Investigating Factors Affecting Reaction Time

Section 1 of 7What reaction time is

Definition

• Definition Reaction time is the interval between a stimulus being detected and the body making a response.
  • For a simple reflex-type task it is usually well under one second.
• The pathway involved is receptor, sensory neurone, coordinator (brain or spinal cord), motor neurone and effector (muscle).

Factors that change it

• Factors that change it Age, tiredness, stress and distraction can all lengthen reaction time.
• Drugs alter the speed of nerve transmission.
  • Caffeine is a stimulant and tends to shorten reaction time, whereas alcohol and many sedatives lengthen it.

The hypothesis tested here

• The hypothesis tested here In this practical the hypothesis is that reaction time improves with practice,
  • so later attempts should give shorter times than early ones.
• A hypothesis is a testable prediction; the results then support it or fail to support it.

Section 2 of 7The measuring principle

1Ruler is released

• Ruler is released The ruler falls freely from rest, so the longer it falls the further it travels.

2Brain processes the stimulus

• Brain processes the stimulus The volunteer sees it move, and the signal travels through the nervous system to the hand muscles.

3Fingers close

• Fingers close The ruler is caught after a delay. A slow response means the ruler has fallen further.

4Distance gives time

• Distance gives time A bigger catch distance means a longer reaction time.
  • A conversion table or the relationship between distance and free-fall time turns centimetres into seconds.

Section 3 of 7Method

1

Seat the volunteer upright with the forearm resting on the table edge and the hand hanging over the edge, so that the arm is supported but the hand is free.

2

Hold a 30 cm ruler vertically so that the 0 cm end is level with the top of the volunteer's open thumb and forefinger, with the ruler between them but not touching.

3

Without warning, let go of the ruler. The volunteer catches it as quickly as possible between thumb and forefinger.

4

Read the number on the ruler level with the top of the thumb. This is the catch distance in centimetres. A smaller number means a faster response.

5

Record five trials for the same volunteer, using the same hand each time, then repeat with at least four more volunteers.

6

Calculate the mean catch distance for each trial number, and use the conversion table to change each mean distance into a reaction time.

Section 4 of 7Variables and apparatus

Type	Detail	Why it matters
Independent variable	The person catching the ruler, and the trial number (amount of practice)	This is what is being compared
Dependent variable	Reaction time, found from the catch distance on the ruler	This is what is measured
Control: hand	Always the dominant hand	Different hands may respond at different speeds
Control: ruler	The same ruler, released from the same height, 0 cm end downwards	A different release point would change the distance fallen
Control: environment	Same room, same level of distraction, volunteers eyes on the ruler	Distractions lengthen reaction time
Apparatus	30 cm ruler, chair and table, at least five volunteers, results table	Simple equipment keeps the test repeatable

Section 5 of 7Analysis and evaluation

Processing the data

• Processing the data Convert distance to time to translate the data from one form into another.
  • Plot the mean reaction time against trial number to see any trend.
• Decide whether the trend supports the hypothesis.
  • If times fall as trials increase, practice appears to improve reaction time, but only for this small sample.

Sources of error

• Sources of error It is hard to read exactly where the fingers meet the ruler, and the start position may differ slightly each time.
• A volunteer may anticipate the drop, for example by watching the dropper's hand, which gives an unfairly fast result.

Improvements

• Improvements Use a computer-based test or light gates, which remove human error from timing and can record in milliseconds for greater precision.
• Use more volunteers and more trials, and discard clear anomalies before calculating means.

Section 6 of 7Key terms

Term	Meaning
Reaction time	The time taken to respond to a stimulus after it is detected.
Stimulus	A change in the environment that is detected by a receptor, such as the ruler starting to fall.
Hypothesis	A testable prediction that an investigation is designed to support or reject.
Control variable	A factor kept the same throughout so that it cannot affect the result.
Mean	The average value, found by adding the readings and dividing by how many there are.
Anomaly	A result that does not fit the pattern of the others and may be due to error.

Section 7 of 7Exam technique

1

Saying the person who catches the ruler is the dependent variable. The person is the independent variable; reaction time is dependent.

2

Reading the catch distance from the bottom of the ruler rather than at the top of the thumb, which gives the wrong number.

3

Believing a larger ruler reading means a faster response. The further the ruler falls, the slower the reaction.

4

Writing 'human error' as an evaluation point without saying what the error is, such as misjudging the catch position, or how to fix it.

5

Using only one trial per person and treating it as reliable instead of repeating and calculating a mean.