How We React Like Computers When Stressed
The Effect Of Increased Demand During Divided Attention
Abstract
Introduction
Method
Results
Discussion
References
ABSTRACT
What is the limiting factor on our ability to "pay
attention". Attention is the criteria which determines which stimuli
achieve conciousness.
The two main theories are Filter and Capacity. Neither
theory is all-encompassing. Some of the differences in opinion arise from
liberal interpretations of "at the same time".
A computer can appear to do many things concurrently
(even though it can NEVER process 2 inputs simultaneously) due to it's
fast speed. Conceivably,the brain can operate at a similar speed and use
similar selection criteria.
119 Psychology students performed a Response Task whilst
concurrently reading words on a computer screen. The hypothesis that
increasing the difficulty of the reading task would increase Reaction Time
for the other task was supported. Treisman's (1971) experiment
which concluded parallel processing was possible can be re-interpreted
without parallel processing and should be re-conducted with additional
manipulations of the variables.
INTRODUCTION
Why is it that if we are doing something difficult
(e.g. fixing something) we don't notice someone talking to us - even if
they are right next to us? Or we stop talking in a car when turning into
heavy traffic? How many aircraft at once can an Air Traffic Controller
handle? Situations like this suggest that humans have a limited amount of
"attention" to go around amongst tasks,and if one becomes quite
difficult,then the other(s) suffer a reduction in attention. What are the
biological bases of this phenomenon?
Before proceeding,we need to define just what is meant
by "attention". Kahneman (1973) defined "attention" as "A label for some
of the internal mechanisms that determine the significance of stimuli,and
thereby make it impossible to predict behaviour by stimulus considerations
alone" (p2). Johnston and Heinz (1978) called it "The systematic admission
of perceptual data into conciousness".
Most previous theories have been built on Broadbent's
(1958) Filter Theory. The three stages involved are;
1. Sensory Registration (e.g. the ear "registers" that there is a sound)
2. Perceptual Analysis (e.g. is the sound my name? A noise?)
3. Response Selection (take appropriate action).
At one or more stages there is a "bottle-neck" - if
there is more than one stimulus - causing a filtering of the
stimuli. Different theories place the bottleneck(s) at different
stages. Leading proponents of this model are; Treisman (1960,1964),Erdelyi
(1974),Deutsch and Deutsch (1963),and Norman (1968). They have made
considerable "improvement" on this model,as the original theory "per
se" didn't hold up too well under experimentation.
These theories talk of "Modes Of Selection". An Early
Mode involves an easily discriminated stimuli (e.g. a voice
vs. noise) which makes little demand on the system - it is filtered at or
near Stage 1. A Late Mode involves harder to discriminate stimuli (e.g. 2
sounds - both the same voice,similar sounding words,but different
meanings) which makes a high demand on the system - it isn't filtered
until at or near Stage 3.
An alternative theory (e.g. Kahneman,1973) states that
there is a limited capacity of attention,and that increased capacity
requirements by a task reduces the capacity available for other tasks.
The key problem in the author's view is the definition
of "at the same time". Numerous experiments show that subjects exposed to
2 words simultaneously (literally at the same time) almost invariably only
recall hearing one word. Often they are aware of another sound,but don't
comprehend it. This is taken as evidence that stimuli CANNOT be processed
concurrently (they are processed serially). Kahneman (p5) states that
there is a CONTRADICTION since people CAN do things concurrently,such as
driving and talking (the stimuli are processed in parallel).
To reconcile this apparent contradiction,consider a
mainframe computer (as used by banks,etc.). At any ONE instant of time it
can only do ONE thing. This is known as Executing an
Instruction. However,it can Execute 30,000,000 Instructions PER SECOND
(30MHz). Thus HUNDREDS of people can use the computer AT THE SAME
TIME,since each person only requires a small number of Instructions,each one
only taking 0.000000033 of a second! Note that this is STRICTLY serial
processing.
This leads One to the question "How fast can the brain
operate?" Studies in the 50s (which subsequently led to the advent of
Sub-liminal Advertising - which was subsequently banned) showed that the
brain can visually perceive 100,000 bits of information per second
(100kHz),but only some of that information makes it to conciousness (as
per Divided Attention theory). The rest remains SUBLIME (from SUB-LIMEN
meaning "below the Limen or Threshold"- it is unconcious).
In fact - it could be argued that visual stimuli are
only admitted into conciousness at a rate of less than 30Hz (every 0.033
seconds). Consider a movie - which consists of still pictures being shown
at a rate of 30Hz. If visual stimuli were making conciousness at a faster
rate,then at least 2 consecutive stimuli would be of the same picture,and
"motion" would not appear fluid. We would really see lots of still
pictures (which clearly isn't the case - except for those old movies which
are very "jerky").
Therefore (I propose),when driving you are constantly
changing your "attention" from sight (watch the road) to sound (listen to
your passenger). Moray (1969) first proposed this "changing
channel" process,but at a much slower rate. Treisman (1971) challenged
this based on her Parallel Processing findings,but her findings can be
re-interpreted using one of her own ideas(!) - that of a "Dictionary
Unit" (in fact,many researchers have had the same idea,but under different
names).
The "Dictionary Unit" is a pre-conciousness structure
which recognizes specific stimuli. This could over-ride the current
"channel setting" for something important (e.g. hearing one's own name at
a party while listening to someone else). This is in fact what happens in
computers - a newly-arrived task can cause a LESS IMPORTANT task to be
interrupted (this will be discussed further).
The hypothesis then is that increasing the difficulty of
a primary task (the most important task) will cause the performance of
other tasks to suffer (an increase in reaction time) due to a reduction in
space capacity.
METHOD
Subjects: 119 Male and Female first year Psychology Students at the
University of Sydney.
Apparatus: Apple Macintosh computers with mouse (the program is described
below)
Procedure: In the first condition subjects were required to click on the
mouse whenever a black-box appeared on the screen. This occured at random
intervals. The computer recorded base-line reaction times (R.T.) for
subsequent comparison. Subjects were then split into two random groups
(A/B). In the second condition,in addition to the black-box,words appeared
in the corners of the screen,in a random fashion. Group A subjects then
had to read these words aloud (this being the primary task) while still
responding to the box (this being being the secondary task). Group B
subjects monitored Group A with a list of the words being presented,making
note of any errors. In the third condition,Group B subjects had to say
aloud the Super-Ordinate Category the words belonged to,while Group A
monitored for errors. This therefore increased the difficulty of the
primary task. The categories used were Animal,Seascape,Cookery. One
problem with the program was that if a word and the box appeared
simultaneously,then clicking in response to the box also caused the word
to dis-appear.
RESULTS
Mean Reaction Times for the three conditions were
calculated on the computer,as well as Standard Deviation,and Standard
Error of Measurement. These are summarised in Table 1. The error-rate was
analysed and not found to be significant.
A One-way Analysis of Variance was performed on the results
yielding: F=106.65 p<0.0001
Table 1
Mean Reaction Times In The 3 Conditions
--------------------------------------------------
| | | mean RT | Std | |
| condition | N | in secs | Dev | SEM |
|---------------|-----|---------|-------|--------|
| 1- simple | 119 | 0.316 | 0.065 | 0.006 |
| 2- words | 119 | 0.486 | 0.148 | 0.014 |
| 3- categories | 119 | 0.722 | 0.336 | 0.031 |
--------------------------------------------------
DISCUSSION
The results of this experiment support the hypothesis
that as the difficulty of a primary task increases (from no
vocalization,to saying words,to saying their super-ordinate
category),spare capacity available for other tasks decreases (increasing
R.T. to the appearance of the black-box - due to serial processing of
stimuli).
There is no indication at all of parallel processing in
this experiment,so let's revisit Treisman's (1971) claim that this is
possible in more detail.
In the first condition subjects listened to a single
list consisting of numbers and nonsensical syllables,and had to respond to
hearing a number. In the second condition subjects listened to two
simultaneous lists,and had to press the appropriate key for no numbers or
one number. The two conditions were then repeated,but the subjects were
first told what number to listen for - this is called pre-cuing. Pre-cuing
is known to reduce R.T. The logic was that the following steps would occur
if there was only serial processing;
1. Determine if the item on one of the ears is a number.
2. If it's not - switch to the other ear.
3. Determine if that's a number.
The first condition is finished after stage one (only
one list). Treisman therefore expected that the reduction in R.T. for the
second condition would be twice as much as the first. In fact the R.T. in
both conditions reduced by the same amount (0.115s),however overall
R.T. in the second condition was 0.080s longer than the first. Treisman
therefore concluded that there was parallel processing occuring in the
second condition,but that it was less efficient than in the first.
The problem here is that an active strategy is assumed
(i.e. listen to one ear first). In light of our computer theory consider
this:-
The subject knows that he only has to listen for A number (NOT 2
numbers),therefore the importance of the number Dictionary Unit is raised
(in the same way as our "Name" Dictionary Unit always has a high
importance),THEREFORE a PASSIVE strategy can be adopted. i.e. which
stimulus has a high importance? "listen" to that one! The data supports
this hypothesis also (increase in R.T. when going from actively listening
to passively listening).
The author would suggest re-running the experiment in
the following way;
1. Present a single list of numbers and syllables for a base-line R.T.,AND
ask the subjects to recall what numbers they heard (active listening).
2. Present 2 lists simultaneously and again ask for recall (passive
listening).
3. Again present 2 lists BUT this time allow 2 numbers to co-incide. Don't
tell the subjects to expect this (remember in the original experiment
there was never more than one number at a time). Thus the subject will
still be passively listening (only expecting no more than one number). NOW
when the subject is asked to recall I would predict that he will only be
able to remember one number of a pair OR he will notice that there were 2
numbers and complain ("which button do I press?"). Either way there will
be the same R.T.
4. NOW tell the subject to expect 2 numbers. He will now revert back to an
active strategy - listen to one ear,then listen to the other. There will
now be a noticeable increase in R.T. (double the processing) and an
increase on recall from condition 3 (if the subject didn't notice the
duality at that point).
Done in this manner there should then be very strong
evidence that parallel processing is not possible.
In conclusion,we have seen that when required to
perform multiple tasks,if one becomes harder our performance on the others
decreases. This suggests a limited capacity for attention. Further
research can quantify exactly what this is - and then we can make sure
that we're employing sufficient Air Traffic Controllers to safely
accomodate the number of aircraft in the sky.
REFERENCES
Johnston, W. A. & Heinz, S. P. (1978)
Flexibility and Capacity Demands on Attention
Journal of Experimental Psychology:General,107,420-435
Kahneman, D. (1973)
Attention and Effort
Engelwood Cliffs, NJ: Prentice-Hall
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