Fig. S2.

Responses to luminance-varying stimuli from the example recording sites shown in Fig. 1C and Fig. S1 (Upper and Lower panels here correspond to Upper and Lower panels of Fig. 1C and Fig. S1 A and C). To distinguish object size tuning from tuning to mean display luminance, we recorded responses to a stimulus where the mean luminance of the object size stimulus was distributed evenly across the largest object in the stimulus set, 1.3° diameter. During the long period that contained a 3.7°-diameter circle in the object size stimuli, the sequence also contained a 3.7°-diameter circle. Responses differed considerably from responses to stimuli of varying object size: They did not show tuned responses to a specific, low luminance, and response amplitudes increased when a larger circle was shown, which covered visual field positions that were not stimulated by the rest of the stimulus sequence.