Subject: Re: streams and groups From: Bruno Repp <repp(at)ALVIN.HASKINS.YALE.EDU> Date: Wed, 16 May 2001 09:59:17 -0700In 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 >it. 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 >crowd. 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 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(at)haskins.yale.edu