Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!decvax!wivax!linus!allegra!eagle!mhuxt!mhuxi!mhuxa!houxm!hocda!spanky!burl!duke!mcnc!ncsu!fostel From: fostel@ncsu.UUCP Newsgroups: net.ai Subject: Re: Visual After-effects Message-ID: <2199@ncsu.UUCP> Date: Fri, 3-Jun-83 12:04:29 EDT Article-I.D.: ncsu.2199 Posted: Fri Jun 3 12:04:29 1983 Date-Received: Thu, 9-Jun-83 01:29:07 EDT Lines: 36 The effects described such as the railroad track and video after effects are well know by psychologists, and indeed are one of the tools used to study the levels and types of processing in the optic system. Most introductory texts on the subject will include a few pictures to stare at in certain ways to acheive some of types of after effects you noted. I beleive Scientific American even gave away a resubscription freebie on the subject a few (6?) years ago. The earliest description of the phenomenon I know of (circa 1910) by a reputable psychologist was from a fellow who had a small area of his retna with a blind spot. (Was this Lashley?) He observed once at a party, that when a person stood against a highly regular wallpaper and their face was in his "spot" their head would be "removed" and replaced by the Wallpaper Pattern! The visual system was simply making its best guess of what should be simulated for those bad receptors. A bit of experimenting later, it was shown that the effect could be reproduced with anyone by simply fatiguing the receptors at one spot (simulating a defect) by staring intently at one object without blinking, moving the head or sacading the eyes. If the level of fatigue is great enough and the background suitably benighn and predictable, the object stared at will indeed disapear, actually being replaced by the visual systems best guess for what the fatigued cells would report if they were sending out a better signal. My own experience with video games provides some confirmation of the "modern" experience. I play Robotron, occassionally for several hours (takes a while to recycle the 9,999,999 score) which involes LOTS of little glowing things moving about, some of which must be avoided and shot, and some of which must be "rescur rescued". (Sorry, key-board burped.) After such a binge, I will see afterimages of the little Good guys I must recue, but never the bad killer robots. Now THAT is a high level of processing in the optic system: it seems to be able to tell good from bad!! ----GaryFostel----