Effects of Previous Color Exposure on Vision
Sarah Noffsinger, Madison Buchanan and Natalie Wanner
CU Boulder, Fall 2006
The basis of all behavior begins with the recognition and processing of sensory information. In the human eye, the retina uses two types of cells to detect light and color, rods and cones. Cones detect color while rods are more sensitive to light and donÕt distinguish color. These photoreceptors communicate with other neural cells leading to the brain by an action potential a light stimulus initiates. We tested the effects of extended exposure to mono-color light on the ability to see and react to that same color. Because time is needed for these hyperpolarized or depolarized cells to reset, we hypothesized extended exposure to a specific color causes cone cells to fire to the point where that color is no longer visible.
To test this hypothesis we placed a subject in a dark room for two minutes as a control and proceeded to test the subjectÕs ability to see and respond to each color stimulus. We then exposed the subject to red light (white light bulb covered with translucent red film) for two minutes in the dark room and afterward tested the subjectÕs visibility of a red stimulus light located on the reaction timer. We continued these same procedures for the colors green and blue. We ran three trials with different subjects in each trial. Because time is needed for hyperpolarized or depolarized cells to reset, we predicted the reaction time to a specific color after extended exposure to that same color will be longer than with no previous color exposure.
Our results demonstrated an increase in response time after previous color exposure for each color stimulus. However, after running three separate t-tests, testing no treatment versus treatment for each color stimulus, not all of the data showed a significant difference (p-value of red = .027, green = .041, and blue = .085).
Our results are consistent with predictions based on our hypothesis. The data, supported by significant p-values, displays a correlation between previous exposure and reaction time among all of the different color stimulus lights (as exposure time increases, reaction time increases). Therefore, the results consistently demonstrate extended exposure to a specific color causes cone cells to fire to the point where that color is no longer visible. One potential problem with our experimental design was varying intensities of color among the exposure and stimulus lights. Reaction times may have been affected by the subjectÕs anticipation versus actual visibility of the stimulus. Reaction times may have also decreased due to the subjectÕs improved familiarity with the machine. We needed to run more trials and randomize the order of colors being presented to decrease the anticipation effect on the data. Also, we needed to previously test the intensities of the stimulus and exposure lights so all are equal. Results of another experiment run by Hemminger and Borsken et al. 1984 suggests eyes are most sensitive to a mixture of colored and white light when the two are in equal proportions. Therefore, combined light results in an increased stimulation of cones which may have enhanced the firing of cones in our experiment and drastically changed our data and conclusions, but their experiment continues to support our hypothesis of an increased reaction time with previous exposure to colored light. Buck et al. 2002 showed there are separable rod hue biases operating over different time courses and overall rod influence on hue appearance depends on the temporal properties of the stimuli, probably because rods interact in different ways with different portions of the neural pathways that mediate human color vision. Therefore, the delay we see in our data may not be a result of rodsÕ and conesÕ behavior, but rather the behavior of the nerves and synapses that connect these photoreceptors to the brain. Overall, their experiment still supports a delay in color perception and reaction time. Another study by Fry et al. 1982 proposed our retina is not a heterogeneous mixture of all three types of cones, but rather the colors of cones may concentrate with similarly colored cones, enabling different regions of the eye to see colors better than others. Therefore, we could have tested different areas of the retina within our experiment. Although similar experiments did not test our precise hypothesis, our results were consistent with other studiesÕ results in demonstrating the basis of all animal behavior begins with the recognition and processing of sensory information and leads to the production of a motor reaction.