Transfer effects from listening to frequency-controlled and frequency-shifted accelerated speech

Two experiments examined intelligibility of sentences reproduced with increased tonal frequency (the spectrum of the speech signal shifted upward), increased speech rate, or both frequency and speech rate increased. The first experiment showed that both the frequency and speech rate increases independently impaired sentence intelligibility. Sentences played back at increased rates and increased frequencies also were perceived as having been spoken more rapidly. In the second experiment subjects listened either to practice sentences played back at frequency-shifted (FS) or frequency-controlled (FC) accelerated rates. Subsequent to this practice, an intelligibility test was given on 10 FS and 10 FC accelerated sentences played back at double speed. The accelerated sentences were more intelligible for practice groups than for a no-practice control group, and FC accelerated rates produced more intelligible sentences than FS acceleration. The specific training experiences produced an interaction with the type of test-sentence acceleration early in transfer. The FS accelerated sentences were more intelligible following FS practice compared to FC practice, and the FC accelerated sentences were more intelligible following FC practice compared to FS practice.