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an optical illusion?



Help me out in understanding this one:

Riding home from a wedding today I was looking at the list of songs on the
Santana 'Supernatural' CD. The titles are written in many different colors.
What struck me was that they appeared VERY 3-D, with reddish letters
standing out and blue being pushed into the background--except that one
title (The Calling--if you have the CD) had the red letters on dark
background stand out while the red letters on blue background were pushed
back.

OK, my 'experimental observations'. The number one feature was that I only
observe the 3D behavior when looking through my glasses (blended bifocals)
but I can hold the case away and look with the distance part or closer and
use the reading part and maintain the 3-D look. The phenomenon does require
both eyes (not surprising) but does not require the plastic case of the CD.
It seems to require pretty good illumination, but both sunlight and
fluorescent light work.

Anybody want to explain? My main concern is whether the phenomenon somehow
is related to a 'fault' in my glasses. Can anyone with this CD and glasses
see the same behavior.

Rick

**************************************************
Richard W. Tarara
Associate Professor of Physics
Department of Chemistry & Physics
Saint Mary's College
Notre Dame, IN 46556
219-284-4664
rtarara@saintmarys.edu

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