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Review and Assessment of the Health and Productivity Benefits of Green Schools: An Interim Report 5 Noise, Acoustics, Student Learning, and Teacher Health Various studies show that noise exposure affects educational outcomes, and other research provides evidence of mechanisms to explain these effects of noise on learning. Speech intelligibility studies have found that students’ ability to recognize speech sounds is decreased by even modest levels of ambient noise, and this effect is magnified for younger children. This problem may not be appreciated by adults, who are better able to recognize speech in the presence of noise. Most learning in school classrooms involves speaking and listening as the primary communication modes: Students learn by listening to the teacher and to each other (Goodland, 1983). Excessive background noise or reverberation (i.e., many delayed reflections of the original sound) can interfere with speech perception and, consequently, can impair educational outcomes. Careful attention to acoustical design requirements is essential for creating an effective learning environment. Nonetheless, a 1995 report of the U.S. General Accounting Office estimated that approximately 22,000 U.S. schools attended by 11 million students had unsatisfactory acoustics for noise control: 28 percent of the schools in the survey reported unsatisfactory or very unsatisfactory environments related to acoustics for noise control (GAO, 1995a). In 2002, the American National Standards Institute (ANSI) issued voluntary standard S12.60, “Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools,” which calls for a maximum ambient noise level of 35 dB(A) and includes recommendations for the required sound isolation between classrooms and adjacent spaces or the outdoors (ANSI, 2002). Many classrooms currently do not meet the recommendations of this standard, but at least one state, Connecticut, has already adopted the use of ANSI S12.60 for its schools. People’s ability to understand speech is influenced largely by the level of speech sounds relative to the level of ambient or background noise. Reverberant sound causes one word to smear into the next and can decrease the intelligibility of speech. Acoustical design involves designing to control sound to facilitate improvement in the perception of speech sounds. Controlling sound should focus primarily on reducing unwanted noise, and secondarily on controlling excessive reverberation. Good acoustical design can allow for more accurate verbal interaction and less repetition among teachers and students because spoken words are clearly understood, and as a consequence, it can facilitate learning. There is also evidence that good acoustical design may have a health benefit for teachers, by reducing the incidence of voice impairment. Excessive noise can also interfere with learning by affecting memory (Hygge, 2003) and acting as a distraction that impairs a student’s ability to pay attention. The ability to pay attention is most important when students are engaged in tasks that demand higher mental processes, such as learning new concepts or when teachers are verbally presenting new or complex information (Hartman, 1946). (See also Anderson, 2004, for a review of the effects of noise on children and classroom acoustics issues.)
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Review and Assessment of the Health and Productivity Benefits of Green Schools: An Interim Report Excessive background noise in a classroom can originate from outside the building (aircraft and traffic noise, lawnmowers and leaf blowing) or from within the building (heating, ventilation, air-conditioning, plumbing systems, noise from adjacent classrooms or hallways, gymnasiums or music rooms) or noise from the students themselves. However, it is important to note that the level of residual noise from the students is strongly related to the general level of ambient noise in the room. That is, student chatter will increase as the general level of ambient noise increases, an example of the Lombard effect (Junqua, 1996). Speech perception studies have investigated how interference from noise and reverberation influences the perception of syllables, words, or sentences in classrooms. The importance of ambient noise levels is mostly related to speech-to-noise ratios. Kindergarten and first and second grades are the primary years in which children learn to break down written words into their phonetic components and acquire the ability to read. This requires careful listening to develop the ability to discriminate among minor differences in words such as pet, pit, pot, put, and pat (Anderson, 2004). Such differences can be lost in a noisy environment, and hence younger children require higher signal-to-noise ratios corresponding to quieter conditions. The impacts of excessive noise vary according to the age of the students because the ability to focus on speech is a developmental skill that evolves with maturation of the brain and mastery of language. Because the auditory mechanism does not fully mature until age 13 to 15 years, young children … require better acoustical environments than do adult listeners to achieve equivalent word recognition scores. (Anderson, 2004, p. 119) For that reason, a student’s difficulty in understanding speech in noisy situations may not be recognized by teachers, building designers, or other adults. Said another way, adults cannot recognize the level of children’s difficulty by using their own ability to perceive speech under the same adverse listening conditions. Elliott et al. (1979) found that the ability to recognize sentences in noisy environments improves systematically with age for children ages 7, 9, 11, 13, 15, and 17 years. This has recently been shown in extensive studies in actual classrooms (Bradley and Sato, 2004). There are also studies suggesting that the negative effects of excessive reverberation are more acute for younger listeners (Nábĕlek and Robinson, 1982), but the requirements for children of various ages have not been determined. Although most standards (e.g., ANSI S12.60) recommend approximately a 0.6-s reverberation time, some studies have suggested that much shorter reverberation times would be better (Nábĕlek and Picket, 1974). However, some of these studies are flawed and their results cannot be relied upon. These experimental results are incomplete because they include only the negative effects of increased reverberation but not the positive benefits (i.e., increased speech levels). Further research is required to more precisely confirm optimum reverberation times for children of various ages. NOISE AND STUDENT ACHIEVEMENT Since the 1970s, a number of studies have been conducted that compare the reading skills of students in schools exposed to transportation noise with the reading skills of students in schools in quieter areas. A study in the early 1970s looked at the performance of children in a New York school that was parallel to the tracks of an elevated train. During a 3-year
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Review and Assessment of the Health and Productivity Benefits of Green Schools: An Interim Report time period, a comparison of aggregate scores for students in grades two, four, and six was made between students on the noisy side and students on the nonnoisy side of the school. Students on the noisy side lagged behind in reading an average of 3 to 4 months compared with students on the quieter side. After the train tracks were treated to abate the noise, reading levels of children on what had been the noisier side of the building improved (Bronzaft and McCarthy, 1975; Bronzaft, 1981). A 1982 study of students in New York schools under and not under flight paths matched the students for socioeconomic status, race, gender, hearing loss, mother’s education level, and English as a second language (Green et al., 1982). The study found that high levels of environmental noise were inversely related to reading ability in elementary school children. A later study of students in New York matched students/schools for low socioeconomic status, student absentee rates, and teacher experience and then analyzed reading achievement test scores for grades two through six (Evans and Maxwell, 1997). The analysis found that a higher percentage of students in noisy schools were reading 1 to 2 years below their grade level. A study of schools near Munich Airport looked at the cognitive effects on children when the airport was in operation and then after the airport was moved to a new location. The study found impaired reading comprehension in third and fourth grade children in schools located near the airport. Children from noisy communities had significantly more errors on a standardized reading test when compared with students from quieter communities. Further, reading comprehension deteriorated in children in schools near the new airport (Hygge et al., 1996). A 1997 study comparing students from two schools near Heathrow Airport found a significant association between noise and reading comprehension that could not be accounted for by annoyance, social class, or other factors (Haines et al., 2001a,b). In one of the most comprehensive and rigorous studies to date, Stansfeld et al. (2005) conducted a cross-national, cross-sectional study to assess the effect of exposure to aircraft and road traffic noise on cognitive performance (reading comprehension) and health in children. The study assessed 2,844 children ages 9 to 10 in 89 schools located in the United Kingdom, Spain, and the Netherlands in 2002. Schools in all three countries were selected on the basis of increasing levels of exposure to aircraft and traffic noise. The selected schools were matched by students’ socioeconomic status, the primary language spoken at home, and other factors. External noise was measured, and reading comprehension was assessed using standardized and normalized tests routinely used in each country. Tests were also conducted to measure students’ recognition and recall (episodic memory), sustained attention, working memory, and prospective memory. Socioeconomic characteristics were assessed as potential confounding factors, and pilot studies were conducted to assess the feasibility, reliability, validity, and psychometric properties of the cognitive tests to be used. The pooled data gathered through the study were analyzed statistically using multilevel modeling, and the final results were adjusted for a number of factors including children’s long-standing illness, parental support for schoolwork, and home ownership. The authors noted that the study’s limitations were that it was cross-sectional, not longitudinal; was restricted to 9- and 10-year olds; did not focus on noise exposure in the students’ homes; and used different noise assessment techniques in the three countries. This study found that chronic exposure to aircraft noise “was associated with a significant impairment in reading comprehension…. [A] 5-decibel difference in aircraft
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Review and Assessment of the Health and Productivity Benefits of Green Schools: An Interim Report noise was equivalent to a 2-month reading delay in the United Kingdom and a 1-month delay in the Netherlands” (Stansfeld et al., 2005, p. 1946). This outcome was consistent with findings from other studies on the effects of aircraft noise on reading comprehension. Because it was a cross-sectional study, the effect of long-term noise exposure to aircraft noise could not be measured. Socioeconomic status was not found to be a factor in the size of the effect, a finding that differs from findings of other studies. The study also found that aircraft noise was “not associated with impairment in working memory, prospective memory, or sustained attention” (Stansfeld et al., 2005, p. 1946). Stansfeld et al. (2005) also looked at the effect of traffic noise on the children. The authors noted linear exposure-effect associations between exposure to road traffic noise and increased functioning of episodic memory, in regard to information and conceptual recall (Stansfeld et al., 2005, p. 1947). NOISE AND TEACHERS’ HEALTH Teachers who work in noisy classrooms must constantly raise their voices to be heard over various other sounds. Over time, this can lead to vocal fatigue and other voice problems. One study published in 1993 found that four out of five teachers who participated in the study indicated some problems with vocal fatigue (Gotaas and Starr, 1993). A 1995 study of populations in the U.S. workforce that rely on voice as a primary tool of their trade found that teachers constitute more than 20 percent of the voice-clinic load or five times the number expected by their prevalence in this segment of the workforce (Titze et al., 1996). FINDINGS AND RECOMMENDATION Finding 5: In regard to noise, acoustics, student learning, and teacher health, the committee has found the following: Sufficient evidence exists to conclude that there is an association between decreased noise levels in schools and improvement in student achievement. Although there is strong evidence that reduced noise levels are most important for younger children because they are still developing speech discrimination, additional research is required to more precisely define possible needs for control of reverberant sound for younger children. Some available evidence indicates that teacher health, in regard to voice impairment, may be adversely affected by noisier environments, although the magnitude of the effect cannot currently be estimated as a function of exposure to noise. Recommendation 4: To facilitate student learning, guidelines for green schools should include requirements to meet American National Standards Institute (ANSI) Standard S12.60, “Acoustical Performance Criteria, Design Requirements, and Guidelines for Schools.”
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