual subject diferences A major factor contributing towards differences in awakening thresholds from ordinary noise or boom exposure is age, older people being more easily awakened [lo, 171. Assessed by questionnaires and subjective tests, the quality of sleep appears to depend, in part, upon temperament, health and responsiveness to sound during sleep [ 151,the distribution of which in the population has not clearly been specified. The evidence of both laboratory and field studies on aircraft noise and sonic boom suggests that women are more easily awakened than men [20,22-251. 2.3.3. Stimulus variables The auditory stimulus itself plays a role in the awakening reaction. Stimuli with little or no information content for the sleeper are less likely to induce a response than a stimulus having some significance: e.g., his name [5,6,20,26]. However, the significance of a stimulus,
SONIC BOOM EXPOSURE EFFECTS : II.2
513
particularly one having no inherent meaning such as a name, may vary. With repeated exposures habituation to sounds which initially interfered with sleep may occur, particularly when sounds are regular, frequent and not temporarily associated with any subsequent noxious event [5, 121. Experimental data suggest that adaptation to the laboratory environment is still present after several consecutive nights of exposure to sonic booms [14, 15, 241. This indicates that sleep experiments have to be conducted over periods of at least two to three weeks. Additional research is required on adaptation and spontaneous awakening rates in particular sub-groups. 2.3.4. Intensity efects As discussed previously, the intensity of a sound which will awaken a sleeper varies with sleep stage, accumulated sleep time, individual subject differences, as well as the type of sound. Recent experiments also indicate that awakening rates are intensity dependent, and that certain predictions may be made with respect to threshold values for behavioural awakening [lo, 11, 15, 17, 24, 27-301. In the range 25-300 N/m2 (as measured outdoors) children are relatively insensitive to simulated sonic booms whilst middle-aged people awaken to about 30 % of the stimuli [25]. Young men are awakened by 10-30x of stimuli depending upon the experimental conditions and techniques [14, 15, 17, 301. 2.3.5. Psycho-physiological variables
Biochemical and physiological effects have been reported following prolonged sleep deprivation, and behavioural activity of subjects may be affected also during the deprivation period [31, 321. Performance tests sufficiently sensitive to detect the effects of reduced sleep ration and possible sleep interference have been described to some extent [33-351 but results from such tests although important [6,36] are not considered to be sufficient to form criteria at this stage. From the medical point of view and the risk to health in the wider sense, transitory physiological changes do occur, but their importance is unknown [5,37]. There is insufficient evidence available to judge the effect which existing environmental noises have on sleep patterns and health in the population. Little is known of the subjective effects of noise induced sleep interference although techniques to assess the effects are being currently used in laboratory studies on sonic booms [IO, 14, 151. Preliminary results suggest that such subjective scales merit attention when relating laboratory work to field situations, and they may be as valid a measure of sleep disturbance as is behavioural awakening [15]. 2.4.
FIELD EXPOSURE DATA
Very few field experiments have involved study of the awakening effect of real sonic booms. In the Oklahoma study (see paper II.4 by Borsky) around 15 % of the respondents reported sleep disturbance, but the boom exposures took place during the day-time only. A limited study was performed in Sweden where a community was exposed to 7 sonic booms of around 60 N/m2 at 04.25 on irregular days during a three month period [30]. The reaction was evaluated by using a postal questionnaire on 220 persons. More than 20 % of this random sample of the population had heard all the booms and about 40% indicated difficulties in returning to normal sleep. 2.5.
FACTORS TO CONSIDER IN LABORATORY EXPERIMENTATION
In order to concentrate research efforts on sleep disturbance due to the sonic boom, standardization of experimental techniques among laboratories is necessary. Workers in the field have felt this need for some time [6], and the following factors are particularly relevant. 33
514
C. G. RICE
2.5.1. Sonic boom simulators Simulators for sonic boom sleep research should ideally take account of both the acoustic and the vibratory responses of typical bedrooms. Literature surveys [38,39] of field measurements of sonic boom induced building vibrations show that vibration levels extend from those below man’s threshold of perception to levels sufficient to cause whole body vibration, and to even higher levels which may cause feelings of physical unpleasantness or unease. The vibratory response of the room and bed may therefore be of importance especially to certain subgroups of people (e.g., the light sleeper, the elderly or people with hearing defects). Consonant with the above, measures of vibration induced in the room and bed should be provided in research reports. It is suggested that peak acceleration (in g units) and the predominant frequency in the 2 (vertical)-axis measured in the centre of the test room be reported. In the case of the bed, if possible, the peak vibration acceleration of a mass of about 60 kg located in the centre of the bed should be obtained. The acoustic response characteristics of the indoor boom produced by the simulator should be specified and measured as follows: (i) at the head positions, but in the absence of the sleepers; (ii) in terms of “short term root mean square overpressures”, preferably in one-third octave band spectral values integrated over 0.5 s intervals; (iii) in terms of the indoor and equivalent outdoor boom signatures; the time taken to reach peak overpressure as measured indoors, regardless of discontinuities in the leading edge, is acceptable as a definition of rise time; the outdoor boom signature will be specified as measured at ground level; (iv) in addition to the above methods of specifying the sonic boom or other standard noises used in sleep experimentation, and in order to compare data more easily among laboratories, measurements on the dBA (fast) scale using a precision sound meter should also be reported. 2.5.2. Equipment In addition to simple behavioural awakening response indicators (button pressing, bed movement indicators), it is recommended that certain EEG measures of sleep stage be obtained. A distinction between light (stages REM, 1 and 2) and deep (stages 3 and 4) sleep has to be accepted in the absence of details concerning the relative importance of the different sleep stages for the quality of sleep. In the experiment, response frequencies to stimuli occurring in these stages should be described, and if possible, the time for returning to sleep following an awakening by noise. 2.5.3. Experimental methods Techniques will vary among different experiments, but it is proposed that at least one standard noise be used during each experiment. This will facilitate comparison of data obtained in different laboratories, and enable some comparison of subjects’ particular response patterns to a relatively neutral stimulus. It is proposed that the standard noise be a one-half second of pink noise (100 Hz-l 1 kHz) at a standard intensity of 90 dBA (fast). For boom experiments the times of presentation of this standard stimuli could be made to correspond to estimated flight schedules, in order to provide useful information regarding real-life situations. 2.5.4. Subjects It is imperative that as much personal information as possible be obtained for each subject. Individual sensitivities to noise, attitudinal factors, personality variables, personal problems at time of experimentation, normal sleeping habits, motivation, hearing acuity, etc., are all factors which need careful definition. Sleep questionnaires and subjective tests to assess fatigue, stress, etc., are felt to be very good indicators of sleep disturbance, although their interpretation with small numbers of subjects can sometimes be uncertain [15].
SONIC BOOM EXPOSURE EFFECTS: II.2
515
Subgroups of particular importance are thought to be those most easily disturbed during sleep. For example, it appears more useful to study subjects over 50 years of age rather than college students. 2.6.
CONCLUSIONS
It is not yet possible in terms of sonic boom variables and subject responses to ascertain the factors of greatest importance in predicting sleep disruption and its physiological and psychological significance. For reasons described above, more information is necessary. However, to assume that specification of these factors alone will permit accurate prediction of the community response seems unwarranted since sonic booms may be only a small part of total noise in the environment. Existing information [40] indicates that the behavioural and attitudinal reaction of a community to noise may be predicted with reasonable accuracy only by combining the annoyance due to the noise in question with the total human reactions to other noises in the environment. There is no reason to suppose that the sonic boom should be treated any differently. 3. SUMMARY
OF RECOMMENDATIONS
A close co-operation should exist between scientists engaged in field and laboratory experiments concerning the use of similar techniques as well as the exchange of results. A better specification of the subgroups of the population at risk of sleep interference is required. The extent of day sleepers in a population must be ascertained if the relative importance of the day-night problem is to be resolved. A knowledge of the distribution of sleep stages through day- and night-time exposure periods for selected subgroups is important, if predictions concerning the awakening effects of sonic booms are to be made with a reasonable research effort. Studies investigating the intensity dependent relationships of sex and age by selected subgroup should be continued. The question of adaptation to a sonic boom environment during sleep is very important. Little data are yet available on this phenomenon because of the long term nature of the research involvement. It is felt that such studies ought to be encouraged. Serious consideration should be given to the use of subjective testing procedures, which appear to be as least as reliable an indicator of sleep disturbance as is behavioural awakening. Sonic boom simulators need to be carefully designed and constructed in order to reproduce the correct acoustic and vibratory environment. The characteristics of such environments also require standardization of specification and measurement. REFERENCES
1. P. N. BOR~KY 1965AMRLTR-6.5-67, AD 613 620, Wright-Patterson AFB. Community reactions to sonic booms in the Oklahoma City area. 2. D. F. KRIPKE, B. &JK and 0. F. LEWIS1971Psychophysiology 7, 377. Sleep of night workers: EEG recordings. 3. G. S. TUNE1968 Ergonomics 11,183. A note on the sleep of shift workers. 4. C. M. O’CONNOR 1970 Monthly Labour Review-November 1970, 37. Late shift employment in manufacturing industries. 5. K. S. -y-I-RR 1970 Tire E&cts of Noise on Man. New York and London: Academic Press. See pp 516-526. 6. M. E. DOBBS 1972Journal of Soundand Vibration 20,467-476. Behavioural responses to auditory stimulation during sleep. 7. P. A. MORGAN 1970 Institute of Sound and Vibration Research, University of Southampton, Technical Report No. 40. Effects of noise upon deep.
516 8.
C. ‘3. RICE
A. RECHTSCHAFFEN and A. KALES(eds.) 1968 NationaZZnstituteofpublic Health, U.S. Department of Health, Education and Welfare, Washington, Publication No. 204. A manual of standardized
terminology, techniques and scoring system for sleep stages of human subjects. 9. J. S. LUKAS and K. D. KRYTER 1968 National Aeronautics and Space Administration, Report No. CR-1193. A preliminary study of the awakening and startle effects of simulated sonicbooms. 10. J. S. LUKAS,M. E. DOBBSand K. D. KRYTER1971 National Aeronautics andSpace Administration, Report No. CR-1780. Disturbance of human sleep by subsonic jet aircraft noise and simulated sonic booms. 11. R. W. BECKER,J. S. LUKAS, M. E. DOBBSand F. POZA 1971 National Aeronautics and Space Administration, Report No. CR-1840. A technique for automatic real-time scoring of several simultaneous sleep electroencephalograms. 12. A. RECHTSCHAFFEN, P. HAURI and M. ZEITLIN 1966 Perceptual Motor Skills 22, 927. Auditory awakening thresholds in REM and NREM sleep stages. 13. A. SHAPIRO, D. R. G~~DENOUGH and R. B. GRYLER 1963 Psychosomatic Medicine 25, 174. Dream recall as a function and method of awakening. 14. P. A. MORGAN and C. G. RICE 1970 Znstitute of Sound and Vibration Research, University of Southampton, Technical Report No. 41. Behavioural awakening in response to indoor sonic booms. 15. J. LUDLOW 1971 Institute of Sound and Vibration Research, University of Southampton. Unpublished data (report in preparation). 16. H. L. WILLIAMS,J. T. HAMMACK,R. L. DALY, W. C. DEMENTand A. LUBIN 1964 Electroencephalography and Clinical Neurophysiology 16,269. Responses to auditory stimulation, sleep loss and the EEG stages of sleep. 17. J. S. LUKASand K. D. KRYTER 1970 National Aeronautics and Space Administration, Report No. CR-1599. Awakening effects of simulated sonic booms and subsonic aircraft noise on six subjects, 7 to 72 years of age. 18. A. KALES(ed.) 1969 Sleep: Physiology andPathology. A Symposium. Philadelphia and Toronto: Lippincott. See pp. 17-205. 19. I. OSWALD 1971 Proceedings NATO Advanced Study Institute, Basic Sleep Mechanisms, Bruges, Belgium, 24-30 June 1971. Influence of drugs on sleep and correlations with behaviour. 20. W. P. WILSONand W. M. K. ZUNG 1966 Archives of General Psychiatry 15 Nov., 253. Attention, discrimination and arousal during sleep. 21. G. GLOBUS,E. PHOEBUS,R. BOYD, R. DRURY and T. LEVENTHAL1971 Proceedings First Znternational Congress of the Association for the Psychophysiological Study of Sleep. Bruges, Belgium, June 19-23. The effect of a tranquilizer on the temporal organization of sleep. 22. A. MCGHIE and S. M. RUSSELL1962 Journal of Mental Science 108,642. The subjective assess-
ment of normal sleep patterns. 23. G. S. TUNE 1969 British Journal of Psychology 60,43 1. The influence of age and temperament on the adult human sleepwakefulness pattern, 24. J. S. LUKAS 1972 Journal of Sound and Vibration 20,457-466. Awakening effects of simulated sonic booms and aircraft noise on men and women. 25. Second Survey of Aircraft Noise Annoyance Around London (Heathrow) Airport. London: H.M.S.O. 26. I. OSWALD, A. M. TAYLORand M. TREISMAN1960 Bruin 83, 440. Discriminative responses to stimulation during human sleep. 27. G. J. THIE~SENand N. OLSON 1968 Sound and Vibration 2, 10. Community noise-surface transportation. 28. M. KRAMER 1970 CPE-69-132, Veterans Administration, Ohio. Interim report: Noise-sleep study. 29. B. BERRY and G. J. THIE~~EN1970 National Research Council, Canada, Division of Physics, Report APS-478. The effects of impulse noise on sleep. 30. R. RYLANDER,S. SORENSENand K. BERGLUND 1972. Sonic boom effects on sleep-a field experiment on military and civilian population (to be published). 31. R. T. WILKINSON1966 In Sleep in Physiology of Survival (0. G. Edholm and A. L. Bacharach, eds.). London: Academic Press. Sleep deprivation. 32. W. B. WEBB 1969 In Sleep in Physiology and Pathology, A Symposium (A. Kales, ed.). Philadelphia: Lippincott. Partial and differential sleep deprivation (pp. 221-231). 33. R. T. WILKINSON,R. S. EDWARDSand E. HAINES1966 Psychonomic Science 5,471. Performance following a night of reduced sleep.
SONIC BOOMEXPOSUREEFFECTS: II.2
517
34. R. T. WILKINSON1968 Progress in Clinical Psychology 8, 28. Sleep deprivation: performance tests for partial and selective sleep deprivation. 35. T. ROTH, M. KRAMERand J. TRINDER 1971 Proceedings 124th Annual Meeting of the American Psychiatric Association, Washington D.C. Noise-sleep, and post sleep behaviour. 36. A. COHEN 1969 Noise as a public health hazard: The American Speech and Hearing Association, Washington, Report No. 4, 74. Effects of noise on psychological state. 37. G. JANSEN1969 Noise as a public health hazard: The American Speech and Hearing Association, Washington, Report No. 4, 89. Effects of noise on physiological state. 38. J. C. GUIGNARDand E. G~JIGNARD1970 Institute of Sound and Vibration Research, University of Southampton, Memorandum No. 373. Human response to vibration-a critical survey of published work. 39. J. R. MCKAY 1971 Institute of Sound and Vibration Research, University of Southampton, Memorandum No. 435. Human perception of whole body vibration. 40. K. S. KRYTER 1970 The Eficts of Noise on Man. New York and London: Academic Press. See pp. 443444.