The Effect of Low-Pass Filtering on Identification of Nonsense Syllables in Quiet by School-Age Children With and Without Cochlear Dead Regions

Abstract

Objectives: 

The presence of cochlear dead regions (DRs) can have a significant effect on speech perception. Some studies have reported that adults do not benefit from amplification of frequencies well inside an extensive DR. However, the importance of high-frequency amplification for hearing-impaired children has been emphasized by many researchers. This study investigates the benefit of high-frequency amplification for children with various degrees of high-frequency hearing impairment, with and without DRs.

Design: 

The children, aged 8 to 13 years, were divided into two groups according to the severity of their hearing impairment. Group MS had moderate to severe impairment (9 ears without DRs and 3 ears with restricted DRs). Group SP had severe to profound hearing impairment (7 ears with DRs and 1 ear without a DR). The vowel-consonant-vowel stimuli were subjected to the frequency-gain characteristics prescribed by the desired sensation level fitting method and presented via headphones broadband and under various low-pass filtering conditions.

Results: 

Group MS benefited from high-frequency amplification whether or not a restricted DR was present. In contrast, ears in group SP with continuous extensive DRs showed limited benefit from high-frequency amplification. For the latter, performance improved with increasing cutoff frequency up to approximately 1 octave above the edge frequency of the DR and generally stayed the same, or deteriorated, with further increases in bandwidth. In one case of severe to profound hearing impairment without evidence of DRs, performance increased with increasing cutoff frequency up to 2 kHz and remained almost constant with further increases in bandwidth.

Conclusions: 

For children with severe to profound hearing impairment and continuous high-frequency DRs commencing from approximately 1 kHz, applying amplification only for frequencies up to approximately 1 octave above the edge frequency of the DR may be of benefit. Tests with more participants are needed to confirm this finding.

In Brief

Some studies have reported that adults with extensive continuous dead regions (DRs) in the cochlea do not obtain benefit from amplification of frequency components well within the DR. This study investigates the benefit of high-frequency amplification for children with various degrees of high-frequency hearing impairment, with and without DRs. Vowel-consonant-vowel stimuli were amplified and presented through headphones, broadband and under various low-pass filtering conditions. Percent-correct-response scores showed that children with moderate-to-severe hearing impairment benefited from high-frequency amplification whether or not they had (restricted) DRs. Children with severe-to-profound hearing impairment and extensive continuous DRs showed limited benefit from high-frequency amplification. The results need replication with a larger number of children and different speech materials.