Reference no: EM13845226
Assignment: Illusion of the Mach Bands
Introduction:
The goal of lateral inhibition is to facilitate edge detection. Edge detection is the process of distinguishing where one object ends and the next begins. That is, it works to make edges as clear as possible. Edge detection is important-think about trying to see a camouflaged predator, perhaps a lioness-in the tall dry grass. The lioness's fur and the grass are roughly the same color, important for the lioness as she slowly stalks her prey (you, in this case). However, the fur and the grass are not identical, and you want your visual system to pick up where the grass ends and where the lioness begins. It is for this reason that edge detection evolved.
Lateral inhibition accentuates the edges of the stimulus. Ernst Mach (1838-1916) noticed that when two bars, one dark and one bright, are next to each other, you see little bands of extra dark at the edge of the dark band and extra light at the edge of the light bar. These bands do not exist but are an illusion caused by lateral inhibition via our center-surround receptive fields. Examine the figure below to witness Mach bands for yourself. The left edge of each bar should appear lighter than the right edge. To prove that this is an illusion, cover the bars around a single bar in the figure and note that the bar is indeed a single shade of gray.
1. Explain why the Mach bands illusion occurs by describing the activity of neurons (e.g. photoreceptors) in the retina when viewing the figure above. Be sure to explain the patterns of excitation and inhibition of adjacent photoreceptors when viewing the edge of each bar versus the middle of each bar.
2. Receptive fields are groupings of photoreceptors in the retina that send information to a single ganglion cell. Receptive fields demonstrate a center surround organization in which the center of the receptive field responds in an opposite manner to the surrounding area of the receptive field. This pattern of excitation and inhibition is known as lateral inhibition. In the figure below, which receptive field (1, 2, or 3) would be most likely to result in the illusion of Mach bands. Briefly explain why you selected this receptive field.