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Poster A79, Wednesday, November 8, 10:30 – 11:45 am, Harborview and Loch Raven Ballrooms

Oral cavity numbing reduces sensorimotor adaptation to altered auditory feedback

Hardik Kothare1,2, Inez Raharjo1,2, David Klein3, Danielle Mizuiri1, Kamalini Ranasinghe1, Shethal Bearelly1, Steven W. Cheung1, Srikantan Nagarajan1, John F. Houde1;1University of California, San Francisco, 2University of California, Berkeley, 3New York University

Sensorimotor adaptation experiments in speech have shown that the speech motor control system learns to partly compensate for consistent alterations of auditory feedback. These compensatory changes persist for some time even after the feedback alteration is removed. It has long been postulated that somatosensory feedback plays a modulatory role in constraining such adaptation to altered auditory feedback. Here, we examined this role by assessing the effect of orosensory numbing on adaptation to altered formant feedback. We conducted formant adaptation experiments with real-time alteration of formant frequencies. Participants (20 subjects in the lidocaine group, and 15 subject in the placebo group) were prompted to produce the word ‘head’ (vowel /ɛ/) 90 times. The repetitions were split into a baseline non-altered-feedback block of 20 trials, followed by a hold block of 50 trials where the auditory feedback was altered by raising the first formant (F1) by 200 Hertz, followed by a non-altered-feedback washout block of 20 trials. Participants then swished for a minute with a numbing solution of 5ml of 4% lidocaine and 5ml of strawberry lemonade or (in the placebo group) 5ml of water flavoured with lemon rind and 5ml of strawberry lemonade. Effectiveness of numbing by lidocaine was verified using nylon monofilament sutures that mapped the tactile threshold of the tip of the tongue at various time points in the experiment. After swishing with either numbing or placebo solution (depending on group), the same formant adaptation experiment was then repeated. Pre-swish and post-swish adaptive responses were calculated in both the lidocaine group and the placebo group. Adaptation values along the F1 axis were normalised to individual baseline F1 frequency values. A generalised linear model (GLM) revealed that adaptation values were significantly reduced in the post-swish adaptation experiment for the group that swished with lidocaine (p<0.0001). This reduced adaptation for the lidocaine group remained significant in the washout block (p=0.0019). Reduced adaptive response in the hold block and washout block was not seen in the placebo group. To verify that somatosensory feedback was indeed altered by the lidocaine solution and not by the placebo solution, buckling force data for the filaments was run through a similar GLM model. Tactile sensitivity of the tip of the tongue was reduced significantly for the lidocaine group (p<0.05) and sensitivity remained unaltered for the placebo group. The observed reduction in adaptation to altered auditory feedback resulting from oral numbing runs counter to the enhancing effects numbing has been shown to have on immediate compensation for transient auditory perturbations in speaking. Nevertheless, these results are consistent with our State Feedback Control model of speech motor control.

Topic Area: Speech Motor Control and Sensorimotor Integration

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