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An auditory illusion

>>I am looking for a recording of an acoustic
>>illusion which I heard a while ago:  You hear some garbled noise, then
>>someone tells you that a message, such as "My name is Al" is in there
>>among the noise.  Upon hearing the garble again, the message can be heard

The easiest way to create an 'illusion' like this (and the extent to which
it is 'illusory', and the extent to which it is not, are debatable), is
simply to take a digital speech waveform and randomly invert the polarity of
its samples, with a probability of 1/2. This is equivalent to multiplying
the speech waveform by a white noise, resulting in a signal that is still
white, but with much temporal structure. If you hear this kind of signal
blind (so-called signal correlated noise, Schroeder, 1968), you may not even
realise that it is speech. Once knowing the sentence, however, one 'hears'
even more than the wide varity of speech information known to be in this
processed signal. I just used this technique in a public lecture, and it
worked extremely well.

Rosen, S. (1992) Temporal information in speech: acoustic, auditory and
linguistic aspects. Philosophical Transactions of the Royal Society London
B, 336, 367-373.

Schroeder, M. R. (1968) Reference signal for signal quality studies. Journal
of the Acoustical Society of America, 44, 1735-1736.

Van Tasell, Soli, Kirby, & Widin (1987) Speech waveform envelope cues for
consonant recognition. Journal of the Acoustical Society of America, 82
4, 1152-1161.

Van Tasell, D. J., Greenfield, D. G., Logemann, J. J., & Nelson, D. A.
(1992) Temporal cues for consonant recognition: Training, talker
generalization, and use in the evaluation of cochlear implants. Journal of
the Acoustical Society of America, 92, 1247-1257.


Stuart Rosen
Department of Phonetics & Linguistics
University College London
4 Stephenson Way
London NW1 2HE

Tel: (44 171) 380-7404
Fax: (44 171) 383-0752