The location of a school can affect the success of pupils at that school, as evidenced by previous research studies that link poor performance with exposure to aircraft noise and to traffic-related air pollution. Now, in a study led by the Barcelona Institute for Global Health (ISGlobal), a center supported by the “la Caixa” Foundation, researchers have tested whether cognitive development in pupils at 38 primary schools in Barcelona, Spain, is linked to the levels of traffic noise in the streets outside the school.
Road traffic noise is a widespread problem in cities and yet its impact on children’s health remains poorly understood. The current study, which forms part of the BREATHE project and was led by ISGlobal researchers Maria Foraster and Jordi Sunyer, included 2,680 children between the ages of seven and ten years. Over the course of a year (between 2012 and 2013), the children completed sets of cognitive tests four times: these tests focused on measuring the children’s working memory and attention skills, as well as enabling the researchers to study the evolution of these cognitive skills over time.
Over the same period, noise measurements were taken in front of the 38 participating schools, as well as in their playgrounds and classrooms. The two cognitive skills investigated, namely working memory and ability to pay attention, are known to develop rapidly during preadolescence and are essential for learning and for achieving success at school.
Attention includes processes such as selectively attending to specific stimuli or focusing on a specific task for a prolonged period of time. Working memory is the system that allows us to hold information in the mind and manipulate it over a short period of time. When we need to process information stored in the working memory, we use what is known as complex working memory.
The findings of the study, published today in the journal PLoS Medicine, show that the development of working memory, complex working memory and attention skills during the year was slower in students who attended schools with higher levels of traffic noise. More specifically, the results showed that a 5 dB increase in outdoor noise levels resulted in working memory development that was 11.4 percent slower than average and complex working memory development that was 23.5 percent slower than average. Similarly, exposure to an additional 5 dB of outdoor traffic noise resulted in attention capacity development that was 4.8 percent slower than average.
In terms of traffic noise outside the classroom, both higher average noise levels and greater fluctuation in noise levels were associated with poorer student performances on all tests. Inside classrooms, greater fluctuation in noise levels was also associated with slower progress on all cognitive tests over the course of the year. But inside these same classrooms, exposure to higher average noise levels over the year was only associated with worse performance on attention tests, and not on tests of working memory.
“This finding suggests that noise peaks inside the classroom may be more disruptive to neurodevelopment than average decibel level,” commented Foraster, lead author of the study. “This is important because it supports the hypothesis that noise characteristics may be more influential than average noise levels, despite the fact that current policies are based solely on average decibels.”
“Our study supports the hypothesis that childhood is a vulnerable period during which external stimuli such as noise can affect the rapid process of cognitive development that takes place before adolescence,” explained Sunyer.
The researchers also investigated whether cognitive development in the children was associated with average noise levels at each participant’s home. To do this, they estimated the levels of ambient noise using a 2012 road traffic noise map of the city of Barcelona. The analysis showed no association between residential noise and the cognitive development of the school children.
“This could be because noise exposure at school is more detrimental as it affects vulnerable windows of concentration and learning processes,” explained Foraster. “On the other hand, although noise measurements were taken at the schools, noise levels at the children’s homes were estimated using a noise map that may be less accurate and, in any case, only reflected outdoor noise. This, too, may have influenced the results.”
The researchers emphasize the need for further studies on road traffic noise in other populations to determine whether these initial findings can be extrapolated to other cities and settings.