Required Practical: Reaction Time (AQA GCSE Combined Science: Trilogy: Biology): Revision Note
Exam code: 8464
RP7: Reaction time
Aim: to plan and carry out an investigation into the effect of a factor on human reaction time
Method: a number of experiments will be carried out to measure reaction time in which a single factor will be investigated at a time
Reaction time is the time taken to respond to a stimulus; reactions are usually very quick responses typically taking less than a second to occur
Reaction time can be affected by factors such as age, stress or use of drugs (e.g. caffeine)
Examples include the effect of background noise or consumption of caffeine on how quickly a person catches a ruler
Reaction time can be measured in this way using the principle that the further down the length a ruler is caught, the slower an individual's reaction time
The experiment can be repeated several times to calculate a mean average distance caught and this can be equated to a reaction time
The process is then repeated after a condition is changed (the person drinks a can of caffeinated drink or has to repeat the experiment when loud background music is playing)
Only one factor (independent variable) should be changed in the investigation
There are many control variables that should be considered in this experiment such as:
the person catching the ruler using their dominant hand each time
dropping the same ruler from the same height each time, with the ruler orientated in the same direction (0 cm facing down)
if the effect of caffeine is being investigated then none should have been consumed before the start of the experiment, or the room is silent for the first run if background noise is being altered
It is possible to carry out a reaction time investigation using a computer; this is obviously more precise as it removes human error from measurements
Reaction time can also be recorded in milliseconds which is more accurate than seconds
Diagram of method for carrying out an investigation into reaction time
Examiner Tips and Tricks
This experiment is prone to many errors and there are many factors that can affect the results. Repeat as many times as possible.
Interpreting information about the nervous system
It is necessary to be able to extract and interpret data from graphs, charts and tables about the functioning of the nervous system
This includes calculations such as mean reaction times or evaluating whether a mean is reliable if any anomalous results were included
Worked Example
Three students played a computer game which measured their reaction time to click when they saw a blue light flash on the screen
Their results were recorded in the table below:
Attempt Number | Student A Time (ms) | Student B Time (ms) | Student C Time (ms) |
|---|---|---|---|
1 | 259 | 276 | 270 |
2 | 267 | 260 | 266 |
3 | 250 | 252 | 573 |
4 | 255 | 262 | 264 |
5 | 243 | 261 | 268 |
Mean | 255 | 262 | 328 |
Question: Which student had the fastest reaction time?
There is an anomaly recorded for student C on their third attempt – 573 ms is much higher than the other results recorded. This should not be used to calculate a mean.
The lowest reaction time equates to the person with the fastest reaction time.
Student A has the fastest reaction time at 255 ms
Student C the slowest reaction time at 267 ms
Examiner Tips and Tricks
You could be asked to express answers in standard form or as ratios in an exam question.
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