OIS response to low vs. high amplitude stimulation. OIS images taken from three subjects (A, B, C). All images are anatomically oriented as shown in the top left image. Images were obtained by averaging across 10 experimental trials and then summing frames taken from the time of stimulus onset to 5 seconds after stimulus offset to better show regions of high absorbance indicated by dark pixels. The left column shows responses acquired in the absence of stimulation (control), while the middle and right columns show the stimulus-evoked response to 50 and 400 μm respectively in the same subjects.