{"id":60,"date":"2022-04-27T07:13:02","date_gmt":"2022-04-27T11:13:02","guid":{"rendered":"https:\/\/pressbooks.library.upei.ca\/danceofphotons\/chapter\/12-photons-as-retinal-images\/"},"modified":"2022-05-12T17:58:45","modified_gmt":"2022-05-12T21:58:45","slug":"12-photons-as-retinal-images","status":"publish","type":"chapter","link":"https:\/\/pressbooks.library.upei.ca\/danceofphotons\/chapter\/12-photons-as-retinal-images\/","title":{"raw":"PHOTONS AS RETINAL IMAGES","rendered":"PHOTONS AS RETINAL IMAGES"},"content":{"raw":"
\r\n

p. 37<\/p>\r\nLenses are how our eyes sort the confusion of rays to produce an image<\/em><\/strong> that contains the information about where the rays came from. They do this by forming an image -\r\n

\"image\"<\/p>\r\n \r\n

p. 38<\/p>\r\n- an IMAGE like this on the retina<\/em><\/strong> at the back of the eye:<\/span>\"\"\r\n\r\nWhen inversion and reversal of the image in our eye was discovered in the Middle Ages, it mystified philosophers.5<\/sup>\r\n\r\n<\/div>\r\n

The answer to that \u201clittle\u201d inconsistency between optics and perception turns out to be more profound than any mystery in physics.<\/span><\/p>\r\n

It is not explainable by some possible 1800 twist of neural connections from the retina<\/em>. Here\u2019s why: After a few days\u2019 confusion, persons wearing \u201cglasses\u201d that turn the image right side up find the world appearing normal.<\/span><\/p>\r\n

Evidently the <\/span>visual<\/em><\/strong> image is not constrained by neuroanatomy.<\/span><\/p>\r\n \r\n

p.39<\/p>\r\nConsider the retinal image. Though it appears to be continuous, that image is sensed by individual receptor cells in the retina<\/em>.\r\n\r\nThe ability to sense the direction from which photons have arrived depends on the size of the retinal receptors and focal length of the eye. A typical photoreceptor has a diameter of 2.5 micrometers and is located at the focal point of the eye, some 25 millimeters behind the lens. By trigonometry the receptor subtends a 22 second angle with respect to the lens\u2019 center. Because congruent angles are equal, that is the receptor\u2019s field<\/em><\/strong> of<\/em><\/strong> view<\/em><\/strong> - how much of the world it responds to.\r\n

\"image\"<\/p>\r\n*<\/strong>NB In vertebrate eyes the light sensitive end of the photoreceptors not only faces away from the lens, it is also covered by the rest of its cell body and by several types of nerve cells and nerve fibers that, fortunately, are nearly transparent. (Why this backwards design, and only in vertebrates? That\u2019s another story.)6<\/sup>\r\n\r\n \r\n

p. 40<\/p>\r\n \r\n\r\n \r\n\r\n \r\n

However,<\/strong> the<\/strong> photoreceptors<\/strong> would not respond<\/strong> to<\/strong> the<\/strong> photons<\/strong> in the<\/strong> image<\/strong> w<\/strong>ere<\/strong> it<\/strong> not for<\/strong> another<\/strong> property<\/strong> of<\/strong> photons:<\/strong><\/h3>\r\n

<\/p>","rendered":"

\n

p. 37<\/p>\n

Lenses are how our eyes sort the confusion of rays to produce an image<\/em><\/strong> that contains the information about where the rays came from. They do this by forming an image –<\/p>\n

\"image\"<\/p>\n

 <\/p>\n

p. 38<\/p>\n

– an IMAGE like this on the retina<\/em><\/strong> at the back of the eye:<\/span>\"\"<\/p>\n

When inversion and reversal of the image in our eye was discovered in the Middle Ages, it mystified philosophers.5<\/sup><\/p>\n<\/div>\n

The answer to that \u201clittle\u201d inconsistency between optics and perception turns out to be more profound than any mystery in physics.<\/span><\/p>\n

It is not explainable by some possible 1800 twist of neural connections from the retina<\/em>. Here\u2019s why: After a few days\u2019 confusion, persons wearing \u201cglasses\u201d that turn the image right side up find the world appearing normal.<\/span><\/p>\n

Evidently the <\/span>visual<\/em><\/strong> image is not constrained by neuroanatomy.<\/span><\/p>\n

 <\/p>\n

p.39<\/p>\n

Consider the retinal image. Though it appears to be continuous, that image is sensed by individual receptor cells in the retina<\/em>.<\/p>\n

The ability to sense the direction from which photons have arrived depends on the size of the retinal receptors and focal length of the eye. A typical photoreceptor has a diameter of 2.5 micrometers and is located at the focal point of the eye, some 25 millimeters behind the lens. By trigonometry the receptor subtends a 22 second angle with respect to the lens\u2019 center. Because congruent angles are equal, that is the receptor\u2019s field<\/em><\/strong> of<\/em><\/strong> view<\/em><\/strong> – how much of the world it responds to.<\/p>\n

\"image\"<\/p>\n

*<\/strong>NB In vertebrate eyes the light sensitive end of the photoreceptors not only faces away from the lens, it is also covered by the rest of its cell body and by several types of nerve cells and nerve fibers that, fortunately, are nearly transparent. (Why this backwards design, and only in vertebrates? That\u2019s another story.)6<\/sup><\/p>\n

 <\/p>\n

p. 40<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

However,<\/strong> the<\/strong> photoreceptors<\/strong> would not respond<\/strong> to<\/strong> the<\/strong> photons<\/strong> in the<\/strong> image<\/strong> w<\/strong>ere<\/strong> it<\/strong> not for<\/strong> another<\/strong> property<\/strong> of<\/strong> photons:<\/strong><\/h3>\n

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