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Does a Cell Phone Conversation Affect Reaction Time?

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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.


Areas of Science
Time Required
Average (6-10 days)
Material Availability
Readily available. You will need a cell phone with hands-free operation capability.
Very Low (under $20)
No issues
Andrew Olson, 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. http://cssf.usc.edu/History/2004/Projects/J0312.pdf


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


A cartoon by Ian Falconer, from the cover of The New Yorker (August 22, 2005): two little boys, in swim trunks, playing catch with a big beach ball. Wait a sec—one of them holds up his hand. The other is left holding the ball, waiting, as the first one takes a cell phone from his pocket to take a call. They're everywhere, these days, cell phones.

What happens if the person taking the call is behind the wheel, 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: "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



Materials and Equipment

Experimental Procedure

Note 1: Human Subjects. ISEF affiliated fairs often require an Informed Consent Form for every participant who is questioned or observed. Please refer to the ISEF rules for additional requirements on studies involving human subjects: http://www.societyforscience.org/page.aspx?pid=317.

Note 2: Make you sure you understand the terms of the calling plan for the cell phone(s) you use during the experiment. Talk this over with a parent or guardian. You will want to be sure that you arrange it so that your calls do not end up costing you per-minute rates! The cost estimate for this experiment (above) assumes that the cell phone calls will not result in extra charges on your regular monthly bill.

  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 assure 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.
    • Perform a pilot study (with a separate group of subjects) to determine how many trials you need to get a consistent measure of reaction time. This is the number of measurements you will need to make for each of the trials in your experiment.
    • 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. Recruit your volunteers and run the tests.
    • You will need to test a sufficient number of subjects to assure that your results are statistically significant. We suggest that your study should include at least 20 experimental subjects. If your results are ambiguous, repeat the experiment with an additional group of subjects. Keep the experimental conditions the same for both groups.
    • You will test your subjects' reaction time during each of three conditions:
      • while the subject is talking with your assistant on a hands-free cell phone,
      • while the subject is talking with your assistant on a hands-on cell phone,
      • while the subject is concentrating exclusively on the reaction-time test (control).
    • We suggest that you perform at least three trials for each condition (9 trials total per subject, minimum). So, if your pilot study determined that you need 15 ruler-drops to get an accurate measure of reaction time, this means that each subject will be tested with 15×3×3=135 ruler-drops during the entire experiment.
    • 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.
    • Here are some considerations if you conduct your experiment over multiple days.
      • 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.
      • For an individual subject, complete all of the trials within the same experimental session.
  5. Analyze the results.
    • Average the results for each participant.
    • Think about how to compare results between participants. Here are some possibilities.
      • 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.
      • 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.
    • 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?
    • Prepare one or more graphs to present your results.
    • If you do find a difference in reaction time, an interesting graph might be to show what the change in reaction time translates to in terms of stopping distance for a car traveling at different speeds.
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  • 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.
  • 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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MLA Style

Science Buddies Staff. "Does a Cell Phone Conversation Affect Reaction Time?" Science Buddies, 20 Nov. 2020, https://www.sciencebuddies.org/science-fair-projects/project-ideas/HumBeh_p009/human-behavior/does-a-cell-phone-conversation-affect-reaction-time. Accessed 3 Feb. 2023.

APA Style

Science Buddies Staff. (2020, November 20). 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: 2020-11-20
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