This paper deals with the effect on contrast thresholds of the fluctuations in the background luminance or “luminance noise.” Targets of several sizes are produced on a television screen, imbedded in fine-grain luminance noise of controllable magnitude. The results indicate that luminance fluctuations of small magnitude do not affect the threshold very much when the mean luminance of the screen is 0.01 and 0.1 ft-L, while they do change it appreciably at 1.0 ft-L. When luminance fluctuations are large, contrast thresholds at the above three luminance levels are nearly the same, indicating that the degree of luminance fluctuation governs the contrast threshold.
The extent to which luminance noise increases the contrast threshold is used to estimate the internal noise of the vision channel and an attempt is made to compare this with the noise that might be expected on account of fluctuations in the number of quanta absorbed in the retina.
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