10. In what other ways can sound exposure affect children and adolescents?
The SCENIHR opinion states:
3.9. Non-auditory effects
The non-auditory effects of noise on children and adolescents basically fall into two categories. (1) At the psychological level, seen as changes in reading, memory, attention, school achievement, and motivation and (2) other effects, mainly those who show up at biological or physiological level.
3.9.1. Psychological effects
Pertaining to the psychological effects on cognition and attention, there is no reported research on noise from PMPs. However there are reliable findings of the noise effects from other noise sources on cognition and attention in children and young adults. Thus, to consider possible outcomes of PMP-use it is worthwhile to briefly summarize relevant research, coming mainly from studies of aircraft and road-traffic noise.
220.127.116.11. Reading and memory
The best documented impact of noise on children's performance is research showing negative effects on reading acquisition. Close to twenty studies have found indications of negative relations between chronic noise exposure and delayed reading acquisition in young children (Evans and Lepore 1993). There are no contradictory findings and the few null results are likely due to methodological problems, such as comparing children across school districts who have different reading curricula (Cohen et al. 1986).
There are fewer studies of other cognitive processes and noise among children relative to reading. However, noise effects on memory have been the focus of a handful of studies. The most ubiquitous memory effects occur in chronic noise, particularly when complex, semantic materials are probed (Hygge 2003). Several studies of both chronic (Evans et al. 1995, Haines et al. 2001a, Hygge et al. 2002) and acute noise (Boman 2004, Boman et al. 2005, Hygge 2003, Hygge et al. 2003) have found adverse impacts of aircraft or road traffic noise exposure on long term memory for complex, difficult material. Stansfeld et al. (2005) replicated these effects on long term memory for chronic aircraft noise.
In the experimental acute noise studies by Boman (2004), Hygge (2003), Hygge et al. (2003) worse (approx. 15-20 %) long-term learning and memory in children was induced by exposure to aircraft and road-traffic noise and speech noise at 66 dB(A) Lequ during 15 min exposure time while reading a text and tested for memory of the text an hour later or a week later. For aircraft noise there was impaired memory also from 15 min exposure to 55 dB(A) Lequ.
For chronic aircraft noise exposure the Munich study (Hygge et al. 2002) and the RANCH study (Stansfeld et al. 2005) indicated that children exposed to chronic aircraft noise showed cognitive deficits compared to children not having been exposed to chronic aircraft noise. It was also found that the children at the old airport in Munich, who got rid of aircraft noise, improved their cognitive performance. Thus, there was some reversibility in the negative effects of noise on cognition when the noise ceased. To what extent this recovery is dependent upon the age of the children in question (11-12 years) and the accompanying continuing growth in cognitive development, we do not know.
Thus, short time exposure (15 min) to noise with average levels of 65 dB(A), impairs memory and learning. Long-time chronic exposure to, at least aircraft noise, indicate that there will be statistically significant impairments of memory and language skills when the noise levels increase from around or below 55 to above 60 dB(A) Lequ.
18.104.22.168. Attention and distraction
Use of music is sometimes employed to distract from a noisy working environment, and sometimes this is beneficial. One reason for this to happen is that the more boring, repetitive and simple a task is, the more will it benefit, both in quality and quantity, from being performed in noise (Kryter 1994). On the other hand, the more complex and difficult the task is, the more it is prone to be hampered by excessive sounds.
When the noise is preferred music from PMP one would in addition expect more of a perceived comfort. Further, when the music from the PMP also masks distracting sounds in the environment, devoid of relevant information or warning characteristics, it will most likely be a subjective advantage to listen to the PMP rather than to shut it off. On the other hand, the more cognitively demanding the task is, the more it is dependent upon speech communication, and the more there are of potential warning sounds in the close environment, the more to the disadvantage of the task performance and the security of the listener the PMP-listening is.
With regard to attention, there is always a risk that the sound of the music listened to from the PMP will acoustically mask warning sounds e.g. from approaching cars, street crossings or reversing trucks. Even if the music is not in a physical sense masking the warning sound, the focused attention on the music will from time to time make the listener inattentive to other sounds, some of which my be warning sounds.
22.214.171.124. School performance
There are a several cross-sectional studies that have reported a covariation between high noise levels (from aircraft or road traffic) and low grades or low levels of school achievement (Cohen et al. 1981, Cohen et al. 1986, Green et al. 1982, Evans and Maxwell 1997, Haines et al. 2001a, Haines et al. 2001b, Haines et al. 2001c, Haines et al. 2002, Maser et al. 1978, Stansfeld et al. 2005). However, cross-sectional studies suffer from two possible short-comings. The first is the differential socio-demographic composition of the noise dose groups, which may favour children in quiet middle-class housing and living areas. Adjusting statistically for the social class effects may not be sufficient to control for this. The second is the possible confound between being exposed to noise both while learning and when tested for what is learnt. Noise at testing may lower the test scores without learning being effected, but the effects of noise on learning and performing can not be disentangled. Thus, cross-sectional studies are not the best platform for a strong inference on cause-effect relationships.
One laboratory study (Glass 1977) and several field studies (Bullinger et al. 1999, Cohen et al. 1986, Evans et al. 1995, Maxwell and Evans 2000) have found that children chronically exposed to noise are less motivated when placed in achievement situations where task performance is contingent upon persistence. Cohen et al. (1986) also found that a second index of motivation, abrogation of choice, was affected by chronic noise exposure. Children chronically exposed to noise, following a set of experimental procedures in quiet conditions, were more apt to relinquish choice over a reward to an experimenter, in comparison to their well matched quiet counterparts. Haines et al. (2001a) could not replicate the effects of aircraft noise on puzzle persistence in elementary school children although they administered the task in small groups rather than individually.
Perceived control is at the heart of the theorising about noise after-effects. When the noise exposed person perceives that (s)he has control over the noise exposure or noise source, the motivational after effects vanish. Thus, we can not really expect that the persons that freely expose themselves to music from PMPs will lose any motivation just because of that.
126.96.36.199. Lasting after effects on cognition from listening to PMPs
No directly relevant study of lasting after effects (effects that last also after the cessation of noise exposure) of listening to PMP on memory, learning, attention or other facets of cognition has been located in the international research literature. Studies of lasting cognitive effects from involuntary exposure to chronic aircraft and road traffic noise (Hygge et al. 2002, Stansfeld et al. 2005) have indicated impaired memory and learning with an increased noise level. It is questionable though whether those studies validly can be stretched to make any inference about voluntary, non-chronic exposure to music. And even if the studies of chronic noise and cognition in some ways are applicable to PMP-listening, they can not state in any detail how long (years) the chronic noise must be present to result in impaired cognition, and whether this cognitive impairment will be permanent or not. For instance, in a study around the Munich airport (Hygge et al. 2002) children chronically exposed to noise at the old airport, and lagging behind their silent control group on memory and language performance, recovered from their deficits within 18 months after the airport was closed down.
Thus, there does not seem to be sufficient research on PMPs to conclude anything about long lasting effects on cognition, and the available evidence from research on other noise sources is not detailed enough to give any strong indications about exposure duration and permanence of cognitive deficits.
3.9.2. Other Effects
The obvious beneficial effect of listening to PMPs is indulging in a preferred activity, which is also the intended outcome. As long as this activity does not interfere with intended or required task performance, there should be no need to restrict listening to PMPs.
Although there is not much of relevant research, the little research there is point to children having somewhat better sleep than adults. Lukas (1972) stated that children are not as easily awakened by noises adults are. Öhrström et al. (2006) compared children aged 9-12 years with their parents in a road traffic study and reported that for parents there was a significant exposure-effect between noise and several self reported sleep parameters, but this relationship was less marked for children.
188.8.131.52. Cardiovascular and other physiological effects
Twelve studies found some association between increased blood pressure and noise-induced hearing loss (Pyykkö et al. 1981, Lang et al. 1986, Pyykkö et al. 1987, Verbeek et al. 1987, Milković-Kraus 1990, Talbott et al. 1990, Solerte et al. 1991, Starck et al. 1999, Souto Souza et al. 2001, Toppila et al. 2001, Narlawar et al. 2006, Ni et al. 2007). In contrast eleven other studies did not find such an association (Lees RE, Roberts JH. 1979, Willson et al. 1979, Ickes and Nader 1982, Kent et al. 1986, Gold et al. 1989, Kontosić et al. 1990, Tarter and Robins 1990, Hirai et al. 1991, Garcia and Garcia 1993, Zamarro et al. 1992, Barberino 1995). Overall both groups of positive and negative studies are quite comparable in sampling and other methodologies. It must be noted however that the positive findings report moderate average differences sometimes restricted within studies to sub-groups such as only the more exposed or the youngers or those who also smoked showing altered blood pressure. The question of causality remains open, the cardiovascular differences having been simply observed as concommittant. Two studies (Tomanek 1975, Dengerink et al. 1982) produced experimental temporary threshold shifts which were found related with altered cardiovascular parameters, however physiological processes underlying temporary and permanent threshold shifts are known to be notably different. A recent extensive review by Babisch (2006) dealing specifically with exposure to road or aircraft noise on blood pressure, hypertension and ischaemic heart disease concludes that there is no clear evidence of increased blood pressure. Whereas for aircraft noise (but not road noise exposure) most recent studies (Babisch 2006) indicate some significant relationship, finally concerning ischeamic heart disease more recent studies also suggest a trend towards increased risk as compared with previous studies.
Exposing oneself to music from a PMP is a matter of a personal choice of leisure activity. Harmful lasting and irreversible non-auditory effects of excessive listening to PMP can be expected in three areas: (1) Cardiovascular effects, (2) cognition and (3) distraction and masking effects. Cardiovascular effects, in particular increases in blood pressure, build up and accumulate over time, when there is not enough silent time in between noise exposures to recover. However, we do not have sufficient evidence to state that music from PMPs constitutes a risk for hypertension and ischaemic heart disease in children and young adults.
Effects on cognition (memory and learning) of excessive sound exposure has been shown from acute noise exposure and from chronic noise exposure. Noise exposure for 15 min to 66 dB(A), and for aircraft noise down to 55 dB(A) has been shown to cause impaired learning and memory of a text. We have no study stating that the same is true also for music, but we also have no reason to believe that music should be substantially less harmful to cognition that aircraft noise, road traffic noise or speech noise. Thus, listening to music from PMP while at the same time trying to read a text and learn from it, will hamper memory and learning. This learning impairment has been shown at fairly short (15 min) exposure times and at sound levels that are moderate (55-65 dB(A)).
Prolonged exposure to chronic aircraft noise has been shown to impair cognition in children, but there is also one indication that children may recover from the noise induced cognitive deficit when the noise exposure stops.
We do not as yet have a sufficient scientific basis to assume that excessive voluntary PMP-listening leads to lasting and irreversible cognitive and attention deficits after the cessation of the noise.
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