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ARRoGANT CoURiERS WiTH ESSaYS
Grade Level: Type of Work Subject/Topic is on:
[ ]6-8 [ ]Class Notes [Lab: Response Results ]
[x]9-10 [ ]Cliff Notes [from Stimulus ]
[ ]11-12 [x]Essay/Report [ ]
[ ]College [ ]Misc [ ]
Dizzed: o4/95 # of Words:951 School: ? State: ?
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Part 1
In this signal detection experiment, there were 3 parts, each with 50
trials. On half of the trials, a signal 'x' was presented along with
visual noise 'z'. The other half of the trials showed only visual noise.
The task was to locate the signal stimulus 'x' among all other noise
signals 'z' present. All this was done on a computer generated program.
Another 2 students' results of the experiment were obtained for
further analysis of signal detection.
During the trials there were many 'z' flashing on the screen. The
objective was to determine if the symbol 'x' was also flashed on the
screen. The responses to be given were :
If you are sure you saw 'x' press 5
If you are fairly sure you saw 'x' press 4
If you are unsure you saw 'x' press 3
If you are fairly sure you didn't see 'x' press 2
If you are sure you didn't see 'x' press 1
The dependent variable in this experiment was the response in
pressing 1,2,3,4 or 5. The independent variable was the signal stimulus
'x' which flashed across the screen.
The design of this experiment is the within-subject design since the
conditions were randomized from trial to trial and students were tested
under mainly the same experimental conditions.
The Questions which can be addressed with this design are how would
the results have changed if the design had been a between- subject design?
Also what would happen if the trials were not randomized? How would this
factor distort the results in this within-subject design.
Part 2
Results
Group 1
Condition 1 Condition 2 Condition 3
0.01 sec. 0.05 sec. 0.1 sec.
1+2+3+4+5 5
1+2+3+4+5 5
1+2+3+4+5 5
Signal 20 13 29
29 25 24
Noise 30 0 21
2 25 1
P(Resp +/S) 0.6875 1 1
P(Resp +/N) 0 0.952 3.846
D' -4.7652 -1.374 -1.797
Group 2
Condition 1 Condition 2 Condition 3
0.01 sec. 0.05 sec. 0.1 sec.
1+2+3+4+5 5
1+2+3+4+5 5
1+2+3+4+5 5
Signal 25 7 25
24 25 24
Noise 25 0 25
6 25 1
P(Resp +/S) 0.68 0.96 0.96
P(Resp +/N) 0 0.24 0.04
D' -4.794 -0.857 -1.752
Group 3
Condition 1 Condition 2 Condition 3
0.01 sec. 0.05 sec. 0.1 sec.
1+2+3+4+5 5
1+2+3+4+5 5
1+2+3+4+5 5
Signal 18 13 5
20 4 25
Noise 19 0 25
0 20 0
P(Resp +/S) 0.419 0.84 0.862
P(Resp +/N) 0 0 0
D' -4.491 -4.933 -1.602
In group 1, the probability of the response signal stimulus 'x' was
the greatest in condition 2 and condition 3 where it was 1. The
probability of a noise signal was lowest in condition 1 where it was zero.
The distance between the means of the two distributions was closest in
condition 2. The value for D' in condition 2 was -1.374. So overall in
group 1, the best response for the signal stimulus is shown in condition 2,
where the stimulus flash duration was 0.05 seconds.
In group 2, the probability of the response signal stimulus was
greatest in condition 2, with 0.96. The lowest probability of a noise
response was in condition 1, with the result of 0. The closest distribution
of the 2 means was in condition 2 with -0.857.
The best response to the signal stimulus 'x' was again in condition 2
with a stimulus flash duration of 0.05 seconds.
In group 3, the highest probability of a response signal being a 'hit'
was in condition 3, which was 0.862. The lowest probability for a false
alarm was in all 3 conditions which equalled 0. The distance between the
means of the two distributions was the lowest in group 3. Therefore in
group 3 the best condition for responding to a hit was in condition 3,
which had a stimulus flash duration of 0.1 seconds.
Signal detection approaches provide ways of examining sensory factors
and response bias. A hit rate in signal detection gives us an estimate of
the subjects sensitivity. The higher the hit rate is, the more sensitive
the subject. Also the higher the false alarm rate, the less the subject
is going to respond with a hit rate. In responding to the stimuli the
subject will either sense or not sense the stimuli, and in addition will
also decide what to report. So because the subject decides what to report
this is why all three groups had quite different results.
Part 3
Two other variables that could influence the sensitivity dimension of
the subjects response are:
1) The number of choices to be made if the signal stimulus was present.
Five choices are too many (1,2,3,4,5). It would have been better if there
were only three choices : sure you saw 'x', unsure, and sure you didn't see
'x'.
2) The time when the signal stimulus appeared on the screen. If it was
the first or last signal shown, 'x' could be identified very easily.
Another variable that may influence the response-criterion dimension
of the subjects response was how dispersed the signals were on the screen.
Sometimes they were bunched together and so it was easier to locate 'x'.
But if the signals were all spread out across the screen then it was harder
to locate the signal stimulus.
A confounding variable in this signal detection experiment could be
how you were positioned in your distance from the computer screen. If you
were not positioned a constant distant away from the screen, this would
affect how you saw the signals. If the signals were spread out and you
were very close to the screen then you would not be able to clearly
recognize the signal stimulus 'x' among all the other noise signals 'z'.