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

["Richard F. Lyon" <dicklyon@xxxxxxx>]

Jennifer,

I believe the answer is primarily in the transducer:  to make the beeper cheep, they use a resonant transducer, which has a slow buildup at the onset and makes the resulting signal not very broadband at all, depriving you of all ITD cues.  And they make the beeps so brief that you don't have much chance to turn your head and vary the ILD cue; and so far apart in time that you get impatient waiting for the next beep for your next chance to find it.  And you're in a very echoic environment where the echos of the narrowband beep off the walls make standing nulls to further confuse the ILD cue.

The beepers on carts in airports have the same problem.  They can come up behind you and make a loud beeping noise, but you have no  idea they are there -- they seem to be designed to defeat any possible usable spatial cues.

There ought to be a law ... oh, wait, there probably is, contributing to the problem.

Dick

On Tue, Jun 25, 2013 at 1:46 AM, Jennifer M. Groh <jmgroh@xxxxxxxx> wrote:

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.

Thoughts?

Best wishes,

--Jennifer Groh

--
Jennifer M. Groh, Ph.D.

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


B203 LSRC, Box 90999
Durham, NC 27708

919-681-6536
www.duke.edu/~jmgroh