Effect of field size and position on mesopic spectral sensitivity

The transition from scotopic to photopic vision in 3-month-old infants and adults: an evaluation of the rod dominance hypothesis

The scotopic to photopic transition was tested in adults and 12-week-old infants using a large field motion nulling technique at a series of luminances between -3.57 and 2.70 log cd m(-2). The stimuli were composed of 0.25 cyc deg(-1), 5.6 Hz blue/black and yellow/black sinusoidal grating components, superimposed and moving in opposite directions. The contrasts of the two components were traded off to determine motion nulls at each luminance level. An eye movement based response measure was used for infant subjects, whereas self-report was used in adults. In both age groups, the motion null values approached a scotopic asymptote consistent with V'(lambda) at the lowest luminance levels, and a photopic asymptote consistent with V(10)(lambda) at the highest luminance levels. The scotopic to photopic transition was gradual and occurred over about 3 log units between about -2 and 1 log cd m(-2) in both groups. The null values for infants and adults were highly similar at each luminance level, and the shapes of the transition curves were virtually identical at the two ages. These data suggest that at each different luminance level, the balance between rod-initiated and cone-initiated signals in the extrafoveal luminance channel is similar or identical in 12-week-old infants and adults.

Luminance

Luminance was introduced by the CIE as a photometric analog of radiance. This implies that an additive spectral-luminosity function characterizes the human observer. In practice, many different spectral-sensitivity functions characterize human vision, although few produce the additive spectral-luminosity function V (lambda), which is suitable for use in practical photometry. Methods that give rise to additive spectral-sensitivity functions that most resemble V (lambda) tend to have in common the use of spatial or temporal frequencies that will discriminate against signals from the short-wavelength-sensitive cone pathways or against signals in other chromatic pathways. Some of the difference among results obtained with different techniques seems to reflect the extent to which the methods can bring about changes in the state of chromatic adaptation, but it also seems likely that not all tasks tap the same postreceptoral mechanisms. Psychophysical evidence is equivocal regarding the nature of the postreceptoral mechanisms: some evidence suggests just three mechanisms, one of which has a spectral sensitivity that is like V (lambda); other evidence suggests the existence of multiple mechanisms with different spectral sensitivities. Physiological recordings from neurons in the macaque's visual pathway suggest that the properties of the magnocellular system may be sufficient to account for spectral-sensitivity functions measured with the techniques of heterochromatic flicker photometry, minimally distinct border, and critical flicker fusion. These are the psychophysical methods that yield spectral sensitivities that are most like V (lambda). Other methods of measuring spectral sensitivity seem more likely to depend on signals that travel through the parvocellular system.

Brightness matching and flicker photometric data obtained over the full mesopic range

Three normal observers made visual matches from 0.03 to 100 td on a 10 degree central field at 445, 560 and 630 nm, using two different methods: heterochromatic flicker photometry and direct comparison brightness matching. In a relative sensitivity vs illuminance plot, the brightness matches underwent smooth changes, while the flicker curve exhibited a step-like transition around 1 td, between two separate branches. A reverse Purkinje shift was found on the high mesopic branch at 630 nm, possibly due to cone-cone interactions, and on the low mesopic branch at 445 nm, with questionable origin. At 630 nm and 0.03 td, both methods yielded matches that were not truly scotopic but might not have addressed the same mechanisms.

Brightness luminous-efficiency functions for 2 degrees and 10 degrees fields

CIE V lambda is not representative of luminous-efficiency function based on heterochromatic brightness matching. CIE Technical Committee 1.4 Vision (TC 1.4) presented a 2 degrees brightness-matching luminous-efficiency function based on studies of a total of 31 observers to supplement the V lambda. In view of their importance to illuminating engineering and physiological optics, we analyzed the various conditions under which these seven studies were conducted. Data from three of the groups are considered inappropriate, and we revised the TC 1.4 brightness luminous-efficiency function based on the remaining 19 subjects. Data from 18 Japanese subjects, coming from five research groups, are added to the above subjects, and an averaged luminous-efficiency function is derived. The result does not appreciably differ from the revised TC 1.4 function and is considered to represent a brightness-matching standard luminous-efficiency function for a 2 degrees field. A brightness luminous-efficiency function for a 10 degrees field based on nine Japanese subjects is presented. It differs from the 2 degrees function only at short wavelengths when the functions are normalized at 570 nm. A theoretical approach for using the brightness-matching luminous-efficiency function to assess the brightness of 2 degrees broadband sources is introduced, and some numerical examples are given.

Mesopic luminous-efficiency functions

In order to establish the luminous-efficiency function for mesopic vision of the standard observer, luminous efficiency functions were measured with the direct heterochromatic brightness-matching method at retinal illuminance in the range of -2-2 log photopic trolands in order to cover the scotopic, mesopic, and photopic conditions. A steady visual field of 10 degrees arc was presented foveally. The functions underwent the usual complicated change from a rod type of luminous-efficiency function close to V'(lambda) to a cone function that had a wide and almost double-peaked shape. A simple formula to represent the mesopic luminous-efficiency functions was derived in which log sensitivities of scotopic and photopic vision were linearly added after being multiplied by coefficients that were dependent on the luminance level. Saturation functions were also obtained at the various luminance levels for which luminous efficiency was investigated. In spite of a great variation of luminance level, the saturation function remained more or less the same, which indicates that the chromatic channels retain their contributions to the brightness sensation at low retinal illumination.

Photopic, mesopic, and scotopic vision

This paper analyzes the work relating to the visibility curve as well as to the spectral efficiency of radiation in regard to visual acuity and contrast sensitivity. Methods of calculation of the visual efficiency for various types of light sources are presented. The results of an investigation of the brightness-luminance relation are analyzed. Recommendations regarding the photometric conditions for the small luminance range are indicated. Certain physiological characteristics of the spectral sensitivity of the eye are examined.

Degree of applicability and consequences of inappropriate use of units of light

Since light is defined quantitatively as radiant energy evaluated according to the CIE photopic luminosity curve, ordinary t units are inappropriate whenever the organism's spectral sensitivity differs markedly from the CIE curve. Examples of differing spectral sensitivities include those of animals, of color defective individuals, and curves for all individuals under low light levels or with large fields. Calculations are presented of the amount of error involved when units of light are used for these inappropriate conditions; alternative solutions to the problem are discussed.