2001 Conference Proceedings
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DETERMINING OPTIMAL DISPLAY MODIFICATIONS AND ASSESSING THEIR
IMPACT
Ian L Bailey
Kuang-mon Tuan
Richard T Wacker
Scott N Fitz
Angelika Angermann
School of Optometry
University of California, Berkeley, CA 94720
Lawrence H Boyd
Pasadero Inc. ,Tempe, AZ
Christopher Piedmonte
Eagle Creek Systems Inc. , San Diego, CA
Summary
We describe the development and applications of ColorFitter, a
program to select optimal display colors, and LabTester for
assessing the functional and subjective impacts.
Given the rapidly increasing use of computer displays in our
society, it is appropriate to give attention to special needs of
reading disabled people to enhance their access to information
from computer systems. Computer technology provides enormous new
flexibility to tailor the various characteristics of screen
displays in order to suit the needs or preferences of individual
subjects.
Persons with visual or reading disabilities can benefit from
customized modifications of their computer displays. Larger print
and reversed contrast have long been employed to make reading
tasks easier for persons with reduced visual acuity. Over the
past few years several computers and software products have been
developed to facilitate the changing of visual displays by
changing print size, font selection, font styles, spacings,
layout, scrolling methods, synthesized speech augmentation,
colors for letters, backgrounds and surrounds. Such display
parameters can be tailored to best suit the individual vision
characteristics of visually impaired and reading disabled
persons.
In the Assistive Devices Program of the Low Vision Clinic of the
University of California Berkeley, we conduct evaluations of
visual abilities and attempt to determine which visual display
parameters are optimal. Our normal clinical measurements of
visual acuity and contrast sensitivity help determine print size
and contrast requirements. Color is a parameter that is
relatively easy to manipulate on computer display screens and we
have developed a program called ColorFitter that allows for the
systematic evaluation of an individual's color needs. A second
program called LabTester is used for quantitatively evaluating
consequences of changing display parameters. The program
administers tests of performance and obtains feedback from the
subjects as they perform visual tasks with the various display
parameters under consideration. These two programs have been
developed by Pasadero Inc. and Eagle Creek Systems Inc. working
with a group from the Low Vision Clinic at UC Berkeley.
We shall describe these two programs and their application to
choosing display parameters for reading disabled persons.
RATIONALE FOR THE DEVELOPMENT OF COLORFITTER
Tinted lenses are often recommended for individuals with certain
eye diseases. Sometimes the tints are neutral or gray but at
other times there are special chromatic requirements. Orange or
amber filters are often recommended in retinitis pigmentosa and
other retinal diseases. In macular degeneration, yellow filters
can be beneficial. Persons with achromatopsia typically have a
pronounced aversion to light, and red or magenta filters give
best functional vision and comfort. Reading disabilities
associated with dyslexia are sometimes treated with tinted
lenses. Tinted lenses and colored filter overlays have been
advocated by Irlen. Solan and his colleagues have used blue
filtered and find improved reading performance, better
comprehension and altered eye movement behaviors in reading
disabled children. Wilkins and his co-workers have a method for
prescribing tinted lenses and overlays using an optical system
for selecting a most favored color for individual subjects. They
find the tinted lenses can give improved performance and comfort
in dyslexics and in persons with migraine.
DEVELOPMENT OF COLORFITTER
Color Coordinate System
For this program we developed our own coordinate system for
specifying color and we call this the CPB system and the initials
indicate Color, Purity and Brightness. In the Color domain, we
have
effectively distorted the Hue dimension of HSL space by applying
a polynomial function to force equal spacing of Red, Yellow,
Green and Blue. Effectively we create a color circle where Red =
0, Yellow = 90, Green = 180 and B = 270 degrees. This causes
complementary colors to be opposite each other and we have white
in the center. Along a radius from the circumference to the
center, the purity varies as the hue remains the same and the
appearance gets paler moving towards white. The third dimension
is Brightness, and represents a darkening created by turning down
the signals to all three guns (R,G and B) in proportion.
The Subjects' Task
Subjects are presented with printed material seen against display
fields with different color characteristics and they assign a
score of relative preference - or goodness of appearance. There
is one of the alternative displays chosen to be the reference and
it has a reference point-score of 50 points.There are 4 different
routines available.
(1) Color Sweep
In sequence of 16 different Colors (C values), each is compared
to a reference white field. The P and B values can be selected to
make the color appearance less Pure or less Bright. The reference
white color has an assigned value of 50 points
(2) Color Select
There are 5 different C values equally spaced from a region of
the spectrum that the user defines. The Purity and Brightness
levels are specified. The color in the center of the range
becomes the reference (50 point) field. This enables fine or
coarse tuning of color preference within the selected region of
the spectrum.
(3) Purity Select
There are 5 different Purity values equally spaced from a region
of the Purity scale that the user specifies. The Color and
Brightness levels are specified. The Purity value in the center
of the selected range becomes the reference (50 point) field.
This enables fine or coarse tuning of Purity preference within a
selected region of the Purity range.
(4) Brightness Select
There are 5 different Brightness values equally spaced from a
region of the Brightness scale that the user specifies. The Color
and Purity values are specified. The Brightness value in the
center of the selected range becomes the reference (50 point)
field. This enables fine or coarse tuning of Brightness
preference within a selected region of the Brightness range.
Alternative Modes for Presenting the Comparison Fields
There are three basic modes of presentation available in
ColorFitter.
Five-Segment display.
This allows simultaneous presentation of the reference (50 point)
display as a rectangular block in the center of the screen and
surrounded by four other comparison display fields, one in each
corner. A sequence of four such displays is required to complete
the Color Sweep that presents 16 colored fields for evaluation.
Only one display is needed for each of the Selection routines.
Bipartite Field Display.
The screen display may be split in two - either vertically of
horizontally. On one half field will be the reference condition
(50 points) On the other half is one of the colored field samples
from the current routine. In the case of a Color Sweep, there is
a sequence of 16 displays in which one half of the screen has a
white background, and the other has one of the 16 colors at the P
and B values that the operator has selected. For any of the C, P
or B Selection routines, one half of the screen always presents
the midpoint sample a with its assigned 50 points. In a series of
4 sequential displays, each of the other 4 color fields are
presented up against the reference and the subject assigns a
point score. Here the subject is assigning points making binary
comparisons of simultaneously viewed half fields.
Full Field Displays in Successive Presentations.
Here the full field display has only one color filling its field.
The first display to be presented is the reference display filled
with its pre-assigned score of 50 points. The subject uses the
keyboard to switch to the comparison field with its different
color appearance. The subject may go back and forth between the
reference field and the test field as many times as needed before
assigning a score to the test field. This mode of display and
comparison is the most time-consuming. For a Color Sweep routine
there must be at least 32 changes of field where every second
field is white and every other is one of the 16 C values from
around the color circle. For the 3 different Select routines, at
least 8 display fields are required. The first has the midpoint
value for the variable parameter as the reference field and it
has a pre-assigned score of 50 points. In turn, the 4 comparison
fields are shown. Based on successive observations, points are
assigned to the 4 comparison fields. When each routine has been
completed, the scores assigned by the subject are recorded in a
tabular format. The results and the details of the display
parameters presented up to this point can be viewed before
selecting the fixed parameters and/or the range for the next
routine. Within these results tables, the display parameters are
expressed in CPB terms.
DEVELOPMENT OF LABTESTER
A major question is whether there is improved performance of
visual tasks under favored display conditions and whether there
are any measurable improvements in visual comfort or subjective
perceptions. To test this, flexible and sophisticated computer
software is necessary. Our group has developed a program that we
call LabTester for testing subjects' performance at screen-based
tasks and testing of visual resolution on display screens on
which the appearance or display characteristics have been
modified. Within LabTester there are a series of questionnaires
that can be used to solicit the subjects' opinions and subjective
impressions as they perform tasks or view different kinds of
displays.
Performance tests
Within LabTester, there are two different tasks that we use to
assess visual performance as we change the screen display
conditions. We have a Reading and Comprehension Task and a Letter
Counting Task.
Resolution tests
We have generated displays within LabTester that have printed
material arranged in progressively decreasing size. We have tests
for Letter Chart Acuity and Word Reading Acuity.
Questionnaires
Questionnaire screens can be authored in LabTester to suit the
experiment being conducted. For evaluation of the effect of
display parameters we mainly use questionnaires that ask for
responses in the form of magnitude estimations. For this the
subjects use a visual analog scale in the form of a screen-based
slider-bar. By positioning the slider, subjects indicate the
severity of visual
symptoms or discomfort, or they can indicate the strength of
their opinions about the noticeability or the relative
acceptability of the display features under consideration.
Test Sequencing
In LabTester, a sequence of events can be scheduled for an
experimental session. In setting up an experiment, instructions
need to be developed to specify the test tasks, the display
parameters, and the associated questionnaires. Within an
experimental session there may a series of trials using selected
tasks that are performed under chosen display conditions.
Interspersed strategically with the sequence of trials,
questionnaires can be administered to get feedback from the
subjects.
The Performance Tasks
Text Reading Task: Using the LabTester program, the subject first
views an alert screen, which can carry basic instructions about
the test task to be performed. Then the subject brings up a
passage on the screen by pressing the space bar. Once the passage
has been read, a second press of the space bar removes the
displayed text and the duration of exposure is recorded. Then,
three questions appear on the screen in turn and each question
offers three "multiple-choice" answers. The subject is asked to
select the correct answer. These questions serve as a measure of
comprehension. We have created collections of close to 200
passages, about half being chosen excerpts from stories in
Reader's Digest Condensed Books. We generated question sets for
most of these passages. In setting up an experimental session, a
set of instructions is required to specify the reading task. The
instructions specify the path to the locations of the text
passages, and these are linked to files that contain the
comprehension questions for the passages.The text reading task is
reasonably representative of reading prose on a screen display.
It is designed to provide measures of reading speed and add a
second measure to represent comprehension or attention.
Letter-Counting Task:
We have a letter-counting task in which the subject is required
to count the number of occurrences of an assigned letter within a
screen display of "pseudo-words." The text display is generated
from letters being randomly arranged into strings of letters of
variable length. The minimum and maximum "word" length is chosen,
as well as the number of lines of "pseudo-words" presented, the
minimum and maximum number of occurrences of the "target letter,"
and how many non-target letters should always be presented before
possible repetition of the "target letter." Typically, only
capital letters are used. We have used as search letters B, K, N,
M, R, and W in Times Roman font, as preliminary experiments had
found that these letters were about equally difficult to count
within this task. The target letter is identified on the "Alert"
screen presented at the start of each trial. By a press of the
space bar, the subject initiates the display of the test task. A
second press of the spacebar removes the task when the counting
is completed. The exposure duration becomes the measurement of
the search speed performance. For each task, the letter count is
recorded by the subject using the keyboard to enter the count
into a window on the display after the test screen has been
removed. Unlike reading text, cues from word shapes and syntax
are of no help and there are few clues that enable the subject to
anticipate where a designated search letter will appear and what
the total count will be for a given task segment. While it is not
like real tasks commonly encountered in the workplace, it does
demand very careful visual attention.
Specifying the Display Parameters for the presentation of the
test tasks
A second set of instructions can be used by the experimenter to
design the appearance of the task material presented on the
screen. The experimenter can vary display parameters in various
combinations. Variable display parameters include the font size
(in points), style (normal, bold or italic), and type (e.g.,
Times New Roman, Arial), margin widths, line and letter spacing,
background color, text color order of presentation for distinct
tasks and number of repetitions of the tasks. There is an option
for including a "spotlight" function in designated trials. We can
create moving highlights of selectable lengths, colors, and mode
and speed of movement.
A number of "Feedback" questions can be presented within the set
of trials, and these can include questions about the text passage
read, questions about the subject's rating of the display, or
questions about visual symptoms. For ratings of subjective
opinions, we use visual analogue scales. On a horizontal line on
the screen, the ends and the center are designated with short
vertical hash marks. The hash marks carry labels to indicate
magnitude or degree of severity or preference. The subject uses a
computer mouse to move the slider. One question is asked at a
time.
Some Applications of ColorFitter and LabTester Programs
During the evolution and development of the ColorFitter and
LabTester programs, numerous informal and semi-formal pilot runs
were done with normally sighted and reading disabled subjects.
These programs have been applied to more formal studies. The
programs are used within a clinical setting for application to
specific patient needs in the School of Optometry's Assistive
Devices Program within its Low Vision Clinic.
Two research applications of the LabTester and Color Fitter will
be described. The first involves testing for the effects of
colored display s on the reading performance of dyslexic and
normal subjects. The other involves testing for the effects of an
electronic place-keeping aid (moving highlight) on subjects with
Macular Degeneration.
REFERENCES
Irlen, H. (1991) Reading by the Colors. New York: Avery
Publishing Group Inc.
Solan HA, Ficarra AP, Brannan JR, Rucker F, (1998) Eye movement
efficiency in normal and reading disabled children: effects of
luminance and wavelength. J Amer Optom Assoc, 69: 455-64.
Wilkins AJ, Evans BJW, Brown J, et al. Double-masked
placebo-controlled trial of precision spectral filters for
children who use coloured overlays. Ophthal Physiol Opt, 1994;
14:365-70.
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