الفهرس 
Frequency lowering technologyOnly 14 pages are availabe for public view
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Abstract
Summary
Audibility of sounds across all speech frequencies plays an important role in acquisition of speech for hearing-impaired subjects. High frequency information is important for the perception of many speech and environmental sounds. Higher speech intelligibility is the principle target in hearing aid amplification. Most of conventional hearing aid technology doesn‟t provide adequate amplification in the high frequencies. To solve this problem, frequency-lowering techniques have been proposed, whereby the frequency of the sounds from the disabled region is shifted into more sensitive frequency regions.
One of the frequency lowering techniques is the nonlinear frequency compression wherein certain frequencies above a variable cutoff point are compressed and signals below the cutoff are not compressed. Therefore, it allows better perception of high frequency consonants and environmental sounds, whilst preserving the mid and low frequency information.
Validation of hearing aids benefit includes subjective tests and objective tests. The cortical auditory evoked potentials (CAEPs) as an objective test, represent the summed neural activity in the auditory cortex in responseto sounds. Aided CAEPs measured before and after a given auditory training program may reflect the efficiency of the program and confirm the plasticity of the auditory pathways.
The current study was designed to study CAEPs P1 cortical evoked responses using speech stimuli in children with severe to profound SNHL fitted with nonlinear frequency compression hearing aids and to study the variables related to perception of speech p1 in the studied subjects, if any. The study group children were hearing impaired with severe to profound sensorineural hearing loss, fitted with binaural hearing aids. A group of normal hearing children served as a control group. All children in the study group were submitted to full history taking, Otological examination, Age based hearing evaluation using 2 channel AC40 audiometer, Immittancemetry using Maico model MI 34, Fitting with binaural Naida III UP according to the default setting using HIPRO WITH Noah software, IPFG phonak (IPFG version 2.4) + wired cable connection. Hearing aid evaluation was done with and without nonlinear frequency compression enabled in the form of: sound field testing in sound treated room using warble tone 500-4000 Hz, speech recognition thresholds, word recognition score and obligatory cortical auditory
evoked potentials P1 was studied using Smart evoked potential, version 2.39.
The speech stimuli used were /ga and /da/ representing mid and high frequencies respectively. They were presented from a loudspeaker at zero degree azimuth at a distance one meter, p1 was measured at three intensities (75, 65, 55) dBSPL.
The results of the study pointed to statistical significant improvement in high frequency threshold detection in sound field testing and detection rate of p1 using NFC technology for the da stimulus, no statistical significant difference using ga stimulus except at low intensity (55 dBSPL). P1 detection did not need an acclimatization period with NFC. However, the latency of p1 differed after long term use of the technology. No effect on speech reception thresholds or word recognition scores using NFC was detected. Age and duration of hearing loss and hearing aid use were variables affecting p1 perception. There was a negative correlation between presence of p1CAEP and age of child and duration of hearing loss and a positive correlation with the duration of hearing aid use, reflecting the effect of prolonged auditory deprivation.
In conclusion, NFC improved high frequency aided thresholds and the detection of p1 response using speech stimuli in children with severe to profound SNHL. CAEP can be used as an objective validation tool in hearing aids assessment in children. It is recommended to compare these results with other frequency lowering technologies. Monitor changes over time in p1 amplitude and latency changes with effect on speech recognition and production would be beneficial.