Brightness Discrimination as a Function of the Duration of the Increment in Intensity

Abstract

Recent discussions of intensity discrimination in vision have focussed attention on initial events in the process. Hecht (1935), in particular, has proposed a theory which states that brightness discrimination is due to the photochemical processes which take place at the initial moment when the eye, already adapted to a given intensity, is exposed to a just discriminahly higher intensity. Results of recent observations by Smith (1936) and Steinhardt (1936) lend support to the hypothesis.An important question which arises when we consider a theory in terms of initial events is the problem of how such a formulation may be related to the Bunsen-Roscoe law. This law states that, for brief flashes of light, the product of intensity and duration is constant for the production of a constant photochemical effect. It has been found to apply within well marked limits of exposure to both the fovea and periphery of the human eye, for threshold (Graham and Margaria, 1935;Karn, 1936) and supraliminal excitation (McDougall, 1904;Blondel and Rey, 1911;Graham and Cook, 1937). Adrian and Matthews (1927) and Hartline (1928) have demonstrated the law for the eyes of lower organisms, and Hartline's findings for the single fiber of Limulus (1934) give adequate evidence on the nature and limitations of its application. The strict reciprocity relation fails for exposures longer than a "critical duration" beyond which, in the Limulus eye and probably in the human eye (Karn, 1936), the relation I. t = Constant is superseded by the relation I = Constant.These considerations have led us to perform the experiments reported here. It has seemed important to us, because of the emphasis on initial events in brightness discrimination, to determine the effect 635

Intensity Discrimination in the Human Eye

“…2 and 3. This is the equation which originally (Hecht, 1935) was found to fit Blanchard's data, those of Steinhardt, of Koenig and Brodhun, and has since been found to describe the more recent data of Smith (1936) and of Graham and Kemp (1938). Its agreement with the present measurements is obvious.…”

Spatial numerosity discrimination as contingent upon sensory and extrinsic factors

“…That is, it would appear that discrimination of small number is sensorily based and essentially noncognitive in character, in that the process of subitizing seems to have some basis for explanation in the Bunsen-Roscoe law. Although there is some disagreement concerning the generality of the law (LeGrand, 1957;Pieron, 1952) and whether discriminatory responses made under conditions of reciprocity require a peripheral (Hunter & Sigler, 1940;Kahneman, Norman, & Kubovy, 1967) or a more central (Boynton, 1961) explanation, the Bunsen-Roscoe law has been found to hold for physiological and psychophysical measures of visual responses under a variety of conditions and for many types of discrimination, viz, absolute threshold (Sperling & Jolliffe, 1965), intensity (Graham & Kemp, 1938), visual acuity (Graham & Cook, 1935), velocity (Brown, 1955), digit identification (Kahneman & Norman, 1964), number discrimination (Hun ter & Sigler, 1940), and shape (Leibowitz, Toffey, & Searle, 1966). Regardless of the pathway specification of the temporal integration responsible for the Intensity by Time reciprocity, the Bunsen-Roscoe law is explained customarily on the basis of transduction in the receptor cell [Hartline (1934) has discussed the conversion of photic energy over time into frequency of discharge] .…”

A reduction in stimulus duration can improve wavelength discriminations mediated by short-wave cones

“…Moore, 1973). In the case of vision, analogous results are found not only for the simple detection and discrimination of luminance (Graham & Kemp, 1938), but also for a variety of other functions, such as vernier acuity (Foley & Tyler, 1976), judgement of orientation (Andrews, 1967), shape constancy (Leibowitz, Mitchell & Angrist, 1954), discrimination of spatial phase (Nyman, Laurinen & Campbell, 1986;Tyler & Gorea, 1986), and judgement of the sharpness of edges (Westheimer, 1991). The same principle generally applies to colour vision.…”