While it should be of little surprise that previous studies have generally found flashing
signals to be superior to steady ones in capturing attention {Conners 1975), the gains
reported are not as high as one might expect. Gerathewohl (1957), for example, compared
detection times to a steady light with times to detect lights flashing at i to 4 Hz under
differing conditions of brightness contrast. Detection time was related to both flash rate
and contrast. Maximum gain (49 percent) was achieved using the highest flash rate and
lowest contrast; the same flash rate under high contrast conditions yielded a gain of only 26
percent. Conners (1975), in a study designed to investigate characteristics of aircraft signal
lights that would enhance a pilot's ability to “see and avoid" other aircraft, compared
detection of point source steady lights with lights of differing frequency and brightness
presented against a star background. Although detection times to the flashing conditions (1
to 4 Hz) were numerically superior to those obtained to steady lights, the differences reached
significance only at the medium and low intensity levels. Using data reported in this study,
maximum gains under medium and low intensity levels were computed to be 25 and 37
percent respectively.

It is evident. then, that the gain in conspicuity that resulted from the use of flashing
events in the present study is greater than that reported by others. This might be attributed
in part to differences between studies in experimental conditions and procedures employed:
for example, assigning a value of 90 s to missed signals to obtain a single measure of
detection efficiency. With regard to this latter procedure, however. even with these 90-s
missed signal values eliminated from the latency distributions, the resulting gain over
shape alone was still found to be 61 percent.

Parasuraman (1986), in a recent review of monitoring research, asks the question
“Does the effectiveness of a warning device signaling the failure of a component in a semi-
automated system {or the failure of the warning system itself) vary with the operator's level
of vigilance?” The findings of the present study would suggest the answer to this question to
be a qualified "yes." While all of the triangle conditions became less eifective in attracting
attention as monitoring progressed, this decline in effectiveness was found to be
significantly less for those conditions in which flashing was employed. The fact that color
failed to show a similar interaction with time on task was somewhat surprising, although it
should be noted that virtually no research has actually examined the effects of color on the
performance of vigilance or monitoring tasks. The one study of this sort of which the
authors are aware employed a meter monitoring task in which the meter hands were
colored red, while numbers. frames, and background were colored blue, green and yellow
respectively (Pfendler and Widdel, 1986). A comparison of monitoring perfonnance using
the colored display with performance under achromatic conditions revealed a progressive,
significant increase in detection time under achromatic conditions, but not when color was
employed. The intent of this particular study, however, differed somewhat from that of the
present one, since it dealt with the effectiveness of color in sustaining arousal, not with the
relative effectiveness of color as an alerting or warning signal during prolonged monitoring.

Numerous studies have shown that increasing the attentional demands of a primary or
central task tends to impair performance on secondary tasks (Bahrick, Fitts and Rankin,
1952: Bursill, 1958: Esterbrook, 1959; Leibowitz and Appelle, 1969; Webster and Haslerud,
1964, Williams, 1982, 1985). Consequently, we anticipated that increasing the attentional
demands of the primary task used ‘1 the present study would have a similar adverse effect
on secondary task performance. What was not known was the extent to which adding
flashing or color as redundant secondary task cues might mitigate this expected
impairment. Varying the time available for conflict detection, coupled with loss of a portion
of the financial incentive each time the conflict alert occurred, proved to be an effective
means of manipulating task demand; the condition in which subjects had only 26 s
available before the conflict alert occurred was rated as being more difficult and with
greater effort requirements than the condition in which 90 s was available for detection of
possible conflicts. The expected adverse effect of high primary taskload on secondary task
performance, however, was found to apply only te nonflashing targets; these took
significantly longer to detect under high than under low taskload conditions. Flashing
targets were detected with equal rapidity under either taskload condition. Color was of no

1


search times were obtained to target symbols that appeared as either high contrast, as
flashing, or as static (neither high contrast nor flashing) symbols against a backgrounG of
nontarget symbols. He hypothesized that, relative to search times for static symbols, search
times for the flashing target condition would be shortest,followed by search times for the
high contrast condition. Surprisingly, high contrast targets were detected significantly
faster than flashing targets. The author concluded that the superiority of contrast over
flashing was because high contrast signals could be discriminated from background stimuli
almost immediately through automatic preattentive processes. Flashing signals, however,
because of the 1 Hertz (Hz), 50 percent duty cycle employed, required at least .5 second (s)
before they could be seen as a flashing signal against a steady background.

The present study differed from the Nesthus study, as well as most other studies of
signal conspicuity, in that a continuous monitoring task, rather than a discrete trials
approach, was employed. Subjects performed a simulated ATC monitoring task under either
high or low primary taskload conditions. A principal requirement of the primary task was
to detect possible conflict situations between “tracked” targets; the secondary task involved
the detection of small, triangular targets representing nontracked, non Mode C aircraft that
had entered the subject's controlled airspace without authorization. Secondary targets were
presented infrequently, at different screen locations, and in the presence of similar-sized
green circles representing radar clutter. Depending on the condition to which subjects were
assigaed, secondary targets could appear as ()) nonflashing triangles of a noncontrasting
(green) color, (ii) nonflashing triangles of a contrasting {red) color, {iil) flashing green
triangles, or (iv) flashing red triangles. The study was designed to address and provide
answers to the following questions:

1. What are the relative gains in conspicuity that might be realized if flashing or color
were added as redundant cues to indicate the presence of unexpected, nontracked aircraft
targets?

2. What are the effects, if any, of prolonged monitoring and increased primary taskload
on the relative gains in conspicuity that are achieved through the use of flashing and color?

In addition to performance measures, subjective measures of attentiveness, tiredness,
strain, boredom, irritation, effort. and difficulty were also obtained.

METHOD
Subjects

Sixty-four men and women, all paid university students, were assigned to eight equal-
size experimental groups {high or low primary taskload and one of four triangle signal
conditions). Subjects ranged in age from 18 to 29 years, and none had prior experience with
the task used or previous ATC training. None were currently taking any prescription
medication on a regular basis. All had normai color vision (as determined from the
Ishihara test) and 20/30 or better visual acuity at 26.23 inches as determined from a Titmus
II vision tester. This distence corresponded closely to the distance that a subject would
normally be viewing the visual display. The Titmus II Peripheral Fields Test was also
administered, with no subject failing to detect any of the lights positioned 0 to 85 degrees in
both Jeft and right horizontal visual fields.

Apparatus and Task Description

The basic experimental equipment consisted of a Digital Equipment Corporation (DEC)
VS11 19-in (49-cm) graphics display, keyboard, and joystick, all of which were interfaced
with a VAX 11/730 computer (DEC). The computer was used both to generate input to the
display and to process subject responses. The VS11 was incorporated into a console designed
to closely resemble an ATC radar unit. Two diagonal, nonintersecting flight paths were
located on the display, along which aircraft targets could move in either direction. A given
aircraft's location was displayed as a small rectangle on the flight path, and an adjacent
alphanumeric data block identified the aircraft and gave its altitude and groundspeed.
Aircraft targets were updated every 6 s io reflect their new positions and any change in the

2


20r
ist = [_] NON-FLASHING
16+ QB rvasuine
14h
Bieb
6
8 tob
6 Bt
6
4 =
2 a
6 WU,
Low HIGH
TASKLOAD

Figure 3. Mean detection time for ponfiashing ani flashing secondary task targets
under high and low primary taskload condiiions.

In order to clarify the taskload by flash interaction, the data were plotted in the form
of a bar graph and are shown in Figure 3. Although detection time for nonflashing targets is
shown to exceed that of flashing targets under both taskload conditions, detection of non-
flashing targets appears to be influenced far more by an increase in taskload than detection
of flashing targets, which actually shows a slight decrease in detection time with increased
taskload. Tests of simple effects of the interaction revealed detection time for nonflashing
targets to be significantly greater than detection time for flashing targets under the high
taskload condition (F(1/53)=30.6, p<.001); under low taskload, detection time for flashing
and nonflashing targets did not differ (F(1/53)<1.00).

With regard to the significant flash by period interaction, it is evident from Figure 2
that detection times for nonflashing stimuli, whether colored or not, increase more from
the first to the second hour than do detection times for flashing targets. Although the figure
suggests this to be almost entirely restricted to the high taskload condition, the tasktoad by
flash by periods interaction failed to reach significance (F(1/53)=2.56, p>.05)}.

Location Effects

it will be recalled that half of the secondary targets were presented at outer locations of
the display and half at inner locations. To examine possible relationships of flashing,
color, and taskload to detection of targets in central and peripheral locations, a second
ANOVA was conducted that was essentially the same as the previous one, except that
“location” (inner, outer) replaced “period” as the within-group factor. Since only within-
groups effects are pertinent, only these wiil be discussed. The main effect of location was
found to be significant (F(1/53)=21.35, p<.001)}, with detection time for outer locations
(Mn=12.93 s) exceeding detection time for inner ones (Mn=5.10 s). Such “edge effects” have
been reported by others for both visual search (Baker, Morris, and Steedman, 1960; Enoch,
1959) and radar moni.oring tasks (Baker, 1958), so this was an expected finding. The only
other significant effect was the flash by location interaction shown graphically in Figure 4.


detected, a console button was pressed and the target would disappear shortly thereafter. A
target would also disappear if not detected within a 90-s timeout period.

Nine primary task and two secondary task critical events occurred during each 30 min
of task performance, with no more than one event present at any given time. Time of
occurrence of each type of event was fixed. Location of each successive secondary task target,
however, was randomly assigned without replacement for each subject. Thus, although
interstimulus intervals were fixed for triangular targets, the order of locations differed for
each subject. Subjects were given no information regarding the frequency of events or their
order of occurrence.

Color and Luminance Measurement and Specification

~ All color and luminance measurements were made using a Pnoto Research Spectrascan
with the recording head of the instrument located 22 cm from the face of the visual display.
The 22 cm distance corresponded to the average distance of a subject's eyes from the display.
To »pproximate real-life radar viewing conditions, no attempt was made to restrict head
movements, although task requirements to use the keyboard and panel buttons kept head
locations of subjects at a reasonably constant distance from the screen. The particular red
and green colors used were selected from the available DEC VS11 colors and were chosen to
be as close as possible to the CIE (Wyszecki and Stiles, 1982) coordinates (red X=.650, Y=.336;
green X=.329, Y=.600) specified for the FAA's Advanced Automation Sector Suites (FAA,
1985). While it was not possible to achieve a perfect match of the red/green lumimances with
the VS-11 display, luminances of the colors selected were reasonably close. Color and lumi-
nance values are shown in Table 1.

TABLE 1
Color and Luminance Values of Display Elements

[ Display CIE Luminance
Elements Hue Coordinates (in foot-

x Y lamberts)
Alphanumerics }j Green .233, .628 4.94
Ciutter Green} 233 628 4,94
Triangle Green .233 -623 4.94
Triangle Red 615 342 6.72

Video Recording Methodology

The outputs of separate Sony Charge Coupled Device (CCD) cameras, used to monitor
both the subject's facial orientation and the visual display, were combined by means of a
special effects generator and displayed on a video monitor. A small indicator light, not vis-
ible to the subject, was located above the console and was illuminated each time a secondary
target (triangle) was displayed on the screen. Continuous videotape recordings enabled sub-
sequent playback and analysis of the subject's visual behavior during times when secondary
targets were presented. Indirect lighting was used in the subject's room, and the level of
illumination at the display was 23 lux.

Procedure

Upon arriving at the laboratory, subjects were given general information about the
task and tested for color vision and visual acuity. Subjects then received detailed task
information describing each kind of critical event along with the appropriate responses to
each. Short practice sessions followed the description of each type of event. A final com-
bined session provided practice on all primary and secondary task events and also famil-
iarized subjects with the conflict alert alarm. (For the secondary task, subjects received
practice only on the particular triangle condition to which they had been assigned.)


alphanumerics. There were 8 aircraft on each flight path at all times; as one left the screen,
another appeared.

In addition to the primary (alphanumeric) targets, the display also contained station-
ary “clutter” in the form of 4-mm diameter green dots. The triangular targets representing
nontracked aircraft were similar in size to the dots and could appear in any one of eight
different locations: four of the locations were near the extreme corners of the display and
four were more centrally located. Figure 1 shows all of the possible triangle locations as
well as the clutter and a typical pattern of alphanumeric targets.

_ Accession For

| NTIS GRARI

Figure 1. Subject's display showing clutter, all triangle locations, and a typical pattern of alph-
anumeric targets. .

The primary task consisted of monitoring for two types of critical events. The first type
was readily detectable and consisted of the appearance of three X's (designated an altituds
malfunction event) in place of the three altitude numbers in a given data block. Subject:
were told that ihe three X's signified that a malfunction had occurred in an aircraft's alti-
tude transponder. Upon detection of such an event. subjects pressed a designated console
button and performed a joystick/keyboard response to correct the malfunction.

The second type of critical event was considerably more difficult to detect because it
was not immediately apparent: two aircraft at the same altitude on the same flight path.
Any time such an event was detected, the subject was instructed to press an appropriate con-
sole bution. If the event was not detected within a predetermined time limit, a “conflict
alert” occurred signifying a possible conflict situation. (The two aircraft targets at the same
altitude commenced flashing at a 1 Hz/s rate in conjunction with a 600 Hz/s, 65 dbA tone
that pulsed at a 2 pers rate.) Any time a possible conflict was detected, either by the subject
or following a “conflict alert" alarm, a decision response occurred. This was followed by a
set of subsequent behaviors that differed depending on whether or not the event was deter-
mined to be a conflict situation. These aspects of the task, which have been described else-
where (Thackray and Touchstone, 1989), are not relevant to the present study and will not
be discussed here.

As previously indicated, the subject's secondary task was the detection of triangular
targets representing nontracked, unidentified aircraft (designated as VFR intruders) that had
entered the subject's controlled airspace. These targets were presented under the four possi-
ble color/flash conditions described earlier. For the flashing conditions, a flash rate of 4 Hz
was used with a 125 ms on, 125 ms off duty cycle. Whenever one of these types of targets was

3



TABLE 2
Percer cage of Secondary Targets Missed Under the Various Task Conditions.

Primary Task Secondary Task | Total Missed) Percent of Total
Condition Condition Across all Ss Presented
High Taskload |[Nonflashing/noncolored 14
Nonflashing/colored
Flashing/noncolored
Flashing /colored
Low Taskload [Nonflashing/noncolored
Nonflashing/colored
Flashing/noncolored
Flashing/colored

O] ~] ] bo] O] OF CF col

OP SPS cof OF OF ov

— ——-

A four-way repeated measures analysis of variance (ANOVA) was used io analyze the
data shown in Figure 2. Between-group factors were Primary Taskload (Hig, Low}, Flash
(Flashing, Nonflashing), and Color (Colored, Noncolored}, with Period (First Hour, Second
Hour) as the within-group factor. Because of recording problems, data for 3 of the 64 subjects
tested were incomplete and these subjects were not included in the analysis. The ANOVA re-
vealed significant effects for Flash (F(1/53)=23.41, p<.001), Color (F(1/53)=3.85, p=.05), and
Periods (F(1/53)=18.40, p<.001). In addition to these main effects, there were significant in-
teraction effects for Primary Taskload by Flash (F(1/53)=4.81, p<.03) and Flash by Period
(F(1/53)=5.44, p<.02). No other effects were significant (p>.05).

Examination of Figure 2 clearly reveals the significant period effect to be the result of a
general increase in detection time across the session for virtually all conditions.
Interpretation of the significant effect of flash is also quite apparent: Under both high and
low taskload, and for both colored and noncolored stimuli, shortest detection times were
associated with flashing conditions. Likewise with color, Figure 2 reveals that under both
flashing and nonflashing conditions and within each taskload condition, colored stimuli
were invariably detected sooner than noncolored stimuli.

287 HGH TASKLOAD
24h
20-
16
iar
on Br
a
Zab
roy
is)
w
o 4-—4 NONFLASHING, NONCOLORED
&—4 NONFLASHING, COLORED
ior Q--O FLASHING, NONCOLORED
LOW TASKLOAD @—-@ FLASHING, COLORED
12r
4h

HOURS

Figure 2. Mean detection times during first and second hours for each secondary task condi-
tion under high and low primary taskioads.



oid

DOT/FAA/AM-90/3 Effects of Monitoring under
High and Low Taskloau on

Office of Aviation Medicine Detection of Flashing and

Washington, D.C. 20591 Colored Radar Targets

Richard I. Thackray, Ph.D.
R. Mark Touchstone, M.S.

Civil Aeromedical Institute
Federal Aviation Administration
Oklahoma City, OK 73125

January 1990

AD-A220 313

Final Report

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

©

U.S. Department
of Transportaticn
Federal Aviation
Administration

96 04.10 099


=z

FREQUENCY

@— HIGH TASKLOAD
O——O LOW TASKLOAD

y,
A 1 4

SECONDS

30 MINUTE PERIODS

Figure 5. Mean detection times across 30-min periods for altitude malfunction events under
beth taskload conditicns. Also shown in this figure are the frequencies with which detection
times for conflict/no conflict events equaled or exceeded 26 s under the two taskioad
conditions.

Subjective Data

Although manipulation of primary taskload exerted no significant effect on measures
of primary task performance. this was not the case with most of the subjective measures
that were obtained. These data are shown in Table 3.

As indicated in the table. both groups experienced a significant decline in
attentiveness, accompanied b- significant increases in tiredness, boredom, irritation, and
effort from beginning to end of the monitoring sessicn. However, in additi.a to these main
effects, there were significant interactions of period with {a) attentiveness {F{1/62}=6.83,
p<.01), (b} boredom (F{1/62)=3.91, p=.05). {c) irritation (F{1/62)=5.71, p<.01). {d) effort
{F(1/62}=4.34, p<.05), and {ej difficulty (F{1/62}=6.78. p<.C1}. Interpretation of these
interactions is clearly revealed by examining the data of Table 3. Relative to lov: taskload,
high taskload was associated with < greater decrease in attentiveness along with a greater
increase in boredom, ‘ritation, effort, and difficulty.


[] non-FLasuins
GZ FLASHING

SECONOS
te)
T

INNER OUTER

Figure 4. Mean detection time for zonflaching and flashing targets presented at inner and
outer display locations.

Tests of the simple effects of the interaction revealed no difference between in ~ and
outer locations when stimuli were flashing (F{1/62)=2.29, p>.05), but a significant . cation
effect when flashing was not employed {F{1/62Z)=26.85. p<.00%).

Primary Task Performance

With a visual taskload of 16 primary targets, we have shown previously that time to de-
tect altitude maifunction events (three X's) in a data block iakes approximately 8-10 s. with
no increase in this time over 2 h of monitoring (Thackray and Touchstone, 1989).
Consequently, detection time for this type of event serves as a useful estimate of general
scanning activity during a monitoring session.

Mean time to detect altitude malfunction events for subjects in the high and low
taskload conditions is shown in Figure 5. A repeated measures ANOVA revealed no signifi-
cant change across the 2-h session in detection time for these events (F{3/183}=1.21, p>.05),
no difference between conditions (F{1/61)<1.00), and no significant interaction
(F13/183)<1.00}.

Determination of the effects of primary taskload manipulation on time to detect possi-
ble conflict situations (designated conflict/no conflict events} was somewhat more difficuit
because distributions of detection times under the high taskioad condition were truncated at
26 s (the allowable detection time before the “conflict alert” alarm occurred}. The approach
adopted was to determine for each 30-min period the frequency of detection times equal to
or greaier ihan 26 s. For the high taskload condition, this consisted simply of counting the
number of alarms produced by each subject during successive 30-min periods; for the low
taskicad condition, all detection times equal to or exceeding 26 s during these periods were
counted. Mean frequencies of occurrence are shown in Figure 5. A repeated measures ANOVA
of these data revealed a significant main effect for periods (F{1/61)=59.58, p<.001), but no
difference between taskload conditions (F{1/61)<1.00} and no significant interaction ef
taskload by periods (F{1/62}=1.03, p>.05). .


Following the practice sessions, subjects completed a nine-point subjective rating scale
to describe their present feelings of attentiveness, tiredness, strain, boredom, and irritation.
The final set of task instructions explained that the conflict alert alarm was essentially the
same as that used in contemporary ATC systems to warn controllers of possible conflict sit-
uations, and that in this particular experiment the alarm would go off whenever the com-
puter determined that they had failed to detect a possible conflict in the minimal allowable
time. Subjects were told that completing the experiment without the alarm occurring more
than once would earn them a $16 bonus. Each time the alarm occurred after that, however,
would halve the remaining bonus until, with 5 or more alarms, no bonus would remain. It
was emphasized that, while the bonus was dependent only on the speed with which they
were able to detect possible conflict situations between controlled aircraft, it was :mportant
that they continued to maintain constant scanning for VFR intruders and for altitude mal-
function events. Subjects assigned to the high taskload condition had only 26 s to detect a
possible conflict situation before the alarm would occur; subjects in the low taskload condi-
tion had 90 s to detect possible conflicts before the alarm was triggered. (The 26 s value cor-
responded to the mean detection time, as obtained from several of our previous studies, for
this type of event.)

In order to add a greater element of realism to the task, a tape recording of background
noises recorded in actual air traific control radar rooms was played continuously during the
2-h task session. Sound level of this noise at the sudject's head location was 62 dbA.

At the completion of the 2-h task period, subjects were administered a secord version
of the rating scale that contained additional items relating to perceived task difficulty and
the amount of effort required to maintain task concentration. This was followed by a
thorough debriefing concerning the purposes of the experiment.

RESULTS
Di nm fe T:

Initial examination of the response data for the four secondary target conditions re-
vealed that subjects failed to detect nonflashing/noncolored targets most frequently, with
nonflashing/coiored targets showing the next highest failure rate. (For purposes of this
paper, “noncolor" refers to targets having the same color as the green background ciutter,
while "color" refers to the red targets.) Further. in both cases, poorest detection appeared to
occur under the high primary taskload condition. Table 2 shows miss rates (targets not de-
tected within the 90-s stimulus duration period) for the various conditions.

Because missed events occurred so infrequently, it seemed desirable to combine them in
some way with measures of detection latency in order to arrive at a composite measure that
would mere adequately reflect the totality of detection performance. Assuming that subjects
were engaged in monitoring the display during times when everits were missed, it is to be
expected that each event would eventually have been detected within some period of time in
excess of the 90-s stimulus duration period. In order to verify this assumption, videotape
recordings of visual behavior during the session were examined, specifically with regard to
visual activity during times when a triangle target was rot detected. This analysis revealed
that all missed events occurred during periods in which subjects had their eyes open and
were actively scanning the display. Each missed event, then, was arbitrarily assigned a
value of 90 s and averaged in with detection latencies in order to yield a single overall mea-
sure of detection performance. The values thus obtained under conditions of high and low
primary taskload are shown in Figure 2. Only two triangle events occurred during each half-
hour period; therefore, to provide more stable measures of detection performance, the data
were plotted, and subsequent analyses conducted on the combined data for first and second
performance hours.


EFFECTS OF MONITORING UNDER HIGH AND LOW TASKLOAD
ON DETECTION OF
FLASHING AND COLORED RADAR TARGETS

On August 31, 1986, an Aeromexico DC-9 collided with a single engine Piper Cherokee
Archer aircraft over Cerritos, California resulting in a total loss of 82 lives. According to
the National Transportation Safety Board (NTSB) report, the Aeromexico flight was within
the Los Angeles Terminal Control Area (TCA) and under radar control at the time, while the
Cherokee, proceeding under visual flight rules (VFR) conditions, was noi in radio contact
with any air traffic control (ATC) facility. The accident occurred in clear weather with 14
mile visibility. The controller providing service to the Aeromexico flight stated that he did
not observe the Cherokee's radar retumm on his display and therefore did not provide any
traffic advisory to the Aeromexico flight regarding the VFR aircraft in its vicinity prior to
the collision (NTSB, 1987).

While fortunately such midair collisions are extremely rare occurrences, "near midair"
incidents are more common. In a review of near midair collision (NMAC) incidents occur-
ting between the period 1983 to 1986, a recent FAA Office of Aviation Safety Report (FAA,
1987} revealed that pilot reported NMAC incidents increased from 475 in 1983 to 840 in
1986, a gain of 77 percent. Such an increase cannot be attributed simply to increased air
traffic, which increased by only 7 percent over those years. The largest number of reports
were associated with instrument flight rules (IFR) cperators conflicting with VFR traffic
during VFR flight conditions below 12,500 feet. The typical NMAC event was found to occur
most frequently under good visibility conditions, during daylight hours (late morning to
early afternoon), and in the vicinity of towered airports and/or within the radar coverage of
the approach/departure environment. 't should be noted that this set of circumstances is
precisely the set that characterized the Cerritos collision.

There are many ways in which the likelihood of such near misses and mid-air colli-
sions in air traffic control TCA's might be reduced. Following the Cerritos crash, the FAA
completed a study of the TCA concept leading to 40 recommendations for improvement.
These included, among others, such recommendations as specialized training to improve
controller scanning techniques, improved radar equipment to minimize the possibility that
a target may, at times, not be detected or displayed by the system, more rigid enforcement of
Tegulations governing unauthorized intrusions of VFR aircraft into a TCA, and a require-
ment that all aircraft entering a TCA be equipped with altitude encoding (Mode C) transpon-
ders. (Without altitude reporting transponders, aircraft, such as the one involved in the
Cerritos accident, typically appear simply as symbols -- dots, slashes or triangles -- on the
radar screen; with a Mode C transponder, altitude is displayed adjacent to the symbol.) The
Mode C requirement has been implemented and is now a requirement for 138 of the nation's
busiest airports. That is, for an aircraft to operate within these TCA's, it must have a Mode
C transponder. While this recent requirement will provide the controller with useful alti-
tude information on nontracked targets, there is no assurance that such a requirement will
completely eliminate further accidental or intentional intrusions of aircraft not equipped
with Mode C transponders into controlled airspace. Indeed, there is the danger that the low-
ered expectancy of such aircraft being present in controlled airspace may reduce the
controller's ability to detect these targets.

One obvious method of increasing the likelihood of such targets being detected would be
to add, as a redundant cue, either flashing or a contrasting color to the displayed symbols.
Both flashing and colored indicator lights are often used in visual displays for signaling
purposes. However, although studies have been conducted to evaluate parameters related to
the conspicuity of each type of signal (see Conners 1975, Gerathewohl 1957, and Markowitz
1971, for representative studies of flash rate and Kopala 1979, Luder and Barber 1984,
Macdonald and Cole 1988, and Reynolds, White, and Hilgendorf 1972 for representative
studies of color), little or no research has been conducted in which the relative effectiveness
of flashing and colored signals has been compared within a single study. Although not
actually employing color, Nesthus (1984) did report a study of this type in which visual

1



apparent benefit in offsetting the apparent reduction in the functional field of view thai
resulted from an increase in taskload.

Not only were detection times of flashing targets unaffected by tasklead conditions,
they were also unaffected by the location on the display in which these targets appeared.
Nonflashing targets, on the other hand, were detected significantly more slowly when
presented in peripheral locations than when they appeared in the more central locations.
Thus, the “edge effect” reported by others for both visual search (Baker, Morris, and
Steedman, 1960; Enoch, 1959) and radar monitoring tasks (Baker, 1958}, was found to apply
only to nonflashing targets.

Although the principal reason for manipulating primary taskload was to examine its
effect on secondary te: performance, some mention of the effects of this manipulation on
the primary task itself is in order. The lack of any performance decrement associated with
the readily perceivable altitude malfunction events, coupled with evidence of a significant
decline im detection efficiency for conflict/no conflict events, is consistent with our
previous findings using essentially the same visual task, albeit without the secondary or
VFR targets (Thackray and Touchstone, 1989). Evidence presented in this earlier study led us
to hypothesize that monitoring under relatively high visual taskloads requires considerable
effort, and that the fatigue resulting from this effort adversely affects detection efficiency
for critical events requiring considerable information processing for detection, but has
little effect on target changes that are readily perceivable {e.g.. altitude malfunction events).

On the basis of our previous research, we would have expected that VFR intruder events,
which are similar in information processing requirements to altitude malfunction events,
likewise to show no increase in detection time over the monitoring session. That these
events did show an increase suggests that our earlier hypothesis requires some
modification. Possibly, fatigue resuliing from the effort required to sustain attention during
prolonged monitoring acts to focus one’s diminishing or narrowing attention on those task
aspects to which highest priority has been assigned. This could account for the finding that
VFR intruders, as secondary task events, showed a significant decline in defection efficiency
over time, while altitude malfunction events, embedded as they were within the primary
task of searching for possible conflicts, showed no increase in detection time.

CONCLUSIONS AND RECOMMENDATIONS

It was not the intent of this study to address the technical problems that undoubtedly
would be associated with adding color or flashing to selected types of radar targets in
contemporary ATC systems. Rather, the purpose was simply to evaluate the extent to which
the conspicuity of unexpected, nontracked aircraft radar targets might be enhanced if it
were feasible to add color or flashing as redundant cues to such targets, and how such gains
might be affected by prolonged monitoring and increased taskload. With this in mind, the
findings clearly suggest that if one wishes to increase the conspicuity of unexpected,
unidentified aircraft entering a controlled airspace in a manner that is minimally
influenced by changes in primary taskload, by location of :he target on the radar screen, or
by the fatigue associated with prolonged monitoring. one should employ flashing, rather
than color, as a redundant cue to attract attention. Flashing is such a compelling cue.
however, that its alerting qualities must be weighed against its potential for distraction. In
terms of practical cpplication in ATC displays, it is recommended that flashing be used
much as it was in the present study, i.e. as a means of directing initial attention to an
unexpected, unnoticed target. Once this is achieved, the controller's response to the event,
preferably through use of a touch sensitive display, would serve both to deactivate the
flashing and to confirm that the controller had located and acknowledged the target.

12


Technical Report Documentation Page

1. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
DOT/FAA/AM-90/3 | :
4. Title and Subtirie i S Report Date :
EFFECTS OF MONITORING UNDER HIGH AND LOW TASKLOAD i January 1990 i
ON DETECTLON OF FLASHING AND COLORED RADAR TARGETS *EBerferming Orgam zation coe

Beriormag O-gamization Report No

7 Aumor's

Richard I. Thackray, Ph.D, and R. Mark Touchstone

9. Performing Orgen: zation Name and Address Work Un.t No. TRAIS)

FAA Civil Aeromedical Institute

!P. 0. Box 25082 TF. Contract or Geant No.
: Oklahoma City, CK 73125

[130 Type of Report and Period Covered

12. Sponsoring Agency Name and Address
Office of Aviation Medicine
Federal Aviation Administration

800 Independence Avenue, $.W. Ya Sponsoring Agency Code
Washington, D.C. 20591

15. Supplementary Notes

This work was performed under tasks AM-C-89-HRR-111 and AM-C-88-HRR-111.

16. Abstrect

“while midair collisions between aircraft are extremely rare occurrences, \near
midair’ incidents are more common. The present study sought to evaluate the
gains in conspicuity that might be realized if flashing or color were added as
redundant cues to indicate the presence of unexpected, nontracked aircraft
entering controlled airspace and to examine the extent to which increased
taskload and fatigue might influence the expected gains. Sixty-four subjects
monitored a simulated air traffic control task over a 2-hour period for possible
conflict situations (their primary task) under either high or low primary
taskload conditions. They also monitored for occasional intrusions by light
aircraft identifiable on the basis of target shape alone or with color and/or
flashing added as redundant cues. Flashing as a redundant cue was found to be
superior to color in ali aspects tested; unlike color, detection of flashing
targets was unaffected by screen location and by changes in primary taskload.
Flashing was also least affected by monitoring fatigue. It was concluded that
the superiority of flashing over color in attracting attention to objects in a
display must be weighed against its possible potential for distraction. A
Practical means of accomplishing this in operational situations is through the
use of touch sensitive displays to both acknowledge/confirm target location and
to deactivate flashing,

—

——

17 Key Words Si . ~__ | 18. Distribution Statement
sy Words “sir traffic control, attention

color, flashing, monitoring, performance, Document is available to the public
vigilance, warning signals, ~ - through the National Technical

a Information Service, Springfield,
a Virginia 22161.

19. Security Classif. (of this report) 20. Security Clossif. (of this page) Zl. No. of Pages | 22. Price

Inclassified Unclassified 17

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized



NOTICE

This document is disseminated under the sponsorship of
the U.S. Department of Transportation in the interest of
information exchange. The United States Government
assumes no liability for the contents or use thereof.


TABLE 3

Mean Rating Scale Values for High and Low Taskload Con -tions. Also Shown are
Combined Values Across Conditions.*

Measurement Periods

Variable Taskload Pre Task | Post Task Fre Pp
Attentiveness } High 76 4.3

Low 7.7 5.3

Combined 7.6 5.1 71.93 <.061
Tiredness High 5.0 65 =

Low 45 59

Combined 4.7 €.2 37.27 <.001
Strain High 46 54

Low 46 45

Combined 46 49 L74 NS
Boredom High 2.7 62

Low 2.8 5.2

Combined 2.7 5.7 130.91 <.001
Irritation High 13 3.0

Low 13 2.0

Combined 13 2.5 43.04 <.001
Effort*** High 3.4 6.8

Low 338 5.8

Combined 3.6 63 67.17 <.001
Difficulty’TM* | High 32 49

Low 3.0 2.8

—_ Combined 3.1 3.8 4.71 <.05

* Higher numerical values indicate higher levels of the variable. with 5 representing the
midpoint or middle value.

** Only the F values for the Periods effects are shown here; between-groups and
interaction effects are discussed in the text.

*** Measures for these variables were obtained at the etd of the session and reflect
perceived effort and difficulty as experienced at the beginning and end of the task period.

DISCUSSION

An effective warning or alerting signal should literally capture attention by “Popping
out" as an automatic preattentive segregation of figure from background. (Treisman, 1982).
One's attention can then be focused on those aspects of the signal that may require further
information processing. This study compared the use of color and flashing as redundant
cues to aid in the detection of small, triangular targets signifying unexpected and
unidentified aircraft that had intruded into controlled airspace. As expected, addition of
either color or flashing as redundant cues significantly reduced detection time relative to
detection on the basis of shape alone. When shape served as the only cue, mean detection
time was 17.96 s. With the addition of color, detection time decreased to a mean of 10.37 s, a
gain of 42 percent over shape alone. This gain compares quite favorably with Christ's
findings that the use of color (regardless of whether it is a completely or partially redundant
cue) will reduce search time for objects differing in shape by at least 34 percent (Christ,
1975, p. 561). Flashing, however, proved to be considerably more effective than color in
reducing detection time. When added to shape, flashing further reduced detection time to a
mean of 5.29 s, a gain of 71 percent over shape alone. An additional, but much smaller.
inerement resulted from combining color with flash. Mean detection time with this
combination was 3.20 s, or a gain of 82 percent.

10


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