In 2011, the WHO reported the negative impacts of environmental noise on health outcomes as burdens of disease, focusing mainly on cardiovascular disease, cognitive impairment, sleep disturbances, tinnitus, and annoyance. The report mentioned that every year in the EU, cities at least 45,000 disability-adjusted life years are lost for children aged 7-19 years due to environmental noise. These findings compare with at least 22,000 years for tinnitus and 61,000 years for ischemic heart disease [1]. In addition, they recommended that future research on noise will need to focus on vulnerable groups; noise exposure may be worse for certain subgroups, including children, older people, and lower socioeconomic groups.

The cognitive impairment from noise negatively influences children’s academic ability. A negative relationship between noise exposure and delayed reading acquisition in young children has been reported [2]. Children who were chronically exposed to aircraft noise at school have poorer reading ability and memory and poorer performance on standardized tests compared than children who are not exposed [3]. The largest study of noise and children’s cognition undertaken to date is the RANCH project (Road Traffic Noise and Aircraft Noise Exposure and Children’s Cognition and Health). This project examined the effects of noise (aircraft and road traffic) on cognition for 2,844 elementary school students (9-10 years) around three large international airports. They found linear exposure-effect relationships between aircraft noise exposure at school and children’s reading comprehension and recognition memory [4-7].

Experimental studies have shown the negative impacts of acute exposure on speech perception, listening comprehension, and non-auditory tasks, such as serial recall of visually presented lists and reading [7]. Studies of the impact of acute noise on reading performance have been mixed [8]. Acute noise does not affect mathematics performance, but noise might adversely impact the mathematics performance of hyperactive children or children with lower cognitive abilities [9]. Three studies examined reading and memory in children during acute traffic noise exposure [10-12]; these studies measured attention capacity, which did not mediate the memory deficits created by noise. Among these three studies, negative impacts due to road traffic noise were reported by only two: Hygge [11] and Hygge et al. [12]

Dockrell and Shield analyzed the effects of babble and babble mixed with traffic sounds on the performance of third graders on psychological tests, including attention. The overall scores for babble noise were lower than those for quiet conditions. However, the attention test error rates were greater for quiet conditions than those for both noise conditions [13]. Ljung et al. [14] examined the effects of road traffic noise and irrelevant speech on children’s reading speed, reading comprehension, basic mathematics, and mathematical reasoning among 187 pupils (89 girls and 98 boys), 12-13 years old, who were tested in their ordinary classrooms and showed that road traffic noise impaired reading speed (p<0.01) and basic mathematics (p<0.05). Although the impact of acute noise on cognitive function has been studied extensively, there is still no adequate explanation of the circumstances under which noise affects cognitive performance.

Vulnerable groups can easily be distracted by noise [15]. Children with language or attention disorders perform worse on auditory tasks than normally developing children exposed to noise due to the mediating roles of linguistic competence and selective attention [16]. Other researchers have focused on noise exposure in vulnerable groups [15,17-21], such as neonates, children younger than 10 years old, and children with autism spectrum disorder. Because the neurocognitive functions associated with academic performance in the classroom are influenced by noise, vulnerable groups with lower academic potential could be more significantly influenced by noise, but there have been no reports on this vulnerable group in school-age children.

The purpose of this study was to investigate the effects of experimental traffic noise (>15-17 dB over background) on the attention and cognition of elementary school students and to evaluate whether vulnerable groups are more substantially influenced by noise disruptions.

The demographic results of this study are summarized in Table 2. Generally, the paternal education level and monthly income at school C were greater than those at schools A and B. There were significant SES differences among the three schools (χ²=65.0, p<0.001 for the paternal educational levels; χ²=33.0, p<0.001 for the monthly incomes). The hearing levels of the enrolled children were within the reference values (0-20 dBHL, average hearing level 0.5, 1, and 2 kHz).

The attention and cognitive performance test scores are summarized in Table 3, as follows. There were significant differences between the CG and NG on the KEDI-WISC, CAT, CCTT, and Stroop tests (children’s version).

For the KEDI-WISC, the arithmetic, vocabulary, picture arrangement subtest, and full-scale IQ scores were significantly different for experimental simulated noise, except for the block design component, after adjusting for socio-demographic covariates. The full-scale IQ scores (116.71 for the CG vs. 109.68 for the NG, p<0.001), arithmetic subscores (12.11 for the CG vs. 11.30 for the NG, p=0.006), vocabulary subscores (13.37 for the CG vs. 11.80 for the NG, p=0.002), and picture arrangement scores (11.59 for the CG vs. 9.99 for the NG, p=0.001) were significantly decreased in the NG.

General linear models demonstrated significant differences in the CPT scores between the CG and NG: 1) the response time on the auditory selective attention test differed (85.19 for CG vs. 91.51 for NG, p=0.007); 2) the omission error and response time on the divided attention test were different (92.98 for the CG vs. 86.01 for the NG, p=0.034, and 98.84 for the CG vs. 104.72 for the NG, p=0.047, respectively); and 3) the forward memory span and forward correct response on the spatial working memory test were different (96.80 for the CG vs. 91.42 for the NG, p=0.045, and 95.21 for the CG vs. 89.23 for the NG, p=0.020, respectively).

For the Stroop test, the word score was significantly affected by the experimental noise (50.82 for the CG vs. 48.22 for the NG, p=0.030). However, the differences in the word scores between the CG and NG showed borderline statistical significance after adjusting for the sex, grade, monthly income, and paternal education level of each student (50.29 for the CG vs. 48.03 for the NG, p=0.056). For the CCTT tests, the CCTT-1 total time of the NG was significantly delayed compared with the CG (20.51 for the CG vs. 22.50 for the NG, p=0.021).

In addition to these analyses, we divided the participants into four groups, according to the Learning Disorder Scale (LD Risky and non-Risky groups) and noise exposure (CG and NG). As shown in Figure 1, there were significant differences between the noise+LD risky group and the other groups for the attention subtasks, such as the commission error (Visual Attention Test), reaction time standard deviation variability (Visual Attention Test), commission error (Auditory Attention Test), and commission error for the Divided Attention Test (Visual+Auditory). Additionally, there were significant differences between the N+LD risky group and the other groups for spatial working memory (forward memory span, forward correct response, backward memory span, and backward correct response), as shown in Figure 2.

The objective of this study was to investigate the impacts of experimental traffic noise (approximately 15-17 dB higher than background noise) on the attention and cognitive functions of elementary school students. The comparisons of a battery of tests showed that experimental traffic noise negatively impacted the attention and cognitive performances of children after controlling for their socioeconomic status. In addition, the negative impacts were more prominent in the lower academic performance group.

Regarding IQ scores, according to the KEDI-WISC, the full-scale and verbal IQ scores were affected by experimental traffic noise. Few studies have examined the impact of acute environmental noise on IQ scores. However, the students with relatively low verbal and nonverbal intellectual abilities had lower performance in multisensory integration under either the quiet or noise conditions. Previous studies on the impact of noise on IQ scores showed that lower IQ groups were affected by noise for multisensory integration [30]. In our study, there were lower IQ scores in the environmental traffic noise group after adjusting the socioeconomic variables. This finding aligned with the results of the controlled tests done by Shield & Dockrell that demonstrated that classroom babble (at a steady level of 65 dB[A] LAeq) has a detrimental effect on children’s performance in verbal and nonverbal tasks. In their study, the levels of environmental noise events from various sources (e.g., sirens and trucks) at random intervals (at a level of 58 dB[A] LAmax noise) were similar to those in our study. However, Barutchu et al. [31] did not find a significant relationship between the cognitive test results in a noisy environment and nonverbal IQ in children when IQ was measured using Raven’s Progressive Matrices Test.

In our CPT analysis of the reaction speed, the reaction times for the auditory attention test (using a simple auditory cue) and the divided attention test (consisting of both visual and auditory cues) were faster in the noise group. Therefore, children exposed to noise can have enhanced performance for their reaction speeds with auditory stimuli; however, in more complicated tasks with visual cues alone, they are more likely to experience a delay in neurocognitive processing. Barutchu et al. [31,32] reported that children’s motor reaction times were significantly faster for audiovisual stimuli and that the effect is age-related (younger than 12 years old). Barutchu et al. [30] also demonstrated that auditory background noise has a greater adverse effect on audiovisual integration in children than in adults. Children seem to have more immature multisensory integration and are thus more susceptible to the effects of noisy environments.

One explanation for their faster reaction times in auditory tasks during the noise situation is found in the Moderate Brain Arousal model [33], which reported that noise can have some beneficial effect on cognitive performance depending on the neurotransmitter dopamine level. However, they reported that for children (with or without an ADHD diagnosis) who performed a set of short-term memory tasks, there was an antagonistic interaction between noise and the activity performance in the participant group. The noise had a small but beneficial effect on recall for the ADHD-group, whereas the opposite pattern was observed in the controls. However, several investigators found that noise was particularly detrimental to cognitive processing in children with ADHD. However, differences in the reaction time for the visual attention test in our study were insignificant, and the CCTT-1 time was delayed with noise, suggesting that noise can exert a beneficial effect on cognitive functions in response to the auditory stimuli, whereas other cognitive functions will be negatively affected. In addition, the omission errors in the divided attention task were negatively associated with the noise condition, which was in concordance with the fast reaction time in our CPT results. This result indicates that there is inefficient acceleration of mental processing with errors.

In the spatial working memory component of the CPT test, the forward memory span and the forward correct response were affected by the noisy condition. A possible explanation is that exposure to experimental traffic noise produced observable increases in distractions and off-task times [34]. In addition, the word score for the Stroop test and the CCTT-1 total time for the noise group were significantly affected by exposure to the experimental traffic noise. These tests are used to assess frontal lobe function, such as attention, cognitive inhibition, and mental operation speed. Both the Stroop and CCTT tests indicated that reading speeds were significantly affected by the experimental traffic noise. These results are in agreement with the results of earlier studies that reported a negative relationship between reading and noise [3,12].

Some studies have reported that for the groups with attention problems, cognitive performance can be moderated differently compared with that in normal groups by adding external background white noise stimulation [35-37]. Other studies have reported that students with learning disorders experience speech perception deficits in response to noise exposure. In addition, several other researchers have focused on the risky groups that are vulnerable to noise exposure, such as neonates, children younger than 10 years old, and children with autism spectrum disorder [15,17-21]. In this study, we divided the participants into four groups, according to the Standardized Learning Disability scale and noise level and found that the children who were at risk of learning disabilities were significantly affected by noise conditions compared with the other groups. Therefore, we must think more carefully about the vulnerable groups and make plans to teach them in less noisy conditions, thereby avoiding classroom distractions.

This study has some limitations. We used only two levels of traffic noise (background and experimental noise); therefore, the effects of other noise levels are still unknown. Further study will be needed to assess other environmental noise, such as from aircraft, railway systems, and babble at various noise levels. Furthermore, other neurocognitive functions must be examined using neurobiological measures to assess various memory and emotional changes. Finally, vulnerable populations in particular should have their noise levels reduced in academic environments.

Together, the results demonstrate that noise affects attention and cognitive functions, as measured by the CAT, KEDIWISC, CCTT, and Stroop tests. Moreover, the impacts were consistent after controlling for demographic confounders. These findings suggest that noise (approximately 15-17 dB higher than background) is hazardous to the attention and cognitive performances of elementary school students, particularly for vulnerable groups with low academic potential. Further study is needed to elucidate the effects of various noise levels on cognitive function.