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

From: bejoya rakshit (blr197@soton.ac.uk)
Date: Mon Mar 02 1998 - 12:25:34 GMT

Hi everyone, here is my part of the magic number seven in
kid-sib style.

A researcher named Pollack was interested in the ability to
judge different tones of pitch. Pollack took differences
tones of frequency ranging from 100-8,000 cps and a different
number was given to each tone.These tones were arranged at
equal intervals. A tone was then played and the participant
had to say which number it was. The participant was told
straight away if they were right, and if not, what the
correct number was, before the next tone was played.

The amount of tones in the range was varied to see if there
was any difference in the amount the participants could
remember.

If there were just 2 or 3 tones in the range the listeners
named all the numbers correctly. When there were 4 tones in
the range there were mistakes but hardly ever. The
participants frequently made mistakes when the range
consisted of 5 or more tones. When the range had 14 tones
the participants made lots of mistakes.

As the amount of information increases, the amount that can
be remembered also increases until it reaches a point at
which it is not possible for the brain to be able to sort and
recognise it. The maximum the brain can deal with is known
as the capacity. In this case the information is measured in
bits. 2.5 bits is the point whee if it is increased,
confusion will occur and mistakes will be made. (it is the
capacity). 2.5 bits is equal to 6 different categories. In
other words the participants can only identify 6 different
pitches without making mistakes. (there are exceptions to
this e.g musicians with perfect pitch).

Participants who were able to correctly identify 5 high
pitched tones in one test and 5 low pitched tones in a second
test are expected to be able to identify all 10 in one
combined test. But when this was vtried the capacity was 6.

Garner did similar research on identifying different
intensities of loudness. In this case the capacity was 2.3
bits or 5 categories.

The results of these two experiments were very close ad it is
not possible to establish if they are significantly different
from one another as they used different methods of obtaining
and analysing data abd they were done in different lab
conmditions. The conclusion is that we are slightly more
accurate in our judgement of pitch than that of loudness.

Beebe-Center, Rogers and O'connell experimented with
judgements of taste intensities using different
concentrations of salt solutions. Tihe results for this
showed that auditory senses are more accurate then taste.
The capacity for taste was 1.9 bits or 4 categories.

Hake and Garne tested for the capacity of visual judgements.
Participants were told to say where a pointer was between two
markers. In one experiment they could use any number between
0 and 100 to describe the position of the pointer. in the
second experiment the participants were restricted with the
numbers hey could use to describe the position. There was no
real real difference in the results of the two experiments.
The capacity for visual judgement was 3.25 bits.

Coonan and Klemmer later repeated the experiment and found
3.2 bits to be the capacity when tho pointer position was
only exposed for a short time. When the pointer was exposed
for a longer time the capacity was 3.9 bits.

These results show visual judgements to be the most accurate
of the senses mentioned so far.

Other research has looked at the ability to judge the sizes
of squares (2.2 bts, 5 categories), brightness (2.3bits) and
hue (3.1 bits).

The mean and standard deviation of all the reults were
calculated and showed the total range of categories we can
judge is from 3 to 15 depending on the sense in question.
The cause of the limitation we have for judging categories is
unknown but we all have it. Maybe it is learnt or it could
be biological.

----------------------
bejoya rakshit
blr197@soton.ac.uk

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