Re: streams and groups (Al Bregman )

Subject: Re: streams and groups
From:    Al Bregman  <BREGMAN(at)PSYCH.MCGILL.CA>
Date:    Sun, 13 May 2001 21:03:51 -0400

Dear Bruno, Chuck, and List: I guess I don't know exactly how the word "group" is used or whether different people use it in the same way. Here is my own take on the terminology of streams and units. For me, a stream is a mental construct, portraying either single or multiple sounds extended in time. The critical factor is that they are treated as an extended output of a single sound source. Whether they truly come from single or from multiple sound sources is a physical or environmental description, not a psychological one. (Of course, the psychophysical question is how the physical descriptions map onto the psychological ones.) Within streams there can be "units". A unit is a perceptual entity, perceived whenever the sound is partitioned by discontinuities. The unit may emerge because it is bracketed by silences, by its own sudden rise in intensity, or the sudden rise in intensity that defines the beginning of the next unit (see the work of Yoshitaka Nakajima). A musical "note" (in the auditory sense) is an unit within a melody; a single footstep is a unit within a sequence of steps. A unit is a perceptual entity that is intended by Mother Nature to correspond with a single "event" in nature (a single step of an animal; a single activation of a piano key, a chirp of a bird). Units--being psychological--are the outputs, not the inputs, of the auditory system. The temporal variation of acoustic energy is the input. Perhaps the word "group" should be used to mean a cluster of units within a stream -- perceived as a cluster due to the fact that the acoustic differences are greater between the groups than within the groups, or to the fact that there exist discontinuities or silences that are greater between successive groups than between the successive members of the same group. It appears from the complex rhythms in music that groups can be hierarchically organized as well (see the work of Mari Jones and others on the representation of rhythms). Like the streams in which they reside, "groups", as defined above, are psychological entities, not physical ones. So they could, under unusual circumstances, actually include sounds coming from physically different sources. However, the purpose (from an evolutionary perspective) of this grouping of units would appear to be the representation of environmental events that have a common physical cause (e.g., the grouping of a set of running steps within a longer set of walking steps). I welcome any comments, Al ------------------------------------------------- Albert S. Bregman, Emeritus Professor Dept of Psychology, McGill University 1205 Docteur Penfield Avenue Montreal, QC, Canada H3A 1B1 Office: Phone: +1 (514) 398-6103 Fax: +1 (514) 398-4896 Home: Phone & Fax: +1 (514) 484-2592 Email: bregman(at) -------------------------------------------------

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