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Psychometric functions for luminance grating pairs of different contrast combinations, drift speeds and grating types for observer HS. (A–D) Luminance sinusoidal or square-wave gratings at 8 Hz. There are clear phase shifts between the upward and downward conditions. (E–H)Luminance sinusoidal or square-wave gratings at 2 Hz. There is little or no significant phase shift between the upward and downward conditions. The format is the same as in Fig. 1.
