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Does a Cell Phone Conversation Affect Reaction Time?

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Abstract

Does talking on a cell phone make one a more dangerous driver? Here is an experiment you can do to investigate whether reaction time is adversely affected by a simultaneous phone conversation.

Summary

Areas of Science
Human Behavior
Difficulty
Method
Scientific Method
Time Required
Short (2-5 days)
Prerequisites

None

Material Availability

Readily available. You will need a cell phone with hands-free operation capability.

Cost
Very Low (under $20)
Safety

No issues

Credits
Andrew Olson, PhD, Science Buddies Alumni

Ben Finio, Ph.D., Science Buddies
Ghez, C., 1991. "Voluntary Movement," in Kandel, E., J.H. Schwarz and T.M. Jessell. Principles of Neural Science: Third Edition. Norwalk, CT: Appleton & Lange.
Goldrich, A.M., 2004. Does Cell Phone Usage Affect Reaction Time? California State Science Fair, Project Number J0312.

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Objective

The goal of this project is to determine whether or not engaging in a cell phone conversation adversely affects reaction time.

Introduction

What happens if a person talking on a cell phone is behind the wheel of a car, traveling at highway speed, or negotiating busy downtown traffic? Is a cell phone conversation enough of a distraction to make the driver more dangerous? If the phone is a distraction, does using a hands-free cell phone improve the situation?

Here is a science fair project that you can do to try and address some of these questions. You'll design and conduct an experiment to measure the effect of cell phone use on reaction time. Reaction time is the time that elapses between a sensory stimulus and the response to that stimulus. Thus, it is a measure of the total time necessary for a chain of internal events (Figure 1):

a timeline showing reaction time. Image Credit: Ben Finio, Science Buddies / Science Buddies
Figure 1. This drawing shows that reaction time is the time from the presentation of a stimulus (in this example, the stimulus is the black circle) to the time of a reaction to that stimulus (when the user clicks the mouse button).

"Under optimal conditions of attention, we can respond to a sensory stimulus in 120 to 150 ms." (Ghez, 1991) The shorter time (120 ms) is for proprioceptive or auditory stimuli. (Proprioceptive stimuli result from mechanical displacement of the muscles or joints. An example is when your doctor taps your knee to test your reflexes. Your doctor is checking your reaction time.) The longer time (150 ms) is for visual stimuli, due to additional synapses in the retina. Reaction time will be even longer if we need to decide between several alternative choices of response (Ghez, 1991).

You'll read about one simple method for measuring reaction time in the Experimental Procedure section. If this sounds like an interesting project for you, read on for some suggestions to get you started on background research.

Terms and Concepts

Questions

Bibliography

Materials and Equipment

Experimental Procedure

Download PDF of Procedure
This project follows the Scientific Method. Review the steps before you begin.

Working with Human Test Subjects

There are special considerations when designing an experiment involving human subjects. Fairs affiliated with Regeneron International Science and Engineering Fair (ISEF) often require an Informed Consent Form (permission sheet) for every participant who is questioned. Consult the rules and regulations of the science fair that you are entering, prior to performing experiments or surveys. Please refer to the Science Buddies documents Projects Involving Human Subjects and Scientific Review Committee for additional important requirements. If you are working with minors, you must get advance permission from the children's parents or guardians (and teachers if you are performing the test while they are in school) to make sure that it is all right for the children to participate in the science fair project. Here are suggested guidelines for obtaining permission for working with minors:

  1. Write a clear description of your science fair project, what you are studying, and what you hope to learn. Include how the child will be tested. Include a paragraph where you get a parent's or guardian's and/or teacher's signature.
  2. Print out as many copies as you need for each child you will be surveying.
  3. Pass out the permission sheet to the children or to the teachers of the children to give to the parents. You must have permission for all the children in order to be able to use them as test subjects.
Note: there are two options to do this project. You can use a computer program to measure reaction time (Option 1) or you can use a physical test called the "ruler drop test" (Option 2). If it is difficult for you to get enough volunteers to do the experiment in person, you can send them a link to the computer program so they can participate remotely.

Option 1: Computer Program

click to edit code image
  1. This option uses a beginner-friendly computer programming language called Scratch to create a reaction time "game" where you click on a circle as soon as it changes color. The program automatically measures the amount of time from when the circle changed color to when you clicked on it. Scratch is a great way to learn coding for people with no previous coding experience. See Getting Started with Scratch from the Raspberry Pi Foundation to learn more about programming in Scratch.
  2. We have prepared a test program to help you get started.
    1. Click the green flag in the program on this page.
    2. Hover your mouse over the circle.
    3. Click on the circle as soon as the color changes from white to black. 
    4. The program will tell you your reaction time in seconds.
    5. Click the green flag again to start a new test.
  3. You can edit the code yourself to change the program.
    1. Read the comments (yellow note boxes) to learn more about how the program works and what you can change. 
    2. To save a copy of the code, you must first create an account on the Scratch website. You can do this using the "Join Scratch" button in the top right.
    3. After creating and logging in to your own account, click the "Remix" button at the top of the code page. This will create a "remixed" copy of the code that is saved in your own account. 
https://www.youtube.com/watch?v=a30aAugNGFo
  1. After you have made changes to the program, click the "See project page" button at the top of the Scratch page, then click "Copy link" in the bottom right. You can email this link to your volunteers.
  2. You can now follow the procedure outlined under Option 2 using the computer program instead of the ruler drop test.

Option 2: Ruler Drop Test

  1. Do your background research.
  2. Prepare a list of questions and topics for engaging your subjects in conversation.
    • Keep in mind that your assistant will need to keep a conversation going with each subject during multiple trials (at least 9).
    • It is a good idea to do one or more "test runs" with the questions, (using a separate group of people who will not take part in the experiment) so that your assistant gets some practice, and so that you can refine the list of conversation topics.
  3. Prepare the test of reaction time. Verify the number of trials required to ensure consistent results. A simple method for measuring reaction time is to have the subject grab a ruler as you drop it. The details are covered on the Reaction Time page. If you decide to use the ruler drop test, make sure that you use consistent sensory cues each time you drop the ruler. For example, if you give the subject an auditory cue ("Go!"), then be sure to give it each time, and in the same way.
  4. Test each volunteer's reaction time during each of the following three conditions. We suggest that you perform at least five trials for each condition (15 trials total per subject, minimum).
    1. while the subject is talking with your assistant on a hands-free cell phone (either using a headset or with the phone in speaker mode so they do not need to hold the phone)
    2. while the subject is talking with your assistant on a hands-on cell phone (holding the phone up to their ear)
    3. while the subject is concentrating exclusively on the reaction-time test (control)
  2. Note the experimental conditions and record the results of each trial, along with any observations you make during the experiment. It will help to organize your results in a table.
  3. Here are some considerations if you conduct your experiment over multiple days.
    1. Make sure that your experimental conditions are as consistent as possible. For example, you should always use the same assistant to carry out the phone conversations and try to do the trials at the same time of day.
    2. For an individual subject, complete all of the trials within the same experimental session.
  4. Analyze the results.
    1. Average the results for each test condition for each participant.
    2. Think about how to compare results between participants. Here are some possibilities.
      1. You could simply average results for each of the three conditions, but if your subjects' normal reaction times vary significantly, then averaging could obscure your results.
      2. You could calculate the average difference in reaction time between the control and experimental conditions for each subject, and then average this number across all subjects for each condition.
    3. Prepare one or more graphs to present your results.
    4. If you do find a difference in reaction time, an interesting graph might show what the change in reaction time translates to in terms of stopping distance for a car traveling at different speeds.

icon scientific method

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Global Goals

The United Nations Sustainable Development Goals (UNSDGs) are a blueprint to achieve a better and more sustainable future for all.

This project explores topics key to Good Health and Well-Being: Ensure healthy lives and promote well-being for all at all ages.

Variations

  • You performed this experiment while volunteers were talking on the phone. What happens if they are texting or doing some other task that requires looking at the phone, like checking email or social media? What about using voice commands with a smart assistant like Siri or Alexa?
  • Do an experiment to compare the two reaction time measurement methods (the ruler drop test and the Scratch program). Does one method give more consistent results? Does one measure faster times than the other? Is this related to the required muscle movements?
  • On the face of things, a phone conversation is primarily an auditory task (however, the process of thinking about the conversation in progress complicates matters). Does it make a difference if the sensory cue is visual (e.g., simply dropping the ruler, or pointing a finger as the ruler is dropped) or auditory (e.g., saying the word, "go!" as the ruler is dropped)? Design and conduct an experiment to find out.
  • Analyze the statistical significance of your results. Formulate the null hypothesis against which you are comparing your results. What is the probability that your results could be explained by the null hypothesis?
  • Reaction time is only one aspect of the complex behavior required to drive safely. Perhaps you can come up with a video game that simulates the attentional requirements for safe driving, and use performance on the video game to quantify your results. Again, you should run a pilot study to determine a consistent scoring method for game performance.

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Cite This Page

General citation information is provided here. Be sure to check the formatting, including capitalization, for the method you are using and update your citation, as needed.

MLA Style

Olson, Andrew. "Does a Cell Phone Conversation Affect Reaction Time?" Science Buddies, 5 Nov. 2024, https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBeh_p009/human-behavior/does-a-cell-phone-conversation-affect-reaction-time. Accessed 3 June 2026.

APA Style

Olson, A. (2024, November 5). Does a Cell Phone Conversation Affect Reaction Time? Retrieved from https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBeh_p009/human-behavior/does-a-cell-phone-conversation-affect-reaction-time


Last edit date: 2024-11-05

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