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>From: Stephen Black <[EMAIL PROTECTED]>
>To: TIPS <[EMAIL PROTECTED]>
>Subject: How do I get those @#$%& complementary after-images?
>Date: Wed, Oct 27, 1999, 9:12 AM
>
> Preparatory to a big song-and-dance (or dog-and-pony show, take your
> pick) about the opponent-process theory of colour vision, I opened
> with a demonstration of complementary after-images, using PowerPoint
> to display them. It was underwhelming. Very few agreed that they saw
> the "correct" complementary colour (red-green; yellow-blue).
>
> I displayed them as a rectangle covering about 10% of the screen, on a
> dark background, exposed for about 30 sec. They looked for the
> after-image against a white screen. The room was dim.
>
> Any suggestions as to how to get an optimum effect? Ideally, you might
> suggest exactly what parameters to use, specifying the colours in
> terms of PowerPoint numbers.
Stephen,
You _probably_ did something like the following, but since you didn't
specifically say so, I'll bring it up...
Did you instruct students to fixate on a specific point, rather than letting
their gaze wander over the image? I've found it helpful to put a small mark
of some kind on the image (a dot or cross, e.g.) which helps them fixate on
that point.
The other things I usually do differently are use a longer
exposure--generally about 60 sec--although I would think that 30 sec would
be sufficient to produce a noticeable after-image; and use a white
background (I use white simply because I do this with overhead
transparencies, rather than PowerPoint).
John
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John Serafin
Professor of Psychology
Saint Vincent College
300 Fraser Purchase Rd.
Latrobe, PA 15650
[EMAIL PROTECTED]
