Understanding Mach bands and radiating lines, (the perception of bright and dark areas that physically do not exist in the stimulus) requires our understanding the concept of lateral inhibition and receptive fields. We will consider receptive fields first.
There are many millions of receptors in the retina. There is only about one million optic nerve fibers sending visual signals up to the high brain centers. Consequently, individual receptors do not have private lines up to the visual cortex. Rather, multiple receptors converge on to subsequent neural units on their way to the higher visual centers. This convergence results in a physiological concept known as receptive fields.
To put it another way, a receptive field is the receptor area which when stimulated results in a response of a particular sensory neuron. If you clicked on the receptive field diagram then you already have seen a cartoon of a hypothetical set of neurons which shows how this works. You can also jump to a more detailed explanation. You may have already read this explanation if you clicked to it from the receptive field diagram.
If you feel that you now understand the concept of receptive fields, we can proceed to use this idea to explain Mach bands and Radiating lines. Let's look again at Mach band diagram but this time with a receptive field overlay, or the Radiating line figure.
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