El argumento neoliberal y las políticas impuestas

Earlier prelim inary research

Early studies in the 1960s and 1970s found preliminary evidence of cognitive impairments in children chronically exposed to noise (for a full review of the earlier research see M ills, 1975). Exposure to traffic noise at school was associated with deficits on measures of varying reliability of sustained attention, among elementary school children (Karsdorf & Klappach, 1968; Kyzar, 1977). Not all studies found noise effects on performance (Slater, 1968). These earlier studies examining the effect of noise on child attention suffer from methodological flaws that limit their interpretation such as: inadequate controls for socio-demographic factors (Kyzar, 1977; Kardorf & Klappach, 1968, Slater, 1968); inadequate screening for normal hearing (Kyzar, 1977; K ardorf & Klappach, 1968, Slater, 1968); and lack of objective noise measurements (Heft, 1979).

1970s fie ld studies

In the 1970s the first well-designed naturalistic field study was conducted by Cohen, Glass & Singer (1973) who studied elementary school children living in four 32-floor

apartment buildings that were located on an expressway. The sample of 73 children were tested for auditory discrimination and reading level. Children living on lower floors of the 32-story buildings (i.e. higher noise levels) showed greater impairment of auditory discrimination and reading achievement than children living in higher-floor apartments. It was concluded that the results supported D eutsch’s hypothesis (1964), because auditory discrimination appeared to mediate an association between noise and reading deficits and length of residence in the building affected the magnitude of the correlation between noise and auditory discrimination. The results indicated that with a longer exposure duration, the association between noise and deficits in auditory discrimination become stronger. This seminal study has many elegant design features because it was a field study where noise exposure levels varied naturally but it also had limitations that either reoccur or are improved upon in the later field studies. First, it is difficult to accurately characterise the noise exposure of each child taking into account school noise exposure and other sources of noise apart from road traffic in the home (e.g. television, shouting, radio) in order to be certain that the deficits in reading are due exclusively to road traffic noise at home. This is a methodological problem that hinders most field research. It can be argued that there is no good reason to suppose that other sources of noise in the home differ across the noise exposed and the non-noise exposed groups. Alternatively, it is possible that to counter the effects o f higher levels of road traffic noise in the home the television and radio are played at louder levels and family members need to shout to be heard. Second, given the small sample size it is possible that there is something else that may characterise people who live on the top of high rise apartments that could confound the effect.

Bronzaft & McCarthy (1975) argued that a more direct association m ay exist between noise and reading difficulties that was not mediated by auditory discrimination.

They compared reading scores of elementary school children who were taught in classes on a noisy side o f a school near a railway line with the scores o f the school children in classes on the quiet side of the same school. They found that children on the noisy side of the school building had poorer performance on the school achievement tests than those in classes on the quiet side of the school. The mean reading age of children in the classes on the noisy side of the school was three to four months behind the children in the quiet classes.

The finding that there was a significant direct relationship between train noise and depressed reading scores supports one part of the Deutsch (1964) hypothesis that low reading achievement may be related to noise exposure. However, these data do not provide any evidence that this association may or may not be mediated by impaired auditory discrimination. In order to achieve their aim of testing whether the association between high noise exposure and impaired reading was a direct association or mediated by auditory discrimination, Bronzaft & M cCarthy (1975) needed to measure the

auditory discrimination and then conduct a mediational analysis. It is also possible that the effect of noise on reading was due to acute train noise at the time of testing and not to chronic exposure. This is because children who attended classes on the noisy side of the school took their reading tests in the same rooms. These testing conditions make it impossible to determine whether the noise effects on reading were the result of acute noise interference at the time of testing or whether the noise related deficits were due to chronic exposure to noise. This issue was addressed with refined methods in later studies where testing was conducted in sound proof trailers (Cohen et al., 1980; Evans et al., 1995; Evans & Maxwell, 1997).

A strength o f Bronzaft & M cCarthy’s (1975) results is that they cannot be attributed to self-selection, a methodological problem found in many field studies, because the noise effects were found in the same school. Children were not assigned in any systematic manner to classrooms on the noisy or quiet side o f the school. Supplementing the laboratory research, these results in the field in the 1970s (Cohen et a l., 1973, Bronzaft & McCarthy, 1975) demonstrated that noise exposure may have long-term behavioural consequences for children living and going to school in noisy environments in spite of noise adaptation, but more conclusive evidence was required.

1980s fie ld studies

In order to provide a stronger answer to the question of whether laboratory findings applied to chronic environmental noise exposure, more well-designed field research on children who routinely live and go to school in high noise exposed areas was conducted in the 1980s and 1990s (Bronzaft, 1981; Cohen et al., 1980, 1981; Evan et al., 1995; Evans et al., 1998; Evans & Maxwell, 1997; Hygge et a l, 1996).

In the 1980s, impaired performance on a difficult cognitive task was found in primary school children aged 8- 9 years in a systematic well-controlled naturalistic field study

around Los Angeles Airport (cross sectional results Cohen et al., 1980; longitudinal results Cohen et al., 1981). The aim of this study was to examine the association between aircraft noise at school and child cognitive and motivational performance and non-auditory physiological responses. Four o f the noisiest elementary schools near Los Angeles International Airport (mean peak 74 dB) were matched to three quiet control schools (mean peak 56 dB) for grade level, ethnic distribution of children, percentage o f children whose families were receiving government assistance, and for occupation and education of parents. There were 142 high noise children and 120 low noise children in years 3 and 4. All the tasks and questionnaires were administered in a sound insulated trailer and the children were pre-screened for hearing loss. Interior sound levels were measured inside each classroom and sound levels outside the homes were obtained from noise contours. The main outcome measures were: helplessness motivation

performance measure, auditory discrimination, selective attention, scores on standardised reading mathematics tests collected from the school records, noise annoyance, and systolic and diastolic blood pressure. Socio-demographic data was collect from the parents. The samples were well matched on most factors except that the high noise group contained more Afro-American children and children who were more geographically mobile. The analyses were adjusted for number o f children in the child’s family, the grade at school, length of time at school and race.

The results strongly showed that high noise exposed children had higher noise annoyance, and higher systolic and diastolic blood pressure than the control children. The results provide suggestive evidence that children exposed to high levels of aircraft noise were less capable of performing a cognitive task (puzzle solving) and were more likely to give up on a difficult task (poorer motivation, greater helplessness). There was some evidence that noise impairs selective attention during distraction but this was only significant after 4 years of chronic aircraft noise exposure in the school. Mathematics, reading and auditory discrimination were unrelated to noise exposure. Cohen and colleagues (1980) concluded that there results were strikingly similar to those reported in the laboratory setting, but that replication was required before definitive conclusions could be reached.

Cohen and colleagues (1981) report a one year follow-up of this same sample. They were asking the question of whether children re-tested one year later continue to show baseline effects or whether they adapt to noise over the one year period. The response

rate of the sample was 163 (high noise sample = 83 and quiet sample = 80) which indicates a moderate response rate of 62% and high attrition. The follow-up results showed that the noise effect on annoyance, selective attention during distraction and performance on a moderately difficult cognitive task were stable over time. At follow- up they did not replicate the baseline effects of noise on blood pressure and rate of giving up on a difficult task (Cohen et al., 1981). In general, it was concluded that there was little evidence for adaptation to noise over the one year period and that the effects related to noise exposure are stable over a one year period (see the introduction to Chapter 4 for a more detailed discussion of this work).

In agreement with their previous work, Cohen and colleagues (1986) in an analysis of a new sample of 165 grade 3 school children around Los Angeles Airport found that children in noisy schools: a) had higher blood pressure if they were enrolled for 2 years or less; b) were more likely to fail on a difficult cognitive puzzle; and c) suffered more impaired selective attention during distraction than the control children in quiet schools. They found no effect on auditory discrimination. These results, obtained in a small independent sample, broadly replicate their previous work confirming the existence of child noise effects, but do not provide any further understanding or stronger evidence for these noise effects.

Stronger evidence to suggest the existence of noise effects comes from intervention studies and natural experiments where changes in noise exposure are shown to be accompanied by changes in cognition. To date, there have been three studies examining the effects of noise reduction on children’s cognition: two intervention studies

(Bronzaft, 1981., Cohen et al., 1981) with methodological flaws that limit their

generalisability and one well-designed natural experiment (Evans et a l, 1998; Hygge et al., 1996). Bronzaft (1981) found that following attenuation in rail noise there were no longer significant differences, as there had been previously (Bronzaft & McCarthy,

1975) in reading achievement between children from classrooms close to elevated train tracks and children on the opposite side of the building. Noise was lowered by

acoustical treatment of classrooms and by one inch thick butyl-rubber pads on the rail tracks closest to the school (6-8 dB A reduction in total). Teacher self-reports showed that they really did notice a huge reduction in noise interference. Cohen and colleagues (1981) found that noise abatement in classrooms (7 dBA reduction) had small

intervention studies (Bronzaft, 1981; Cohen et a l, 1981) suffered from no comparisons of reading ability before and after noise reduction; no objective measure of actual noise reduction; and insufficient sample sizes which makes the potential for selection bias more likely. The M unich Airport Study provides the best evidence that a reduction in noise level of only one year duration reduces noise-induced cognitive impairments (Hygge et a l, 1996), but further intervention studies are needed to test practical and affordable interventions, such as insulating classrooms against noise exposure in areas where external noise levels are unlikely to change.

1990s fie ld studies

Stronger evidence for similar noise related cognitive effects found in the 1970s and 1980s has been found in experimental field research around Munich Airport in older children with a mean age of 10.8 years (cross-sectional results Evans et a l, 1995; longitudinal memory results Hygge et a l, 1996; longitudinal psychophysiological results Evans et a l, 1998). In 1992 the old Munich airport closed and a new airport was opened, which gave the researchers an unprecedented opportunity to conduct a

prospective longitudinal natural experiment with a change in noise exposure. Testing occurred in a climate-controlled, sound attenuated trailer at the children’s school, where they could disentangle chronic from acute noise effects. Beginning in 1991, before the change over of airports, children at both sites were recruited into two experimental and two control groups. The two experimental groups were: 1) the children at the old airport who were exposed to high levels of aircraft noise and 2) children at the new airport who were to become exposed to high levels of aircraft noise. The two control groups, one for the old airport and one for the new airport, were selected from areas that were not or would not be exposed to much aircraft noise. One wave of data collection occurred prior to the change over of airports, the second wave one year later, and the third wave a year after that.

The cross-sectional results of the first wave of data collection, compared the cognitive performance o f 135 children living a high noise impact neighbourhood (24-hr Leq=68.1 dBA) with children from a quiet neighbourhood (24-hr Leq=59.2 dB A) around the old Munich International Airport indicate a mixed pattern of results. There were

significant associations between high noise exposure and a) poorer long term memory; b) poorer performance on a German standardised reading test with the effect becoming more marked in the difficult section of the test and ; c) selection of a lower signal-to-

noise ratio indicating resistance to auditory distractors on a signal-to-noise task and this perceptual adaptation generalised across different noise sources (Evans et a l, 1995). The two groups did not differ in performance on an embedded figures attention task, nor a simple choice reaction time task, or working memory. Overall, it was concluded that these cognitive results support the previous field and laboratory research that indicate selective impairments in cognitive functioning among children exposed to chronic aircraft noise.

Longitudinal analyses of the cognitive results are not yet complete but some results are known (Hygge et a l, 1996). After three waves o f testing, these results indicate

improvements in long term memory recall task and the reading test (only significant for the difficult section) after closure of the old airport (Staffan Hygge, personal

communication). Strikingly, these effects were parallelled by impairment of the same cognitive skills after the new airport opened (Hygge et a l, 1996).

Even though the M unich study provides the strongest evidence to date of cognitive noise effects in children, the study is limited because it does not address the important question of what mechanisms cause these effects and the role of potential confounding factors. The overall sample size was 327 children at both sites (135 at the old airport, 192 at the new airport). In the cross-sectional analyses (Evans et al., 1995) there were approximately 68 children in each group (control and noise exposed groups). Even though the control and noise exposed groups did not differ in level o f parental

education, or occupation or in family size, there were not enough subjects in each group for the cross-sectional analyses to rule out the possibility o f selection bias influencing the cognitive results. Munich does not have the same social class, ethnic and school differences that are present in the UK or USA, which means that these results need to be replicated in the UK and USA to test whether they generalise after adjustment for these potentially relevant confounding factors.

Evans & Maxwell (1997), in a field study around New York, directly tested possible mediating factors. The primary objective of this study was to determine whether the relation between noise exposure and reading is caused by deficits in language

acquisition. They compared the cognitive performance o f 58 children exposed to high levels of aircraft noise (65 Leq contour) from one school with the performance of 58 children from one school exposed to lower levels of noise. They found that chronic

noise exposure was significantly correlated with low er reading ability and poorer speech perception. Sound perception and phonemes did not differ between the two groups. They found that speech perception functions as a partial mediator of the association between aircraft noise exposure and the reading effects. This study is severely limited because the small sample of children wAS drawn from only two schools which might not be repesentative and because there were no objective noise measurements. These results need to be replicated in a much larger sample and across a wider range of children. For these reasons it is best to treat this New York study as pilot research that replicates previous noise effects on reading and provides suggestive evidence that the noise effect is mediated by speech perception.

Summary o f findings

In studies examining the effects of chronic aircraft, train and road traffic noise on school children’s cognitive performance, the following results have been found in children exposed to high levels of environmental noise:

1) deficits in sustained attention and visual attention (Hambrick-Dixon, 1986;

Hambrick-Dixon, 1988; Heft, 1979; Karsdorff & Klappach, 1968; Kyzar, 1977; Moch- Sibony, 1984; Sanz et al., 1993)

2) difficulties in concentrating in comparison to children from quieter schools according to teachers’ reports (Crook & Langdon, 1974; Ko, 1979; Ko, 1981; Kryter, 1985)

3) poorer auditory discrimination and speech perception (Cohen et al., 1973; Cohen et al., 1980; Cohen et al, 1986; Moch-Sibony, 1984, Evans et al, 1995, Evans & Maxwell, 1997)

4) poorer memory that requires high processing demands (Fenton et al, 1974; Evans et al, 1995; Hygge, 1994; Hygge et al, 1996)

5) poorer reading ability and school performance (Bronzaft, 1981; Bronzaft &

McCarthy; Cohen et al., 1973; Green et a l, 1982; Lukas et a l, 1981; Michelson , 1968; Maser et al., 1978; Evans et a l, 1995, Evans & Maxwell, 1997)