Investigating the effect of discomfort on reaction time Purpose and method The purpose of this investigation was to investigate the effect of discomfort on reaction time in humans, measured by dropping a ruler into a subject’s hand. Discomfort was caused by a bowl of ice. Background information Information is carried from the sensory receptors to the central nervous system and back the to effectors by means of nerves. When a number of different processes are involved (a situation informally known as multitasking, research has shown that the brain tends to split to deal the different parts to carry out the tasks.
The topic of interest is how having two problems to solve affects the speed of the brain in carrying out these tasks, and this will be tested by testing reaction time, or mental chronometry. Hypothesis The hypothesis is that when the subject is experiencing discomfort they will be likely to take longer to catch the ruler. This is because, according to my background information, the brain will have fewer resources to put at its disposal as its attention will be split and this will result in slower reactions. Variables
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The independent variable is the presence or absence of the cause of discomfort; in this experiment, ice. Due to the polar nature of the variable no error is associated with it. The dependent variable is the distance in millimetres of ruler that passes through the subject’s hand before it was caught. It has an error of ??0. 5 mm. Below is a list of controlled variables. Variable| Method of control| Amount of ice| Variation in the amount of ice would lead to different amounts of discomfort, so this was kept the same for each subject. Age of the subject| Age would naturally affect reaction time as older people are known to be less agile, so all of the subjects were the same age, 17 years. | Dominant hand of subject| All subjects were right-hand dominant. | Amount of time hand kept under ice| Variation in the amount of ice would lead to different amounts of discomfort, so this was kept at 30 seconds for each subject. | Equipment used * Ruler, used to measure the speed of reactions. * Bowl of ice, used to cause discomfort for the second half of the experiment. * Eight willing human subjects.
Method Eight volunteers were experimented on. Reaction time was measured by dropping a ruler between the subject’s thumb and index finger and measuring on the scale of the distance on the ruler when it was caught; a larger distance would mean a slower reaction time. This was done six times with each subject; for three of those six the hand was placed in a bowl of ice prior to testing. Annotated diagram of experimental procedure. Data collection and processing Subject| Discomfort absent (mm)| Discomfort present (mm)| 1| 213| 312| 92| 178| 160| 213| | 392| 140| 139| 302| 215| 242| 3| 273| 47| 134| 92| 70| 162| 4| 260| 413| 254| 156| 154| 250| 5| 89| 190| 126| 302| 194| 94| 6| 166| 255| 142| 292| 351| 189| 7| 245| 221| 299| 270| 497| 212| 8| 150| 80| 100| 180| 190| 260| The error for each measurement was ??0. 5mm. First of all the means of these values will be calculated to provide two values for each subject (all values to 3 significant figures). The mean is calculated by the following formula: Example calculation for the mean. Example for the ‘discomfort absent’ values for the first subject. Values: 213, 312, 92. (213 + 312 + 92) ? 3 = 206 i. e. distance on the ruler divided by three. Subject| Discomfort absent (mm)| Discomfort present (mm)| 1| 206| 184| 2| 224| 253| 3| 151| 108| 4| 309| 187| 5| 135| 197| 6| 188| 278| 7| 255| 326| 8| 110| 210| These values will then be plotted into a simple bar chart. A graph showing the differences in reaction times with discomfort present and absent for eight different subjects. From the bar chart it appears that there is not a significant difference between reaction times depending on whether discomfort it present and absent.
For five of the subjects discomfort increased reaction times, while for three discomfort decreased reaction times. This seems like slight support for the hypothesis but in reality it is probably statistically insignificant as will be tested next. Because the deviations are so great for the data, it is likely that this difference is not statistically significant. In order to statistically test the significance of this apparent relationship the means and standard deviations for both ‘discomfort present’ and ‘discomfort absent’ data will be calculated. Distance when discomfort absent (cm)| Distance when discomfort present (cm)| Mean| 197| 218| Standard deviation| 95. 3| 89. 9| (All values to 3 significant figures. ) This information will then be plotted into a graph to produce two normal distributions. This still suggests that there is no statistical correlation between the two sets of data, as so much of the two curves overlap. In order to formally prove this, however, a third statistic must be calculated, a t-test. The t-test is defined as where
This comes to a value of 2. 44. I must now also calculate the number of degrees of freedom (the sum of the number of values minus 2) which is 46, and determine an alpha level, or level of risk, which I will set at a standard 0. 05. Looking these values up in a table of significances, the result is 2. 01. The value was larger than the value from the table, leading to the conclusion that there is a statistical difference between the two sets of data. Conclusion and Evaluation In conclusion, the hypothesis i. e. hat reaction times would be slower when discomfort is present does appear to be supported by the data that I have. The bar-chart that was drawn showed that a majority of the subjects did have slower reaction times. The means also were fairly different, and the statistical significance of this was confirmed by carrying out a t-test. Looking at the bar chart, most of the ‘discomfort present’ data bars are significantly higher. There is one very high bar for ‘discomfort absent’ for Subject 4, which in retrospect I might have classified as an outlier.
Precision of the data seemed fairly poor, judging by the high standard deviations and the t-test value which was only slightly over the value from the table. It is difficult to judge its accuracy, as I have no other values to compare with. As time was not measured, the experimenter avoided including his own reaction time in the data. If necessary the values in centimetres could have been converted to time using kinematic equations. However this was done as it did not meet the needs of the experiment. Due to the simplicity of the equipment, there were no real experimental problems.
An exception was the use of the ruler. It was difficult for the experimenter to drop it consistently i. e. from the same height each time, and the subject seemed to improve over the six tests they did. As the ‘discomfort present’ tests were done last, it seems this might account for the faster times which were observed and which would have brought the means closer together. Were this experiment to be repeated, a computer program with a button that could be pressed would instead be used, and the subjects would be given some time to familiarise themselves with the program.
Another problem was that the ice causes vasoconstriction which slows blood flow and potentially slows the muscles, which means the slower responses could be due to changes in the cardiovascular system rather than the nervous system which is being tested. In the future therefore a different form of discomfort would be used, perhaps a needle. The number of subjects used (eight) was probably not enough. This is because of the large amount of variation in reaction times seen in humans, and it is not very likely that this sample was a perfect representation. Instead a sample of 50 would be used.
It would also be interesting to carry out the experiment with another age group, perhaps 50-year olds, to see if the conclusion was still true. ——————————————– [ 1 ]. http://users. rcn. com/jkimball. ma. ultranet/BiologyPages/C/CNS. html, accessed 22. 09. 11 [ 2 ]. http://news. sciencemag. org/sciencenow/2010/04/multitasking-splits-the-brain. html, accessed 22. 09. 11 [ 3 ]. http://www. plosbiology. org/article/info:doi/10. 1371/journal. pbio. 0030051, accessed 22. 09. 11 [ 4 ]. http://www. jeremymiles. co. uk/misc/tables/t-test. html, accessed 21. 09. 11