title: Unilateral cochlear implant use promotes normal-like loudness perception in adolescents with childhood deafness.
abstract: OBJECTIVE
  Behavioral measures of cochlear implant (CI) device stimulation levels can be difficult to obtain in individuals with limited or no hearing experience. Loudness measures are particularly challenging. It would therefore be useful to have a battery of objective and behavioral measures to determine CI stimulation levels in listeners with childhood deafness. In the present study, the authors characterized loudness growth in 20 adolescents: 8 with normal hearing and 12 CI participants with pre/perilingual bilateral sensorineural hearing loss. They asked (1) do adolescent CI users with childhood deafness experience similar increases in loudness as their peers with normal hearing? and (2) can loudness be predicted by objective measures of auditory activity? The authors hypothesized that loudness perception would be significantly different between CI and normal-hearing groups and that it would correlate with objective measures.
  
  
  METHODS
  CI users were recruited from the Cochlear Implant Program at The Hospital for Sick Children and all had used unilateral Nucleus CIs for at least 2 years. The dynamic range for each participant was defined as the difference between the behavioral threshold and the electrically evoked stapedius reflex (ESR) threshold. Loudness growth was assessed within this range behaviorally on a continuous visual scale and objectively with physiological measures. Auditory brainstem responses (ABRs) and ESRs were recorded in both groups and electrically evoked compound action potentials (ECAPs) of the auditory nerve were recorded in addition in CI listeners. The regression line slopes of ECAP and ABR amplitude growth functions were then calculated and compared with behavioral loudness growth slopes in the upper portion (40-100%) and lower portion (0-40%) of the dynamic range. Electrical pulse stimuli (in CI users) and acoustic clicks (in normal-hearing participants) were presented within each participant's dynamic range.
  
  
  RESULTS
  The mean dynamic range in CI listeners was more variable than in normal-hearing individuals. Despite this difference, loudness at the ESR threshold was not significantly different in CI adolescents from their normal-hearing peers, and CI users exhibited normal-like loudness growth. There was a significantly positive correlation between ECAP amplitude growth and loudness growth in CI users in the upper portion of the dynamic range, while ABR wave V amplitude growth was not related to loudness growth in either group.
  
  
  CONCLUSIONS
  We confirmed that the ESR threshold is a good measure of comfortably loud levels in adolescents with cochlear implants and their normal-hearing peers. Adolescents using CIs show normal-like rates of loudness growth on average, despite having highly variable dynamic ranges of hearing. Individual rates of loudness growth in the upper dynamic range in CI users can be predicted by the rate of amplitude growth of the ECAP. Thus, the rate of neural recruitment with increasing CI current is important for loudness perception in pre/perilingually deaf listeners and should be considered when programming their CIs.
authors: 1Institute of Medical Science, University of Toronto, Toronto, Ontario, Canada; 2Department of Otolaryngology, The Hospital for Sick Children, Toronto, Ontario, Canada; 3Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada; 4Department of Otolaryngology-Head and Neck Surgery, University of Toronto, Toronto, Ontario, Canada; and 5Department of Communication Disorders, The Hospital for Sick Children, Toronto, Ontario, Canada.
authors: Morrison Mansour
authors: MM
authors: Steel
authors: Parvaneh
authors: P
authors: Abbasalipour
authors: Claire A M
authors: CA
authors: Salloum
authors: David
authors: D
authors: Hasek
authors: Blake C
authors: BC
authors: Papsin
authors: Karen A
authors: KA
authors: Gordon
mesh_terms: D000293:Adolescent; D016022:Case-Control Studies; D002648:Child; D019929:Cochlear Implantation / Q000379:methods*; D003638:Deafness / Q000534:rehabilitation*; D016057:Evoked Potentials, Auditory, Brain Stem; D005260:Female; D006801:Humans; D008144:Loudness Perception / Q000502:physiology*; D008297:Male; D012018:Reflex / Q000502:physiology*; D013198:Stapedius / Q000502:physiology*; D055815:Young Adult