Scotopia: First Dusk

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Evidence has accumulated that rod activation under mesopic and scotopic light levels alters visual perception and performance. Here we review the most recent developments in the measurement of rod and cone contributions to mesopic color perception and temporal processing, with a focus on data measured using a four-primary photostimulator method that independently controls rod and cone excitations.

We discuss the findings in the context of rod inputs to the three primary retinogeniculate pathways to understand rod contributions to mesopic vision. Additionally, we present evidence that hue perception is possible under scotopic, pure rod-mediated conditions that involves cortical mechanisms. This is accomplished, in part, by switching operations between two photoreceptor classes in the retina, rods and cones, which have partially overlapping operating light ranges.

Under high illuminations, rods are in saturation and photopic vision Maxwell, ; Helmholtz, ; Hurvich and Jameson, ; Hering, ; DeValois and DeValois, is initiated by the outputs of three cone photoreceptor classes L-, M-, and S-cones with overlapping spectral sensitivities Smith and Pokorny, to provide trichromatic color perception. With intermediate, mesopic illuminations when rods gradually become sensitive and cones are still active, there are subtle changes and a reduction in both the perceptual quality and gamut of perceivable colors Nagel, Under dim, scotopic illuminations, only rods are active and color perception is still possible by different physiological computations than the trichromatic system Pokorny et al.

Photoreceptor outputs are transmitted from retina to brain for image forming vision via three major classes of retinal ganglion cells in primates that process distinct aspects of visual information Dacey, ; Kaplan, ; Lee et al. The parasol ganglion cells display ON-center, OFF-surround antagonistic receptive field structures, with L- and M-cones contributing to both the centers and surrounds spatial opponency; Rodieck, The MC-pathway is believed to the physiological substrate of the luminous efficiency function Lennie et al.

The second class, known as midget ganglion cells, receives differential L- and M-cone inputs in the receptive field center and surround. The surround of midget ganglion cells, however, can receive mixed inputs from both L- and M-cones instead of only one type of cone input Lee et al. These cells project to the koniocellular KC layer of the LGN and are believed to mediate blue—yellow chromatic processing. Because the spectral signatures of the primary retinogeniculate neurons differ from human color perception DeValois and DeValois, , cortical transformations of these retinal projections Calkins, and small populations of LGN cells with circuitry matching hue perception Tailby et al.

Rod contribution to visual perception under mesopic illuminations is believed to be mediated via rod and cone inputs to the three pathways Lee et al. This paper reviews current progress in understanding rod contributions to chromatic and temporal aspects of vision. The study of mesopic vision within a range of log units of illumination CIE, , when there is a dual processing of rod and cone signals, is about revealing the nature of interactions between rod and cone photoreceptor signals. Between daylight and darkness namely, dawn and dusk , as well as in many modern indoor lighting settings and most nighttime outdoor and traffic lighting environments, the visual system combines rod and cone signals and rod—cone interactions can modify perceptual experience and alter almost every aspect of visual processing, including visual detection Buck et al.

Buck , has comprehensively reviewed the effects of rod and cone interactions on human vision. Determining the physiological substrates and mechanisms of rod—cone interaction, and how these give rise to the altered perceptual experience under mesopic illumination are largely unresolved problems in visual neuroscience. Historically, many estimates of sensitivity, magnitude, and timing of the interaction are limited by methodological approaches that inadvertently alter the relative excitation of rods and three cone classes in an undesirable manner with variation in the stimulus parameters.

A central challenge in the study of mesopic vision is therefore to develop methodologies to measure rod and cone signal contributions separately and during rod—cone interaction. In one method, measurements are obtained during adaptation to darkness after exposure to a bleaching light; first for the initial cone plateau adaptation phase during which only cones are sensitive, and then during the full dark-adapted phase in which both rods and cones are sensitive, but when rods are more sensitive than cones Hecht and Hsia, As fully sensitive cones are functional during the later dark adaptation phase, rod responses can be affected by cone involvement and so there may be incomplete rod isolation.

The adaptation state of rods and cones affects their relative sensitivities such that short wavelength adaptation decreases the slope of the scotopic threshold versus intensity TvI curve [0. The scotopic TvI function is more sensitive at higher illumination levels Sharpe et al. Note that thresholds for acuity and contrast sensitivity are more complex than simple TVI curves for the rod and cone systems Barbur and Stockman, Importantly, because rod activity is optimized for low illumination and cones for high illumination, mesopic rod—cone interactions reflect signal processing at the extremes of the photoreceptor operating ranges.

Visual functions under scotopic, mesopic and photopic illumination. The luminance level log cd. The reported values align approximately with the photopic retinal illuminance photopic Troland is shown in bold of the measurement conditions in the referenced study. When rod and cone values are both reported, rod values are italicized. Note that the reported values can vary with the observer, stimulus and measurement condition; see References for details of the experimental conditions: 1 Estimate of the light level under starlight and full moon from Smith et al.

Foveal and parafoveal measurements have been used to compare cone and rod function because cones are the predominant photoreceptor class in the fovea and rods are most prevalent in the parafovea Curcio et al. This approach is limited by eccentric variations in the relative rod and cone densities, the temporal properties of rod vision Raninen and Rovamo, and chromatic properties of cone vision Moreland and Cruz, Moreover, rod—cone interactions may be affecting measurements and foveal and parafoveal stimuli may not truly reflect isolated cone or rod function.

There is also no single eccentricity with only rod photoreceptors, unlike that for cones. The receptive fields sizes of the rod and cone system also differ. Compared to the spatial integration properties of the cone system, the rod system has larger areal summation up to 0. The different spectral sensitivities of the two systems provide basis for isolating their responses. Long-wavelength adapting lights have been used to preferentially desensitize cones, but complete rod isolation is not achieved because rods and cones have roughly the same sensitivity at long wavelengths in the dark-adapted eye, and short-wavelength S and middle-wavelength M cones are not completely desensitized by long wavelength adapting lights Crawford and Palmer, Another method is to use high temporal frequencies to bias detection to cones Coletta and Adams, Rod and cone temporal sensitivities may be more similar, however, depending on the mesopic adaptation level, spectral properties of the illuminant and stimulus eccentricity, and complete cone isolation may not be achieved.

Another approach is to take advantage of the Stiles—Crawford effect and focus the light from the test field near the edge of a fully dilated pupil, which reduces the quantal efficiency of the cones, but not rods Aguilar and Stiles, Taken together, the aim is to develop a method that controls for the distinct functional response properties of the rod and cone systems, in addition to differences in their retinal distributions, spectral sensitivities, sensitivity regulation, retinogeniculate, and higher order processing, factors that underlie the challenges and complexities encountered in the study of mesopic visual function.

Standard signal generators with three-primary lights are sufficient to achieve independent control of rods and two cone photoreceptor classes in dichromatic observers Knoblauch, ; Kremers and Meierkord, , but not the rods and three cone photoreceptors in trichromats to study rod—cone interactions.

To do this, isoscotopic lines can define the combination of three primary lights with a constant scotopic luminance fixed level of rod activity within the domain of combinations with a constant photopic luminance, but even so it is not possible to control both scotopic and photopic luminance using three primaries in trichromats Shapiro et al.

To achieve independent control, the number of primary lights must be no less than the number of active photoreceptors. The four-primary method overcomes limitations of traditional methods to allow independent control of the excitation of the rod and three cone photoreceptors at the same chromaticity, adaptation level and retinal locus Sun et al. The theoretical basis for four-primary photostimulating methodology is silent substitution, as defined by Shapiro et al. Considering silent substitution in color matching provides an example of independent control of rod and cones experimentally.

In color matching, the chromaticity of an equal-energy spectrum light can be metamerically matched using a combination of three primary lights of different wavelengths e. The same chromaticity can also be matched using a different set of primary lights e. When a metameric match is determined for each of the sets of primaries, the L-, M-, and S-cone excitations will be equal for both matches.

In this example, the two stimuli differ in only one primary either or nm while the other two primaries and nm are the same in both stimuli. Since rods are more sensitive to nm light than nm light, switching these two sets of metameric primaries over time produces rod modulation while maintaining constant cone excitations.

A similar approach can be applied to isolate L-, M-, or S-cones. The four-primary photostimulating method offers several advantages in the study of mesopic vision. First, it can modulate one photoreceptor class while keeping the excitations of the other three photoreceptors constant, thereby allowing analysis of the contribution of only one photoreceptor to visual perception. Second, the four-primary colorimeter can maintain the same mean cone chromaticity and luminance level, while changing rod or cone excitations.

The four-primary photostimulating method is a better method for studying mesopic vision because direct measurements of isolated rod and cone functions and their interactions can be achieved, whereas other methods infer rod and cone functions from a comparison of measurements obtained under different conditions. Finally, the colorimeter calibration process can compensate for individual differences in pre-receptoral filtering e. Since mesopic vision is a transitional stage between photopic and scotopic vision, it would be expected that both rod and cone signals would be sent to the cortex in mesopic conditions.

The neural circuitry of the retina has been shown to allow both cone and rod signals to be transmitted to the pathways that carry information to the lateral geniculate nuclei LGN and then to the cortex. Physiological studies have demonstrated that, in addition to cone input, rods contribute to all three major retinogeniculate pathways.

At mesopic and scotopic illuminations, physiological recordings from macaque retina indicate that parasol cells of the MC-pathway are the primary transmitter of rod signals Gouras and Link, ; Virsu and Lee, ; Virsu et al. The analysis of natural image statistics also indicates that rods provide input to all of the three major pathways Barrionuevo and Cao, The sharing of neural pathways allows for rod and cone signal interactions in visual system processing and provides the neural basis for rod contribution to color vision.

However, studies have shown that, at certain light levels, both retinal rod pathways are active simultaneously in mesopic vision Sharpe et al. Therefore, the visual system has potentially a transitional stage from the rod bipolar pathway to the rod—cone gap junction pathway.

The transitional range during which both retinal rod pathways are potentially functioning is thought to occur at high scotopic and low mesopic light levels. Neural pathways related to mesopic vision. Rod signals input to all three primary retinogeniculate pathways, namely the magnocellular MC , parvocellular PC , and koniocellular KC pathways. Only rod inputs to the MC pathway are shown in this schematic. Green circles indicate chemical synapses.

The red zig—zags indicate electrical synapses. When both rods and cones are operational, rods influence all aspects of color vision Lythgoe, ; Gilbert, ; Trezona, ; Stabell and Stabell, a , b, , , ; Smith and Pokorny, ; Montag and Boynton, ; Buck, ; Cao et al. Conversely, the dichromatic retina behaves similarly to the trichromatic retina with large or peripherally viewed mesopic stimuli when rods operate as the third photoreceptor class Smith and Pokorny, Rods have been consistently shown to enhance brightness Ikeda and Shimozono, ; Benimoff et al.

On the FM hue test, rod intrusion causes discrimination loss and increased errors on the tritan axis Knight et al. The degradation in cone chromatic discrimination that occurs in the presence of rod activity was attributed initially to rods weakening the cone signal to produce a desaturation effect Lythgoe, ; Gilbert, Color percepts associated with rod activations have been studied using unique hue measurements and hue scaling Nerger et al. Reports indicate that the rod percept is bluish, with evidence for multiple hue percepts e.

Rod activity also causes a shift or bias in perceived hue as demonstrated by Buck et al. The critical area up to which there are no further perceived changes in hue or saturation at a given eccentricity, increases with rod activity Pitts et al. These experimental designs, however, do not yield results easily interpretable in terms of the underlying physiological mechanisms, and may be methodology dependent; for a discussion see Volbrecht et al. One reason is that a single hue sensation may not be associated with a given cone class Knoblauch and Shevell, The most unambiguous approach is to measure the appearance of a rod signals in terms of cone activation at the same retinal location under the same adaptation conditions as achieved with a four-primary colorimeter.

This negates the problems associated with a change in rod—cone excitation resulting from differences in a retinal eccentricity, illumination, or stimulus wavelength. When the four photoreceptor excitations are independently controlled Pokorny et al. Chromaticity shifts in the color appearance of cone signals due to rod excitation. The arrows indicate the effect of increased rod excitation on the direction of the color shift from the stimulus chromaticities unfilled circles to the matching chromaticities filled circles. Ellipses show the chromaticities of eight non-dark appearing basic colors.

Adapted from Cao et al. Because post-receptoral pathways have no information about the photoreceptor class rod or cone initiating the signal, rod percepts matched to cone-mediated percepts can be linked to PC-, MC-, and KC- pathway signaling. Rod contributions to mesopic color perception involve differential rod signal weightings in the PC-, MC- and KC-pathways as a function of illumination level and rod contrast.

The cone contrasts that perceptually match a rod signal are linear as a function of rod contrast. The data were measured at 2, 10, and Td observer IS. The dashed lines are fits based on a physiologically plausible model. In addition to affecting the perceived hue, brightness, and saturation, rod activity can alter cone-mediated chromatic discrimination Stabell and Stabell, ; Nagy and Doyal, ; Knight et al. In comparison to measurements under photopic illumination, chromatic sensitivity measured under mesopic illuminations is differentially altered in the areas of the protan, deutan, and tritan confusion lines, with the greatest sensitivity loss near the tritan axis, but in general, the magnitude of the rod intrusion is small when measured with luminance contrast masking techniques Walkey et al.

Rod incremental signals degrade chromatic discrimination and rod decremental signals improve chromatic discrimination, with rod activity causing a shift in the ellipse origin and a change in the length of the minor axes Cao et al. Textbook descriptions of rod contributions to color vision often state that rods signal only achromatic percepts, yet vision in twilight illumination is not always colorless e.

The viewing conditions used in these studies, however, may not exclusively involve rods. Nagel noted that for illumination levels below cone threshold, many observers perceive short-wavelength reflective paper samples as blue, although he suggested that such observations do not contradict the notion of color blindness under scotopic light levels, but rather the impossibility of discriminating colors as qualities that are different from one another.

Recent evidence in trichromats and dichromats brings this view into question Pokorny et al. With photopic illumination, cones dominate vision; the rod system is in saturation for all but the longest visible wavelengths, and their contribution to visual perception is minimal as rods in saturation do not signal stimulus change.

Rod—cone coupling can, however, extend the range of rod signaling Hornstein et al.

Dusk Becomes a Dawn

At high illuminations, rods make significant contributions to non-image forming functions via the melanopsin pathway to the circadian system Altimus et al. With reductions in light level from daylight to twilight, both rods and cones contribute to visual perception and further reductions lead to a selective loss in S-cone sensitivity and a progressive increase in rod sensitivity Brown, ; Verriest, ; Walkey et al.

Whilst L- and M-cones remain active, rods and L-cones primarily mediate percepts since rods are more sensitive than M-cones to mid- and short-wavelength light under twilight illumination Pokorny et al. As rods gradually become dominant during dark-adaptation, the peak of visual sensitivity shifts toward shorter wavelengths so that objects predominantly reflecting mid- and short-wavelength light appear relatively brighter than objects reflecting long-wavelength light Purkinje, For wavelengths greater than nm, the photochromatic interval approaches zero and the rods and cones have about equal dark-adapted thresholds Hecht and Hsia, ; Wald, Thus, with reductions in light level and long-wavelength stimuli, there is no situation where rods alone merdiate vision.

Accessibility Links

With progressively shorter wavelengths, however, rod sensitivity increases by a factor of or greater than cones in the mid- and short-wavelength regions of the visible spectrum Kohlrausch, McCann and Benton observed multi-colored percepts in complex scenes illuminated with a red appearing light nm set just above L-cone threshold and superimposed with a monochromatic light or nm set below cone threshold scotopic.

Such percepts were also present with Mondrian patterns McCann, The rod contribution to this effect was determined by setting the threshold level for perception of faint blue—green, red, or yellow hues to each of 10 monochromatic lights — nm in the presence of the nm light set just above L-cone threshold ; the scotopic luminosity function matched the threshold levels of the 10 monochromatic lights McKee et al. When the nm light was increased by 1. Finally, the criterion optimum color was similar irrespective of whether a nm light was imaged in the pupil center or pupil periphery; rod function was implicated by an absence of the Stiles—Crawford effect.

The Stiles—Crawford effect for cones was found only when the irradiance of the nm light was further increased and the irradiance of the nm light at the criterion optimum color needed to be set at a level above cone threshold McKee et al. The percepts appear brighter, sharper, and slightly more saturated under photopic conditions. Taken together, these studies clearly demonstrate that multicolored percepts can be generated through interaction of L-cone and rod signals whereas independently, only achromatic lightness percepts are signaled.

See McCann et al.

Purkinje effect

Pokorny et al. When observers are presented with an array of reflective paper samples under scotopic illumination, trichromatic participants perceive brighter appearing stimuli as blue—green—gray, and darker appearing stimuli as reddish-orange, irrespective of the photopically assigned color names. This rod color was termed relational because the color appearance of a paper samples changed depending on the lightness of other paper samples in view Pokorny et al. Such scotopic color perceptions are not restricted to trichromats; congenital dichromats have a rich color gamut under scotopic viewing conditions Pokorny et al.

Although dichromats can name color in fair agreement with color normal observers under photopic conditions Scheibner and Boynton, ; Nagy and Boynton, , the assigned color names under scotopic illuminations are not consistent with the scotopic lightness of the samples as were the names assigned by deuteranomalous trichromats and color normals. Surface color perception under scotopic illumination reveals relational hue percepts mediated exclusively via the rod pathway.

Symbols show the reported color names from four trichromatic observers of the gray OSA-UCS color sample as a function of photopic illuminance. Light levels below about Adapted from Pokorny et al. To understand rod color vision in complex viewing environments, Elliott and Cao investigated perceived hue in natural scene images under scotopic light levels.

They showed that when a test patch had low variation in the luminance distribution and was a decrement in luminance compared to the surrounding area, reddish or orangish percepts were more likely to be reported compared to all other percepts. In contrast, when a test patch had high variation and was an increment in luminance, the probability of perceiving blue, green, or yellow hues increased. In addition, when observers had a strong, but singular daylight hue association for the test patch, color percepts were reported more often and hues appeared more saturated compared to patches with no daylight hue association.

This suggests that some cortical mechanisms, which integrate experience in daylight conditions with the bottom—up rod signal processing under scotopic illumination, can modulate scotopic color perception. Rod—cone interactions are best illustrated with stimuli that change overtime because these conditions exploit the different temporal response properties of rods and cones.

While it has been demonstrated that both rods and cones contribute signals to the retinogeniculate pathways, the relative contributions of rods and cones to each of the pathways are not known. To understand how rod and cone signals are combined in different post-receptoral pathways, summation paradigms were developed to measure threshold changes as a function of the phase, contrast, and adaptation state of rods and cones Ikeda and Urakubo, ; van den Berg and Spekreijse, ; Benimoff et al.

A linear vector sum model demonstrates that a temporal combination of rod and cone signals may mediate flicker detection MacLeod, ; van den Berg and Spekreijse, A non-linear combination of rod and cone signals has been shown to mediate other tasks Buck and Knight, This is not a major factor for incremental or decremental stimuli, however, as the faster signal is processed before the slower signal Cao et al.

The type of summation also depends on the pathways mediating detection. Using a four-primary colorimetery to measure thresholds for mixed rod and L-cone or M-cone modulations as a function of their relative phase and frequency 2 or 10 Hz , Sun et al.

The Three Types of Twilight

Consistent with this observation, physiological recordings of sinusoidal stimulation of macaque parasol cells show linear summation of rod and cone signals Cao et al. Mesopic vision can change depending on whether signaling involves both the faster rod—cone gap junction pathway and the slower rod bipolar pathway, or when signaling shifts between these pathways. When higher cone light adaption promotes cone signaling via the faster pathway and rod signaling via the slower pathway, cone signaling is 60—80 ms faster than rod signaling MacLeod, ; van den Berg and Spekreijse, ; Barbur, ; Sharpe et al.

On the contrary, when cone and rod latencies are estimated under conditions of comparable mesopic light adaptation and all photoreceptor signals are transmitted via the faster rod—cone gap junction pathway, the cone—rod latency difference is reduced to 8—20 ms Sun et al. The transition from the slower to the faster pathways also changes the system gain, which has been noted in rod reaction time models during the transition from high scotopic to low mesopic light levels Cao et al. When rods are dark-adapted in the region surrounding a cone-detected target lateral interaction , rods suppress cone flicker detection Lythgoe and Tansley, ; MacLeod, ; van den Berg and Spekreijse, ; Goldberg et al.

The mechanism and physiological substrates of lateral rod—cone interaction has been the subject of considerable debate. It was initially inferred from psychophysical studies that rods primarily interacted with L-cones when flicker sensitivity measured using stimulus conditions that caused rod excitation to vary with the wavelength of the test light Coletta and Adams, , ; Frumkes et al.

Use of red lights

Although early physiological reports in amphibians indicated that horizontal cells were the neural locus Frumkes and Eysteinsson, , horizontal cell inputs in primates are additive and synapse primarily with cones Dacey et al. The lateral rod—cone interaction decrease cone critical fusion frequency CFF by about 6 Hz Cao et al. Suppressive rod—cone interactions with cone isolating flicker stimuli on dim backgrounds are not significant for S-cone modulations Cao et al. Interactions between rods and S-cones might be more complex, with evidence from four-primary colorimetry for linear summation of the two signals in the KC pathway which produces antagonistic, phase dependent threshold changes Zele et al.

These rod and S-cone interactions depend on the relative photoreceptor contrast ratios and a mutual, non-linear reinforcement, possibly originating at the photoreceptor level, that acts to decrease threshold supra-additivity with increasing contrast ratios Zele et al. It is known from physiological studies that KC-pathway units respond vigorously to S-cone and luminance containing modulations Yeh et al. Physiological recording in ganglion cells have indicated that the PC-units have weak inputs from rods Lee et al. The relative rod contributions to the three pathways depends on the rod temporal profile.

The implication is that the nature of the rod—cone interaction changes with the relative weighting of the rod and cone signals in the three pathways Zele et al. The perception of motion of peripherally fixated, small circular stimuli at photopic illuminances are distorted such that the circle takes on a comet like appearance, yet long temporal responses are not typically associated with photopic vision Barbur et al. Interestingly, the spectral response of the comet effect is consistent with rod—cone interactions, the implication being that rods in saturations can inhibit cone signaling Barbur et al.


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Rod—cone interactions produce large transient sensitivity reductions at stimulus onset and offset Buck et al. The temporal adaptation response for non-opponent cone—cone interactions is monophasic whereas opponent cone—cone interactions are biphasic Zele et al. In contrast, different adaptation processes regulate rod and cone vision He and MacLeod, and so an increase in the local rod adaptation level facilities rod signaling through temporal summation, pointing to some intrinsic difference in the processing of rod and cone signals in post-receptoral pathways Zele et al.

Post-receptoral rod signaling weights in the MC, PC, and KC pathways depend on the temporal properties of the rod signal. Data were measured using a perceptual matching paradigm at 5 photopic Td two observers; darker and lighter columns. Adapted from Zele et al. An examination of the relationship between rod—cone interactions for stimuli that are temporally modulated periodic or pulsed aperiodic found the interactions are a general visual phenomenon affecting both periodic and aperiodic stimuli, causing the cone pathway temporal impulse response function IRF amplitude to decrease and the time-to peak to be delayed Zele et al.

This suppressive effect is analogous to reducing cone system contrast sensitivity and increasing the integration time Zele et al. Rod—cone coupling may be important for these processes. Simple reaction times for rod or cone stimuli with various contrasts and retinal illuminances were measured Cao et al. These measured reaction times can be modeled by rod and cone IRFs Cao et al.

In a separate investigation, the effects of rod—cone interaction on reaction time mediated by chromatic and luminance pathways were studied. Lateral rod—cone interactions increase cone-mediated RTs with the strongest rod—cone interactions in a dark surround Zele et al. Reaction time has been explored as a basis for developing a real world, performance based mesopic luminous efficiency functions He et al.

Recent evidence, however, indicates there is an involvement of chromatic pathways Walkey et al. At present there are numerous outstanding problems in the study of the dual processing of rod and cone signals. The range and impact of rod—cone interactions on human visual function and performance is only becoming known, and the subtlety and significance of these effects is becoming apparent. The cortical mechanisms for scotopic color vision are still to be defined Pokorny et al. The quantification of the effects of rod—cone interaction on motion processing is also incomplete.

To fully understand these processes under conditions best able to control for the differences between the rod and cone systems, the four-primary colorimetric method will be central. The generality of this methodology is becoming clear with new applications beyond psychophysics in the areas of physiology Cao et al. Combinations of these techniques will be critical for determining the physiological substrates, both in the retina and cortex, in addition to answering questions about the mechanisms of rod—cone interaction including how the relative rod and cone weights change in the post-receptoral pathways and their affects on visual function and performance.

Computational descriptions of mesopic vision derived from functional data in humans will be important for industrial applications that require optimal lighting conditions. The effects of rod—cone interaction in visual function and performance are directly applicable to many occupational environments, including transportation i. There are well-accepted luminosity functions for photopic and scotopic lighting conditions that are often used in science and industry, but complex nature of rod and cone contributions in mesopic illuminations means there is currently no accepted mesopic luminous efficiency function CIE, ; Stockman and Sharpe, It will be important to determine general mesopic luminous efficiency functions CIE, , whether they be performance based He et al.

The use of an inappropriate spectral luminous efficiency function in the mesopic region has energy efficiency and economic consequences, not to mention safety issues in, for example, lighting for nighttime transportation.

See a Problem?

Future developments in this area will include practical lighting standards for mesopic illuminations that are energy efficient and optimize visual performance. Advances in the study of mesopic vision should provide needed information for solutions to many industrial application problems. The development of a widely applicable, mesopic luminous efficiency function will be one of the most challenging problems encountered in this area of research.

We anticipate that the development of new tests for the study of rod—cone interaction in normal eyes will have great potential for translation to applied investigations Alexander and Fishman, ; Arden and Hogg, ; Alexander et al. New developments of clinical mesopic vision tests will be important because most acquired retinal diseases involve both the rod and cone systems.

Moreover, impaired vision in the mesopic range is probably the most sensitive and earliest sign of a range of retinal diseases Petzold and Plant, The number of complaints about disturbances in mesopic and scotopic vision after corneal refractive surgery is also increasing, indicating the importance of developing new measures of these visual disturbances Fan-Paul et al. In general, decision processing in perceptual detection or action tasks is cortically mediated and, therefore, the photoreceptor source of information in these tasks should not be a salient factor at the level of the cortex.

In mesopic decision processing, rod and cone signals should be considered as largely interchangeable in terms of postreceptoral visual processing and decision processing for final perception Cao and Pokorny, However, if a retinal disease preferentially affects a particular photoreceptor class, thereby affecting rod and cone contributions to the retinogeniculate pathways and rod and cone interactions, visual perception may be affected. Therefore, the study of changes in rod and cone contributions and interactions in neural pathways in diseases may be helpful in understanding the mechanisms of visual loss.

Expanding the study of retinal diseases by examining visual perception under mesopic conditions may prove to be illuminating. The Authors made equal intellectual contributions to the paper and are accountable for all intellectual aspects of the work. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Europe PMC requires Javascript to function effectively. Recent Activity. The snippet could not be located in the article text.

This may be because the snippet appears in a figure legend, contains special characters or spans different sections of the article. Front Psychol. Published online Jan PMID: Andrew J. Reviewed by: John L. This article was submitted to Perception Science, a section of the journal Frontiers in Psychology. Received Oct 14; Accepted Dec The use, distribution or reproduction in other forums is permitted, provided the original author s or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice.

No use, distribution or reproduction is permitted which does not comply with these terms. This article has been cited by other articles in PMC. Abstract Evidence has accumulated that rod activation under mesopic and scotopic light levels alters visual perception and performance. Keywords: vision, rods, cones, scotopic, mesopic, photopic, color, temporal. Open in a separate window. Conflict of Interest Statement The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Saturation of the rod mechanism of the retina at high levels of illumination. Acta 1 59—65 Rod-cone interaction in flicker perimetry. Mechanisms of rod-cone interaction: evidence from congenital stationary nightblindness. Vision Res. Rods-cones and melanopsin detect light and dark to modulate sleep independent of image formation. Hue discrimination in peripheral vision under conditions of dark and light adaptation.

Multiple processes mediate flicker sensitivity. Rod-cone interactions and analysis of retinal disease. Reaction-time determination of the latency between visual signals generated by rods and cones. Ophthalmic Physiol. The perception of moving comets at high retinal illuminance levels: a rod-cone interaction effect.

Scotopia First Dusk by Spencer Pizzani

Oxford: Elsevier; , — Temporal and spatial summation in human vision at different background intensities. Contributions of rhodopsin, cone opsins, and melanopsin to postreceptoral pathways inferred from natural image statistics. A Opt. Image Sci. Assessing rod, cone, and melanopsin contributions to human pupil flicker responses.

Submarines are dimly lit to preserve the night vision of the crew members working there, but the control room must be lit to allow crew members to read instrument panels. By using red lights, or wearing red goggles , the cones can receive enough light to provide photopic vision namely the high-acuity vision required for reading. The rods are not saturated by the bright red light because they are not sensitive to long-wavelength light, so the crew members remain dark adapted.

Red lights are also often used in research settings. Many research animals such as rats and mice have limited photopic vision, as they have far fewer cone photoreceptors. He reasoned that the eye has not one but two systems adapted to see colors, one for bright overall light intensity, and the other for dusk and dawn. Purkinje effect Simulated appearance of a red geranium and foliage in normal bright-light photopic vision, dusk mesopic vision, and night scotopic vision. Eye : appearance phenomena. Eyeshine Leukocoria Red-eye effect Red reflex.