Different discrimination strategies for vowels and consonants
Bert Schouten, Arjan van Hessen · The Journal of the Acoustical Society of America · 1991
In speech perception research, one is often interested in the relationship between phoneme identification and discrimination of stimuli drawn from the same stimulus continuum. If discrimination performance is completely predictable from identification, perception is often said to be completely categorical: In both tasks, subjects (can) only use phoneme labels. How should one compare a one-interval identification task with a two-interval forced-choice discrimination task in which subjects have to determine the order of the stimuli? Using standard SDT assumptions about optimal processing [D. M. Green and J. A. Swets, Signal Detection Theory and Psychophysics (New York, 1974)], it was found that identification and discrimination of natural vowels were nearly equivalent, but with natural stop consonants identification d′ was, paradoxically, twice as high as discrimination d′. It was concluded that subjects probably use a different strategy for the discrimination of natural stops: They do not subtract the traces of the two stimuli, but the estimated distances between the stimuli and the phoneme prototypes. Such an assumption yields d′ values that are twice as high as the standard values.