Color and Light in Nature

Lynch, D. K.; Livingston, W.; Mallmann, A. James

doi:10.1119/1.18431

Cited by 57 publications

(80 citation statements)

References 0 publications

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“…Because light sources are generally extended, the rays reaching the shadow-casting object do not arise from a single point in space. As a result, the edges of shadows are blurred to a degree that depends on the extent of the source, the distance of the shadow-casting object from the shadowed surface, the clarity of the atmosphere, and a variety of other factors (Lynch & Livingston, 1995;Minnaert, 1937Minnaert, /1992. Thus, penumbras not only indicate that a particular luminance profile is a shadow (rather than, say, the result of a gradient of surface reflectance) but also convey a range of additional empirical information about the illumination of a scene (see, for example, Rock, 1995, p. 47).…”

Section: Some Simple Tests Of This Predictionmentioning

confidence: 99%

Perceiving the Intensity of Light.

Purves¹,

Williams²,

Nundy³

et al. 2004

Psychological Review

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The relationship between luminance (i.e., the photometric intensity of light) and its perception (i.e., sensations of lightness or brightness) has long been a puzzle. In addition to the mystery of why these perceptual qualities do not scale with luminance in any simple way, "illusions" such as simultaneous brightness contrast, Mach bands, Craik-O'Brien-Cornsweet edge effects, and the Chubb-Sperling-Solomon illusion have all generated much interest but no generally accepted explanation. The authors review evidence that the full range of this perceptual phenomenology can be rationalized in terms of an empirical theory of vision. The implication of these observations is that perceptions of lightness and brightness are generated according to the probability distributions of the possible sources of luminance values in stimuli that are inevitably ambiguous.A fundamental problem in vision (and perception generally) was recognized at the beginning of the 18th century by George Berkeley (1709Berkeley ( /1975, who pointed out that the sources underlying visual stimuli are unknowable in any direct sense. The light that falls on the eye from any region of a scene conflates the contributions of reflectance, illumination, and transmittance (as well as a host of subsidiary factors that affect these parameters). As a result, the physical provenance of light reaching the eye-and therefore the significance of the stimulus for visually guided behavior-is profoundly uncertain. This fundamental fact presents a biological quandary. Successful behavior in a complex and potentially hostile environment clearly depends on responding appropriately to the physical sources of visual stimuli rather than to the stimuli as such. If, however, the retinal images generated by light cannot uniquely define the underlying reality the observer must deal with, how then does the visual system produce behavior that is generally successful?The purpose of this review is thus to consider evidence, much of it derived from our own experiments over the last few years, about the way the uncertain relationship between the physical world and the perceptual world is resolved by the nervous system (see Purves & Lotto, 2003). The gist of this body of work is that what one sees at any moment appears to be fully determined by the probability distributions of the possible sources of the stimulus rather than the physical qualities of the stimulus (which are ambiguous) or the properties of the objects and conditions that generated the stimulus (which cannot be known directly). Although this framework has several important precedents (see below), it differs from most mainstream neurobiological thinking in recent decades and suggests other ways of conceptualizing the purposes served by the known physiology of visual system circuitry. The context here for exploring the merits of this conception of vision is sensations of lightness and brightness, which are arguably the most fundamental qualities of human visual experience. Luminance, Brightness, and LightnessLuminance is ...

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Section: Some Simple Tests Of This Predictionmentioning

confidence: 99%

Perceiving the Intensity of Light.

Purves¹,

Williams²,

Nundy³

et al. 2004

Psychological Review

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“…The enhanced polarization sensitivity of ocellar UV photoreceptors might reflect the fact that scattered skylight is polarized most strongly at short wavelengths (e.g. Snyder, 1973;Lynch and Livingston, 1995). The enhanced polarization sensitivity of ocellar UV photoreceptors thus will increase the UV-green contrast between the terrestrial panorama and the sky even further.…”

Section: The Polarization Sensitivity Of Uv and Green Receptorsmentioning

confidence: 99%

Regional differences in the preferred e-vector orientation of honeybee ocellar photoreceptors

Ogawa

Ribi

Zeil

et al. 2017

Journal of Experimental Biology

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In addition to compound eyes, honeybees (Apis mellifera) possess three single-lens eyes called ocelli located on the top of the head. Ocelli are involved in head-attitude control and in some insects have been shown to provide celestial compass information. Anatomical and early electrophysiological studies have suggested that UV and blue-green photoreceptors in ocelli are polarization sensitive. However, their retinal distribution and receptor characteristics have not been documented. Here, we used intracellular electrophysiology to determine the relationship between the spectral and polarization sensitivity of the photoreceptors and their position within the visual field of the ocelli. We first determined a photoreceptor's spectral response through a series of monochromatic flashes (340-600 nm). We found UV and green receptors, with peak sensitivities at 360 and 500 nm, respectively. We subsequently measured polarization sensitivity at the photoreceptor's peak sensitivity wavelength by rotating a polarizer with monochromatic flashes. Polarization sensitivity (PS) values were significantly higher in UV receptors (3.8± 1.5, N=61) than in green receptors (2.1±0.6, N=60). Interestingly, most receptors with receptive fields below 35 deg elevation were sensitive to vertically polarized light while the receptors with visual fields above 35 deg were sensitive to a wide range of polarization angles. These results agree well with anatomical measurements showing differences in rhabdom orientations between dorsal and ventral retinae. We discuss the functional significance of the distribution of polarization sensitivities across the visual field of ocelli by highlighting the information the ocelli are able to extract from the bee's visual environment.

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“…The apparent divergence and convergence of the rays are effects of perspective. More detailed explanations and numerous photographs of crepuscular phenomena can be found in articles such as Lynch and Livingston (2001) and Cowley (2004).…”

Section: Unusual Anticrepuscular Ray Displaymentioning

confidence: 99%