Mary Katherine Hill

Matthew Hoops

Amanda McWhirter

Human Reaction Times to Light vs. Sound

The question we aimed to answer in our experiment was: Do humans react faster to light or sound stimuli? Most sensory information is transmitted in the same manner via afferent neurons to the brain, where it is processed by the thalamus and subsequently distributed to the cortex to be interpreted in sensory specific lobes (the occipital lobe for photic information and the temporal lobe for auditory information). When establishing which type of stimuli might produce a faster reaction time, we took into account the speed of light (299,792,458 m/s) as compared to the speed of sound (340.29 m/s). This drastic difference in speeds led us to hypothesize that humans react faster to light than to sound because light travels faster than sound. As a result, we predicted that there would be a statistically significantly higher mean reaction time to sound than to light.

We used a reaction timer to record the timed responses to light and sound. The variables we controlled for were color and frequency of light, frequency of sound, body position, location, time of day, finger used to hit the button, and we also gave each person an initial unrecorded test run so that they could become familiar with how to work the machine. We tested a total of ten people (five boys and five girls.) Each person received ten tests for light and ten for sound.

We ran a t-test based on the tabulated average individual reaction times to each stimuli, and established that the mean average individual reaction time to light (0.28005 sec.) was statistically significantly different than the mean average individual reaction time to sound (0.20407 sec.; P-Value= 1.79E-07 < .05, the statistical level of significance). However, such results conflicted with our initial prediction that there would be a statistically significantly higher mean reaction time to sound than to light.

We encountered several problems in conducting our experiment, such as our inability to test brain functions and answer why humans react faster to audio stimuli than to light stimuli. In addition, because of the design of the reaction timer used in the experiment, there was a slight possibility that the test subjects might have heard the experimenter push the button to activate the various stimuli, thereby contaminating evidence. The test results may have been further influenced by distractions, such as people walking through the hallway in which the tests were administered. In order to counter the potential effects of such problems and enhance the validity and reliability of our experiment, we performed one hundred individual trials in total for each type of stimuli and then based our conclusions on the averaged results.

Our original hypothesis was flawed, in part, because we failed to take into consideration the complex and relatively slow mental processing speed of the human visual system. That is, despite the fast speed of light relative to the speed of sound and the similar nerve connections in the eyes and ears, the brain takes longer to process visual data as compared to audio data. Based on these considerations, as well as our statistical results, we have modified our original hypothesis to state that humans react faster to sound stimuli than to light stimuli because visual data takes longer to process in the brain than audio data.

Literature Cited

Barnett-Cowan, M., Harris, LR. (2009). Perceived Timing of Vestibular Stimulation

Relative to Touch, Light, and Sound. Experimental Brain Research 198(2-3): 221-

231. New York, New York.