Lateral Inversion

[houtsma@xxxxxxxxxx]

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    -----Original Message-----
    From: Heinrich Zimmermann [mailto:hzimmer@IAM.UNIBE.CH]
    Sent: zaterdag 25 september 1999 11:39
    To: AUDITORY@LISTS.MCGILL.CA
    Subject: Re: Lateral Inversion in Spatial Hearing


    First Summary: Lateral Inversion in Spatial Hearing

    On September, 2nd, I have put the following query on this list:

    > I wonder if anybody on the Auditory List knows something about a lateral
    > inversion phenomenon I discovered when preparing sounds for a series of
    > experiments on spatial hearing: certain binaural recordings of
    > bandpass-filtered clicks with interaural time differences but without
    > interaural intensity differences seem to be lateralized as predicted by
    > cross-correlation models in a frequency range below 2 Kilohertz but on the
    > opposite side than predicted by these models in a frequency range above
    > 8 Kilohertz.

    In response to some of your questions I have put an example sound file for
the lateral inversion phenomenon on http://Heinrich.Zimmermann.com.


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    Dear Heinrich (and other binaural fans),

    I listened to your sound sample and, indeed, the chirp apears to come from
the right. Analysis of the sound, however, shows several confounding artifacts.
    (1) There is an annoying ringing in the 'silent' portion of the signal
        before and after the click particularly in the right channel. It is a
        mix of a 2-kHz and 8-kHz tone, corresponding to the edges of your
        extremely steep bandpass filter. This tone sets a strong bias towards
        the right ear and could explain the 'lateral inversion' phenomenon.
    (2) The right signal is not only 500 microsec. delayed, but also phase
        distorted. Did you use separate independent filters?. This phase
        distortion causes the image to diffuse.
    (3) Measured over the signal (click-response) portion, there is an intensity        difference of about 0.5 dB between the signals, the left signal being
        the more intense.

    I therefore generated a somewhat cleaner signal this morning, starting with
    an (analog) 10-microsec. pulse bandpass filtered between 2000 and 8000 Hz by    two Kemo filters in series (about 190 dB/oct). This signal was put in the
    left channel of a stereo wav file. In the right channel was either exactly
    the same signal (click.wav) or that same signal delayed by 500 microsec.
    (clickster.wav). Each file contains 5 clicks, 1 sec. apart. If you play
    them in this order, you will quite convincingly hear the first five clicks
    in the center and the next five clicks to the left of the center. Just as
    the textbooks tell you.

    I have attached both files as wav attachments. Enjoy the clicks.

    Adrian Houtsma

[ binary-encoded click.wav and clickster.wav removed by dpwe 1999sep28 ]