Letter to the editor : A note on classification experiments in acoustic phonetics

In recent years, several classification experiments have addressed the value of global spectral properties for the classification of stop consonants by humans or machines. The results of some of these studies seem to be at variance with each other. While Blumstein & Stevens (1979) and other investigators found invariance in global spectral properties, Suomi (1985) reports that the global spectral properties are highly dependent on the vowel context, and classification of stops based on these properties needs to operate in a context-dependent fashion. Through a theoretical exposition, as well as a comparison of past classification studies, it is shown that the results of classification experiments may strongly depend on the employed classification strategies. In particular it is shown that, when the study of Suomi (1985) is interpreted in accordance with some basic principles of the theory of classification, the general claim of the absence of invariance in the global spectral properties of stop consonants is not warranted on the basis of the reported results.