Articulatory compensation for low-pass filtered formant-altered auditory feedback.

Auditory feedback while speaking plays an important role in stably controlling speech articulation. Its importance has been verified in formant-altered auditory feedback (AAF) experiments where speakers utter while listening to speech with perturbed first (F1) and second (F2) formant frequencies. However, the contribution of the frequency components higher than F2 to the articulatory control under the perturbations of F1 and F2 has not yet been investigated. In this study, a formant-AAF experiment was conducted in which a low-pass filter was applied to speech. The experimental results showed that the deviation in the compensatory response was significantly larger when a low-pass filter with a cutoff frequency of 3 kHz was used compared to that when cutoff frequencies of 4 and 8 kHz were used. It was also found that the deviation in the 3-kHz condition correlated with the fundamental frequency and spectral tilt of the produced speech. Additional simulation results using a neurocomputational model of speech production (SimpleDIVA model) and the experimental data showed that the feedforward learning rate increased as the cutoff frequency decreased. These results suggest that high-frequency components of the auditory feedback would be involved in the determination of corrective motor commands from auditory errors.