The intensity–time relationship at threshold of the human eye has been investigated with special attention to temporal-summation effects and Bloch’s Law. The four parameters selected for this study include (a) narrow-band spectral stimuli of different dominant wavelengths, (b) foveal and peripheral retinal locations, (c) several stimulus sizes, and (d) light and dark surrounds. The results, obtained with three subjects, show that the intensity–time relationship is dependent upon the wavelength of the spectral stimulus when a large (45′) foveal stimulus is employed. No significant wavelength dependency was indicated with smaller (4.5′) foveal stimuli and varying stimulus diameters in the periphery. Data taken with a dark surround exhibited more temporal summation than that taken with a light surround. Results are discussed in relation to evidence for differently sized receptive fields for the red and blue cones and for the rod receptors.
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