Michelson contrast, RMS contrast and energy of various spatial stimuli at threshold.

Contrast sensitivity was measured as a function of median spatial frequency for vertical cosine gratings, narrow-band noise stimuli, and spots with luminance increment or decrement. Contrast sensitivity was expressed in terms of Michelson contrast, RMS contrast, and contrast energy in order to demonstrate the characteristics of various contrast measures. Gratings and noise stimuli had either constant stimulus area or constant number of cycles. Michelson contrast sensitivity was better for gratings than for noise stimuli or spots, whereas RMS contrast sensitivity was almost equal for gratings and noise stimuli but lowest for spots. Contrast energy sensitivity takes into account the stimulus area and was therefore best for spots.