W3C home > Mailing lists > Public > w3c-wai-gl@w3.org > July to September 2001

RE: guideline 7.1 about screen flickering (fwd)

From: Steven Livingstone <stv_es@hotmail.com>
Date: Wed, 1 Aug 2001 16:18:01 -0700
To: <w3c-wai-gl@w3.org>, "'Marja-Riitta Koivunen'" <marja@w3.org>
Message-ID: <000001c11ae0$35ea2b60$0157a8c0@dev.citix.com>
Just on this note. I recently demonstrated a simple but nevertheless
effective example of this kind of flickering.
Using DHTML (which is becoming more standardized) as client script, you
can accomplish various kinds of “filters”.
I have encountered gradually more sights which do this as…
a.       An introductory or splash screen to their sight. Quite often
(unlike MOST flash sites) there is no stop. You also cannot stop it by
clicking on the browser stop button. My example used a document click to
stop it and provided the non-animated version. My fear is that as this
gets easier to do many more sites will have stuff like this.
b.       For some reason best known to god knows who, some creators feel
that the site should have a slide show look to it. So as you move from
page-to-page, simple DHTML is used to checker in the next page, or slide
in the next one.
c.       Although not really commonplace yet, I guess these filters will
be used more and more to provide ads and other multi-media features.
Now, I should say that relative to most of you I am very new to the
Accessibility scene and my best skills lie elsewhere, so these may not
be particularly valid points. But nevertheless, hopefully these other
skills will help me bring something to the table :)
Steven Livingstone,
Author Pro XML 2e and others.
-----Original Message-----
From: w3c-wai-gl-request@w3.org [mailto:w3c-wai-gl-request@w3.org] On
Behalf Of Marja-Riitta Koivunen
Sent: Wednesday, August 01, 2001 1:00 AM
To: Anne Pemberton; Jonathan Chetwynd; gregory j. rosmaita;
Subject: Re: guideline 7.1 about screen flickering (fwd)
I agree we learn to see but many things also develop normally in a
certain way e.g. in our visual cortex there are cells specialized in
detecting movement and it is hard keep the eye saccades out of the
movement if it is strong enough. That is why advertisers want to use
movement in the banners as it easily get's the user's attention.

I tried to find a good reference from the Web, but it was difficult
without going too deep and I don't have more time now. The more
understandable references are similar to this one:

In the visual periphery we can instantly detect even slight movement. 
This is an important safety feature, developed long ago to recognize
stalking predators. The eye’s periphery reports a movement, the brain
thinks it’s important, and the vision is automatically centered on the
threat. It is so imprinted on us that we can’t do anything about it, and

Also Jacob Nielsen refers to it.
<http://www.useit.com/alertbox/9512.html> html


At 10:51 AM 7/30/2001 -0400, Anne Pemberton wrote:


        While your point is well taken, your reason is not based on
fact. A cognitive system is not built and dropped in place, it is
*built* or developed over one's lifespan, and not all cognitive systems
are built to respond the same way to all stimuli whether movement,
sound, or images (including images of text, since for perhaps most web
user, text comes to them as an image).

        Most of us trained our cognitive systems before the stimuli
under discussion was invented. Children growing up with this type of
stimuli will learn to respond to it more appropriately than us old
geezers do.

        Have you tried to read material close to a flickering source?
What site? so we can all test it. Or do you mean to say that you have
tried to read material close to a moving source, an animation, for
example (like that RADAR icon), and you were unable to read the text?
How close was the animation? Was text size appropriate to the icon or
did one overpower the other? What site did you test it on? Were there
any contributing factors preventing your understanding other than the
problem graphic? Does this happen whenever you encounter certain type of
graphics? Is there any reason that hitting the stop button (or the
equivalent in your browser) is insufficient? Does it help to enlarge the
text size near a competing graphic?

        An remember, that being irritated or annoyed is not a


At 09:52 AM 7/30/01 -0400, Marja-Riitta Koivunen wrote:

At 06:49 AM 7/27/2001 +0100, Jonathan Chetwynd wrote:

given that placements are a more subtle way of advertising, perhaps in
RADAR case and given the client group, it might make sense to advise
that an
animated gif is liable to irritate, rather than rely on a medical

And not only to irritate. Sometimes it makes it almost impossible to
read a text that is near a flickering image as our cognitive system is
built to pay attention to the movement.


jonathan chetwynd
IT teacher (LDD)
http://www.peepo.com <http://www.peepo.com       />        "The first
and still the best picture directory
on the web"

Anne Pemberton

Received on Wednesday, 1 August 2001 16:18:52 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 16 January 2018 15:33:38 UTC