Continuity Based Grouping Affects the Perception of Vowel-nasal Syllables

Auditory scene analysis (ASA) is a theoretical framework that aims to explain the auditory perceptual organization. We test the hypothesis that formant continuity is used to link speech segments. Three experiments are described that investigate listeners’ ability to use the formant continuity cues to categorise the synthetic nasal /m/ and vowel-nasal syllables. The first experiment shows that, without formant transitions, the perception of a synthetic nasal /m/ changes from /m/ for vowels with low second formant (F2) values to /n/ for vowels with high F2s, this switch is consistent with the use of formant proximity for perceptual organization. The effect of introducing formant transitions as continuity cues into the stimulus was investigated in a second experiment which shows that transitions of only 5ms duration are sufficient to transform the /en/ percept to a /em/. The final experiment addresses the question of whether transitions are analysed in fine detail by adding frequency modulated tones into the stimulus. The addition of chirps changes the percept if the chirp position is in the same position and direction as a formant transition, although the fine spectral structure of the sound is very different. If the chirp moves in the opposite direction, it also changes the percept but to a lesser extent, which suggests that only a coarse signal analysis is carried out.