Subject: An auditory illusion From: Stuart Rosen <stuart(at)PHONETICS.UCL.AC.UK> Date: Tue, 29 Apr 1997 11:45:41 +0100>>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 >>clearly. 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 England Tel: (44 171) 380-7404 Fax: (44 171) 383-0752