
Rulers and Reaction Times
Abstract
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. 
<br><br><b>Bibliography</b><br><br>
Cameron, D.L. (1995). Color-specificity to enhance identification of rear lights.
Perceptual and Motor Skills, 80(3): 755 - 769.
Gottsdanker, R. & Shraap, P. (1985) Verification of Donders' subtraction method. Journal of Experimental Psychology: Human perception and performance, 111(6), 765 - 776.
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Rossenbaum, D.A. (1980). Human movement initiation. Journal of Experimental Psychology: Specification of aim, direction, and extent. General 109, 444 - 474.
Weiten, W. (1998). Psychology, Themes and Variations (4th Ed.) California: Brooks/Cole.
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