Objectives: 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.
Methods: 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.
Results: 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).
Conclusion: 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.