PSYC 401 UNH Measuring the Speed of Neural Transmission Project
Background
One of the most widely used dependent variables in psychological research is reaction time, which is the measured time it takes a subject to respond to the presentation of a stimulus. This exercise is based on one of the first scientific uses of reaction time and employs a procedure called the “subtraction method.” The logic behind the subtractionmethod is that the measure of the duration of a process can be found by obtaining two reaction time measurements, one that includes the psychological process of interest and one that does not. Subtraction of the time not including the process in question from the one that does yields an estimate of how fast the process takes. In 1850, Hermann von Helmholtz was the first to use this method scientifically to measure the speed of nerve impulses. In 1868 Franciscus Donders expanded on the subtraction method in what wasarguably the first ever experiment in cognitive psychology. As mentioned in class, Donders developed the idea of choice reaction time which uses the subtraction method to measure the time for a person to make a “mental decision,” i.e., decide whether a light’s color is red or blue.
This exercise replicates von Helmholtz’s experiment in an admittedly less scientific but hopefully fun and interesting way. (No frogs will be harmed…)
Conducting the Experiment
This experiment needs to be conducted by a group of at least four people. Arrange a group of chairs in a straight row with you and the others sitting in the chairs. You should be positioned in an end chair with a stopwatch in your right hand, grasping the right ankle of the adjacent team member with your left hand. Each subsequent person then grasps the right ankle of the adjacent person (on their left) with their left hand. Make sure that everyone grasps (i.e., wraps their hand around) the adjacent person’s ankle – simply touching the person’s ankle won’t work! Once arranged, all participants should close their eyes. Instructions to all are simple: Once you feel your ankle squeezed, squeeze the person’s ankle you are grasping. The process starts with you simultaneously starting the stopwatch and squeezing the ankle you are grasping. When the last person in the row feels his/her right ankle squeezed, they should immediately yell “Stop.” When you hear “Stop,” you should immediately stop the stopwatch and record the time.
There is one other condition of the experiment. This involves the same procedure but now people grasp and squeeze each other’s shoulders rather than ankles.
You will also need to measure the distance (in meters) between each person’s shoulder and ankle and then compute a mean (average) distance for all participants.
You should practice the procedure (both conditions) a few times. When your group is comfortable with the process, start the experimental trials. Use the data collection tableon the Answer Sheet to record your data. Alternate the ankle and shoulder trials until you have five measurements for each condition.
Data Analysis
We can now use the reaction time subtraction method to estimate the speed of neuraltransmission. Given that the only difference in the two conditions is the distance the neural signal must travel, the logic is simple:
1. Compute the mean ankle time and the mean shoulder time and record them in the bottom row of the data collection table.
2. Subtract the mean shoulder time from the mean ankle time and record it in the space on the Answer Sheet. This difference is the mean time it takes the signal to travel between the ankle and the shoulder.
3. Measure (in meters) the distance from ankle to shoulder for each team member (exclude the experimenter) and find the mean. Record your result in the space on the Answer Sheet.
4. Finally, divide the mean distance by the mean time and record it on the Answer Sheet. The result will be an estimate of the speed of neural transmission in meters per second.
