Path: utzoo!utgpu!watmath!clyde!att!pacbell!ames!ucsd!nprdc!trejo
From: trejo@nprdc.arpa (Leonard J. Trejo)
Newsgroups: comp.cog-eng
Subject: Re: subliminal feedback
Summary: Why not use color or lightness contrast differences?
Keywords: feedback windowing interfaces
Message-ID: <1073@arctic.nprdc.arpa>
Date: 20 Nov 88 01:44:41 GMT
References: <318@aratar.UUCP> <651@sdics.ucsd.EDU>
Sender: news@nprdc.arpa
Reply-To: trejo@nprdc.arpa (Leonard J. Trejo)
Organization: Navy Personnel R & D Center
Lines: 83

In article <651@sdics.ucsd.EDU> norman@sdics.UUCP (Donald A Norman-UCSD Cog Sci Dept) writes:
>Clanton thought the indicator ought to be subtle and "subliminal."  I
>suggested it should be fairly significant and available to conscious
>knowledge.  But the signal should not be overwhelming in magnitude,
>because:
>	1. the signal should not distract (flashing the selected
>	  window would be a very poor solution);
>	2. The non-selected windows should still be easy to use,
>	  because one often is reading from or otherwise using the
>	  material in the non-selected windows while working in the
>	  selected one.
>
>So, this leads to the very important set of questions Chuck Clanton
>just asked in his last contribution.
>
>The goal is to make the properties of the system obvious enough that
>the new user can learn them (hence the need for signals that are
>consciously available), yet subtle enough that the frequent user does
>not have the normal work interfered with, so that the usage is
>automatic, and, as a result, the user is not consciously aware of them.
>This is a difficult and delicate question: providing just the level of
>information that can serve these two different requirements.
>
>A very good topic.
>
I agree that this is an important topic for discussion.  Now feeling
a bit guitly for jumping on Chuck's style versus content, I'd like to 
try to contribute something (sorry, Chuck!).

One thing that is becoming increasingly clear in vision research is the
value of color for defining objects against their backgrounds.  Color
is frequently abused in many displays but it does appear to
significantly improve performance for two kinds of things: defining
the extent of an object in the scene and for rapid search for objects
distinguished from the background by color contrast.  The first of
these factors is greatly aided by color and lightness constancies,
which operate to keep objects perceptually unitary in spite of
significant variations in the light being emitted or reflected from
them.  This applies to CRT displays where we can easily ignore large
gradual brightness fluctuations between the center and the edges.  In
addition, research has shown that searching based on large color
differences is essentially automatic.

For these reasons I'd expect that assignment of a unique background
color to the active window would be superior to peripheral spatial cues
(e.g., borders) or to temporal cues (e.g., flicker--I agree with Don
Norman that this would be distracting).  Many unobtrusive, yet easily
discriminable color contrast combinations exist that would work for
nearly all observers including those with red-green color deficiency.
In order to avoid strong luminance contrasts between different
windows--which could produce shifts in light adaptation levels and
afterimages as the observer reads different areas-- the designer could
use white for unselected windows and an isoluminant amber, blue, or
other suitable shade for the selected window.  The degree of saturation
needed to distinguish the selected window needn't be so large as to
produce colored afterimages when looked away from (in fact colors on
CRTs are rarely saturated enough to do this).

A big problem is the increased cost of high resolution color displays
as compared to monochrome.  But in its proper sense, "color" includes
different shades of white.  Therefore, it may be possible to choose a
gray background which is easily discriminable from that of the rest of
the display but which maintains enough luminance contrast to provide
for unimpaired reading.   One design would be to have black text on
white background in the active window and white on black elsewhere.
But having large differences between the different background areas on
the display would impair legibility.  A better design might use maximum
contrast in the active window and 90% contrast in other windows.  A bit
of experimentation could determuine good contrast differences.  

I don't think we can eliminate borders--they will define the edges of
windows much better than color contrast.

			L. J. T.


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