Demonstrations of
Auditory Illusions and Tricks

2nd Edition

Contents Introduction Chapter 1 Chapter 2 Chapter 3 Chapter 4
Chapter 5 Chapter 6 References Archives Demo Index Top Page


IV. Illusory Continuity


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<15> Illusory Continuity of a Steady-State Tone
Pattern (a) gives a typical example of the continuity effect.   A 2550 ms steady-state tone of 800 Hz with a 150 ms temporal gap in the middle is presented.   A 150 ms noise with a frequency range of 400 to 1600 Hz (two octaves) is inserted in the temporal gap.   The level of the tone is 5 dB lower than that of the noise.   The rise time and the fall time at both ends of the pattern are 200 ms, whereas the remaining rise and fall times are 3 ms.   The listener will hear the tone as continuous even though the tone is not present behind the noise.   Pattern (b) is the same as pattern (a), except for a frequency gap in the noise from 566 to 1131 Hz (one octave).   When listening carefully, the tone can be heard as separated in the middle.   In pattern (c), the steady-state tone with the temporal gap is presented alone.  

Warren, R.M. (1999).
Auditory Perception: A New Analysis and Synthesis.   Cambridge: Cambridge University Press.  

Fig.15-1 Fig.15-2 Fig.15-3

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<16> Illusory Continuity of a Glide tone
Pattern (a) gives another example of the continuity effect.   A 2550 ms glide tone ascending from 200 to 3200 Hz with a 150 ms temporal gap in the middle is presented.   The rate of the frequency change is constant on the logarithmic scale.   A 150 ms noise with a frequency range of 400 to 1600 Hz (two octaves) is inserted in the temporal gap.   The first part of the glide tone ends at about 650 Hz and the second part begins at about 985 Hz.   The level of the glide tone is 5 dB lower than that of the noise.   The rise time and the fall time at both ends of the pattern are 200 ms, whereas the remaining rise and fall times are 3 ms.   The listener will hear the glide tone as continuous even though the tone is not present behind the noise.   Pattern (b) is the same as pattern (a), except for a frequency gap in the noise from 566 to 1131 Hz (one octave).   When listening carefully, the glide tone can be heard as separated in the middle.   In the pattern (c), the glide tone with the temporal gap is presented alone.  

Ciocca, V. & Bregman, A.S. (1987).
Perceived continuity of gliding and steady state tones through interrupting noise.   Perception & Psychophysics, 42, 476-484.

Fig.16-1 Fig.16-2 Fig.16-3

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<17> Illusory Continuity of a Glide Tone with a Frequency Jump
This demonstration is a variation of Demonstration <16>.   A frequency jump is introduced to the glide tone, dividing it clearly into two successive glide tones.   The first glide ascends from 200 to 566 Hz and the second from 1131 to 3200 Hz.   In pattern (b), the first glide ends at the lower boundary of the frequency gap of the noise and the second glide starts from the upper boundary.   Here, the listener tends to hear a stronger continuity than in Demonstration <16b>, despite the frequency jump.  

Fig.17-1 Fig.17-2 Fig.17-3

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<18> A Backward Extension of a Tone
In both patterns (a) and (b), two 200 ms pure tones of 800 Hz are presented successively.   In pattern (a), the first tone is immediately preceded by a 1000 ms noise, with a frequency range of 400 to 1600 Hz and a level that is 12 dB higher than that of the tones.   The rise time and the fall time of the pure tones are 6 ms, and the rise time and the fall time of the noise are 200 and 3 ms, respectively.   In pattern (b), the same pure tones are presented without the preceding noise as a control condition.   The duration of the pure tone preceded by the noise tends to be overestimated.   The onset of this tone must be restored perceptually.  

Simons, M. (1995).
Time-swelling: an incomplete heterophonic induction in a non-repetitive design.   Unpublished Master's thesis, Leiden University.

Fig.18-1 Fig.18-2

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<19> Music Sound Restoration

One tone of a melody from 'Turkish March' (W. A. Mozart) is replaced by a pink noise in pattern (a).   Our auditory system restores the missing sound in accordance with the melodic context.   The melody and the noise are segregated from each other perceptually, which makes it difficult to judge the temporal position of the noise.   In the second half of the melody, the corresponding note is simply removed.   In pattern (b), every 8th or 7th tone of the melody is replaced by a pink noise.   Even though several notes are deleted, we can still hear a reasonably consistent melody.   The tendency is clearer when the listener direct his/her attention to the noise sequence.  

Sasaki, T. (1980).
Sound restoration and temporal localization of noise in speech and music sounds.   Tohoku Psychologica Folia, 39, 79-88.

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Contents Introduction Chapter 1 Chapter 2 Chapter 3 Chapter 4
Chapter 5 Chapter 6 References Archives Demo Index Top Page