COLOR THRESHOLD MEASUREMENTS IN SCOTOPIC VISION: Simultaneous color contrast

S tabell , U. & S tabell , B. Color threshold measurements in scotopic vision. III. Simultaneous color contrast. Scand J. Psychol ., 1968, 9, 133–137.—Color may be observed well below the break-point level of the dark adaptation curve, suggesting that the impulse pattern initiated in the rods may trigger a color-related response. Color is induced when the intensity of the inducing field reaches a certain level above the specific threshold, provided the stimulation of the test field is observable.     

TRANSITION FROM ROD TO CONE VISION:III. Successive contrast anew

S tabell , U. & S tabell , B. Transition from rod to cone vision. III. Successive contrast anew. Scand. J. Psychol ., 1969, 10 , 140–144—The relation between the specific threshold level and the upper limit of the scotopic contrast color was investigated. The achromatic interval between the scotopic and the photopic component increased when time in darkness increased, and when pre-stimulation was reduced as regards intensity, duration, or cone/rod ratio. The results are interpreted on the basis of the opponent theory of color vision.     

TRANSITION FROM ROD TO CONE VISION I. Simultaneous contrast

S tabell , B. Transition from rod to cone vision. I. Simultaneous contrast. Scand. J. Psychol ., 1969, 10 , 61–64.—Above the specific threshold, color quality depended on the test filter, while at lower intensities the same color was observed irrespectively of the test filter used, confirming the assumption that colors within the photochromatic interval are triggered by rod activity. The lawful relation between rise of specific threshold and increase of rod sensitivity was not found under the condition of simultaneous contrast.     

TRANSITION FROM ROD TO CONE VISION: II. Successive contrast

S tabell , B. & S tabell , U. Transition from rod to cone vision. II. Successive contrast. Scad J. Psychol., 1969, 10 137–139—Transition from chromatic rod to chromatic cone activity during dark adaptation is interpreted as a kind of color mixing.     

ROD VISION AS CHROMATIC VISION

S tabell , B. Rod vision as chromatic vision. Scand. J. Psychol ., 1968, 9, 282–288.—It was found (I) that the smallest quantity of light of pre-stimula-tion which produces color upon test-stimulation, stands in unique relation to the intensity of the specific threshold, and (2) that the size of the pre-and test-stimulation fields may affect the duration of the after-image. The results are judged to indicate that pre-stimulation of cones creates the disposition for the color-related response, and that the color-related response is generated centrally to the photochemical systems of the receptors.     

CHROMATIC ROD AND CONE ACTIVITIES AS A FUNCTION OF THE PHOTOCHROMATIC INTERVAL

S tabbll , B. & S tabell , U. Chromatic rod and cone activities as a function of the photochromatic interval. Scand. J. Psychol ., 1969, 10,215– 219.—The Sco topic contrast color dominated for longer periods and at higher intensities the larger the magnitude of the photochromatic interval, indicating that the relative responsiveness of the chromatic rod to the chromatic cone activity increases as a function of the photochromatic interval.     

CHROMATIC ROD VISION III. Duration of pre-stimulation varied

S tabell B. & S tabell U. Chromatic rod vision. III. Duration of pre-stimulation varied. Scand. J. Psychol ., 1972, 13 , 136–140.—The scotopic contrast hue was determined as a function of duration of pre-stimulation, together with the additive opponent hue. It is concluded that the red/blue ratio which has to be added to the additive opponent hue to produce the scotopic contrast hue, may change as a function of both wavelength and duration of pre-stimulation.     

FACILITATION OF CHROMATIC CONE ACTIVITY BY ROD ACTIVITY

STABELL, U. & STABELL, B. Facilitation of chromatic cone activity by rod activity. II. Variation of chromatic-related cone activity. Scand. J. Psychol. , 1971, 12, 168–174.–At the cone-rod break of the dark adaptation curve, the specific threshold was found to drop to lower intensity levels, while the threshold curves of fovea proceeded in one step only, confirming the suggestion that rods may facilitate chromatic-related cone activity.     

Rod involvement in peripheral color processing

Abstract.— It has previously been suggested that rods act as blue receptors in peripheral color vision. Two experiments examining this issue were conducted. Experiment 1 investigated the perceived hue of a test light presented at a luminance level above chromatic threshold. At 8° in the periphery, the 500 nm test light was perceived as more blue under conditions of dark adaptation than after light adaptation. Similar differences were not found for foveal presentation. The increased blue in the periphery after dark adaptation was attributed to a rod contribution. In Experiment 2 an attempt was made to mix a rod contribution obtained with a 470 nm light below chromatic threshold, with a cone color obtained from a 670 nm light presented above chromatic threshold. No evidence was obtained to support the idea that a blue produced by rods stimulated below chromatic threshold could mix with a red produced by cones stimulated above chromatic threshold. The results are discussed in terms of a rod contribution to hue which is dependent on the luminance level of short wavelength stimulation.     

CHROMATIC ROD VISION

S tabell B. & S tabell U. Chromatic rod vision. IV. Time between pre-and test-stimulation varied. Scand. J. Psychol ., 1972, 13 , 141–144.—The scotopic contrast hue was determined as a function of time between pre-and test-stimulation. As the interval increased, the scotopic hue was found to change from orange toward yellow in the 440–475 nm region of pre-stimulation and from violet-blue toward violet in the 550–595 nm region. It is concluded that (1) depending on wavelength of pre-stimulation, the processes in the red-green substance may revert to the mid-valued state faster or slower than the processes in the yellow-blue substance, and (2) the red/blue ratio of the violet hue which has to be added to the additive opponent hue to produce the scotopic contrast hue, may change as a function of time between pre- and test-stimulation.     

Disruptive effects of stimulus intensity on two variations of a temporal discrimination procedure

Previous reports using stimulus intensity changes to disrupt temporal discrimination have shown shifts in the psychophysical curve for time, while studies using other disruptors have shown a flattening of the curve. The current study investigated the impact of increases and decreases in stimulus intensity on temporal discrimination in pigeons, to determine if a flattening of the curve could be extended to this disruptor. The brightness of the sample to be timed was manipulated under two procedural variations, in which the response alternatives were differentiated by color or location. Results showed that all subjects in the color procedure, and one in the location procedure, showed a flattening of the psychophysical curve when they experienced increased stimulus intensity in descending order. No subjects exposed to an ascending order of stimulus intensities, and none of the other subjects in the location procedure, showed any impact of changed stimulus intensity. Minimal disruption was found when test sessions presented decreased stimulus intensity levels in a second series. These results, together with those using other types of disruptors, add to the evidence of a flattening of the psychophysical curve when temporal discrimination is disrupted.     

Temporal summation of pain from radiant stimulation

Latency thresholds of pricking pain, using radiant thermal stimulation, were obtained. Ten Ss were tested for 10 sessions, and, in each session, single latency determinations were made at each of 10 stimulus intensities. Each intensity was administered to a different spot along the volar surface of S’s nonpreferred forearm. Thus, 10 latency thresholds were obtained from each S at. each intensity and each spot. Initial skin temperature was controlled so that a threshold determination was made when skin temperature measured 33.5° ± 0.5° C. Analysis of variance of the log₁₀ t (seconds) values revealed a highly significant linearity of regression of log t on log intensity, thus confirming the hypothesized inverse and exponential relationship between latency and intensity. The parameters (slope and x-intercept) of the curve were discussed. The x-intercept may be interpreted as an index of an aversive threshold and could be used as a possible measure of the physiological component of pain.     

NIGHT VISION AS CHROMATIC VISION

Assuming that night vision is an exclusive function of the rods, and that it is colorless, the duplicity theory states that rod vision is achromatic vision. Studies relevant to color in night vision are reviewed. It is concluded that color may be observed well below the breakpoint of the dark adaptation curve, and that the duplicity theory therefore needs revision.     

COLOR THRESHOLD MEASUREMENTS IN SCOTOPIC VISION

The absolute and the color threshold in scotopic vision generally coincide during dark adaptation, indicating that color-threshold intensity is a measure of the concentration of rhodopsin, and that different modes of rhodopsin regeneration are reflected in the measurements of the color threshold.     

Hue discrimination in peripheral vision under conditions of dark and light adaptation

Rod interference is a possible factor contributing to the elevation of chromatic threshold in peripheral vision. It was found that light adaptation lowered peripheral chromatic thresholds. This result was interpreted as being due to the lowering of rod sensitivity. It was also found that light in the photochromatic interval appeared blue, indicating that rods may add a blue component to peripheral color vision.     

Comparison of scotopic sensitivity in diurnal (Anas platyrhynchos) and crepuscular (Dendrocygna autumnalis) ducks.

Scotopic visual adaptation curves were obtained from 4 mallard ducks. A curve of best fit was used to compare the mallards' mean adaptation curve to the curve previously reported for the black-bellied tree duck, a crepuscular species. The curves did not differ significantly in either their slopes or base levels (thresholds). The mallards curve had a rod-cone "break" at approximately 25 min. This break is evident in the scotopic curve for pigeons, but is absent from the black-bellied tree ducks' curve. Examination of retinal tissues indicated that the black-bellied tree ducks had significantly more rods and cones, and a larger rod:cone ratio than the mallards. The mallards' scotopic visual threshold is exceeded by the natural illumination present under several nocturnal conditions.     

Differential luminance sensitivity of the human visual system

In this paper the differential sensitivity of the visual system is investigated by means of two simultaneously presented stimuli in a yes-no procedure. The sensitivity measure σ_I appears to be proportional to stimulus intensity (i.e., Weber’s law). The curve displaying Weber’s law is little affected by variation of the background intensity or of the adaptation level. An increment threshold experiment using only one stimulus yields a proportionality of σ_I with the square root of the background intensity. An additional experiment shows that the sensitivity measure σ_I for two flashes decreases first, from dark up to a particular background intensity, and increases when the background tends to mask the flashes. So, in general, two background levels exist with the same differential sensitivity. The results cannot easily be explained by the simple quantum fluctuation concept. A model based partially on electrophysiological data from the literature is proposed which encounters a particular adaptation mechanism, a transducer with a limited dynamical range, and a range setting mechanism.     

Psychophysical saturation scales and the spectral sensitivity in human vision

Summary For mixtures of white and colored lights, the intensity of the colored light necessary to produce a linear psychophysical saturation curve is determined. This intensity may be defined as equilibrium between chromatic and achromatic excitation. From a measurement of the equilibrium throughout the spectrum, a spectral sensitivity function may be derived. According to the hypothesis of Börsken and Hemminger (1980), this function describes the spectral sensitivity of the achromatic channel in human color vision.     

Scotopic sensitivity in coyotes (Canis latrans).

The absolute scotopic limen for light intensity was measured for three 10-mo-old female coyotes. The methodology was similar to that used by Blough in determining psychophysical thresholds in pigeons. Three coyotes were operantly conditioned to depress one of two foot treadles, left or right, depending on the condition of the stimulus light. Scotopic adaptation curves for each coyote were generated. Nonlinear regression curves were then fitted to the raw data. The mean scotopic thresholds did not differ significantly. However, time to the curves' asymptotes did differ significantly for one of the coyotes. The adaptation curves showed a distinct rod-cone "break," and retinal histology confirmed that the coyote has a duplex retina with a preponderance of rods. In addition, electroretinographic analysis showed the relative contributions of rods and cones at various light intensities and indicated a rod-cone break at approximately 15 min. Scotopic spectral sensitivity curves were also generated. The coyotes' scotopic visual threshold is exceeded by the natural illumination available under many nocturnal conditions. The results are discussed in relation to the ecology of the species.     

RODS AS COLOR RECEPTORS IN PHOTOPIC VISION

Comparing a foveal and an extra-foveal field during dark adaptation, transition from chromatic to achromatic vision at intensity levels above the cone plateau started around the break of the dark adaptation curve. Pre-stimulating the two fields in a dark-adapted state with deep red, and test-stimulating when returning sensitivity had reached absolute threshold of the dark-adapted eye, with green filters at intensities above the specific threshold, the fields matched as to hue and saturation. It appears that rod and cone activities are integrated and function as a synchronized unit during the initial recovery phase of dark adaptation.