title: Effects of Nonlinear Frequency Compression on ACC Amplitude and Listener Performance.
abstract: OBJECTIVE
  Nonlinear frequency compression is a signal processing technique used to increase the audibility of high-frequency speech sounds for hearing aid users with sloping, high-frequency hearing loss. However, excessive compression ratios may reduce spectral contrast between sounds and negatively impact speech perception. This is of particular concern in infants and young children who may not be able to provide feedback about frequency compression settings. This study explores the use of an objective cortical auditory evoked potential that is sensitive to changes in spectral contrast, the acoustic change complex (ACC), in the verification of frequency compression parameters.
  
  
  METHODS
  ACC responses were recorded from adult listeners to a spectral ripple contrast stimulus that was processed using a range of frequency compression ratios (1:1, 1.5:1, 2:1, 3:1, and 4:1). Vowel identification, consonant identification, speech recognition in noise (QuickSIN), and behavioral ripple discrimination thresholds were also measured under identical frequency compression conditions. In Experiment 1, these tasks were completed in 10 adults with normal hearing. In Experiment 2, these same tasks were repeated in 10 adults with sloping, high-frequency hearing loss.
  
  
  RESULTS
  Repeated measures analysis of variance was completed for each task and each group with frequency compression ratio as the within-subjects factor. Increasing the compression ratio did not affect vowel identification for the normal hearing group but did cause a significant decrease in vowel identification for the hearing-impaired listeners. Increases in compression ratio were associated with significant decrements in ACC amplitudes, consonant identification scores, ripple discrimination thresholds, and speech perception in noise scores for both groups of listeners.
  
  
  CONCLUSIONS
  The ACC response, like speech and nonspeech perceptual measures, is sensitive to frequency compression ratio. Additional study is needed to establish optimal stimulus and recording parameters for the clinical application of this measure in the verification of hearing aid frequency compression settings.
authors.affiliation: 1Boys Town National Research Hospital, Omaha, NE; 2Department of Communication Sciences and Disorders, University of Iowa, Iowa City, IA; and 3Department of Otolaryngology, University of Iowa Hospitals and Clinics, Iowa City, IA.
authors.forename: Benjamin James
authors.initials: BJ
authors.lastname: Kirby
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Brown
mesh_terms: D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D044962:Data Compression; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory; D005260:Female; D006310:Hearing Aids; D006316:Hearing Loss, High-Frequency / Q000534:rehabilitation*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017711:Nonlinear Dynamics; D013067:Speech Perception; D055815:Young Adult