Abstract Simultaneous contrast has been ascribed so far to spatial interactions in retinal receptive fields. The antagonistic surround of retinal receptive fields disappears after dark adaptation. The present work shows that simultaneous contrast for large fields and border contrast effects are preceived at low scotopic luminances. Moreover, both the spatial and the temporal psychophysical contrast sensitivity functions show a low-frequency attenuation at scotopic mean luminances. These findings support the conclusion drawn from recent electrophysiological results ( Maffei and Fiorentini , 1972 ) that the analysis of contrast is not performed in the retina, but at a higher level of the visual system.