Using the Warren type experimental method, we required the subjects to determine the order in a sequence of four vowels (a; iv; u; e) repeated continuously without pause.
The duration of each vowel segment was varied from 70 to 500msec, and the vowel order was randomized for each duration value.
The results were as follows:
1. As a scoring method, the 24-point method in which the scoring is based on each vowel is more useful from a clinical point of view than is the 6-point method in which the scoring is based on one sequence unit since the former has a smaller rejection limit.
2. The critical rates for identification (90% correct level) were obtained as 8items/sec. (16bits/sec.) in young adults and as 4items/sec. (8bits/sec.) in healthy elderly individuals.
As the duration of each vowel seqment became shorter, the information processing rate decreased to a half gain in olderly individuals. This phenomenon shows that the speed of conversation is very important for olderly individuals who use hearing aids.
3. The relation between the ability to count interrupted tones and the critical rates for identification, which were both measured at the same time, showed a significant correlation.
This indicates the possibility that they partially share common mechanisms in the central nervous system.
4. The tendencies in hearing the vowel segments was discussed.
5. This experimental method is useful for the differential diagnosis of retrocochlear lesions and for an evaluation of hearing acuity in elderly individuals.