Stable patterns of articulatory movements across inter-subject variability

Abstract

The goal of the present study was to test whether models of portions of curves, representing movements of the crucial articulator for production of place in syllables containing labiodental and alveolar gestures for production of obstruents ('iceberg' portions of demisyllables), that had previously been found to be stable across different prosodic conditions (Bonaventura, 2003; 2005; 2006; Bonaventura and Fujimura, 2007), a) remained stable across different subjects pronunciations, for each consonantal class b) were significantly different for the two different consonantal movements. Curves were previously extracted from microbeam articulatory data, from 3 subjects for Lower Lip movement (LL) for word 'five' and 3 subjects for Tongue Tip (TT) movement for word 'nine'. Curve fitting models were obtained, by using a best fit fourth order polynomial, from a total of 1193 curves representing lower lip vertical displacement for production of [f] and [v] in 'five' and from a total of 610 curves representing tongue tip vertical displacement for production of [n] in 'nine'. Coefficients were statistically compared, to verify presence of a) non significant difference between models across pronunciations by 3 subjects b) significant difference between the two generalized curves for [f] vs. [t] across subjects. Positive results from (a) would support the hypothesis of presence of articulatory pattern that would remain stable across different prosodic conditions and inter-subject variability, possibly indicating properties of an identifiable articulatory unit. Positive results from (b) would possibly indicate a consistent difference between crucial articulator movements for production of labiodental vs. dental consonantal gestures. Results showed no expected similarity between 'movement curves across subjects pronunciations, except for some stability in the TT coefficients in coda. However, the comparison between the coefficients of the generalized models for TT and LL showed significant differences between the two movements in final demisyllable. These results partially confirm the expected difference between models, indicating that at least the fitted curves for TT and for LL in final demisyllable, if more stable across subjects realizations, could be considered as a reference pattern, representing normal speech for comparison with abnormal production.