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|Year : 2003 | Volume
| Issue : 19 | Page : 31--40
The effects of chronic aircraft noise exposure on children's cognition and health : 3 field studies
MP Matheson1, SA Stansfeld1, MM Haines2,
1 Department of Psychiatry, Queen Mary, University of London, London ,UK
2 Department of Psychiatry, Queen Mary, University of London, London ,UK; Health Risk Management Practice, PricewaterhouseCoopers, Sydney, Australia
M P Matheson
Department of Psychiatry, Queen Mary, University of London, Basic Medical Sciences Building, Mile End Road, London E1 4NS, England
This article provides a review of three of the most important field studies to have examined the non-auditory effects of chronic aircraft noise exposure on children's cognition and health. The design of each of the studies is outlined, relevant methodological issues are highlighted and the findings from the studies are reported. Effects are reported on annoyance and quality of life, motivation and helplessness, stress responses as indexed by neuroendocrine tests and blood pressure measurements. In terms of cognitive performance, effects are reported on reading, attention and long-term and working memory.
|How to cite this article:|
Matheson M P, Stansfeld S A, Haines M M. The effects of chronic aircraft noise exposure on children's cognition and health : 3 field studies.Noise Health 2003;5:31-40
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Matheson M P, Stansfeld S A, Haines M M. The effects of chronic aircraft noise exposure on children's cognition and health : 3 field studies. Noise Health [serial online] 2003 [cited 2020 Feb 27 ];5:31-40
Available from: http://www.noiseandhealth.org/text.asp?2003/5/19/31/31700
The effects of noise on hearing have long been the focus of scientific investigation. The nonauditory effects of noise have, by contrast, been relatively neglected. However, it is now clear that chronic exposure to noise can give rise to psychological effects in terms of increased stress levels and impaired performance. As far as research on children is concerned, there have been a number of laboratory and field studies which have examined the non-auditory effects of noise. Laboratory studies are very important and useful in that they allow a greater level of control over the environmental conditions than is possible in the field. They do, however, suffer from the shortcoming that subjects are typically exposed to only short bursts of noise during the experimental procedures and so the generality of these findings to chronically noise-exposed children is questionable. Field studies allow children who have been exposed to noise over a prolonged period of time to be tested and therefore have greater ecological validity. In this article three of the most important field studies to investigate the non-auditory effects of noise will be reviewed. These studies are all principally concerned with aircraft noise exposure but other studies have looked at both road traffic noise (e.g. Lercher, 1996) and train noise (e.g. Bronzaft & McCarthy, 1975). The three studies to be reviewed were respectively carried out in schools close to Los Angeles, Munich and London - Heathrow airports. The first of these studies had a repeated measures design, the second was a longitudinal study, while the third was a cross-sectional study.
The issue of confounding factors is critical for field studies of this type. It may be the case that one or more additional factors may co-vary with noise exposure to give rise to observed effects. This problem can be addressed in two ways. Firstly, by matching different noise groups as far as possible on other factors which might cause effects e.g. social deprivation and, secondly, by making statistical adjustments to compensate for any differences between noise groups on other factors. All three of the studies here discussed have addressed the issue of confounding. Each of the studies will now be briefly introduced.
The Los Angeles Airport Study
The Los Angeles airport study (Cohen et al., 1980, Cohen et al., 1981) was a repeated measures field study which focused on schools in the flight path of Los Angeles international airport. This was the first study of its kind ever to have been conducted and it provided both a methodological template and seminal results which have informed subsequent work. Four schools exposed to high levels of noise were included (N = 142) as well as three low-noise schools (N = 120). The low noise schools were matched with the high noise schools for overall scholastic performance of the children, ethnic and racial distribution of the children, social deprivation, and occupation and education of the parents.
All children were tested individually in a noise-insulated trailer that was taken to each of the participating schools. Testing was carried out in two 45-minute sessions which took place on consecutive days. The study included children from all noise-impacted third and fourth grade classrooms in the noise schools together with children from an equal number of classes in the quiet schools.
The matching process was only partially successful. The noise and quiet schools were well matched for level of parental education but there were significant differences for ethnic distribution. Moreover, there were significant differences in how long the children in the noise and quiet groups had lived in their present homes, those in the quiet schools having lived in the same home for longer, and in terms of how long they had attended their present schools, the quiet-school children again having been at their present school for longer. A regression analysis was employed to address the differences of racial distribution and mobility.
The children were followed up a year later in order to examine whether the effects observed at the first wave of data collection had persisted, become worse, or whether the children had adapted to their environment. A strength of the Los Angeles study was that it emphasised the length of time which the children had been exposed to noise. It is perhaps to be regretted, however, that the study included such a narrow range of cognitive outcome measures.
The Munich Airport Study
The Munich Airport study (Evans et al., 1995; Evans et al., 1998; Hygge et al., 2002) was a prospective study which took advantage of a naturally occurring experiment which resulted from the relocation of this major airport. The old airport was situated in an urban area of the city while the new airport is situated in a rural area outside the city. There were three waves of data collection. Wave 1 was shortly prior to the closure of the old airport, while Waves 2 and 3 were carried out one and two years later respectively.
At Wave 1 the participating children were recruited from the third and fourth grades and had a mean age of 10.8 years. These children were then followed up at Waves 2 and 3. Children were recruited from four groups: old airport - quiet (N = 43), old airport - noise (N = 65), new airport - quiet (N = 107), new airport - noise (N = 111). The children in the noise and quiet schools were matched for sociodemographic characteristics. In order to take part in the study children had to have a minimum of two years residency and be fluent German speakers, thereby ruling out confounds with language proficiency. Children were also screened for normal hearing.
Testing was carried out on an individual basis in a sound-attenuated trailer which was taken to each of the participating schools. The tests were conducted in a fixed order on two consecutive days. The natural experiment which this study took advantage of represents a unique strength of this study and something which no other study has yet to replicate. Whether the size of the sample used in this study is large enough to adequately address the question of the role of confounding factors in the relationship between noise and outcome measures is debatable.
The West London Schools Study
The West London Schools Study (Haines et al., 2001b) was a cross-sectional study which was carried out in schools in the area surrounding Heathrow airport. A total of twenty schools took part in the study, 10 high noise schools (N = 236) and 10 control low noise schools (N = 215).
Attempts were made to match the samples on age, sex, existing noise protection, socioeconomic status and main language spoken at home. Parent questionnaires (N = 361) and teacher questionnaires (N = 25) were also completed.
The matching process was only partly successful. The noise and quiet groups were well matched on age, sex and socio-economic status but the noise group was more likely to be nonwhite and to speak a language other than English at home. Unlike the other two studies the tests were group administered in the classroom. This occurred according to a fixed ordering. While, unlike the other two studies, children were not given a hearing test to screen for hearing difficulties, both teachers and parents were asked to indicate if they had knowledge of hearing problems in the children. The results from this showed no significant differences according to noise exposure group. An important strength of the West London Schools Study over the other two studies was the larger sample size, which allowed the role of confounding factors in the relationship between noise and outcome measures to be adequately accounted for. Another important strength of this study over earlier studies was the use of multi-level modelling statistical techniques. This made it possible to adjust analytically for the potentially confounding effects of school characteristics on associations between noise and outcome measures at the individual level. A weakness of the West London Schools Study was that it was not longitudinal and so could not track the effects of noise over time.
Taken together, these three studies have identified a broad range of effects from chronic noise exposure. In the following sections these effects will be reviewed. For clarity, these are divided into, firstly, stress responses and health outcome measures and, secondly, cognition and performance measures.
Stress response and health outcome measures
[Table 1] summarises the findings from the stress response and health outcome measures across the three studies. A tick indicates that a significant effect was observed while "-" indicates that no test was run.
Annoyance as a consequence of chronic exposure to aircraft noise was assessed in both the Munich study and the WLSS.
In the Munich study the children gave magnitude estimates of noise annoyance. Short bursts of noise were presented over headphones at different levels. Three kinds of noise were used: broadband noise, road traffic noise and aircraft noise. The children also indicated how annoying they found community noise levels. The results show that at Wave 1 children in the noise condition were significantly more annoyed by community noise than those in the quiet condition. No annoyance results appear to have been presented for Waves 2 or 3.
Quality of life was also assessed in the Munich study. For this purpose the KINDL was used, a valid and reliable indicator of the four main areas of quality of life, namely, psychological, physical, social and functional daily life (Bullinger et al., 1994). While the data for each of these subscales at Wave 1 indicated a tendency towards a higher quality of life in the quiet group, there was only a significant effect for the psychological subscale. The prospective data indicates that quality of life became significantly worse in the noise-impacted communities 18 months after the opening of the new airport while in the quiet communities it remained relatively stable F(2, 202) = 3.07, p eq aircraft noise. The results showed no significant effects for the embedded figures test. In the case of the reaction time test, at the old airport the noise group was significantly slower than the quiet group at Wave 2, t(61) = 2.29, p = 0.026. At the new airport the noise group was again found to be significantly slower than the quiet group at Wave 3, t(121) = 2.09, p = 0.039.
The West London Schools Study measured sustained attention by means of the Score task from the Test of Everyday Attention in Children or TEA-Ch (Manly et al., 1998; Version A). This task required children to imagine that they were keeping score of a computer game by counting the number of scoring sounds. In this way the task assessed the children's ability to count tones with irregular stimulus intervals. There were a total of 10 trials and the test was scored according to the correct number of items counted. There were no significant results for this test.
Taken together, these results would appear to provide some evidence for an effect of chronic noise exposure on attention. The results from the Los Angeles study are particularly interesting in that they would appear to suggest that while noise does have an effect on attention that this effect diminishes over time. This finding might reflect adaptation to noise exposure and warrants further investigation.
Despite being carried out in different parts of the World, in different climatic and cultural conditions, and using methodologies which differed in certain respects these studies nonetheless produced a number of consistent findings. In terms of stress and health outcomes it would appear that children chronically exposed to high levels of aircraft noise consistently experience raised annoyance levels and raised blood pressure levels. There is some evidence from neuroendocrine indicators of raised stress response levels. There is also strong evidence from these studies that motivation may be impaired and that noise exposed children may experience a sense of helplessness.
In terms of cognitive and performance outcomes, there is strong evidence from the results of these studies that chronic noise exposure affects reading and attention. This is consistent with the findings from other studies e.g. Bronzaft and McCarthy, 1975, Broadbent, 1971. These three studies also provide some evidence for effects on long-term episodic and also working memory.
The findings from these studies point to a number of directions in which research in this area should now be taken. An important question, which has only begun to be addressed, is the effect of noise exposure over time. In particular, research must examine whether the effects which have been observed in the existing research persist over time, whether they become more severe, or whether children are able to adapt to noise and catch-up with their non noiseexposed counterparts. Another direction in which research should be taken is to address dose-response relationships. At what level of noise do effects begin to appear? This of course may be different for different noise sources. Relatedly, the effect of a combination of noise sources requires to be examined. Both the issues of dose-response relationships and combined effects are currently under investigation as part of a large European Commission-funded project (RANCH). The issue of the effects of chronic noise exposure on sleep were not examined in any of the three studies here discussed. This is however an important area which also requires further research.
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