In auditory neuropathy (AN) children with hearing aids (HAs) or cochlear implant (CI),
the speech perception improvement may not be in a significant degree. These children
may perform speech perception after a few repeats. This condition may show that these
children had difficulties in receiving and processing speech sounds. If the children
with AN cannot distinguish the heard tones one or two in Random Gap Detection Test
(RGDT), their benefit performances between hearing aids or CI may not be significant.
It is thought that the answer of this question is closely related with unique auditory
processing performance of each child. The aim of the study is to investigate the RGDT
and RGDT-Expanded (RGDT-EXP) performance of five children with AN.
In this study, RGDT was applied to five children with auditory neuropathy between
ages of 7 and 13 years (study group) (3 male, 2 female). As a control group, RGDT
was applied to 10 normal hearing children who had not auditory processing problem
between ages of 7 and 16 years (5 male, 5 female). In the first test, all children
were applied to RGDT and RGDT-EXP. Each child responded whether he/she heard one or
two tones. Their responses were taken as verbally and/or hold up one finger or two
fingers. In the second test, they were applied speech discrimination test in quiet
environment and in noise. Gap detection thresholds (GDTs) were detected at 500-4000
Hz; and composite GDTs (CGDTs) were found for the study and control groups. GDT/CGDT>20
ms was considered as abnormal for temporal processing disorder.
Any of the children with AN who has no HAs; with HAs; and CI, could not be able to
perform RGDT. Therefore the RGDT-EXP was applied in this group. In the study group,
GDTs was all over 50 ms at 500-4000 Hz; and CGDTs were all over 50 ms for all children
included into the study group with AN. In control group, except child 9 (GDTs were
25 ms at 3000 and 4000Hz); and child 10 (GDT was 25 ms at 500 Hz); GDTs were all in
normal limits for 500-4000 Hz for all children included into the study as control
group. CGDTs were all in normal limits for the control group, except child 9 (CGDTs
were 22.50, slightly higher than normal limits). In the study group with AN, mean
of the GDTs was all over the normal limits; and in control group, mean of GDTs were
all in normal limits. The difference between the mean GDTs of the study group was
significantly higher than the control groups at all frequencies of 500-4000. In AN
group, CGDT (97.5+/-9.57 ms) was significantly higher than that of the control group
(10.35+/-0.65 ms).
We concluded that these results may only not be explained by auditory processing performance
or temporal aspects of audition of each child. Their gap detection was much worse
for short duration stimuli than for longer duration stimuli. The present study showed
that temporal processing, auditory timing and gap detection skills of the children
with AN were found as delayed in advanced degree. These findings may indicate that
the AN children cannot perform temporal asynchrony. Our results may help to understand
why the children with AN cannot manage the speech perception; and why they understand
the speech after a few repeats.