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Re: streams and groups

In response to John Bates:

I'll sign off soon because my expertise in this area is really
limited, but I have a few reactions to John's latest comments.

  Yes.  We could regard the single clap transient, which is not just a
simple impulse function but is a complex structure of damped resonances and
reverberations, as a stream of intermixed groups of events.  The likelihood
of parsing this stream successfully depends on how you approach the
problem.  We know it can be done because the ear has found a good way to do
I don't think the ear's or brain's ability to do a spectral analysis
of complex signals is evidence of stream segregation. Stream
segregation, I believe, is a phenomenon revealed by explicit
judgments of the auditory scene that are made either directly (by
stating how many streams are heard) or indirectly (by judging timbre,
timing, or the like). In other words, streams are conscious parsings
of the auditory input, or parsings that have consequences in
conscious perception. The complex resonances and reverberations of a
single clap cannot be parsed consciously. To a listener, a single
clap will always be a single sound coming from a single source.

  I was assuming an impersonal interest in the composition of the
applause.  More to the point, there seems to be a certain level at which
our auditory systems decide that the number of clappers (or voices or
raindrops) becomes a single applauding crowd...too many to segregate into
individual sources or groups.   (Apparently you and I have not reached that
level.)  Has anyone found that limit?
Most such projects now seem, at best, to regard more than two sources as a
I believe it is difficult to parse a complex auditory scene into more
than two distinct streams. Perhaps three is the limit (except for
musical experts like conductors). There is evidence for this from
studies of listening to polyphonic music (by David Huron and others),
and there is an interesting paper by Brochard et al. (1999) that
suggests that unattended streams are not segregated, even though they
could be segregated when attended to. Carlyon and colleagues have
also provided recent evidence for a role of attention in auditory
streaming. The conscious perception of two, perhaps three, streams
needs to be distinguished from a vague awareness that there are
multiple sources in a complex sound scene (e.g., an orchestra
playing), which in turn needs to be distinguished from a lack of
awareness of the multiple sources that make up a complex sound.

Brochard, R., Drake, C., Botte, M.-C., & McAdams, S. (1999).
Perceptual organization of complex auditory sequences and frequency
separation. Journal of Experimental Psychology: Human Perception and
Performance, 25, 1742-1759.

Carlyon, R. P., Casack, R., Foxton, J. M., & Robertson, I. H. (2001).
Effects of attention and unilateral neglect on auditory stream
segregation. Journal of Experimental Psychology: Human Perception and
Performance, 27, 115-127.

Huron, D. (1989). Voice denumerability in polyphonic music of
homogeneous timbres. Music Perception, 6, 361-382.


Bruno H. Repp
Research Scientist
Haskins Laboratories
270 Crown Street
New Haven, CT 06511-6695
Tel. (203) 865-6163, ext. 236
FAX (203) 865-8963
e-mail: repp@haskins.yale.edu