A Direct Magnitude Scaling Method to Investigate Categorical Versus Continuous Modes of Speech Perception

The perception of synthetic steady-state vowels, synthetic consonant-vowel syllables and pure tones was investigated using a psychophysical scaling procedure involving direct magnitude estimation. In each of the three stimulus classes, there were thirteen members equally spaced along a physical continuum and the investigation was designed to measure the degree to which the stimulus members appeared to be evenly spaced along a corresponding perceptual continuum. The experimental technique required the subject to judge the members of each set of stimuli in terms of their similarity to each other. The results suggested that for stops, the perceptual spacing depended upon phoneme identification; but for vowels, the spacing was relatively independent of phoneme identity. The vowel data in fact, approximated to the tone data (included to provide a non-speech comparison). The results are interpreted in terms of the notion of categorical versus continuous modes of speech perception.