Brains; How They Seem to Work by Dale Purves

Author:Dale Purves [Purves, Dale]
Language: eng
Format: epub
Publisher: FT Press
Published: 2010-01-08T05:00:00+00:00

The difficulty of explaining lightness or brightness perceptions is compounded by the absence of any cortical region dedicated to processing luminance. And although a relatively close link exists between light intensity and the rate of action potential generation by neurons in the retina and visual thalamus, this relationship breaks down when neurons are tested in the “higher” processing stations of the visual system. Neurons in the visual cortex generally respond only weakly to changes in light intensity. Yet these neurons represent the more complex aspects of stimuli, as evidenced by the selective receptive field properties of complex and hypercomplex neurons, and even neurons that respond to particular objects (see Chapter 7). Although neuronal activity at these higher cortical levels must be generating what we see, the representation of luminance—the most basic of the visual qualities—seems to have been lost in the shuffle.

Figure 8.6 A stimulus pattern that elicits perceptual effects that, as described in the text, undermine explanations of lightness/brightness contrast based on the properties of neurons at the input level of the visual system. The key indicates the physically identical target patches of interest. (From Purves and Lotto, 2003)

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