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The Wisdom of Psychopaths
In this engrossing journey into the lives of psychopaths and their infamously crafty behaviors, the renowned psychologist Kevin Dutton reveals that there is a...
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Alas! Poor Yorick. I knew him well. A fellow of infinite jest, of most excellent fancy; he hath borne me on his back a thousand times; and now, how abhorred in my afterimage he is!
Well… that’s what Hamlet would have said, had he been holding the vintage Pear’s Soap advertisement bearing Yorick’s skull in the accompanying slide, rather than a dug up and rotting Danish cranium. In this antique illusion, you can stare at the X in Yorick’s left eye socket for about 10 to 30 seconds, then look away at a flat surface such as a piece of paper, wall, ceiling or sky, and you will see Yorick’s afterimage as a ghostly apparition.
Afterimages such as this one help us to understand how neurons in various areas of the brain adapt to the visual environment. Adaptation, in this case, is the process by which neurons habituate and eventually cease responding to an unchanging stimulus. Once neurons have adapted, it takes a while for them to reset to their previous, unadapted state: it is during this period that we see illusory afterimages. We see afterimages every day: after briefly looking at the sun, at a bright light bulb or after being momentarily blinded by a camera flash, we perceive a temporary dark spot in our field of vision.
Vision scientists believe that the adaptation effect producing poor Yorick’s afterimage largely takes place in the neurons of the retina. How can we know? Close your right eye and stare at the X again. Then look at the wall again to see the afterimage, but this time switch back-and-forth between closing one eye and the other. Only the left eye—which was open during the adaptation period—will reveal Yorick’s ghost. This result means that the adaptation must have taken place only in neurons responding to stimulation from the left eye. If the binocular neurons of the brain (in the primary visual cortex and higher visual areas) had been adapted, you would see Yorick’s ghost with either eye, despite having adapted only one eye.
This month’s slide show features several afterimage illusions. Each of them illustrates the perceptual effects of neural adaptation at a particular stage of visual processing.
Are you a scientist? Have you recently read a peer-reviewed paper that you want to write about? Then contact Mind Matters editor Jonah Lehrer, the science writer behind the blog The Frontal Cortex and the book Proust Was a Neuroscientist. His latest book is How We Decide.
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9 Comments
Add CommentI read while lying on one side, which means all the light is in one eye. When I switch the light off, for a few minutes I'm effectively blind in that eye. It's disconcerting, to say the least.
Reply | Report Abuse | Link to thisok slywy, I will bite. How can you see anything at all if the light is out?
Reply | Report Abuse | Link to thisThe authors should check their sources before putting electrons to disk drive. The opening quotation before the added material should read: Alas, poor Yorick! I knew him, Horatio. . . ." Their error is only slightly mitigated in that the incorrect quotation is ubiquitous.
Reply | Report Abuse | Link to thisala the Mythbusters; pirates may have used eyepatches to keep one eye adjusted to low light conditions so that when going belowdecks they could switch the patch to the other eye, or flip it up and be able to see well immediately without having to wait for both eyes to adjust. It works so well that when they tested it, they were able to see in almost complete darkness. Since the other eye takes 30 seconds or more to adjust to the same level. Apparently NASA scientists have tested the same phenomenon, with the same results, but also discovered that it temporarily affects a tiny portion of the brain, preventing the person whose eyes are not adjusted to the same light level as the other eye from uttering the phrase; "orange flavored peanut butter ball bingo" until both eyes adjust to the same level of light sensitivity. Odd, but since that phrase is not one that is used often it rarely causes any problems, and the the condition is entirely harmless.
Reply | Report Abuse | Link to thiskatman13, there's still enough to see because of city lights (light pollution—another topic). But the eye open to the 200- watt bulb for reading is nearly blind at first compared to the one that was closed or buried in the pillow. Now whether reading with one eye is good is another story . . .
Reply | Report Abuse | Link to thisHe's probably reading with only the one eye because the other one is not to be trusted, and thus is only allowed to read the comics page...you can't be too careful these days...
Reply | Report Abuse | Link to thisWhat about the flash from a photo radar camera? We have one here in Phoenix that is under an overpass. The flash is supposedely bright enough to cover 4 - 8 lanes. I am with the group camerafraud.com and we are hearing of people swerving after being exposed to the flash. I don't know if this could be seizure activity, temporary blindness, or just a psychological reaction.
Reply | Report Abuse | Link to thisWhat about the flash from a photo radar camera? We have one here in Phoenix that is under an overpass. The flash is supposedely bright enough to cover 4 - 8 lanes. I am with the group camerafraud.com and we are hearing of people swerving after being exposed to the flash. I don't know if this could be seizure activity, temporary blindness, or just a psychological reaction.
Reply | Report Abuse | Link to thisWhat about the flash from a photo radar camera? We have one here in Phoenix that is under an overpass. The flash is supposedely bright enough to cover 4 - 8 lanes. I am with the group camerafraud.com and we are hearing of people swerving after being exposed to the flash. I don't know if this could be seizure activity, temporary blindness, or just a psychological reaction.
Reply | Report Abuse | Link to this