Frequency Modulation System and speech perception in the classroom: a systematic literature review

Purpose: This review aimed at presenting the benefits regarding the speech perception in noise shown by children who wear hearing aid devices and/or cochlear implants with the Frequency Modulation (FM) System at school. Research strategy: A bibliographic survey was conducted in an electronic database with standardized search until the year 2012, and a manual search was performed by using specific keywords. Selection criteria: For the selection and evaluation of the scientific studies chosen in the search, criteria were established covering the following aspects: type of study, participants, adopted intervention, and evaluation of results. Data analysis: The FM system was verified to improve speech perception and speech threshold in noise in all studies. Results: Regarding the performance as to type, the best results were obtained when children used the personal FM system, followed by the table and the sound field systems. Conclusion: After extensive review of national and international literature, it was concluded that the studies indicate the need for further research concerning mainly the impact of the FM system on the school performance of children who have sensory devices coupled to the FM system. Findings in the literature with relation to the publications focused on speech perception in noise did not relate educational and auditory aspects. DOI: 10.1590/2317-1782/20152014103 293 Sistema de FM e percepção da fala em sala de aula CoDAS 2015;27(3):292-300 INTRODUÇÃO Recentes avanços no tratamento de crianças com deficiência auditiva tem possibilitado o acesso à percepção auditiva dos sons da fala para indivíduos com deficiência auditiva neurossensorial, proporcionando valiosos benefícios para a comunicação e qualidade de vida desses sujeitos. Esses avanços são vistos, em sua maioria, nos dispositivos sensoriais aplicados à deficiência auditiva. Entre eles, destacam-se o aparelho de amplificação sonora individual (AASI), o implante coclear (IC) e os sistemas de Frequência Modulada (FM). Com o diagnóstico precoce e com a efetivação da Política Nacional de Atenção à Saúde Auditiva, implantada em setembro de 2004, um grande contingente de crianças com deficiência auditiva passou a ter acesso gratuito aos dispositivos sensoriais como o AASI e o IC, podendo chegar à escola usufruindo desses dispositivos, o que favorece seu aprendizado no contexto escolar. Vivencia-se atualmente um novo momento histórico com a implantação do programa “Viver sem Limites”, que está organizado em quatro eixos: acesso à educação, inclusão social, atenção à saúde e acessibilidade da pessoa com deficiência, o qual prevê a ampliação do direito à educação, a ampliação das ações de prevenção aos deficientes e a implantação de Centros de Referência para oferecer apoio às pessoas com deficiência em situação de risco e disponibilizar ações conjuntas entre União, estado e município. Segundo a Política Nacional de Educação Especial, a integração educativa-escolar refere-se ao processo de educar — ensinar, no mesmo grupo, a criança tanto com como sem a deficiência, durante uma parte ou na totalidade do tempo de permanência na escola. No caso da criança com deficiência, a acessibilidade à educação deve ser assegurada. O Sistema de FM é considerado uma alternativa dentre os recursos de apoio utilizados por estudantes com deficiência auditiva, visando auxiliar a integração educativa-escolar. Para alguns autores, o Sistema FM é a mais importante e essencial ferramenta educacional já desenvolvida para os indivíduos com deficiência auditiva, pois, independentemente do tipo (pessoal, autocontido e campo livre), é o meio mais efetivo para favorecer a relação sinal/ruído, principalmente em ambiente educacional. O benefício em relação à percepção de fala em ambiente escolar da criança com deficiência auditiva usuária de dispositivos sensoriais (AASI e IC) acoplados ao Sistema FM é um fator importante no âmbito escolar e em pesquisas na área da Audiologia. O panorama atual da saúde auditiva nos serviços públicos propicia melhores condições para o desenvolvimento da função auditiva e da linguagem para a criança diagnosticada precocemente com deficiência auditiva e, concomitantemente, mais acesso à intervenção especializada. Porém, sabe-se que essa criança, ainda que apresente bom desempenho funcional em audição e em linguagem oral, no decorrer do seu desenvolvimento e ao chegar à fase escolar, se depara com vários obstáculos, dentre os quais se destacam: o ruído na sala de aula, a distância entre o professor e a criança (falante-ouvinte) e a reverberação na sala de aula. Essas condições adversas se devem, na maioria das vezes, ao grande número de alunos em uma mesma sala e salas de aulas com pouco ou nenhum tratamento acústico, agravado pelo fato de que professores em geral recebem pouca ou nenhuma orientação quanto à deficiência auditiva. Estima-se que orientações sobre o manuseio e as condições necessárias para a valorização do uso dos dispositivos sensoriais também sejam escassas. Essas condições adversas fazem com que a criança tenha dificuldade em adquirir os conteúdos acadêmicos e, em casos mais graves, o desempenho acadêmico fica totalmente prejudicado. Nesse sentido, o Sistema de FM é um dispositivo eletrônico utilizado como acessibilidade pelas pessoas com deficiência auditiva, para uso fundamentalmente no ambiente acadêmico. Ele possibilita que a criança com deficiência auditiva usuária de dispositivos sensoriais perceba a voz do professor em sala de aula, independentemente da distância e do ruído comumente gerado em sala de aula. Por esse motivo, é considerado um instrumento de acessibilidade assistiva que faz parte do tratamento das deficiências auditivas, sendo um recurso utilizado na escola, independentemente da idade, contudo, é potencialmente voltado para crianças. No Brasil, os dispositivos sensoriais (AASI e IC) já são disponibilizados pelo Sistema Único de Saúde (SUS) e o uso do Sistema de FM foi um importante passo na acessibilidade acadêmica das crianças com deficiência auditiva desde a sua inclusão pela Portaria no 1.274, de 25 de junho de 2013, na tabela de Procedimentos, Medicamentos, Órteses, Próteses e Materiais Especiais do SUS.

was verified to improve speech perception and speech threshold in noise in all studies.Results: Regarding the performance as to type, the best results were obtained when children used the personal FM system, followed by the table and the sound field systems.Conclusion: After extensive review of national and international literature, it was concluded that the studies indicate the need for further research concerning mainly the impact of the FM system on the school performance of children who have sensory devices coupled to the FM system.Findings in the literature with relation to the publications focused on speech perception in noise did not relate educational and auditory aspects.

INTRODUCTION
Recent progress in the treatment of children with hearing impairment has enabled the access to the auditory perception of speech sounds for individuals with sensorineural hearing loss, thus providing valuable benefits for communication and quality of life of these people.
Such progress can mostly be seen in sensory devices applied to hearing impairment.Among them, hearing aid devices and cochlear implant (CI) stand out, as well as the Frequency Modulation (FM) systems.
With early diagnosis and the activation of the National Policy of Hearing Health Care (1) , implemented in September 2004, many children with hearing impairment gained free access to sensory devices such as the hearing aids and the CI; so, they could go to school and use these devices, which favors the learning process in the school context (2) .Currently, we are living in a new historical moment, with the implementation of the program "Viver sem Limites" (3) , which is organized in four principles: access to education, social inclusion, health care, and accessibility of people with disabilities in a vulnerable situation, as well as to promote initiatives with the Union, state, and city.According to the National Policy on Special Education (4) , the integration between education and school refers to the process of educating -teaching the child both with and without impairment, in the same group, part or full time at school.
When the child has a disability, it is important to ensure access to education.The FM system is seen as an alternative among all support resources used by students with hearing impairment, aiming at assisting the integration between education and school.For some authors, the FM system is the most important and essential educational tool that has ever been developed for people with hearing impairment; regardless of type (personal, self-contained, and free-field), it is the most effective means that favors signal-to-noise ratio, especially in an education environment (5)(6)(7) .
The benefit regarding speech perception in the school environment of children with hearing impairment wearing sensory devices (hearing aid and CI) together with the FM system is important in school and in studies of the Audiology field.
The current hearing health reality in public services provides better conditions for the development of the auditory function and language among children who received an early diagnosis of hearing impairment; therefore, they have more access to specialized treatment.However, even if these children show good functional performance in terms of hearing and oral language, during their development and when attending school they are faced with many obstacles, such as noise in the classroom, distance between the teacher and the child (speaker-listener), and reverberation in the classroom.These adverse conditions are mostly owed to the large number of students in the same classroom and classrooms with little or no acoustic treatment; besides, teachers in general have little or no prior knowledge regarding hearing impairment.It is estimated that guidance on management and necessary conditions to value the use of sensory devices is also scarce.
These adverse conditions lead to difficulties acquiring academic content, and, in more severe cases, the educational performance is totally harmed.
In this sense, the FM system is an electronic device used for the accessibility of people with hearing impairment, especially in the educational setting.It enables children with hearing impairment who wear sensory devices to perceive the voice of the teacher in the classroom, regardless of distance and noise that is usually generated in classrooms.Therefore, it is considered to be an assistive instrument that is part of the treatment for hearing impairment.This resource is used in school, regardless of age; however, it is potentially addressed to children.
In Brazil, sensory devices (hearing aid and CI) are already made available by the Unified Health System (SUS), and the use of the FM system was an important step toward the academic accessibility of children with hearing impairment since it was included in Recommendation n. 1,274, from June 25, 2013, in the table of Procedures, Medications, Orthoses, Prostheses and Special Materials of SUS (8) .

OBJECTIVE
As the essential principle of a study based on evidence, the question of this study's investigation was: does the child with hearing impairment who wears sensory devices (hearing aid and CI) have benefits regarding speech perception in school environment when using the FM system in the classroom?

RESEARCH STRATEGY
The search strategy used in the literature review was oriented by the combination of nine descriptors indexed in the Health Sciences Descriptors (DeCS), in Portuguese and in English; besides, keywords that are not considered to be health sciences descriptors were also used, however, they were used to help the bibliographic survey in the databases.All of the descriptors were used in groups with, at least, two keywords (Chart 1).
The scientific databases chosen for the study were the following: LILACS, MEDLINE, SciELO, Cochrane Library, PubMed, EMBASE, Institute for Scientific Information (ISI), and Science Direct.The manual search was also conducted, with the objective of finding bibliographic references when they were not present in the electronic bases.

SELECTION CRITERIA
This study considered publications produced from 2000 to 2012, and the last search was made in the electronic databases in October 2012.
The selection of articles followed the inclusion criteria based on the agreement of the limits of the topics and the objectives of this study.The adopted criteria were as follows: • participants: children wearing sensory devices (hearing aids and/or CI) who attended elementary school and high school; • intervention: studies were selected in case the intervention had been performed by standardized tests, aiming at assessing speech perception of the child wearing hearing aid devices and/or CI together with the FM system; • measured outcomes: according to categories of interestresults are expressed as percentage of hits in tests of perception and speech intelligibility, by the classification of scales related to the development of hearing skills and description of academic status; • period: published in the past 12 years (2000-2012); • language: studies in Portuguese, English, and Spanish; and • types of study: published in indexed journals with level of evidence 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B, and 4, according to the classification from the Oxford Centre for Evidence-Based Medicine (9) (Table 1).

DATA ANALYSIS
Studies were selected in three stages, and this process was oriented by the aforementioned criteria.First, three reviewers analyzed all of the studies identified by the combination of the descriptors in all of the proposed databases, by verifying the study title and selecting the ones that presented the predetermined eligibility criteria.
In that stage, it was possible to conduct a manual search of the articles that were not in the electronic databases (first Chart 1. Searching strategies to consult the databases
The descriptive analysis of the selected publications was performed according to the objectives of the review.

RESULTS
In total, 2,241 papers were identified in all of the electronic databases and in manual searches (Table 2).When these texts were preselected, based on the titles and the abstracts of all of the studies located in the electronic search, 2,233 were excluded; therefore, eight papers were fully read (Table 3).
In Figure 1, it is possible to see a summary of the survey conducted in the electronic databases and in the manual search.
Finally, eight papers met the inclusion criteria.From the articles included in the review, seven studies were classified as being cross-sectional, 2B level of evidence, and one was characterized as a systematic review, classified as level 2A, according to the Oxford Centre for Evidence-Based Medicine classification (9) (Table 1).
The systematic review was described in Chart 2 as to the name of authors, title, name of the journal, year of publication, objective of the study, study method and participants, levels of scientific evidence in each study, results, and conclusion.

2B
Significant benefit has been observed with FM for the conditions of S/N 0 and 3 dB.There was interaction between the age of the child and the benefit of FM: older children benefitted more from it.Younger children had varied results.A small 3 dB increase in the level of noise had a negative effect on speech perception, and the use of an FM system helped to control these effects for most children The use of FM provided significant improvement for children in terms of speech perception in noise Iglehart (11) .

2B
Ideal acoustic room: the speech perception results with each model were: 40% hits without the FM system in free field; 50% hits with the FM system in free field close to the wall, and 45% hits with the desktop FM; Acoustically poor room: 10% hits without the FM system in free field, 23% hits with the FM system in free field close to the wall, and 38% hits with the desktop FM system; Both types of the FM system provided significant benefit for students with CI in relation to the nonuse of the device.This benefit was obtained in the two analyzed environments (acoustically poor and ideal); There was no significant difference in speech perception when using the desktop FM system and the free-field system close to the wall when in the ideal room.In the acoustically poor room, the desktop FM system presented more benefits The two amplification systems were beneficial to the speech perception of children wearing CI, regarding the nonuse of these devices both in an ideal and in a poor environment.In an ideal room, both systems were similar, and only for the poor environment, the desktop FM system was the most effective one in terms of speech perception due to the proximity of the microphone and the CI Anderson and Goldstein (12) .

2B
Participants presented better speech recognition with the three types of amplification system.In a room with noise and reverberation, eight participants aged between 9 and 12 years did not present differences in the results of the free-field FM system by infrared and without hearing aid devices.The benefit of speech perception was clear when the desktop FM system and the personal FM system were used.Participants preferred to use the desktop FM system and the personal FM system in a room with reverberation and noise According to the authors, children with hearing impairment need to wear the FM system in the classroom, which allows the access to verbal instruction Anderson et al. (13) .Only hearing aid: 87.3% hits; Infrared: 88% hits; Desktop FM system: 92.4% hits; Personal FM system: 92.6% hits.Group 3: Only hearing aid: 77.0% hits; Infrared: 70% hits; Desktop FM system: 87.6% hits; Personal FM system: 91.8% hits.Word recognition: 1) No significant differences were found with the infrared compared to the use of hearing aid devices and CI alone; 2) There was no difference between the benefits coming from desktop and the personal FM system; From the 28, 11 had higher score of speech perception with the free-field FM system when compared to the isolated use of hearing aid devices or CI.The personal FM system had the highest score among the 28 participants In a normally noisy and reverberating classroom, the isolated use of sensory devices (AASI or IC) is not sufficient, so another device is required (personal FM system).
Continue...The average of speech and noise thresholds without FM was 0 in the S/N ratio, while with the FM system thresholds of up to -15 were reached; the lowest values were up to -5 for the following condition: CI + hearing aid or CI with FM, IC + hearing aid or CI with FM, in which results were better; The average score was similar for both conditions and groups, only with CI and CI + hearing aid device or CI; There was no difference in the thresholds of the S/N ratio for monaural and binaural stimulation, nor regarding bilateral and bimodal stimulation; Speech perception in FM conditions was much better than the same conditions without the FM system in more than 20 dB.
The FM system enables improvements in the S/N ratios of up to 20 dB; Statistically significant differences were detected between the conditions with an FM system, and better when worn in both sides or in the first implanted side Schafer and Kleineck (15) .Improvements in speech recognition using cochlear implants and three types of FM Systems: a metaanalytic approach.

Brazil
To assess the speech perception of children with hearing impairment wearing hearing aid devices and FM system in situations of noise in free field and in the classroom Cross-sectional study; Thirteen children with hearing impairment aged between 7 and 17 years old; HINT was applied with the hearing aid device and with the FM System; The questionnaire Avaliação do Sistema FM, was answered by the children's teachers to perform an individual evaluation of the children's performance in different hearing situations only wearing the hearing aid device and with the hearing aid device and the FM system 2B There were differences for all of the situations with and without a FM system in the HINT.The same was true for the results of the questionnaire; without the FM, the score was always lower than with the FM, regardless of the condition The use of subjective methods, like the questionnaire, is essential to determine the efficacy of the indication of auxiliary devices for the person with hearing impairment.The effectiveness of the FM system can be observed by the "FM advantage" , which is the minimal mean difference of 10 dB found in the speech perception evaluations with and without FM in the different noise situations

SUMMARY OF FINDINGS
On the basis of the analysis of the studies, it was possible to identify the reasons for the exclusion of articles; they were not fully analyzed for being repeated, or for presenting nonrelated themes, for not including the studied age group, for being in another language, among others.Out of the eight studies that were selected for the systematic review, three included only the population wearing CI: studies number 1, 2, and 6.Study number 1 investigated speech perception in noise among children wearing CI together with the FM system, and study number 2 investigated speech perception, noise, and reverberation with a single FM system (free field) in two situations that were acoustically different in the school environment (ideal and poor acoustics).In study number 6, through a systematic review and a meta-analysis, the authors verified if the three types of FM system provide better speech recognition in noise than the CI alone.
The analysis of the selected articles showed that study number 3 investigated speech perception, noise, and reverberation only among children wearing hearing aid devices, by using three types of technology (infrared, desktop FM, and personal FM).
Two other articles analyzed both users of hearing aid devices and CI.Study number 4 investigated speech perception among users of CI and/or hearing aid devices exposed in acoustically poor and ideal rooms, using three types of technology from the FM system (infrared, desktop FM, and personal FM).Study number 5 assessed the improvement in speech perception in noise provided by the three types of stimulation (bilateral, bimodal, and monaural) among users of hearing aid devices and/or CI together with the FM system.Studies number 7 and 8 only assessed children wearing hearing aid devices.
Regarding the evaluations performed in the studies in relation to speech perception in noise, it was possible to observe that six of them evaluated speech perception in noise (studies number 1, 3, 5, 6, 7, and 8) and two of them compared the speech perception in acoustically different environments: one that was acoustically poor and the other that was acoustically ideal (studies number 2 and 4).
From the articles that were fully analyzed, studies number 1, 5, 7, and 8 only assessed the performance with the personal FM system, and the other studies analyzed the following three types of FM: free field, desktop FM, and personal FM, comparing their results.
The analysis of the papers regarding the type and level of evidence of each of them showed that only study number 6 was considered to be a systematic review and a meta-analysis with 2A level of evidence, and the rest of the studies were considered to be cohort, with 2B level of evidence, according to the classification from the Oxford Centre for Evidence-Based Medicine (9) (Table 1).

CONCLUSION
It was possible to verify that the FM system improves speech perception and speech threshold in noise, and these results were found in all of the papers.Concerning the performance with relation to the type of FM system, the best results were obtained when children were wearing personal FM system, followed by desktop FM system and free field.
After a national and an international literature review, it was possible to conclude that studies indicate the need for analyses addressed to the impact of FM system on school performance of children who wear sensory devices together with the FM system because the findings in the eight papers analyzed in this study were addressed to the matter of speech perception in noise.

Table 1 .
Levels of scientific evidence according to the classification from the Oxford Centre for Evidence-Based Medicine 4Case reports (including cohort or case-control of lower quality) 5Opinion without critical evaluation or based on basic subjects (physiological study or study with animals)

Table 2 .
Number of articles identified in the databases and in the manual search

Table 3 .
Reasons to exclude the papers found in each analyzed database and number of papers selected for reading Exclusion criteria of the identified studies FM System and speech perception in the classroom

Chart 2 .
Summary file of the studies included in the systematic review