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----