Speaker normalization of stressed and unstressed vowels in articulatory and formant spaces

One of the goals of phonetic investigations is to find strategies for vowel production independent of speaker-specific vocal-tract anatomies and individual biomechanic properties. In this paper we apply a technique for speaker normalization to formant spaces, lingual vowel target positions and palate midlines. The general goal is to extract speaker-independent strategies for stress production in vowels and relate speaker-dependent strategies to their specific anatomy. The method used here, termed Procrustes Analysis, is a method for translating, rotating and scaling objects to obtain one consensus configuration -in our case a consensus formant space, a consensus articulatory space or a consensus palate. In addition to these consensus configuration the analyses return speaker-dependent coordinates and transformation matrices necessary to transform the original speakerdependent data into their modeled cognates. Procrustes Analysis comes in two guises: One, the orthogonal version, is based on Euclidean geometry, i. e. only transformations are allowed which preserve angles between measured landmarks or objects. A second version, Generalized (or oblique) Procrustes Analysis is based on affine geometry, which means that angles between corresponding landmarks are not necessarily preserved. The advantage of this method is that it can be applied to different kinds of data. Most acoustical speaker normalization procedures cannot be applied to articulatory data and vice versa. Furthermore a comparison of individual models of palate shapes and articulatory vowel spaces can be made to achieve an abstraction from individual biomechanical properties. Data acquisition: Six native speakers of German were recorded by means of Electromagnetic Midsagittal Articulography (AG100, Carstens). The corpus consisted of nonsense words containing /tVt/ syllables with nuclei V=/i,I,y,Y,e,E,E:,ø, ÷,a:,a,u,U,o,O/ in stressed and unstressed positions. Stress alternations were fixed by morphologically conditioned word stress and contrastive stress. Each CVC sequence was embedded in the carrier phrase "Ich habe ’tVte, nicht tV’tal gesagt." (I