Masking and filling-in (Figure 5)
Click the cochleagrams in the figures to hear the corresponding sound.
Perceptual induction (Warren et al., 1972)
A noise flanked by tones could equally well consist of two short tones adjacent to the noise, or a single longer tone overlapping the noise, that happens to be masked when the noise is present.
Warren, Obusek, and Ackroff (1972) showed that listeners hear this latter interpretation as long as the noise is intense enough to have masked the tone were it to continue through the noise. Listeners thus perceptually “fill-in" a continuous, quieter tone behind the noise. Figure 5B shows that the amplitude threshold at which a tone is masked by noise closely corresponds to the threshold at which the tone sounds continuous behind noise.
The following are examples of the experimental stimuli (click the figure hear sounds). Notice that the tone sounds most continuous (top row), when the tones are inaudible in the bottom row: for tones at 2000 Hz and 56 dB.
Finally, the following are model inferences (using sequential inference). In both examples, the tone has an amplitude of 56 dB.
Homophonic continuity (Bregman and Ahad, 1996)
Homophonic continuity is a variant of perceptual induction that involves only amplitude-modulated noise. When an initially soft noise undergoes a sudden rise in intensity, listeners perceive the initial source as continuing unchanged behind a distinct, louder noise burst (Warren, et al., 1972), but not if the amplitude modulation occurs gradually.
Click the figure above to hear the experimental stimuli and the model inferences.
Spectral completion (McDermott and Oxenham, 2008)
Analogous phenomena occur over the frequency spectrum, dubbed "spectral completion". In McDermott and Oxenham (2008), listeners heard a long masker noise, which overlapped with a brief target noise halfway through its duration. The spectrum of the target was ambiguous because the middle band of its spectrum could plausibly be masked by the masker. Listeners were asked to adjust the middle band of a comparison noise until it perceptually matched the target.
To simulate this basic experiment here, we borrow the demonstration from the paper's associated site. The mixture stimulus is presented followed by the comparison, ten times. In each iteration, the level of middle frequency band of the comparison (the adjustable band) is increased. Listeners typically judge a good match between the comparison and target around the eighth repetition.
In the first few iterations, the comparsion stimulus sounds too dull or low and in the very last iterations, the comparison stimulus sounds too tinny or thin.
Finally, the following are model inferences (using sequential inference). The target is inferred to have some energy behind the masker.
Co-modulation masking release (Hall et al., 1986)
Coherently modulated noise bands produce lower tone detection thresholds than unmodulated noise, "releasing" the tone from masking (Hall, et al., 1984). To demonstrate this effect, we present sequences of noise paired with tones of decreasing amplitude. Notice that you can hear more repetitions of the tone in the co-modulated sequence.
