What Determines the Perceived Brightness of Objects?

1745 WordsOct 26, 20087 Pages
What determines the perceived brightness of objects? Luminance is a physical and objective measure of the intensity of light. The sensation elicited by different luminances is called brightness. However brightness is a subjective measure as it is the perceived amount of light emanating from an object. It may seem logical to expect that luminance and brightness are directly proportional and that two objects that reflect the same amount of physical light into the eye will look the same brightness. However, as this essay will discuss, the apparent brightness of objects is not entirely dependent upon the amount of light received from them and other factors are influential in the way we perceive brightness. Our perception of the…show more content…
They imply that cognitive factors are important in the perception of brightness. There are other contradictions to the standard simultaneous-brightness-contrast effect. For example, as first shown by the 19th-century physicist Wilhelm von Bezold, an object surrounded by territory of predominantly higher luminance can, under the right circumstances, look brighter than the same target surrounded by territory of lower average luminance. This can be seen in ‘The white illusion’ (figure 4). Here the grey under the white stripes appears to be brighter than the grey under the black stripes. This is opposite of what the retinal-firing-rate explanation of brightness predicts. Based on the action of lateral inhibition the white stripes should darken the grey rather than lighten it. Shapley and Reid (1985) named this phenomenon ‘brightness assimilation’. In this effect the brightness of the object seems to be determined by the assumptions that the observer makes about the nature of the scene and even the way in which regions of the visual field appear to be arranged (Agostini and Proffitt 1993). The grey under the white stripes is perceived as a transparent object on top of a background but the grey under the black stripes looks like an object behind bars so appears less bright. Here cognitive factors seem important as it is how the observer interprets the scene that determines the
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