From: Patrick Wilken (patrickw@cs.monash.edu.au)
Date: Thu Sep 02 1999 - 17:56:13 MDT
>----- Original Message -----
>From: Matt Gingell
>
>This matches my intuition. I have a terrible short-term memory ñ I canít
>look at
>a phone number and dial it, I have to go 3 or 4 numbers at a time. In
>psychology
>thereís a theory that people can hold and manipulate 7 plus-or-minus 2 symbols
>comfortably ñ Iím way down the bell curve, I can barely do 5 on a good day.
Matt:
Sorry to disappoint you, but you are actually very normal. The original
1956 paper by George Miller used a 7 item limit more for rhetorical device
than because it was that close to actual limits in humans. Since then it
appears that we have two limits: one associated with phonological
short-term memory and another with visual short-term memory (VSTM).
Phonological short-term memory appears to hold about 2 seconds of
information so if you thinking in Welsh you can hold far fewer words than
if you are thinking in Chinese. VSTM appears to hold around 4, but there is
some variation. In experiments I have been doing for my dissertation I
regularly find subjects that appear to have capacity limits up around 7-8
and others down around 2-3. My own belief is that this is probably an
attentional limit as well (there are various studies suggesting that we can
only attend to about 4 items at a time). There is some disagreement as to
where this limit might be many posit something akin to a high-level buffer
than can only hold an absolute number of items (around 4-5).
My view (which is controversial) is that the sorts of capacity limits we
see are caused by low-level noise and not a high level capacity limit.
Basically the more things you try to attend to the poorer the quality of
the signal you (more specifically neurons in the prefrontal cortex) have to
work with. Once you get beyond about four 'things' the quality of the
signal drops off quite quickly (though there is no absolute limit to the
number of things that can attended to).
best, patrick
Refs:
Baddeley, A. (1993). Working memory or working attention? In A. Baddeley & L.
Weiskrantz (Eds.), Attention: Selection, Awareness and Control . Oxford:
Clarendon Press.
Baddeley, A. (1994). The magical number seven: Still magic after all these
years? Psychological Review, 101(2), 353-356.
Logie, R. H. (1989). Characteristics of visual short-term memory. European
Journal of Cognitive Psychology, 1, 275-284.
Luck, S. J., & Vogel, E. K. (1997). The capacity of visual working memory
for features and conjunctions. Nature, 390, 279-281.
Miller, G. A. (1956). The magical number seven, plus or minus two: Some
limits on our capacity for processing information. The Psychological
Review, 63(2), 81-97.
----------------------------------------------------------------------------
Patrick Wilken
Editor: PSYCHE: An International Journal of Research on Consciousness
Board Member: The Association for the Scientific Study of Consciousness
http://psyche.cs.monash.edu.au/ http://www.phil.vt.edu/ASSC/
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