A model of invariant patterns of articulatory movements

The goal of the present study is to model the ‘‘iceberg’’ portions of the demisyllables, previously extracted from the microbeam articulatory data (Bonaventura, 2003), by curve fitting. The polynomial analysis was designed to include an appropriate weighting window centering around the threshold crossing point, and aimed to provide an estimate of how, in the vicinity of the crossing point, the curve deviates from a straight line: this deviation would be represented by the higher order coefficients of the polynomial. The model was obtained preliminarily on the basis of 100 curves for the lower lip movement for /f/ and /v/ (in initial and final demisyllable for ‘‘five’’), and from 100 curves for the tongue tip displacement (for /n/ in ‘‘nine’’). In order to fit the data to the model, a robust least square method (Least Absolute Residuals) has been used, in order to minimize the influence of the outliers, that are present in the read speech data, and cannot be accounted for by ‘‘phrase final lengthening effects.’’ The fit results for the cubic polynomials satisfactorily approximated the ‘‘iceberg’’ curves. The 95% confidence bounds on the fitted coefficients indicated that they were acceptably accurate.