The Continuity Illusion and Vowel Identification

Listeners were required to identify one of four steady-state vowels, each consisting of only two formants (F1 and F2). In one condition, F1 and F2 were pulsed on and off together with a 50% duty cycle, every 100 or 200 ms. Vowel identification in this condition was almost perfect. However, when F1 and F2 were pulsed on and off in an alternating fashion, so that the two were never present at the same time, performance was very poor. Performance was greatly improved by inserting bursts of low-frequency (50–624 Hz) noise in the silent gaps between each instance of F1, and bursts of high-frequency (624–4000 Hz) noise in the gaps between instances of F2. The levels of these noise bursts were set in a preliminary experiment to ensure that the low-frequency noise would cause the F1s to sound continuous, and that the high-frequency noise would cause the F2s to sound continuous. It is concluded that this "continuity illusion" helped the auditory system to combine information from physically non-simultaneous formants. In addition, the data indicate that the neural mechanisms involved in vowel identification receive an input from those responsible for the continuity illusion