disparityanddepthperception

disparityanddepthperception - I am looking at Fig 12.14 in...

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I am looking at Fig 12.14 in our book, pg 303 and I'm finding it confusing. It talks about "near" and "far" disparities and it says that the smaller the disparity the smaller the depth. Is disparity a measure of where an image falls on the retina or how far an image falls on the retina from the fixation point. In the book it says a small disparity means small depth--but does that tell you about "nearness" or "farness", that is, can you have a small, near disparity and a small, far disparity. Or does a small disparity = a near disparity and a large disparity = a far disparity? Thompson: This is seemingly complex, but is really very simple, and I find it wonderously beautiful. Please try to work through the explanation below and let me know if it works for you. Recognize what the book is doing is drawing a ray diagram showing where light coming from 3 individual points in front of the person will project onto the back of the retina. (See if you wish the aside comment 1 below.) The eyes are shown verged together and the lens accomodated to bring point "b" into focus at the fovea of each eye. The drawing is attempting to show you where the images of point "c" and "a" will fall on the retina. They are trying to show you that if an object is in front of the plane of focus, its image will fall in each case to the temporal side of the fovea in each eye. On the other hand, if the object falls in back of the plane of focus, its image will fall to the nasal side of the fovea in each of the two eyes. Exactly how much to the temporal or nasal side the image falls of such a point will depend on how far behind or in front, respectively, the object is located. Imagine now that we connect some of the retinal ganglion cells located at the fovea that image point "b" together to create a cell in the cortex that is a simple cell responding to some particular orientation (this is a subject we covered in class). This cell will have 0 disparity because to excite the cell through the right eye (with the left eye covered) we would have to put the stimulus in the same location (in the plane of focus) as we would if we did the opposite (i.e. opened the left eye, but covered the right). You could say that when this cell in the brain fires really vigorously (and it does so if both eyes are simultaneously stimulated), it would be reporting that an edge or bar of the appropriate
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orientation is located within the plane of focus. Imagine now that we connect some of the retinal ganglion cells
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This note was uploaded on 05/12/2010 for the course BIO 365R taught by Professor Draper during the Spring '08 term at University of Texas at Austin.

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disparityanddepthperception - I am looking at Fig 12.14 in...

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