The reaction time of ten subjects was measured. The subjects were asked to catch
a ruler ten times under five different conditions. The first condition measured
the subject's simple reaction time. Each further condition added an additional
stimulus and the reaction times were measured. There was a clear increase in
reaction time with the addition of further stimulus, however the expected result
of a steady increase in response time with the addition of each condition did
not occur. The third condition displayed the highest response time where as the
final condition displayed the second lowest (after condition 1). Assuming that
no design problems in the experiment affected the results, it cannot be
concluded that cognitive processes occur in separate order and do not overlap.
Given the average reaction time of condition five was lower than condition
three, some cognitive adaption may have occurred to lower the response time of
the subjects or another reason may exist. One aspect not covered by the
experiment, but important to the results was the error factor. Pre-guessing the
experimenter caused a high rate of error, however it lowered the overall
results. Why measure response times? As the world moves forward with technology,
increasing pressure is placed upon humans to be quicker, be smarter and to
operate more efficiently. As the population increases systems are being put in
place to reduce incidences and accidents occurring. An example of this is a
study conducted by Cameron, 1995 examining the influence of specific light
colors, motor vehicle braking and the reaction time of the drivers to these
specific clouds and conditions to avoid rear end collisions. Donders subtractive
method holds that reaction times can be obtained by subtracting the simple
reaction time; or subtracting type A from type B etc. (Cameron, 1995). Given
this, it stands that the more stimulus provided (or thought processes required),
the longer the response time of the subjects. This theory is tested in the
measurement of ten responses to five test conditions. The trial provides
preliminary information to participants and it is expected that reaction times
will be shorter than if no information was supplied. (Rosenbaum, 1980.) Method
Participants Ten participants were selected, four female and six male. Ages
ranged from twenty-two to fifty three. All were fully able bodied and from
English speaking backgrounds. Materials A plastic yard rule was used. The yard
rule was six centimeters in width. Procedure Condition One The experimenter sat
one subject on a chair and instructed them to place their arm out in front of
them at a comfortable height. The yard rule was then placed between the
subject's fingers at a height of 10 centimeters. The subject was then told the
condition 1 (Appendix A) and given three trials. The subject then completed the
ten tries at the condition and the results were recorded. All ten subjects were
tested in the same manner. No abnormal results were obtained. Condition Two The
experimenter sat one subject on a chair and instructed them to place their arm
out in front of them at a comfortable height. The yard rule was then placed
between the subject's fingers at a height of 10 centimeters. The subject was
then told the condition 2 (Appendix A) and given three trials. The subject then
completed the ten tries at the condition and the results were recorded. All ten
subjects were tested in the same manner. An error rate and abnormal results
occurred. Condition Three The experimenter sat one subject on a chair and
instructed them to place their arm out in front of them at a comfortable height.
The yard rule was then placed between the subject's fingers at a height of 10
centimeters. The subject was then told the condition 2 (Appendix A) and given
three trials. The subject then completed the ten tries at the condition and the
results were recorded. All ten subjects were tested in the same manner. An error
rate and abnormal results occurred. Condition Four The experimenter sat one
subject on a chair and instructed them to place both their arms out in front of
them at a comfortable height. The yard rule was then placed between the
subject's hands at a height of 10 centimeters. The subject was then told the
condition 4 (Appendix A) and given three trials. The subject then completed the
ten tries at the condition and the results were recorded. All ten subjects were
tested in the same manner. A high error rate and abnormal results occurred.
Condition Five The experimenter sat one subject on a chair and instructed them
to place both their arms out in front of them at a comfortable height. The yard
rule was then placed between the subject's hands at a height of 10 centimeters.
The subject was then told the condition 5 (Appendix A) and given three trials.
The subject then completed the ten tries at the condition and the results were
recorded. All ten subjects were tested in the same manner. A high error rate and
abnormal results occurred. Results Then ten subjects all recorded faster
reaction times for condition one than any of the other conditions (Fig 1). On
the surface this result would support the theory that the more stimulus the
slower the reaction time of the subject. When examined as a whole, this is not
strictly the case. Condition one averaged 180.3 milliseconds, condition two
240.5, condition three 270, however, condition four averaged 254.4 and condition
five only 238.2 milliseconds. Fig 1 - Average responses of subjects over five
conditions. Initially the introduction of more stimuli slowed the reaction time
of the subject. The reaction time of the subject did not, however slow from
condition three to four and four to five with more additions. The standard
deviation for condition one was also lower than any of the other conditions (Fig
2). The deviation for condition one was 26.5, condition two 37.5, condition
three 31.1, condition four 31.7 and condition five 28.8. The high variation for
condition two may be explained by the fact that it is the first introduction of
an additional stimulus over and above the simple response. Fig 2. Average
responses of subjects and the standard deviation. Discussion The results show
that an initial increase in the complexity of a task increases the reaction
time. According to Donders' Theory (Gottsdanker, R & Shraap, P., 1985)
results for Condition Five (Discrimination + Decoding + Response Selection)
should be greater than condition four (Discrimination + Response Selection) and
condition three (Discrimination and Decoding). Condition five, however, was
faster in reaction time that condition four and three (Fig 1). Shown only these
results the conclusion may be drawn that Donders theory is not entirely correct
until the source, method and type of experiment is examined. The biggest factor
in the reduction of response time between experiments three and four to
experiment five was the error ratio. It was clear in the experiment that the
subjects were pre-guessing the experimenter. This was providing the subject with
a better result than if the subject was legitimately waiting for instructions,
as there was no penalty for incorrect responses. Nine out of the ten subjects
saw the experiment as a competition and therefore concentrated more on speed
that correctness. As in the case when the subject drops the ruler himself or
herself or when pre-advised of the requirement, the results are shorter as the
processing time is shorter when the subject has pre-ordained the response they
will make. This limitation was due mainly to the type of experiment conducted.
Given the materials and the situation it was not an accurate measure of response
times as some subjects had thirty or forty attempts before ten correct responses
could be obtained. Although the logic of Donders' Theory is relevant, in this
case it cannot be ascertained conclusively that an increase in tasks slowed the
reaction time of the subjects.

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