Random gap detection test and random gap detection test-expanded: Results in children with previous language delay in...

The children with difficulty in receiving sounds presented at rapid rates in speech sounds and language learning period, may have delay in speech sounds and language development due to hearing speech sounds not clearly. Auditory temporal processing (ATP) is the ability to perceive auditory signals of brief duration accurately when presented at rapid rates. ATP can be evaluated by the random gap detection test (RGDT), which detects a brief gap between two stimuli. In this study, we investigated performance of children with previous language delay (PLD), currently having disorders in more than one speech sounds, on random gap detection test (RGDT) and RGDT-expanded (RGDT-EXP) tests.

12 children (8 male, 4 female) with previous language delay (PLD) and complaint of expressing speech sounds distorted, were included into the study. They had applied language training for at least one-year period in the past and in the current time, their language development is normal. They expressed one or more speech sounds as distorted. The control group consisted of 10 normal hearing children with normal phonological development and language matched for age; and who had not PLD (5 male, 5 female). Children language levels were evaluated by Preschool Language Scale-4 test; or Clinical evaluation of language fundamentals, fourth edition (CELF-4) according to child's age. Speech sounds development was assessed by Speech Sound Development Test (SSDT). They were applied RGDT and/if necessary, 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.

In the study group with PLD, mean of the GDTs were 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 were significantly higher than the control groups at all frequencies of 500-4000 Hz. In PLD group, CGDT (103.53 ± 11.63 ms) was significantly higher than that of the control group, (10.35 ± 0.65 ms) (p=0.021).

The children with PLD have difficulties in perception of speech sounds at a certain rate, even they have not language learning difficulties. Therefore, difficulty in distinguishing of speech sounds may cause especially receptive language development delay. We believe that perception of the speech sounds and language in a certain speed; and temporally degraded speech programmes should be incorporated into the training programme and may help to prevent delays.