🚀 go-pugleaf

In a previous article, pamws@sunvis1.vislab.olemiss.edu (Mark Sprague) writes:
   >With only two inputs (left headphone and right headphone) it is impossible
   >to distinguish between a sound source in front, behind, above, or below
   >you.  Your ears can only distinguish left and right.  In the "real world"
   >your brain compensates by noting the changes in the directionality of
   >the sound when you turn your head.  

Then, in article <72610@apple.Apple.COM> malcolm@Apple.COM (Malcolm
Slaney) writes:

>  I don't have a reference handy but we can localize sounds that are as short 
>  as 50ms.  Seems unlikely that we can react and move our heads that fast.

In fact, thresholds for interaural time differences using transients
(clicks) through headphones were measured in the 9-28 *micro*second range
(Klump & Eady, 1956) with certain circumstances/conditions producing a
difference limen of 6 microseconds (Tobias and Zerlin, 1959). Note that
a time difference of 10 microseconds corresponds to about 1 degree of
lateral shift.

About vertical localization through headphones, Malcolm continues:
>  There are a number of labs that talk about doing this. Mostly they do this
>  by measuring the sound actually received in people's ears and then filtering
>  with the derived transfer functions.  I've seen lots of attempts to explain
>  how we do this (perhaps pinae echos that cause frequency notches to move)
>  but I'm not convinced yet.

The list of Foster's work is wonderful.  Thanks!  Blauert (Wisconson?)
has done a lot of this work, as Butler (place unknown). I'm probably more
convinced than Malcolm, though I think the pinna (earlobe) frequency
filtering is only part of the story. Some references which folks may wish
to start with for the psychophysical evidence include Blauert (1983),
Freedman and Fisher (1968), and Batteau (1967).  There is also evidence
that we are able to familiarize ourselves with room acoustics very
quickly, probably using pinna cues (Plenge, 1974).

	-Peter "Ear-ly to bed" Marvit

Klump RG and Eady HR (1956). Some measurements of interaural time
      	difference thresholds. JASA 28:859-860

Tobias JV and Zerlin S (1959). Lateralizatio threshold as a function of
	stimulus duratio. JASA 31:1591-1594

Blauert J (1983). Spatial hearing. MIT Press

Batteau DW (1968). Listening with the naked ear. in Neuropsychology of
	spatially oriented behaviour (ed. Freedman SJ). Dorsey Press

Plenge G (1974). On the differenes between localizatio and
	lateralization. JASA 56:944-951
--
: Peter Marvit <marvit@cattell.psych.upenn.edu>                            :
: Psychology Department,  University of Pennsylvania                       :
: 3815 Walnut St., Philadelphia, PA  19104  w:215/898-9208  h:215/387-6433 :