Speech compensation to time-scale modified auditory feedback

We examined speech compensation in response to time-scale modified auditory feedback speech. Time-scale modification was applied to the transitions within the vowel-semi vowel-vowel sequence /iya/ and the vowel-vowel sequence /ia/. The experiment was conducted over three conditions: A control trial (10 utterances, normal feedback environment), a perturbation trial (20 utterances, altered feedback environment) and a return trial (10 utterances, normal feedback environment, again). Speech compensation was analyzed in terms of the phase difference and the maximum velocities of first two formant frequencies in the transition and the transition interval. It was found that speech compensation was mainly characterized by the phase difference between the F1 and F2 trajectories. The amount of the phase difference becomes larger as the time-scale ratio becomes larger. The maximum velocities of F1 and F2 in the transition and the transition interval are not significantly different between the control and perturbed trials. These facts suggest that the speech compensation is not implemented by simply increasing the motion speeds of both jaw and tongue, but by changing their relative timing.