Measuring the perceptual similarity of pitch contours

It has been shown that visual display systems of intonation can be employed beneficially in teaching intonation to persons with deafness and in teaching the intonation of a foreign language. In current training situations the correctness of a reproduced pitch contour is rated either by the teacher or automatically. In the latter case an algorithm mostly estimates the maximum deviation from an example contour. In game-like exercises, for instance, the pupil has to produce a pitch contour within the displayed floor and ceiling of a "tunnel" with a preadjusted height. In an experiment described in the companion paper, phoneticians had rated the dissimilarity of two pitch contours both auditorily, by listening to two resynthesized utterances, and visually, by looking at two pitch contours displayed on a computer screen. A test is reported in which these dissimilarity ratings were compared with automatic ratings obtained with this tunnel measure and with three other measures, the mean distance, the root-mean-square (RMS) distance, and the correlation coefficient. The most frequently used tunnel measure appeared to have the weakest correlation with the ratings by the phoneticians. In general, the automatic ratings obtained with the correlation coefficient showed the strongest correlation with the perceptual ratings. A disadvantage of this measure, however, may be that it normalizes for the range of the pitch contours. If range is important, as in intonation teaching to persons with deafness, the mean distance or the RMS distance are the best physical measures for automatic training of intonation.