Fig. 10. Threshold (delta B) to detect a 7-degree field containing a grating flickering at the rates indicated on the abscissa. Measurements were performed at adaptation levels of 36, 114, 360, and 1140 Td and follow a top-to-bottom order within each panel. At moderate temporal frequencies (8 Hz) and low spatial frequencies (2 cycles per degree [cpd] threshold obey Weber's law and are labeled “W”. The adaptation mechanisms underlying Weber's Law behavior break down at high temporal or spatial frequencies and follow the “square root” or DeVries-Rose Law. At high temporal frequencies and low spatial frequencies (a), the system appears to ignore the presence of the background. The spatial and temporal characteristics of the stimulus thus greatly influence light adaptation. (Data from Kelly DH: Adaptation effects on spatio-temporal sine-wave threshold. Vision Res 12:89, 1972.)