The Visual Discrimination of Intensity and the Weber-Fechner Law

Abstract

1. A study of the historical development of the Weber-Fechner law shows that it fails to describe intensity perception; first, because it is based on observations which do not record intensity discrimination accurately, and second, because it omits the essentially discontinuous nature of the recognition of intensity differences. 2. There is presented a series of data, assembled from various sources, which proves that in the visual discrimination of intensity the threshold difference ΔI bears no constant relation to the intensity I. The evidence shows unequivocally that as the intensity rises, the ratio See PDF for Equation first decreases and then increases. 3. The data are then subjected to analysis in terms of a photochemical system already proposed for the visual activity of the rods and cones. It is found that for the retinal elements to discriminate between one intensity and the next perceptible one, the transition from one to the other must involve the decomposition of a constant amount of photosensitive material. 4. The magnitude of this unitary increment in the quantity of photochemical action is greater for the rods than for the cones. Therefore, below a certain critical illumination—the cone threshold—intensity discrimination is controlled by the rods alone, but above this point it is determined by the cones alone. 5. The unitary increments in retinal photochemical action may be interpreted as being recorded by each rod and cone; or as conditioning the variability of the retinal cells so that each increment involves a constant increase in the number of active elements; or as a combination of the two interpretations. 6. Comparison with critical data of such diverse nature as dark adaptation, absolute thresholds, and visual acuity shows that the analysis is consistent with well established facts of vision.

Intermittent Stimulation by Light

“…Both in intensity discrimination and in visual acuity, K for the rods is many times greater than K for the cones. The relation which this bears to the rate of dark adaptation of the two systems has already been discussed (Hecht, 1924). Here we find precisely the same difference in the K values, those for the rods being about a thousand times those for the cones.…”

A Theory of Visual Intensity Discrimination

“…Measurements of visual intensity discrimination are usually made with a bipartite test field of which one side has an intensity I and the other an intensity I~I. The procedure seems to involve the simultaneous and complete adaptation of the correspondingly juxtaposed retinal areas to their respective intensities, 5 whereas our critical equations depend on the initial effect 5 The formulation of intensity discrimination made ten years ago (Hecht, 1924 b; rests on this basis. It was then assumed that the eye will just discriminate between two intensities when their corresponding stationary states differ by a constant amount of photoproducts.…”

“…Since 1924, when it was shown that, plotted as aI/I against log I, the data of these four observers could be superimposed on a single graph (Hecht, 1924 b), there have been some minor additions to the data. HoUaday (1927), as part of a study of glare, determined 4I/1 for a portion of the intensity range, and secured data which resemble those of Koenig and Brodhun, without, however, going to high enough intensities to confirm or deny the rise of 4I/1 found by them.…”

Towards Internet Scale Quality-of-Experience Measurement with Twitter

“…Most of these approaches incorporate in some way the complexity of human emotion, that are not considered in the framework of the ITU. Some of the human mind's complex relationships have been researched in context of QoE : Egger et al show in [8] the direct applicability of the WeberFechner Law (see [10] for a brief historical outline) to the relationship of waiting time and download experience. They proof this finding empirically for simple waiting tasks and furthermore, they also investigate the applicability of logarithmic relations between bandwidth and mean opinion score for more complex tasks like web browsing.…”