METHOD

Participants
Prior approval for all procedures and use of human

participants was obtained from the Office of Aviation
Medicine/Civil Aeromedical Institute human use com-
mittee. Volunteers were recruited froin the Human
Resources Research Division of the Civil Aeromedical
Institute. The informed consent of every participant
was obtained prior to participation, and each partici-
pant was free to withdraw from the experiment with-
out prejudice at any time during the experiment.
Ten co-workers, 7 females and 3 males, served as
participants for this pilot study. Participants had a
mean age of 35.1 years and a standard deviation of 6.2
years. All volunteers had normal color vision and at
least 20/30 visual acuity in both near and distant
vision as determined with the Bausch and Lomb
Orthorater. Normal color vision was determined by a
battery of clinical color vision tests that included the
Dvorine, the Ishihara 24-plate, the American Optical
~ Hardy, Rand, Rittler (AOC-HRR) Pseudo-Isochro-
matic Plate Tests, and the Farnsworth F2 Plate Test.

Performance Measures:

Performance was measured in terms of accuracy
and search time. Errors included misses (the failure to
select a target), and false alarms (the selection of non-
targets). Two additional accuracy measures were cal-
culated, percent correct of all targets (possible 26 per
condition), and a pass/fail score based on correct trials
(possible 18 per condition), An incorrect trial was
defined as any trial on which at least one target was
missed or a non-target was selected as a target. The
search time measure was defined as the time required
to select targets and terminate the trial.

Procedures

The ATC situation display consisted primarily of
aircraft symbols, each with a block of alphanumeric
data attached by a leader line to the aircraft symbol.
The alphanumeric data, called the data block, con-
tains information about the state of the aircraft, e.g.,
call sign, aircraft type, heading, altitude, and ground-
speed. The aircraft symbols and their data blocks are
positioned about the situation display on paths

describing the flight of each aircraft. Map data de-
scribing boundaries of air traffic control sectors, geo-
graphic data, and navigation references -were also
included in the situation display. The participant was
instructed to locate all of the blinking data block
targets, select them using a mouse, and press the
“ENTER” key to advance to the next trial. They searched
for either 0, 1, 2, or 3 targets within a field of 16
aircraft (data blocks) on the simulated ATC situation
display. Data blocks other than the blinking targets
were called distractors. Each experimental condition
consisted of 1 demonstration trial that illustrated the
amplitude of the blink for the targets in that condi-
tion, followed by 5 practice trials and 18 test trials.
Two trials contained 3 targets, 8 trials contained 2
targets, 4 trials contained 1 target, and 4 trials con-
tained 0 targets. Participants were informed that some
trials would present screens containing no targets. For
those trials, the participant was asked to press the
ENTER key as soon as he or she had determined that
there was no target on the screen.

A control condition was also presented to obtain a
baseline and estimation of the optimum response
time, The control condition consisted of trials with
display screens that were identical to those presented
in the experimental conditions, except that they con-
tained no distractor targets. All data blocks on the
screen were targets, and the participant's task was to
select them as quickly as possible. The targets were
displayed on the same background map as used for
trials with distractors, and the locations of targets
were varied by the same techniques as for trials with
distractors.

The 7 amplitudes of blink were, 100%, 93.75%,
87.5%, 75%, 50%, 25%, and 12.5%. For this study,
target blink amplitude is defined as the percentage of
decrease in luminance from a standard of 51.4 Cd/m?
at a rate of 2 HZ, and the duration of the blink
intensity decrement was approximately 1/10 sec.

The instructions urged the participants to respond
quickly and accurately, with the emphasis on accu- .
racy. All conditions were self-paced and four 5 minute
breaks were programmed into each participant’s unique
random order of conditions, so that the breaks were
evenly spaced throughout the experiment. All partici-
pants completed the experiment within 2 hours.


REFERENCES

Anastasi, D.L., Hill, B.P., Murphy, E.D., Cardosi, K.M.,
Guttman, J.A., & Amaldi, P. (1995). Computer-
Human Interface (CHI) Considerations in Human
Factors in the Design and Evaluation of Air Traffic
Control Systems. DOT/FAA/RD-95/3. Office of
Aviation Research, Washington, DC 20591.

Boff, K.R., & Lincoln, J.E. (Eds.). (1988). Engineering
Data Compendium: Human Perception and Perfor-

mance, AAMRL, Wright-Patterson AFB, OH.

Christ, R.E. (1975). Review and analysis of color coding
roe for visuai displays. Human Factors. 17(6)
570.

Gerathewohl, S.J. (1951). Conspicuity of flashing and
steady light signals. I. Variation of contrast. USAF
School of Aviation Medicine, Special Report.

Gerathewohl, S.J. (1952). Conspicuity of flashing and
steady light signals. II. High contrasts. USAF
School of Aviation Medicine, Special Report.

Gerathewohl, S.J. (1953). Conspicuity of flashing and
steady light signals: Variation of contrasts. Journal
of Optical Society of America, 43, 567-571.

Gerathewohl, S.J. (1954). Conspicuity of flashing light
signals of different frequency and duration. Jour-
nal of Experimental Psychology. 48 (4) 247-251.

Gilmore, W.E., Gertman, D.1., and Balckman, H.S.
(1989). The user-computer interface in process con-
trol: A human factors engineering handbook. New
York: Academic Press.

Mertens, H.W., & Milburn, N.J. (1996, in prepara-
tion). Effects of color vision deficiency on detec-
tion of highlighted targets in a simulated air traffic
control display.

Military Standards, MIL-STD-1472D, (1989). Hu-
man Engineering Design Criteria for Military Sys-
tems, Equipment and Facilities.

Van Orden, K.F., & Di Vita, J. (1993). Highlighti
with flicker: some basic visual search mitted
ations. Proceedings of the Human Factors and Ergo-
nomics Society 37th Annual Meeting—1993. 1300-
1304.

Van Orden, K-F., Di Vita, J., & Shim, MJ. (1993).
Redundant use of luminance and flashing with
shape and color as highlighting codes in symbolic
displays. Human Factors. 35(2) 195-204.

‘WU,S. GOVERNMENT PRINTING OFFICE: 1997 - $99-8797/40096



than 2 errors was arbitrarily established for each
condition, and pass/fail percentage rates are shown in
Table 2. For the 75% to 100% amplitude conditions,
a pass rate of 100% was maintained. A 90% pass rate
was obtained for the 50% amplitude condition. This
may be considered marginal performance, if an aver-
age 8% miss rate is considered unacceptable perfor-
mance. Of course, this depends on the criticality of the
signal. For the 25% and the 12.5% amplitude condi-
tions, the pass rates were 20% and 0%, respectively.
Some blink amplitudes had such poor attention-
getting value that 2 respondents were unable to find
even a single target of the 26 possible during an 18-
trial experimental condition. Figure 1 presents the
percent correct for each condition by the number of
targets. Figure 1 shows the stable performance for
conditions involving a 75% to 100% decrease in
brightness and the steady increase in errors (missed
targets and selection of nontargets) for the 50%, 25%,
and 12.5% decreases in brightness. Performance in
conditions involving amplitudes of 75% to 100% is
clearly stable and acceptable, ranging from 98.75% to
100%, and performance is unacceptable in terms of
errors for amplitudes of 25% or less, ranging from 5%
correct to 72.5% correct for I, 2, and 3 target trials.
Performance on the zero target trials was consistently
100% for amplitudes greater than 50%, but as targets
became more difficult to detect, participants began to
make more guesses, which are reflected in the occur-
rence of false alarms in the 25% and 12.5% amplitude

conditions. The 50% amplitude condition appears to
be at the point at which a statistical test should be used
to determine whether errors significantly increased
from the 75% amplitude condition. Results from a
paired-sample t-test indicated that the increase in
errors was not significant, ¢ (df=9, @=.05) = 1.92, p=
.087. Because the mean errors in the 75% amplitude
condition is zero, these results are identical to a one-
sample t-test that compares the mean for the 50%
amplitude condition (0.8) to zero.

Response time performance by amplitude, as a
function of the number of targets, is presented as bar
graphs in Figure 2. Response time remained steady for
the larger blink amplitudes (75% to 100% decrease in
brightness), but response time substantially increased
as the percentage of change in brightness was reduced
(50%, 25%, and 12.5% conditions). A paired-sample
t-test was used to determine whether the response
times differed significantly between the 75% ampli-
tude condition and the 50% amplitude condition.
Results indicate that there is no significant difference
between those 2 conditions, ¢ (df=9, a= .05) = 2.06,
p= .069. The response times shown are for correct
trials only. The apparent drop in response time for the
3 target, 12.50% decrease in brightness condition was
based on a single participant’s response time for 2
single trial. Only 1 participant correctly identified the
3 targets, but only in 1 trial. All the other participants
missed 1,2, or 3 targets for both of the 3-target trials
at that amplitude.

Table 2
Percent Passing With Less Than
Two Errors For 18 Trials
PASS
CONTROL CONDITION

No Distractors l 100%
PERCENT OF DECREASE IN AMPLITUDE
100 100%
93.75 100%
87.5 100%
75 100%

50 90%

25 20%

12.5 0%



RESULTS

Table 1 presents means and standard deviations for
misses, and means for false-alarms and percent correct
for all trials under each of the amplitude conditions.
On the average, participants made very few false
alarms for any of the different blink amplitude levels.
Most errors were misses, defined as 2 failure to detect
and select a blinking target. When the targets were
difficult to detect, some respondents terminated the
trial without finding any targets, or without finding
all of the targets on the trials that contained multiple
targets. High miss rates and low false alarm rates were
typical in conditions involving a small change in
amplitude ranging from 12.5% to 25%. Of the types
of errors discussed, misses are the most critical type in
air traffic control work. A false alarm might result in
the air traffic controller making some additional men-
tal calculations, with a loss of time, but failure to

quickly find an emergency warning or critical event
displayed on the ATC situation display could resule in
a loss of required separation between aircraft.

Table 1 also contains the mean percent correct for
all 26 targets of a particular amplitude condition
calculated for the 10 participants. For amplitudes
between 50% to 100%, performance was 96% correct
or better. However, for the 25% amplitude condition,
participants averaged only 71% correct and their
response time was more than twice as long as the
average for the 50% amplitude condition.

In a separate analysis, each trial for each individual
was scored as correct of incorrect. For a trial to be
scored as correct, the participant must not have se-
lected any non-targets (false alarms) or missed any of
the blinking targets for that trial. Using this scoring
procedure, 2 single incosrect trial in the scores of 18
trials resulted in 94.4% correct, and 2 incorrect trials
equaled 88.8% correct. A pass/fail criterion of less

Table 1

Means and Standard Deviation by Amplitude for Misses, and Means
for False-Alarms, Percent Correct, and Response Times for Correct Trials

Percent Response
Misses Misses False-Alarms Correct Times
(means) (std dev) (means) (means) (means)
CONTROL CONDITION
No Distractors 0.1 32 [) 99.69 3.93
(Non-Blinking)
PERCENT OF DECREASE IN AMPLITUDE
100 0.1 32 i) 99.69 6.91
93.75 0 0 0 100 7.63
87.5 Qo Qo 0 100 7.76
75 (*) ti) 0 100 8.29
50 0.8 1.32 0 96.88 11.59
25 5.5 4.38 0.1 71.25 28.94
12.5 16.4 7.40 3.0 36.46 22.46



DISCUSSION

The objective of this research was to determine the
level of blink amplitude that can capture the user's
attention quickly and with a high degree of regularity
(at least 95% of the time). Figure 3 illustrates the
relationship between accuracy and response time un-
der each of the blink amplitude and control condi-
tions. Stable accuracy and response time performance
is maintained for amplitudes ranging from 75% to
100%, anda steep decline in accuracy, combined with
increasing response times, is evident for the ampli-
tudes ranging from 12.5% to 25%. This figure should
aid display designers in their selection of an optimum
blink amplitude for attentional purposes based on
both of those perform-nce measures. Other consider-
ations for selection of an optimum blink might in-
clude other parameters of blinking, for example,
frequency, on/off time ratio, and so forth, and the
consequent effects of blink on distractibility and
legibility. A blinking target may be distracting if it
diverts ones attention away from the desired focus.

Distractibility was not examined in this experiment,
but it may be an important factor in creating a user-
friendly display.

Anastasi, Hill, Murphy, Cardosi, Guttman, and
Amaldi (1995) state that, “All coding techniques have
advantages and disadvantages. For example, flash cod-
ing is good for attracting attention, but flashing text
is difficult to read.” Just as ic may be necessary to
accept some degree of distraction to ensure that a
warning alert is noticed, compromises concerning
legibility may also be necessary. The legibility of text
under blinking conditions is an issue for further
research. With blink amplitudes less than 100%, the
legibility of text might be preserved to some degree.
Gilmore, Gertman, and Blackman (1989) suggest
that the legibility of the text can be preserved by
placing a separate blinking symbol near the critical
information. Whichever method is used, if blink is
employed for attention-getting purposes, based on
this pilot study, blink amplitudes less than 75% are
not recommended for safety-critical applications.

Figure 3
Means for Percent Correct and Response Times for the Control and
Experimental Conditions
17 GG tt o- ~~ 7 30
0+
80 + T 2
70 + +20
fot) T
5 50 +15
wot
30+ _. +10
0 I —_— +5
0 + + + + + + — 0

100%
93.75%
87.50%

No
Distractors



DOT/FAA/AM-97/10

Office of Aviation Medicine
Washington, D.C. 20591

19970609 164

Evaluation of a Range of Target
Blink Amplitudes for Attention-
Getting Value in a Simulated
Air Traffic Control Display

Nelda J. Milburn
Henry W. Mertens

Civil Aeromedical Institute
Federal Aviation Administration
Oklahoma City, Oklahoma 73125

April 1997

Final Report

This document is available to the public
through the National Technical Information
Service, Springfield, Virginia 22161.

@

U.S. Department
of Transportation

Federal Aviation
Administration



Figure 1

Percent Correct by Amplitude and by Number of Targets

PERCENT CORRECT

oO
Number of Taygets:0123 0123 0123 0123 0123 0123 0123 0123
No 100% 93.75% 87.50% 75% 50% 25% 12.50%

Distractors CONDITION

Figure 2

Response Time by Amplitude and by Number of Targets

REACTION TIME
8

fa) :
Number of Targets:'0123 0123 0123 0123 0123 0123 0123 0123
No 100% 93.75% 87.50% 75% 50% 25% 12.50%
Distractors CONDITION


EVALUATION OF A RANGE OF TARGET BLINK AMPLITUDES FOR ATTENTION-
GETTING VALUE IN A SIMULATED AIR Trarric CONTROL Display

INTRODUCTION

Several sources (Anastasi, Hill, Murphy, Cardosi,
Guttman, & Amaldi, 1995; Boff & Lincoln, 1988;
Christ, 1975; Gerachewohl, 1951; 1952; 1953; 1954;
Gilmore, Gertman, and Blackman, 1989; Military
Standards, 1989; Van Orden and DiVita, 1993) sug-
gest that blinking targets are more alerting than steady
targets, and can aid the user in finding the targets
quickly. Those sources recommend target size, color,
shape, brightness contrast, frequency of blink and
parametets for the ratio of time the blink should be
“on” relative to the time it is: “off.” However, no
guidelines in the literature were found for an effective,
attention-getting blink amplitude. Since all studies
involved blinking in which on and off states (100%
change in intensity) were alternated, a recommenda-
tion of 100% amplitude change during blinking seems
implied.

A previous study (Mertens & Milburn, 1996) evalu-
ated the effectiveness of redundant color coding for
protecting the performance of individuals.with color
vision deficiency in a simulated air traffic control
search task requiring search for, and identification of,
the data blocks for specific aircraft. The display char-
acteristics of that study simulated the information
coding design used in the situation display of a devel-
opmental system called the Initial Sector Suite System
(ISSS), a system now discontinued, that was originally
intended to provide the next generation of work
stations for radar controllers. Blinking in that study
emulated prototype displays that were observed and
involved amplitude modulation ofapproximately 20%
rather than 100%, as typically used in the licerature on

blinking (flashing, flicker) for highlighting. The fre-
quency was 2 HZ and the duration of the blink
intensity decrement was approximately 1/10 sec. The
small (20%) change in intensity during blink had
little attention-getting value, as confirmed by experi-
mental findings of Mertens and Milburn (1996).

Blinking in the ISSS displays was ostensibly de-
signed to reduce the attention-getting and distraction
effects of blinking and possibly to reduce the effect of
blinking on legibility by maintaining visible presence
throughout the blink cycle. There is some debate in
the literature concerning the distracting qualities of
blinking on a display screen (Van Orden, DiVita &
Shim, 1993; Van Orden & DiVita, 1993). While that
is an area in need of research, the present study focuses
on the attention-getting or alerting value of blinking.
If blinking caused distraction in certain circum-
stances, it would be due to its powerful attention-
getting characteristic, It remainsa cue thatis potentially
useful for attracting attention in critical situations and
may also be useful as a redundant cue in those situations
where color coding is used for attention-getting.

The puspose of this pilot study was to evaluate the
effectiveness of a range of blink amplitudes for aiding
the visual search for, and identification of, aircraft in
a simulated air traffic control situation display. This
experiment is limited to the case of blink involving a
repeated brief decrease from normal intensity. The
amplitude of blink is defined as the percentage of
decrease in fuminance from the normial luminance of
targets, The case of increase in intensity relative to the
normal is not dealt with here.


a

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1. Report No, 2. Government Accession No. 3. Recipient's Catalog No.
DOT/FAA/AM-97/10

“&. Tite ond Subtiie 5. Report Cate

Evaluation of a Range of Target Blink Amplitudes April 1997

for Attention-Getting Value in a Simulated Air 6. Performing Organization Code’
Traffic Control Display

7. Author(s) @. Performing Organization Report No,
Milburn, N.J., and Mertens, H.W.

9. Perfoming Organization Nome ond Address 10. Work Unit No, (TRAIS)

FAA Civil Aeromedical Institute

P.O. Box 25082

Okdahoma City, OK 73125 Tt. Contract or Grant No.

12. Sponsoring Agency nome and Address 13. Type of Report and Period Covered
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15. Supplemental Notes

This work was performed under task HRR-190.

16. Abshact

Several sources suggest that blinking targets are more alerting than steady targets. Those sources recommend target size,
color, shape, brightness contrast, frequency of blink, and parameters for the ratio of time the blink should be “on,”
relative to the time it is “off.” However, no guidelines were found for an effective, attention-getting blink amplitude (the
percentage of decrease in target brightness from a standard). Ten participants located and selected the blinking
information data blocks (targets) from 16 data blocks on a Simulated Air Traffic Control Display. Seven blink
amplitudes, ranging from 12.5% to 100%, were evaluated. Error and response time performance were near optimum
for conditions involving a 75% to 100% decrease in brightness. For the standard luminance (51.4 Cd/m’), frequency (2
HZ), and duration (.10 sec) used in this experiment, a decrease in brightness of at least 75% was necessary for
maximum attention-getting value of a blinking target.

17. Key Words 18, Distribution Statement

Artention-Getting Target Document is available to the public through

CRT display Air Traffic Control the National Technical Information Service,

Blink Springfield, Virginia 22161

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