>----- Original Message -----
>From: Matt Gingell
>This matches my intuition. I have a terrible short-term memory ñ I canít
>a phone number and dial it, I have to go 3 or 4 numbers at a time. In
>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.
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).
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.
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