Investigating Reaction Time and Interpreting Data

Use a metre ruler, a chair, a table and a partner, together with a distance-to-time conversion table. For this investigation, the catcher uses their weaker hand and starts recording immediately, without practising beforehand. This allows any change as they gain practice to be observed.

The independent variable is the amount of practice, represented by attempt number. The dependent variable is reaction time, obtained from the distance the ruler falls. Keep the same catcher, hand, dropper, ruler and starting position throughout each sequence. Otherwise, a change in the results might be caused by something other than practice.

Decide in advance how many attempts to record—for example, ten—and keep the interval between attempts similar. Record each attempt separately rather than averaging all ten together: an overall average would hide any change with practice.

Carrying out the ruler-drop test

1. The catcher sits with their forearm resting on the table and their hand extending over its edge.
2. The partner holds the ruler vertically, with the zero mark at the bottom and level with the top of the catcher's thumb. The thumb and forefinger are held apart without touching the ruler.
3. The partner releases the ruler without warning. The catcher closes their thumb and forefinger as soon as they see it falling.
4. Read the ruler at the top of the thumb. Because the zero mark started at that level, this reading is the distance fallen.
5. Record the distance beside the attempt number, convert it to a reaction time, and continue the sequence.

Vary the waiting time before each release. A countdown or a predictable delay could allow the catcher to anticipate the drop, so the measurement would no longer represent their response to seeing the ruler move. Release the ruler without pushing it downwards, and keep the starting hand position consistent.

Participants should agree to take part and be able to stop if uncomfortable. The person dropping the ruler should wear goggles because a missed ruler could hit the floor and bounce towards the eyes. Follow the teacher's safety instructions.

Converting ruler readings into reaction times

A conversion table contains paired values: a ruler reading in centimetres and its corresponding reaction time in seconds. Locate the distance first, then read its matching time. In a table arranged in several blocks, use the time entry in the same block as the distance, not an entry from a neighbouring block.

These selected conversion values show how to use the table:

For example, a catch at 15 cm corresponds to 0.18 s. Distance and time are not directly proportional: 20 cm is four times 5 cm, but its corresponding time is only about twice as long. Use the conversion table rather than treating a percentage change in distance as the same percentage change in time.

Some tests report milliseconds. Since $1\text{ s}=1000\text{ ms}$, a reaction time of 0.18 s is 180 ms. Convert to the same unit before comparing results.

Translating results into a graph

The following results demonstrate the method.

Put attempt number on the horizontal axis and reaction time in seconds on the vertical axis. Choose evenly spaced scales and plot each attempt-time pair. Joining successive points helps show the change through the sequence.

Data for Showing reaction time across practice attempts

The downward trend represents faster responses, not slower ones. Reaction time falls from 0.25 s on attempt 1 to 0.16 s on attempt 5—a decrease of 0.09 s. These results would support the suggestion that practice reduced reaction time for this person over these attempts.

To translate the graph back into numerical information, locate an attempt on the horizontal axis, move up to its plotted point, and read across to the time axis. For example, attempt 3 corresponds to 0.21 s. The same approach applies to other nervous-system graphs: first identify what each axis measures and its units, then read values and describe the relationship.

Comparing results and judging the evidence

When comparing categories, such as two hands or quiet conditions versus a distraction, collect several readings in each condition. Convert each reading into a reaction time before calculating a mean time. For example, for times of 0.14, 0.16, 0.18, 0.16 and 0.16 s, the total is 0.80 s; dividing by five gives a mean of 0.16 s. A bar chart is suitable for comparing the mean times of separate categories.

Practice can become an unwanted influence when testing another factor. For example, if every quiet test happens before every distraction test, any improvement with practice could affect the comparison. Alternating the conditions or varying their order between participants helps reduce this problem. This differs from investigating practice itself, when the early attempts must be retained.

Look at variation as well as the mean. Widely scattered repeats make a comparison less convincing than closely grouped results. An unusually short time could indicate anticipation; an unusually long time could reflect a lapse in attention. Investigate unexpected readings rather than automatically deleting them.

For the practice investigation, repeating the sequence with more participants helps show whether the pattern extends beyond one person. Results can be compared at matching attempt numbers, preserving the change with practice. A ruler test is limited by reading precision, release cues and variation in attention, so conclusions should reflect the size and consistency of the evidence.

• Align the ruler's zero mark with the top of the thumb; release without warning.
• Catch it and record the distance fallen.
• Convert each distance to time using a conversion table.
• Keep the catcher, dropper, ruler and starting position consistent unless one is the factor being tested.

Investigating practice

• Independent variable: attempt number.
• Dependent variable: reaction time.
• Use the weaker hand and record from the first attempt, without prior practice.
• Plot reaction time against attempt number; a downward trend indicates faster responses.

Handling data

$$\text{Mean} = \frac{\text{sum of values}}{\text{number of values}}$$

• Convert individual distances before calculating mean reaction time.
• $1\text{ s}=1000\text{ ms}$.
• Distance fallen and reaction time are not directly proportional.
• Use a bar chart for separate categories; a line graph can show change with attempt number.
• Compare numerical values, variation and anomalies before drawing a conclusion.

Quality of evidence

Vary the release delay to prevent anticipation. Repeat measurements and use more participants. When investigating another factor, control the influence of practice. Catching a ruler is a conscious response, not a reflex.