Metamorphosis of a critical interval: age-linked changes in the delay in auditory feedback that produces maximal disruption of speech.

Abstract

A developmental study of delayed auditory feedback (DAF) indicated that: (1) DAF disrupts the speech of children more than adults, for all delays in feedback; (2) The delay for maximal interference varies with age. The older a subject, the shorter the delay producing maximal interference with his speech; (3) The peak interference delay remains at 0.2 sec, when adults reduce their rate of speech by drawing out speech sounds. This finding suggested that the critical DAF interval is independent of the duration of speech sounds in the returning auditory signal; (4) Slowing down the rate of speech as described above, reduced the amount of stuttering under DAF; (5) However, a subject's maximum rate of speech was significantly correlated with the duration of the delay producing maximal interference with his speech. The slower the subject's maximum rate of speech, the longer the peak interference delay. A correlation of maximum speech rate and frequency of DAF stuttering was also significant. The slower a subject's maximum speech rate, the more he tended to stutter under DAF. Since voluntary prolongation of speech sounds had the opposite effect, decreasing rather than increasing stuttering, it was suggested that: (l) Mechanisms determining the maximum speech rate are to some extent different from those governing the prolongation of speech sounds; (2) both the amount of stuttering under DAF and the peak interference delay are related to some as yet unknown factor or set of factors determining the maximum rate of speech, and, (3) this factor is age-linked since the maximum rate of speech varies inversely with age.