Taylor Feero, Caitlin Clark, John Armstrong

October 27, 2008

Exercise 7: Student Projects




            We tested the effects that different wavelengths of light have on reaction time. Initially, we connected the relation between wavelength and reaction time to EinsteinÕs Photoelectric Effect. This states that light is actually made up of photons, and the energy of these photons can be found by taking the equation Energy= (PlankÕs Constant) (Speed of Light)/Wavelength. We felt that the more energy a certain wavelength of light had the easier the eye could catch it and the faster the test subject would react to it. This led us to hypothesize that reaction time is determined by the amount of energy in a wavelength of light.

            To test this hypothesis we set up a reaction timer that measured reaction time in seconds. Each trial we performed included one participant, and four different 16 random treatments. These 16 random treatments included 4 white wavelengths, 4 red wavelengths, 4 green wavelengths, and 4 blue wavelengths. We performed 6 different trials, using 3 participants and 2 trials each. Since blue light has the highest energy of these wavelengths, we predicted that reaction time would be the fastest in the blue light treatments.

            Our results indicated that the blue light actually had the slowest mean reaction time of 0.664542 seconds. White had a mean reaction time of 0.643333 seconds, green had a mean of 0.642792 seconds, and red had the fastest with a mean reaction time of 0.640125 seconds. Since white light was our experimental control, we used a t-test to determine if the difference between white and the other three wavelengths was significant. The P value for red vs. white was 0.979219972; the green vs. white P value was 0.964998605, and the blue vs. white P value was 0.502765397. None of these P values are less than 0.05 so there is no significant difference between different wavelengths and their reaction time.

            Our results are clearly inconsistent with predictions based on our hypothesis. One problem with our experimental design, was the buttons on our reaction timer. This could have caused the participant to think about hitting the button more than just reacting to the light. We could have solved this by using bigger buttons. Results of similar study at St. AndrewÕs University revealed that light wavelength does not have an effect on simple reaction time, but when performing a more complex task wavelength has a greater effect on efficiency. An experiment by John Ridley Stroop showed results that when looking at a color you have to think about the color before you could verbally react to it. After performing this lab and looking at othersÕ work we propose a new hypothesis. Wavelength may not have an effect on simple reaction time, but it may have a greater effect on more comprehensive problems. This would result in a greater efficiency under blue light, and a lower efficiency under red light, and would possibly be consistent with our idea that energy level of light has an affect on the rate of processing within the brain.




Eva Loth, Angela Martin, Rachel Powell, Christine Ruschak and Rebecca Tipper, 2006. The Effect of Colour on Reaction Time Performance. http://www.st-andrews.ac.uk/~www_sp/teaching/resources/colour1.pdf


Stroop, John Ridley 1935. "Studies of interference in serial verbal reactionsÓ Journal of Experimental Psychology, 18: 643-622.