Dynamic aspects of the continuity illusion: perception of level and of the depth, rate, and phase of modulation.

The perception of modulation of a tone interrupted by a noise burst was investigated. The tone and its modulation were perceived as continuing through the noise. In experiment 1, subjects rated the similarity of an uninterrupted tone and a tone interrupted by noise, in terms of the perceived level and modulation depth of the sinusoidal carrier. The values of these parameters in the central portion of the uninterrupted tone were systematically varied. Both amplitude and frequency modulation (AM and FM) were used. The results indicated that the perceived level and modulation depth of the carrier did not change greatly during the noise burst. When the modulation rate differed before and after the noise burst, the modulation-rate transition was perceived to occur near the end of the noise burst for the FM stimuli. Hence, for these stimuli, the continuity illusion appears to be dominated by the portion of the tone before, rather than after, the interruption. Results for the AM stimuli showed a non-significant trend in the same direction. Experiment 2 used forced-choice tasks to evaluate the ability to detect a change in the ongoing phase of AM and FM following interruption by a noise burst. The results confirmed earlier findings for FM tones, and extended them to AM tones, showing that listeners lost track of the phase of the modulation, even though the modulation was perceived as continuous.