Perceiving the Intensity of Light.

Abstract

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 ...

The place of white in a world of grays: A double-anchoring theory of lightness perception.

“…Objects that appear to sit in the shadow, or under a dark filter, must be, or have repeatedly turned out to be in the past (Purves et al, 2004), lighter than equiluminant objects sitting in the light, and are therefore seen as such. The right display of Figure 19 is at odds with this argument, and shows that the explanatory power of illumination discounting is, at best, inadequate (see also Bressan, 2003).…”

Odour concentration affects odour identity in honeybees

“…Where such independence is achieved, stimulus intensity does not contribute much to stimulus identity; for example, neither does brightness contribute appreciably to the visual identity of an object (e.g. colour) (Livingstone & Hubel 1988;Lotto & Purves 1999;Purves et al 2004), nor does loudness contribute to the auditory identity of a sound (e.g. frequency) (Zeng & Shannon 1994;Escabi et al 2003).…”

The statistical structure of natural light patterns determines perceived light intensity

“…A central puzzle in understanding how such percepts are generated by the visual system is that brightness does not correspond in any simple way to luminance. Thus, the same amount of light arising from a given region in a scene can elicit dramatically different brightness percepts when presented in different contexts (1,2) (Fig. 1).…”

“…A growing body of evidence has shown that the visual system uses the statistics of stimulus features in natural environments to generate the visual percepts of the physical world (15); if so, the visual system must incorporate these statistics as a central feature of processing relevant to brightness and other visual qualia (2). Accordingly, we suppose that the perceived brightness elicited by the luminance of a target in any given context is based on the value of the target luminance in the probability distribution function of the possible values that co-occur with that contextual luminance experienced during evolution.…”