Subject: Number of concurrent streams. From: Al Bregman <bregman(at)HEBB.PSYCH.MCGILL.CA> Date: Sun, 2 May 2004 19:08:25 -0400Dear Valeriy and List, (Sorry if you get this twice. Apparently the AUDITORY listserv didn't like my new email address and may or may not have sent this message to the list.) I don't think that the question about how many sound sources people can perceive in a mixture has a simple answer. First of all, it depends on what you mean by "perceive". If you mean how many sound sources they can report, then it depends on how much time they are given. The longer they listen, the more they can report. This could mean that they can pay close attention to only one sound at a time, but can shift their attention from one source to another. If you mean, "How many could they report if given a sample of each one in turn and asked whether they could detect it in the mixture, given all the time they needed?", the question becomes one about blending and segregation at a very basic level. (Let's call this last method, "matching a standard"). Often I haven't been able to hear a sound in a mixture until I knew what it was. Assuming that one is using the "matching a standard" method, then one's success will depend on what the sounds are and how intense they are. Obviously a weak sound may be hard to detect -- it may be masked (psychoacoustically or informationally) by the others. Even if this is not true, the similarity of the component sound sources plays an important role. Those researchers who have claimed that only a small number of sources (3 or 4) can be detected are all referring to sets of sounds that resemble one another, such as multiple talkers or singers, or rhythmically playing instruments. Consider the following set of sounds: - a person talking - randomly spaced hits on a bass drum (greatly attenuated) - an ambulance siren - jangling of a set of house keys, - a pure tone playing Morse code, - a person typing on an electric typewriter. - the sound of a motorcycle whizzing by (greatly attenuated) As long as the intensities were balanced appropriately, I think you would eventually detect all of them by the method of matching a standard. As many of the list members know, I believe that there is an early perceptual stage of assigning of links among the parts of the incoming mixture prior to further processing by the mechanisms that we call attention. If what we are asking about is whether this pre-attentive process has some limit concerning the number of discrete subsets (potential streams) it can form, we would have to observe its operation without any contribution from attention. I believe that this is impossible using the standard methods of psychoacoustics. Rather, it has to be addressed using a physiological approach. Some beginnings toward doing this have been carried out by Elyse Sussman and by Claude Alain (working independently), and there may be others who I don't know about. By the way, I referred to the output of the pre-attentive mechanism as "potential" streams because there is good reason to believe that top-down processes play a big role in determining the actually heard streams. Sorry the answer couldn't have been simpler. Al --------------------------------------------- Albert S. Bregman, Emeritus Professor Psychology Dept., McGill University 1205 Docteur Penfield Avenue Montreal, Quebec Canada H3A 1B1 Office: Voice: +1 (514) 398-6103 Fax: +1 (514) 398-4896 ---------------------------------------------. ----- Original Message ----- From: "Valeriy Shafiro" <Valeriy_Shafiro(at)RUSH.EDU> To: <AUDITORY(at)LISTS.MCGILL.CA> Sent: Friday, April 30, 2004 3:26 PM Subject: Re: Computational ASA -- how many sources can humans perceive? > I would like to ask a further question: Do we, in fact, know how many > independent sound sources in a mixture humans can perceive? Thus far I > know of only one research report where human listeners were asked to > identify sound sources in a recorded "real-world" sound mixture (Ellis, D. > P. (1996). Prediction-driven computational auditory scene analysis). We > have been talking about this issue with Brian Gygi, and from the few > related reports that Brian found, it appears that humans may not be that > good in simultaneous perceiving independent sound sources. For instance, > Jennifer Tufts and Tom Frank J. Acoust. Soc. Am. 101 , 3107 (1997) found > that the accuracy of judging the number of talkers in a multitalker mixture > drops considerably when there are more than 3 talkers. There is also a > report by David Huron (Music Perception, Vol. 19, No. 1 (2001) pp. 1-64., > or on-line > http://www.music-cog.ohio-state.edu/Huron/Publications/huron.voice.leading.html > ) that estimating the number of musical lines in > polyphonic music worsens considerably after 3. Some anecdotal evidence > for this limit also comes from movie sound effect designers. This is a > citation from Walter Murch, a renown sound effect artist: "There is a rule > of thumb I use which is never to give the audience more than two-and-a-half > things to think about aurally at any one moment. Now, those moments can > shift very quickly, but if you take a five-second section of sound and feed > the audience more than two-and-a-half conceptual lines at the same time, > they can't really separate them out. There's just no way to do it, and > everything becomes self-canceling." (cited from > http://www.filmsound.org/murch/waltermurch.htm) > > Any thoughts, comments, and references relevant to this issue are > appreciated. > > > > ------------------------------------------------------------- > Valeriy Shafiro > Communication Disorders and Sciences > Rush University Medical Center > Chicago, IL > > office (312) 942 - 3298 > lab (312) 942 - 3316 > email: valeriy_shafiro(at)rush.edu >