Abstract

An experimental determination has been made of the effect of increasing size on the time interval over which the product of intensity and time is a constant. Past research with white-light stimuli has shown It constancy to break down at progressively shorter exposure times as the diameter of a circular test field is increased up to 3 deg. This experiment employed circular fields of red and blue-green monochromatic light centered in the peripheral retina 20 deg from the point of fixation. Thresholds for durations from 3.13 to 1000 msec and areas of 3.43 min, 1 deg, 3 deg, and 8 deg were obtained by the method of constants. The results for four subjects show that with both colors and all areas the product of threshold intensity and time is a constant for all exposure times up to 100 msec. This is in direct contradiction to previous findings. That these differences may depend on the spectral quality of the test light is discussed, as are the theoretical implications of the findings.

© 1961 Optical Society of America

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