Mridula Sharma 1,2
1Department of Linguistics, Australian Hearing Hub, 16 University Avenue, Macquarie University New South Wales 2109, Australia
2The HEARing CRC, 550 Swanston Street, Audiology, Hearing and Speech Sciences, The University of Melbourne, Victoria 3010, Australia
Communication in quiet is a rare occurrence. Noise is ubiquitous, causing interference in classroom, restaurants, malls, and other recreational places. Noise is widely defined as irrelevant/unwanted sound and may include echo/reverberation as well as the original noise source. Noise acts as a simultaneous “energetic” masker whereby less intense signals are obscured such as pauses within sentences and unstressed sounds within words, so that salient cues necessary for understanding the speech signal are lost in the presence of noise. Noise that is meaningful, such as competing speech, can also cause “informational” masking as the noise interferes with the content of the message. Communication and learning is hard for most in presence of noise but it is especially difficult for children with hearing loss and with normal hearing but with deficits of language, reading or auditory processing.
Classroom noise: Even without children each classroom has some inherent noise with contributions from road, playground, rail/air traffic, and building noises such as ventilation systems. There can be other sources of noise such as children walking and talking in the halls, class bells, and/or noise from adjacent rooms . In unoccupied classrooms, multiple studies have recommended that noise levels should be below 35dBA, reverberation time should be 0.6-0.7s and the SNR should be about 16dB [2, 3]. For effective classroom learning in occupied rooms, the SNR of the teacher’s voice should be +15dB for typically developing children and the maximum reverberation time 0.4s . The ANSI S12.60-2002 standard specifies that maximum reverberation times for kindergarten-year 12 classrooms should be 0.6s for small classrooms (total volume < 283m3) and 0.7s for moderate size classrooms (total volume 283-566m3). However, a more realistic value for most classrooms is reportedly between 0.4-1.2s [5, 6]. Although there is some variation in the recommendations, the acoustics of real classrooms are frequently worse than any recommended values. Consequently, one often wonders with such consistent high levels of noise, how the children with auditory processing disorders listen to learn.
Today’s classrooms: Open classrooms were popular in the 1960s and 1970s. They were perceived as less authoritarian, through their introduction of a more child-centric approach, and the creation of a “home-like” atmosphere  and were deemed necessary in the UK due to post war economic constraints . The plan was abandoned after the 1970s due to excessive noise and visual distractions present in the open classrooms . In recent times, however, the concept of open-plan classrooms has been resurrected. In Australia, new classrooms are being designed as open-plan while old classrooms are being retrofitted . In these new open-plan classrooms (e.g. in Sydney), it has been reported that the number of children could be up to 150-200 compared to 20-30 in traditional closed rooms . The newer classrooms are referred to as “modern”, “innovative, “new generation”, or “open learning environments” .
Children in the classroom: Children spend most of their waking hours (45-60%) at school, engaged in learning activities that depend on listening and comprehending. Children need to continually segregate the relevant signal from other irrelevant sounds to listen and learn . While there are multiple sources of noise and distraction, the biggest source of noise in a classroom is other children speaking . There are only a few studies that have compared the levels of noise in open and regular classrooms . In a 2010 review paper, results from four studies were discussed ; more recently, a Sydney-based study was reported . The outcomes of these studies are variable. One study reported comparable noise levels in the two styles of classrooms but only when the number of children in the rooms was similar. The open classrooms had only two groups of 30 children and were reported to have less reverberation due to their open spaces and fewer walls . The noise levels reported by Barnett et al. and in subsequent studies  show considerable fluctuation in levels in open classrooms, which both teachers and students found to be more annoying than a consistent noise with similar average noise levels. A different result was reported by Mealings, Buchholz, et al. for classrooms in Sydney, however. They found higher noise levels in open classrooms, and there were close to 100 children in the space.
Picard and Bradley (2001) reviewed 17 independent studies showing average noise levels for different age groups and reported that younger children, particularly those in day care and kindergarten, tend to have noisier classrooms due to the relatively higher levels of classroom activity. Unfortunately, children in kindergarten – grade 1 have significantly more difficulty understanding speech in intermediate levels of noise (-6dBSNR, which was not uncommon in the classroom environments sampled in their study) compared to those in grades 2-3 . This alone puts typical children in younger age groups at high-risk for poor long-term educational outcomes. Children between kindergarten – grade 3, in particular, require advantageous acoustical listening conditions to learn in the classroom. While this is true for the typical children, one can only assume that children with auditory processing disorders would need the same or better listening environment .
Interestingly, occupied rooms in universities have noise levels of about 44-55 dBA (see Jamieson et al., 2004), which is much softer than any classroom for school-aged children. This is despite the fact that the speech levels required by adults for good speech intelligibility are much lower. Previous research has shown that typical 3-year old children require at least 20dB higher stimulus levels than that needed by adults to understand simple one word utterances . In general to understand speech, young children require higher signal to noise ratios than adults and yet their school classrooms are noisier .
Does noise matter?
Poor classroom acoustics can negatively affect children’s learning within the primary school environment , particularly for children with hearing loss, auditory processing and language learning difficulty, developmental disabilities, or with English as a second language [19-22]. Noise arising from internal or external sources can affect both verbal and non-verbal task performance, including speech perception, reading, and concentration .
It has been suggested that children need to place more effort to learn in adverse acoustic conditions as presence of noise results in reduced availability of resources for further processing of information . The effect of noise (including reverberation) is not limited to children, teacher fatigue and susceptibility to voice disorders are other known concerns . Voice disorders are a known occupational hazard for teachers. Data from the US indicates teachers are one of the major occupational groups to seek treatment from voice clinics . Clinic visits underestimate the full extent of the problem. For example, a recent survey found only 14.3% of teachers had sought treatment for voice disorders, but 58% had experienced voice disorders . Voice disorders also contribute significantly to teachers’ missed days of work .
What is a solution?
While there are modifications which can be made to improve the classroom acoustic environment, these may be difficult to implement. Classroom amplification systems aim to overcome some of the acoustical challenges in classrooms by enhancing the signal-to-noise ratio of the teacher’s voice. Classroom amplification systems have been shown to improve listening behaviours by increasing attention, increasing word and sentence recognition  and minimising disruptive/maladaptive behaviours in all children not just children with auditory processing disorders . In a large scale New Zealand study, specific benefits to listening comprehension and also incidental listening comprehension were observed as a result of sound amplification . The ability to ‘over hear’ teachers providing instructions to students meant that other students picked up on these instructions and less repetition was required by the teacher.
Figure 1. The auditory processing pathway. As detection is the fundamental requirement, it is necessary to ensure that adequate detection of sound occurs . Assistive devices are designed to provide adequate sound detection or perception and the benefits are evaluated at recognition/comprehension level.
Soundfield systems are small, wireless public-address systems. The teacher wears a discrete lapel microphone and the speakers are placed strategically in the classroom to create a uniform speech level within the room. The placement of the microphone near the teacher’s mouth provides a favourable signal-to-noise ratio . Personal FM (frequency-modulated) or DM (digitally-modulated) systems or remote microphones are designed for individuals rather than all students in the class. These devices are referred to collectively as remote microphone (RM) hearing systems. These involve the child having either a loudspeaker on the desk or at ear level while the teacher wears a wireless, lapel (usually) microphone and the loudspeaker delivers the signal at higher signal-to-noise ratio about 10-20dB [6, 32]. The advantage of placing an RM wireless microphone near the speaker’s mouth is that the effects of reverberation and noise are minimised.
The two types of systems have been investigated and provide similar advantages of high signal-to-noise ratios and are cheap, effective solutions . Sound field systems are highly dependent on the acoustic characteristics of the room and require short reverberation times for optimal use, however . Placement of loudspeakers, volume control, and the directional pattern of the loudspeakers are important factors that influence sound quality . Thus determination of benefit from sound field systems needs to include acoustic characteristics of the rooms .
Current evidence of benefits from improving the acoustic signal
An extensive three-year study in Florida involving 1,139 students examined the impact of soundfield system installations in kindergarten, Grade 1, and Grade 2 classrooms . Teacher rating showed that students in amplified classrooms, over a period of 12 weeks, demonstrated significantly greater improvement in listening than students in unamplified classrooms.
In another study in Australia, teachers and students from 12 classrooms were interviewed  when classroom amplification systems were turned on and off. Overall, the teachers reported that the children were more attentive, communicative and showed a significant improvement in behaviour when the sound field systems were in use. Further, students improved on the three academic skills of numeracy, literacy and writing. Students also observed that they were happier when the microphones of the sound fields were used by the teachers as they could hear well. The benefits of soundfield systems have also been shown for listening and academic tasks (including overall listening comprehension, phonologic skills, literacy, reading vocabulary and comprehension and arithmetic skills) for children from diverse socio-economic backgrounds and those disadvantaged by a history of middle ear infections .
With regards FM or RM trials in children with APD, there are a few controlled studies that have shown benefits. These studies are interesting as despite having specific spectral and/or temporal processing deficits and not specifically linked to speech in noise, children showed improvements in listening with FM. The question then remains, is the improvement due to reduced listening effort and is the RM system a compensatory strategy rather than a specific solution? In a study, 50 children diagnosed with APD were randomised into 5 groups where interventions including FM systems were trialled over 6 weeks. The results showed that all children benefitted from wearing FM systems when compared to the control group . In another study, ten children with auditory processing disorders were given FM/RM systems for mostly classroom use for 5 months. The speech perception scores significantly improved only in children who trialled RM systems and not in the control group but the important result was that the improved perception scores were maintained even after the trial with RM systems had ceased .
In a more recent study, children with dyslexia were given FM/RM systems for 1 year. Objectively evaluated brainstem responses showed distinct changes in children with FM compared with those in the control group. The study also showed reading and phonological awareness improvements . This study has a few advantages over the previous studies in that the FM use was over a year, objective measures were included as well as a control group from the same school. The study emphasises the improved acoustic perception may be the key to improvement in reading skills.
Reading benefits were measured in first grade children in another study over a 5-month period with classroom amplification. The reading benefits with amplification were significant for children with reading problems and additional learning needs . The teachers also observed that children were paying more attention in the amplified classroom. However, this study was limited by a lack of control group or control classroom environment or baseline measures to determine the significance of the improvement. In a New Zealand study, the effects of personal FM systems were measured over a six-week period in school-aged children with reading difficulties and showed significantly improved teacher and children’s classroom listening ratings  compared to a control group. However, reading scores did not improve.
There are other studies evaluating the benefits of sound field systems and/or personal RM systems, particularly in school settings. In several studies, there is a lack of appropriate control groups , and/or a stable or consistent baseline is not available to determine whether the observed effects are significant . In addition, there is considerable variability in the duration over which the benefit of assistive devices was evaluated and there is no consensus about what an ideal timeframe is to observe such benefits . Nonetheless, it seems reasonable that a longer duration of experience is needed for more general benefits. Finally, an important aspect is that few studies have evaluated the benefits of assistive devices across a large number of classrooms and involving children with no specific learning needs and on general learning skills. At the same time, more studies need to be undertaken for children with auditory processing disorders with comprehensive assessments and regular observations or assessments to map the impact of trialling an RM to better understand why higher signal to noise ratio translates to improved listening.
Children in the classroom often face poor acoustic environments, specifically poor signal-to-noise ratios and high levels of acoustic reverberation, which may limit their ability to learn new skills and knowledge. Assistive devices, such as sound field systems and personal RM amplification systems, aim to improve signals and the benefit of improved signal level has been shown for general improved listening, less effort but the benefit for reading or academic improvement needs to be demonstrated using more randomised controlled trials.
Academic background includes MSc in Speech Language Pathology and Audiology (India, 2001), PhD in Audiology (Sydney, 2005) and Postdoctoral/Research Fellow in Speech Science, Auckland (2005-07). Since 2007, lecturer, Sn Lecture and now Associate Professor in Audiology (2015-current), Faculty of Human Science, Macquarie University, Sydney, Australia. My research interests include auditory processing skills across life span; auditory training and plasticity; electrophysiology specially at cortical level.
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