Practical: Reflex Actions (SQA National 5 Biology): Revision Note

Investigating reaction times

• Reaction time is the time taken to respond to a stimulus

  • for example, catching a falling object after it is released

• It is an indicator of how quickly the nervous system detects, processes, and responds to sensory information

• Reaction time can be affected by a variety of factors, such as age, stress, fatigue, background noise, or the use of stimulants such as caffeine

• In this investigation, you will measure human reaction time using a ruler drop test and determine how one chosen factor (e.g. caffeine consumption or background noise) influences it

  • The further down the ruler is caught, the longer the person’s reaction time

Apparatus

• 30 cm ruler

• Volunteers x5

Method

1. Each volunteer needs to sit in a chair with a good upright posture 

2. Ensure the volunteer places their forearm on the table so that it extends over the edge 

3. Ask the volunteer to place their thumb and fingers on either side of the bottom of the vertically placed ruler, with the number “0” at the bottom and the “30” near the top

4. Tell the volunteer that the ruler will be "dropped" without warning. The volunteer needs to catch the ruler with their thumb and forefinger as soon as they sense it dropping

5. Drop the ruler. When your volunteer catches it, record the number on the ruler displayed just over the thumb. The lower the number, the faster the reaction time

6. Conduct five trials with the same volunteer

7. Repeat the experiment with at least four other volunteers and record your results in a suitable table. Use a conversion table to convert the measurements into reaction times