Turn It Off? – Does Using a Cell Phone really Increase Reaction Time?


Tori Gunther, Jess Goulart and John


CU Boulder, Fall 2006


         Anyone who has ever driven a car has heard that talking on a cell phone increases reaction time and might lead to more accidents. Common sense tells us that cell phones and cars simply don’t mix, but it’s next to impossible to keep the two separate. So we found ourselves asking the question, is there any truth to cell phones increasing reaction time? We hypothesized that distractions requiring greater concentration hinder the ability to react. We predict that talking on a cell phone will increase reaction time, and that text messaging will increase it even more.

         To test this hypothesis, we designed an experiment that would simulate slamming on the brakes in a car. We had two subjects take turns running four variations of the same test, alternating back and forth between people to nullify muscle memory. During the test, each subject sat in a chair that was two feet away from a wall. The subject would place their right foot at a mark 25 centimeters above the ground on the wall. We would then randomly drop a yardstick from 90 centimeters above the ground, three inches to the left of the mark, and the subject would have to slam his/her foot against the wall to stop the before it hit the ground. We then recorded the distance in centimeters that the yardstick had fallen, and used the equation t = √(distance/490 cm/sec2) to convert distance to time. The first test we ran was our experimental control, in which there were no distractions in the room. This gave us the base reaction times. We used this to determine how much the subject’s reaction time increased when using a cell phone. The second test we ran was to have the subject engaged on the phone in an “easy conversation” (questions like “hi, how’s it going”) while stopping the yardstick. The next test we ran involved having the subject engaged in a “hard conversation” (questions like “explain mitosis”) while trying to stop the yardstick. The last test we ran involved the subject text messaging while trying to stop the yardstick.

         Our mean experimental control reaction time was .19 seconds. Our results indicated that reaction time is significantly worse when a person is engaged in an easy conversation (mean = .20 seconds, P-value = .0456), worse yet when engaged in a hard conversation (mean = .22 sec., P=value = .01059), and increases by an entire tenth of a second when text messaging (mean = .29 sec., P-value = .000592).

Our results were consistent with our hypothesis, and unfortunately do not bode well for the avid text messager/driver. As we predicted, the reaction times got progressively worse, increasing slightly with an easy conversation and substantially with text messaging. We adequately tested our hypothesis, but also had a few experimental errors. First, we used only two test subjects, one boy and one girl, yielding only two sets of experimental data. This is not an extensive enough sample size. If performed again, the experiment should be done with a much larger number of test subjects. Second, to nullify muscle memory we had subjects alternate between tests, but if performed again there should be a five-minute break between scenarios to further prevent muscle memory. Third, we could not find a suitable environment that would allow the yardstick to fall indefinitely, without hitting the ground. Thus it is possible the test subject would have stopped the yardstick if they had had more time to do so. The experiment will do better if conducted in a way that allows the stick to keep falling until the subject stops it.

There was only one study on the class webpage that resembled ours, and it tested music’s affect on reaction time. Blansit et al 2005 found that music did not significantly alter reaction time. Our results are not consistent with theirs, however, as we ran tests that involved more concentration on the subject’s part than listening to music alone. Our subjects’ reaction times were thus more hindered.

We did not modify our hypothesis. Perhaps if the data were collected from a larger number of test subjects we would see a more accurate trend in increased reaction time, which would still be consistent with our predictions. As of now, we would encourage everyone to go ahead and hang up their phones before getting behind the wheel. It’s ok. You can always call them back.