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Re: [AUDITORY] Localizing smoke detectors - why is it so hard?


   Most alarms, such as the smoke alarm you mention, are designed to be highly detectable and annoying.  Thus, alarms generally have most of their power in the ~1-3 kHz range where humans are most sensitive.  However, while these sounds are highly detectable, they are poorly localized due to the limited usefulness of low frequency interaural delay cues at these intermediate frequencies (due to poor phase locking) and the paucity of interaural level difference cues (i.e., the sounds have wavelengths that are not much smaller than the head diameter, thus the head doesn't produce much shadow).  In other words these are some of the very worst sounds for accurate and precise localization!

Daniel J. Tollin, PhD
Associate Professor

University of Colorado School of Medicine
Department of Physiology and Biophysics/Mail Stop 8307
Research Complex 1-N, Rm 7106
12800 East 19th Ave
Aurora, CO 80045
Tel: 303-724-0625
Fax: 303-724-4501

From: AUDITORY - Research in Auditory Perception [AUDITORY@xxxxxxxxxxxxxxx] On Behalf Of Jennifer M. Groh [jmgroh@xxxxxxxx]
Sent: Tuesday, June 25, 2013 10:46 AM
To: AUDITORY@xxxxxxxxxxxxxxx
Subject: Localizing smoke detectors - why is it so hard?

Dear List,

I am writing a book for a general audience on how the brain processes
spatial information ("Making Space"). The chapter on hearing covers many
topics in sound localization, but there is one that I'm currently still
quite puzzled about: why it is so hard to localize a smoke detector when
its battery starts to fail?  Here is what I have considered so far:

- To my ear, the chirp sounds high frequency enough that ILD cues should
be reasonably large.

- At the same time, it seems to have a broad enough bandwidth, and in
any case it has onset-and-offset cues, that ITD cues should be usable.

- A possibility is that the chirp is too brief, and that limits dynamic
feedback, i.e. changes in ITD and ILD as the head turns during a sound.
   However, in my laboratory we have obtained excellent sound
localization performance in head-restrained monkeys and human subjects
localizing sounds that are briefer than the reaction time to make an
orienting movement.

- An additional possibility is that we have too little experience with
such sounds to have assembled a mental template of the spectrum at the
source, so that spectral cues are of less use than is normally the case.

I'm leaning towards a combination of the last two factors, which
together would render the cone of confusion unresolved for these stimuli.


Best wishes,

--Jennifer Groh

Jennifer M. Groh, Ph.D.

Department of Psychology and Neuroscience
Department of Neurobiology
Center for Cognitive Neuroscience

B203 LSRC, Box 90999
Durham, NC 27708