How Changing the Contrast of a Visual Stimulus Affects Neuronal Responses in Humans

We are developing a new methodology for studying how changing the contrast of a visual stimulus affects human neuronal responses. Neurophysiological studies have shown that as the contrast of a stimulus decreases, the response time of visual neurons increases. Eleven male undergraduates and one female Psychology Professor from Wabash College will participate in this experiment. Participants will be subjected to a brightness induction minimal flicker task. There are three conditions for this experiment. The first is a red intense condition in which the stimuli is a bullseye dot with a red center/black surround alternating with a bullseye dot with a green center/white surround. The second is a green intense condition in which the stimuli is a bullseye dot with a green center/black surround alternating with a bullseye dot with a red center/white surround. The third condition is a control condition consisting of a red dot alternating with a green dot. Each condition alternates at 5 Hz. The red/green center dot will be presented at seven different contrasts ranging from low to high in each condition. Participants will minimize the flicker for each condition until the red/green center perceptually disappears. As the contrast of the stimulus is lowered the center should be perceived to flicker slower, thus becoming out of phase with the surround. The center color will then be assimilated instead of induced. This will mean that the lower contrast center is processed more slowly than the surround by visual neurons. Data collection is underway