...children

...research

Research Staff:

Tracy Fitzgerald Ph.D., Postdoctoral Scientist

Leslie Visser-Dumont, M.A., Research Audiologist

Funding:  March of Dimes Birth Defects Foundation

The purpose of this grant was to study the relationship between underlying cochlear function as measured with DPOAE suppression tuning and: 1) sensorineural hearing loss 2) speech perception and 3) success with hearing aids in pediatric subjects. 

The first objective has been addressed in an experiment entitled: Ipsilateral DPOAE (2f1-f2) Suppression in Children with Sensorineural Hearing Loss (Abdala, C. & Fitzgerald, T. (2003). J. Acoust. Soc. Am., 114, (2) 919-931), Distortion product otoacoustic emission (DPOAE ) ipsilateral suppression has been applied to study cochlear function and maturation in laboratory animals and humans.  Although DPOAE suppression appears to be sensitive to regions of specialized cochlear function and to cochlear immaturity, it is not known whether it reflects permanent cochlear damage, i.e. sensorineural hearing loss (SNHL), in a reliable and systematic manner in humans. Eight school-aged children with mild-moderate SNHL and 20 normal-hearing children served as subjects in this study.  DPOAE (2f1-f2) suppression data were collected at four f2 frequencies (1500, 3000, 4000 and 6000 Hz) using moderate-level primary tones.  Features of the DPOAE iso-suppression tuning curves and rate of suppression growth were analyzed for both subject groups.  Results show that DPOAE suppression tuning curves from hearing-impaired subjects can be reliably recorded. DPOAE suppression tuning and suppression growth are abnormal in subjects with mild-moderate SNHL; however, there was not one single trend or pattern of abnormality that characterized all hearing-impaired subjects.  The most prominent patterns of abnormality included: broadened tuning, elevated tip, downward shift of tip frequency, and abnormally steep suppression growth.  Additionally, the unique patterns of atypical DPOAE suppression in subjects with similar audiograms may suggest different patterns of underlying sensory cell damage.  This speculation warrants further investigation.

The second objective in this project was to study the association between cochlear function and speech perception abilities,  as well as success with hearing aids.  This study has been completed and is currently being prepared for submission to Ear and Hearing.  Fifteen children with mild-moderate SNHL were included as subjects in this study.  They ranged in age from 7.5 to 17 years of age (mean = 12.33 years).  Seven of the subjects had present DPOAEs for at least one frequency between 1500 and 6000 Hz. Eight subjects had absent DPOAEs. In subjects with present DPOAEs,  suppression tuning curves and speech perception data were collected; In subjects with absent DPOAEs, only speech perception data were collected. Speech perception testing included two tests of in noise administered with and without hearing aids. The two speech perception tasks were:  (i) ability to identify vowel-consonant-vowel constructs in noise and (ii) the ability to hear and repeat complete sentences in noise.  Additionally, a hearing aid benefit questionnaire was filled out by each caregiver/parent.

Results show that speech perception for subjects with normal or sharper than typical DPOAE suppression tuning (n = 4) was comparable to perception measured in children with broader than normal suppression tuning (n = 3). This result could indicate: 1) DPOAE STCs are not sensitive indicators of residual speech perception abilities and/or 2) the measures of speech perception chosen were not sensitive enough to differentiate between children with normal suppression tuning versus those with abnormal tuning.  Additionally, the low number of subjects in each group made it even more difficult to see a strong and unequivocal result. A second finding is that pediatric subjects that had DPOAEs present (n = 7) generally had better speech perception scores than the group that had no measurable DPOAEs (n= 8). This suggests that nonlinearity in the cochlea associated with residual outer hair cell function, may help preserve speech perception ability.  One confounding factor, however, is that those with present DPOAEs also had better audiometric thresholds overall.  Future research would do well to parse these two factors out and establish a strong correlation between these variables.  This study is being written as a research article at present and will be submitted for publication in 2005.