From Sensorimotor Experience To Speech Unit -Adaptation to altered auditory feedback in speech to assess transfer of learning in complex serial movements
International audienceUsing bird song as a model to understand generalization in motor learning, Hoffman and Sober recently found that adaptation to pitch-shift of birds’ vocal output transfered to the production of the same sounds embedded in a different serial context (J. Neurosc 2014). In humans, speech learning has been found to transfer as a function of the acoustical similarity between the training and the testing utterances (Cai et al. 2010, Rochet-Capellan et al. 2011) but it is unclear if transfer of learning is sensitive to serial order. We investigate the effects of serial order on transfer of speech motor learning using non-words sequences of CV syllables. Three groups of native speakers of French were trained to produce the syllable /be/ repetitively while their auditory feedback was altered in real time toward /ba/. They were then tested for transfer toward /be/ (control), /bepe/ or /pebe/ under normal feedback conditions. The training utterance was then produced again to test for after-effects. The auditory shift was achieved in real time using Audapter software (Cai et al. 2008). Adaptation and transfer effects were quantified in terms of changes in formants frequencies of the vowel /e/, as a function of its position and the preceding consonant in the utterance. Changes in formant frequencies in a direction opposite to the shift were significant for ~80% of the participants. Adaptation was still significant for the three groups in the after-effect block. Transfer effects in the /bepe/ and /pebe/ groups were globally smaller than that of the control group, particularly when the vowel /e/ came after /p/ and/or was in second position in the utterance. Taken together, the results suggest that transfer of speech motor learning is not homogenous and as observed by Hoffman and Sober, depends on the serial context of a sound within the utterance.Cai S, Boucek M, Ghosh SS, Guenther FH, Perkell JS. (2008). A system foronline dynamic perturbation of formant frequencies and results from perturbation of the Mandarin triphthong /iau/. In Proceedings of the 8th Intl. Seminar on Speech Production, Strasbourg, France, Dec. 8-12, 2008. pp. 65Cai, S., Ghosh, S. S., Guenther, F. H., & Perkell, J. S. (2010). Adaptive auditory feedback control of the production of formant trajectories in the Mandarin triphthong/iau/and its pattern of generalization. The Journal of the Acoustical Society of America, 128(4), 2033-2048.Hoffmann, L. A., & Sober, S. J. (2014). Vocal generalization depends on gesture identity and sequence. The Journal of Neuroscience, 34(16), 5564-5574.Rochet-Capellan, A., Richer, L., & Ostry, D. J. (2012). Nonhomogeneous transfer reveals specificity in speech motor learning. Journal of neurophysiology, 107(6), 1711-1717