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Abstract
The importance of high frequency amplification is a complex issue. Only a few studies have been conducted with hearing-impaired children and no studies with infants have been reported (Stelmachowicz et al., 2001).
A general goal of amplification is to restore audibility of high-frequency speech information. Several investigators have shown, however, that not all listeners with high-frequency hearing loss can make efficient use of these cues (Ching et al., 1998). These investigators observed that the efficiency with which listeners with high-frequency hearing losses used audible high-frequency information decreased with increasing hearing loss.
In the past few years, the phenomenon of dead regions in the cochlea had been emerged as a proposed pathology complicating the existence of sensorineural hearing loss and affecting speech intelligibility. It is now perceived that in presence of dead regions the hearing loss as estimated by an audiogram may not be a faithful representation for the degree of handicap as experienced by the listener. So, appropriate diagnosis of presence of dead region may be important, but also difficult in children (Stelmachowicz et al., 2004).
So, this work is designed to study the effect of variable gain reduction of hearing aids on speech intelligibility in children with suspected dead region in the cochlea. It was conducted on twenty children suffering from severe to profound SNHL, aged from 5-12 years and are using digital hearing aids for at least 6 months. Equipment used in this study were double walled sound treated booth, two channel Audiometer, Immittancemeter, 2 BTE digital hearing aids (Oticon model Sumo DM), cassette tape and Compact disc (CD) for Arabic Pediatric Speech Intelligibility (PSI) test (Ali et al., 2003).
All children were examined in 2 separate sessions, in the 1st one they were submitted to full history taking, basic audiological evaluation, aided thresholds, aided SRT using their own hearing aids and language age assessment. While in the 2nd one the research H.As, which have 3 programming options, was programmed according to the patient’s absolute thresholds. The gain was adjusted using DSL pediatric v5 formula as follow: program (1) full amplification, program (2) the gain is reduced 50% in the frequency band of the suspected high frequency dead regions (3-5 KHz) and program (3) the gain is reduced by 100% at the same frequency band.
It was found that upon using full amplification less score in the PSI test was obtained compared to reducing the gain by either 50 % or 100 % Furthermore, there was statistically significant difference between full amplification and gain reduction either by 50 % or 100 % while there was no statistically significant difference between gain reduction either by 50 % or 100 %.
Results of this work also showed that older children scored better in PSI test under full amplification condition. It may be attributed to the increase in the linguistic abilities of the children with increasing their age which help them to extract the meaning even under unfavorable listening conditions.
Also, there was positive correlation between duration of hearing loss of children and, the relative duration of hearing loss of the study group and PSI test scores at full amplification. But there was no correlation between the PSI test scores with each program and either age of onset of hearing loss, duration of hearing aid use and duration of rehabilitation
Finally, it can be emphasized that either 50% or 100% gain reduction may result in improvement of speech intelligibility in children with high frequency hearing loss where a dead region is suspected, more than full amplification.