Reaction time

Test your reaction time. Understand the path of the muscles and neurons that carry out this task.
Science content
Biology: Sensing, Organ Systems (4, 5, 6)
  • a table
  • a ruler
  • a partner

Explain to students that they will be measuring how fast their neurons can transmit information in this activity. They will be using their neurons to see and to contract their muscles, as well as neurons that send messages between these two processes.

Give each pair of students a ruler. Demonstrate how one student rests their arm on the edge of a table their hand hanging over the edge, and holds their thumb and index finger a couple of cm apart. The other student of the pair holds a ruler so that the 0cm mark is between the thumb and finger. Without warning, the ruler is dropped and the partner closes their fingers on the ruler to stop it as quickly as they can.
Students should record the catch distance each time, doing several trials before switching roles with their partner.
They can try the activity with their dominant and non-dominant hand, as well as being distracted while talking about something different.

Ask students to find the mean of their data, and record their average catch distance.
Convert catch distances to reaction time:

Catch distance (cm) Reaction time (seconds) Catch distance (cm) Reaction time (seconds) Catch distance (cm) Reaction time (seconds)
1 0.05 11 0.15 21 0.21
2 0.06 12 0.16 22 0.21
3 0.08 13 0.16 23 0.22
4 0.09 14 0.17 24 0.22
5 0.1 15 0.18 25 0.23
6 0.11 16 0.18 26 0.23
7 0.12 17 0.19 27 0.24
8 0.13 18 0.19 28 0.24
9 0.14 19 0.2 29 0.24
10 0.14 20 0.2 30 0.25


Hockey goalies, and other people in high-speed sports need to have very fast reaction times. They would be able to catch the ruler at about 11cm, giving a reaction time of 0.15 seconds. Some students might have reaction times this fast, but most will fall between 15cm and 20cm (reaction times from 0.18 - 0.2 seconds).

With our rulers, our students got average catch distances of 10, 23, 19, 15, 10, 16, 18, 18cm.

Discuss how with any reaction time, it is amazing how fast the processing happens.
Show image of pathway, then trace pathway on a real brain if possible: the eye sees the ruler drop and a message is sent along a neuron to the thalamus in the centre of the brain, from which another neuron sends a message to the visual cortex. Once the image of the ruler dropping is perceived, there is a signal to close the fingers, down one neuron from the motor cortex to the spinal cord. Then a second neuron all the way from the spinal cord down the arm to the finger muscle. Then the finger muscle contracts.
All this takes milliseconds. The slowest part is the message passing between neurons; the neurons themselves transmit the electric message very fast.

Attached documents

I tried having students graph their reaction time for sequential catches, expecting them to gradually improve. But they do not - it is quite up and down how fast the reaction time is. Recording the fastest, or average, time seems to be the best way to deal with this data.

Graphing student data on one graph shows highly variable results.
Discussion: need better standard way of measuring (make sure students fingers are wide open not touching ruler), need to mix up when each kind of data is collected so students getting better at the task doesn't skew results.

Grades taught
Gr 4
Gr 5
Gr 6