Figure 3

Comparison of SI optical responses evoked at different stimulus amplitudes (0, 50, 100, 200, and 400 μm) in an exemplary experiment. A: Average light absorbance images for each of the stimulus amplitudes (20 trials, 3 poststimulus images per trial). B: 3-D activity maps of the responding cortical region. C & D: Power spectra measured for each stimulus amplitude in the two dimensions sampled. With an increase in stimulus amplitude, the spectral power shifts to lower spatial frequencies for the data sampled in the A-P dimension, but not in the M-L dimension.