Acoustical evaluation of normal productions with online feedback after asymptotic imitation learning for the motor processing deficit (MPD; continuous lines) and the motor + auditory processing deficits (MPD+APD; dashed lines). Top: coarticulation (left) and searching articulatory behavior (right). Bottom: speech sound distortion (left) and token-to-token variability of mean formant frequencies (right). Both deficits lead to an increase in the four selected key phonetic characteristics of MSD after imitation learning with increased severity.