J Am Acad Audiol 2018; 29(07): 568-586
DOI: 10.3766/jaaa.16074
Thieme Medical Publishers 333 Seventh Avenue, New York, NY 10001, USA.

Impact of Personal Frequency Modulation Systems on Behavioral and Cortical Auditory Evoked Potential Measures of Auditory Processing and Classroom Listening in School-Aged Children with Auditory Processing Disorder

Jennifer L. Smart
*   Department of Audiology, Speech-Language Pathology and Deaf Studies, Towson University, Towson, MD
Suzanne C. Purdy
†   Speech Science, Department of Psychology, The University of Auckland, Auckland, New Zealand
Andrea S. Kelly
†   Speech Science, Department of Psychology, The University of Auckland, Auckland, New Zealand
› Author Affiliations
Further Information

Publication History

Publication Date:
29 May 2020 (online)



Personal frequency modulation (FM) systems are often recommended for children diagnosed with auditory processing disorder (APD) to improve their listening environment in the classroom. Further evidence is required to support the continuation of this recommendation.


To determine whether personal FM systems enhance auditory processing abilities and classroom listening in school-aged children with APD.

Research Design:

Two baseline assessments separated by eight weeks were undertaken before a 20-week trial of bilateral personal FM in the classroom. The third assessment was completed immediately after the FM trial. A range of behavioral measures and speech-evoked cortical auditory evoked potentials (CAEPs) in quiet and in noise were used to assess auditory processing and FM outcomes. Perceived listening ability was assessed using the Listening Inventory for Education–United Kingdom version (LIFE-UK) questionnaire student and teacher versions, and a modified version of the LIFE-UK questionnaire for parents.

Study Sample:

Twenty-eight children aged 7–12 years were included in this intervention study. Of the 28 children, there were 22 males and six females.

Data Collection and Analysis:

APD Tests scores and CAEP peak latencies and amplitudes were analyzed using repeated measures analysis of variance to determine whether results changed over the two baseline assessments and after the FM trial. The LIFE-UK was administered immediately before and after the FM trial. Student responses were analyzed using paired t-tests. Results are described for the (different) pre- and post-trial teacher versions of the LIFE-UK.


Speech in spatial noise (SSN) scores improved by 13% on average when participants wore the FM system in the laboratory. Noise resulted in increased P1 and N2 latencies and reduced N2 amplitudes. The impact of noise on CAEP latencies and amplitudes was significantly reduced when participants wore the FM. Participants’ LIFE-UK responses indicated significant improvements in their perceived listening after the FM trial. Most teachers (74%) reported the trial as successful, based on LIFE-UK ratings. Teachers’ and parents’ questionnaire ratings indicated good agreement regarding the outcomes of the FM trial. There was no change in compressed and reverberated words, masking level difference, and sustained attention scores across visits. Gaps in noise, dichotic digits test, and SSN (hard words) showed practice effects. Frequency pattern test and SSN easy word scores did not change between baseline visits, and improved significantly after the FM trial. CAEP N2 latencies and amplitudes changed significantly across visits; changes occurred across the baseline and the FM trial period.


Personal FM systems produce immediate speech perception benefits and enhancement of speech-evoked cortical responses in noise in the laboratory. The 20-week FM trial produced significant improvements in behavioral measures of auditory processing and participants’ perceptions of their listening skills. Teacher and parent questionnaires also indicated positive outcomes.

Portions of this research study were presented orally at Audiology Now! The American Academy of Audiology, Charlotte, NC, April 2–5, 2008, and the XXI Biennial Symposium of the International Evoked Response Audiometry Study Group, Rio de Janeiro, Brazil, June 8–11, 2009.