# George Miller [Magical Number 7 +/-2] Part 5

From: catriona barrett (chb197@soton.ac.uk)
Date: Thu Feb 26 1998 - 17:24:51 GMT

Dear Everyone,

Here are my comments on part five of Miller. Forgive me if it seems a
bit muddled but it was unusually worded most of the time, e.g.
"identify absolutely the magnitude of a unidimensional stimulus
variable", and trying to translate it into everyday English was
difficult, as well as stressful.

Part 5: The Span of Immediate Memory

"There is a clear and definite limit to the accuracy with which we
can identify absolutely the magnitude of a unidimensional stimulus
variable. I would propose to call this limit the span of absolute
judgment, and I maintain that for unidimensional judgments this
span is usually somewhere in the neighborhood of seven."

In this section Miller is stating that there is a limit to the
number of ways in which we can accurately measure or define one
single object, i.e. the amount of information we can hold about any
one object is limited, and Miller suggests that this limit is
approximately seven. This is what he means by 'The Span of Absolute
Judgement'.

"We are not completely at the mercy of this limited span, however,
because we have a variety of techniques for getting around it and
increasing the accuracy of our judgments. The three most important of
these devices are (a) to make relative rather than absolute
judgments; or, if that is not possible, (b) to increase the number
of dimensions along which the stimulus can differ; or, (c) to arrange
the task in such a way that we make a sequence of several absolute
judgments in a row."

Miller suggests ways in which we can increase our span of absolute
judgment:

(a)"Relative rather than absolute judgments" - Instead of looking at
objects as completely non-related, we could, and we do in fact link
objects together by similar characteristics in order to be able to
remember more. An example is looking at an apple, an orange, a
banana and a pear in a bowl. Instead of remembering these as four
different objects out of the approximate seven we are supposedly
limited to, we would usually group all these objects into one group,
fruit. Grouping these four objects together would still enable us to
remember that there was an apple, banana, orange and pear in the bowl
by remembering that they were all pieces of fruit but we would only
be using up one of the seven possible pieces of information that we
are limited to, thus making room for other pieces of information!

(b)"Increasing the number of dimensions along which stimuli can
differ" - Miller suggests that we can make more accurate judgments
An example is looking at a mug and seeing it just as for what it is,
a mug. On the other hand we could define it in more ways. We could
say that the object is a mug, that it is blue, that it is made of
china, that it has a handle, and so on. Miller goes on to say that by
object we can actually increase our span of absolute judgment to
approximately 150. However, he then also goes on to say that this
limit is probably more in the region of thousands if there is a limit
at all. This makes sense as in our everyday life we can remember what
seems like an endless amount of information, not just 7 or 150 pieces.

(c)"Making a sequence of several absolute judgments in row" - An
example of this would be remembering a telephone number. When we look
at a telephone number what we see is approximately six absolute
digits. When we need to remember a telephone number we do not learn
each digit as an absolute but rather we remember all the digits
together as if they were only one number. A way of testing whether or
not this is true is to ask somebody what the fourth digit in their
telephone number is. Although it will not take them long to tell you,
the chances are that they had to recite the number starting from the
beginning until they got to the fourth digit, which means that to
remember the digit they grouped all the digits into one number or one
piece of information.

Miller then suggests that there is a 'Span of Perceptual
Dimensionality', i.e. that a stimulus e.g. a mug can only be defined
in a limited number of ways and he believes that it is approximately
10.

Miller explains (c) in more detail and describes experiments where
instead of just presenting subjects with a stimulus and immediately
asking them to name it, subjects are presented with several stimuli
and are then told to say what they were presented with. Miller
believes that in this way subjects are using their 'immediate memory'
rather than their 'absolute judgement'. Kid-sib probably doesn't
understand this, sorry, but even Miller himself starts to get
confused. He goes on to say that there is a 'Span of Attention' that
will allow us to immediately remember approximately six objects that
are in our field of vision i.e. if the setting was unfamiliar to me,
while sitting at this computer, if I shut my eyes I would only be
able to remember the screen, the keyboard, the mouse, sheets of
paper, my pencil and my purse. Miller says that it may be natural to
consider the span of immediate memory, span of absolute judgment and
span of attention to all be different parts of the same thing i.e.
that they all work together. Miller states that to do this is a grave
mistake, and he actually made it.

Miller originally claimed that the span of immediate memory was
limited to seven pieces of information but managed to raise doubt
about his theory by using the following example. He suggested that if
the span of immediate memory were to remain at a fixed level then it
should automatically follow that the span should be short when items
contain a large amount of information and long when the items contain
a small amount of information. However, this is not necessarily true.
If decimal digits are worth 3.3 bits of information each then
remembering 7 of them would result in 23 pieces of information. The
average English word is worth approximately 10 pieces of information
each and if the amount of information we can recall is to be
regulated then it should follow that we should only be able to
remember 23 pieces of information about English words, as with
decimal digits which would subsequently mean that we could only
recall two or three words at any one time. If that was true we would
be in big trouble when it came to revising for and sitting exams!

Miller refers to experiments carried out by Hayes and Pollack which
reveal that the amount of information that is transmitted to memory
does not remain exactly the same at all times but that the amount of
information increases as the amount of information about each
separate items increases. The limit for binary items was found to be
approximately nine and for monosyllabic English words was found to be
approximately five, hence "The Magic Number Seven Plus Or Minus Two".

In conclusion Miller states that our absolute judgment of a stimulus
is limited by the amount of information attributed to that stimulus
and that our immediate memory is limited by the number of items.
Miller distinguishes between bits and chunks of information but
states that the span of immediate memory does not necessarily depend
on the number of bits in a chunk i.e. digits in a telephone number.
He also states that this area still needs a lot of research.

I'm sorry if this is really confusing but I did find the section
quite hard to understand. See you on Monday.

----------------------
catriona barrett
chb197@soton.ac.uk

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