Cognitive Impairment

Several reviews have been written on the possible effects of noise on the performance and efficiency of people at work. Broadbent [13] worked on this topic for many years and has concluded that many investigations both in the laboratory and industry on the effect of noise on mental or motor performance have been inconclusive. Kryter [6, 7] goes even further to suggest that although any mental motor task that requires the perception of any auditory signal for correct performance will undoubtedly be affected by noise, that in his opinion, experimental evidence shows noise has no adverse effect on nonauditory mental or motor tasks. He suggests that adaptation to noise is responsible for this. However, other researchers suggest although many experiments are inconclusive, there is sufficient evidence to conclude that noise does have an adverse effect on work performance. We may summarize some of the generally agreed findings as follows [14]:

1. Steady A‐weighted noise levels (without meaning) does not interfere with human performance unless the sound pressure level exceeds 90 dB and even then not consistently.
2. Intermittent or impulsive noises are more disrupting to performance than steady noises. Bursts of such noise can be disruptive even for A‐weighted levels below 90 dB.
3. High‐frequency noise (above 2000 Hz) appears more disrupting than low‐frequency noise (below 2000 Hz).
4. Noise does not seem to change the rate of work but rather increases the variability of the work; there may be work pauses compensated by increases in work rate.
5. Noise increases the number of errors made at work rather than the total amount of work.
6. Complex tasks are more affected by noise than simple tasks.

The importance of these findings has been considered in some countries in their occupational noise legislation, limiting maximum noise levels to enhance concentration and prevent stress during mental tasks [15].

However, many more well‐controlled experiments of sufficient duration must be made in industrial work situations before the effects of noise on work performance can be readily established. In particular, the combined effects of noise and other occupational hazards on worker performance, such as work at night, vibrations, heat, illumination, sleep loss, etc. need further research.

Cognitive performance effects due to noise exposure appear to be more significant in children. A number of studies performed on pre‐school and primary school children exposed to high levels of environmental noise have found effects on cognitive issues. These studies have suggested that long‐term exposure to noise effects on sustained visual attention, cognitive functions involving central processing and language comprehension, speech perception, difficulty in concentrating compared with children from quieter schools, and result in poorer school performance on standardized tests [16]. It has also been suggested that children may adapt to chronic noise exposure by filtering out the unwanted noise stimuli [11]. Although the reported effects are sometimes small in magnitude and the experimental evidence may be debatable, authorities and policy makers responsible for noise abatement have been recommended to become aware of the potential impact of environmental noise on children’s development [17].

Table 5.1 summarizes the nonauditory effects of noise on human health and wellbeing [3]. Although not yet conclusive, epidemiological studies report evidence for effects of occupational noise on increased blood pressure and cognitive performance. The evidence for effects of noise on health is more conclusive regarding annoyance and sleep disturbance. The effects of noise are strongest for those effects that, like annoyance, can be classified under wellbeing rather than illness [16].

Table 5.1 Effects of noise on health and wellbeing with sufficient evidence [3]. Definitions of acoustical indicators can be found in Chapter 6.

^a L_den and L_night are defined as outside exposure levels. L_max may be either internal or external as indicated.

^b Threshold is the level above which effects start to occur or start to rise above background.