Searching for an explanation for diphthong perception: dynamic tones and dynamic spectral profiles

The aim was to find a psychophysical explanation for the perception, by naive listeners, of diphthongs as single vowels, even though they are essentially formant movements. Subjects were asked to match sinusoidal tone and resonance glides around 1,000 Hz with two connected steady-state tones or resonances whose frequencies could be controlled independently. The expectation was that short glides (below 120 ms) would give rise to single perceptual events without any movement in a particular direction, so that the two matching steady-state patterns would not show any frequency direction either; long resonance glides (above 120 ms), on the other hand, were expected to be perceived as rising or falling and matched accordingly. The results showed an effect of duration, although it interacted with glide width. At durations shorter than about 120 ms, subjects placed the two steady profiles with which they had to match the dynamic profile closer together than with durations over 120 ms; however, this only occurred if a glide covered more than 500 Hz, and is therefore irrelevant to diphthong perception.