DOT/FAA/AM-95/13

Office ofAviation Medicine

Washington, D.C. 20591

Practical Color Vision Tests

for AirTraffic Control

Applicants: En Route Center

and Terminal Facilities

DISC

ELECTEPI

"JUN 0 7 19951 1

F

H.W. Mertens

N.J. Milburn

W.E. Collins

Civil Aeromedical Institute

Federal Aviation Administration

Oklahoma City, Oklahoma 73125

April 1995

Final Report

This doounient has been approved

for public release and sale; its

distribution is unlimited

This document is available to the public

through the National Technical Information

Service, Springfield, Virginia 22161.

19950605 007

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U.S. Department

of Transportation

Federal Aviation

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assumes no liability
Technical Report Documentation Page

1. Report No.

DOT/FAA/AM-95/13

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Practical Color Vision Tests for Air Traffic

Control Applicants: En route Center and

Terminal Facilities

5. Report Date

April 1995

6. Performing Organization Code

7. Author(s)

Henry W. Mertens, Ph.D., Nelda J. Milburn, M. Ed., and

William E. Collins, Ph.D.

8. Performing Organization Report No.

9. Performing Organization Name and Address

FAA Civil Aeromedical Institute

P.O. Box 25082

Oklahoma City, OK 73125

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

12. Sponsoring Agency name and Address

FAA Office of Aviation Medicine

Federal Aviation Administration

800 Independence Avenue, SW

Washington, DC 20591

13. Type of Report and Period Covered

15. Supplemental Notes

This work was performed under task AAM-B-94-HRR-190

16. Abstract

Two practical color vision tests were developed and validated for use in

screening Air Traffic Control Specialist (ATCS) applicants for work at en route

center or terminal facilities. The development of the tests involved careful

reproduction/simulation of color-coded materials from the most demanding, safety

critical color task performed in each type of facility. The tests were evaluated

using 106 subjects with normal color vision and 85 with color vision deficiency. The

en route center test, named the Flight Progress Strips Test (FPST), required the

identification of critical red/black coding in computer printing and handwriting on

flight progress strips. The terminal option test, named the Aviation Lights Test

(ALT), simulated red/green/white aircraft lights that must be identified in night ATC

tower operations. Color coding is a non-redundant source of safety-critical

information in both tasks. The FPST was validated by direct comparison of responses

to strip reproductions with responses to the original flight progress strips.

Validity was high; Kappa=.91. The light point stimuli of the ALT were validated

physically with a spectroradiometer. The test lights met the FAA and ICAO standards

for colors of aircraft and aviation signal lights. The reliabilities of the FPST and

ALT were estimated with Chronbach' s alpha and were .93 and .98, respectively. The

high job-relevance, validity, and reliability of these tests increases the

effectiveness and fairness of ATCS color vision testing.

17. Keywords

Air Traffic Controllers

Color Vision Standards

Performance Tests

Color Vision Tests

18. Distribution Statement

Document is available to the public

through the National Technical

Information Service, Springfield,

Virginia 22161

19. Security Classif. (of this report)

Unclassified

20. Security Classif. (of this page)

Unclassified

21. No. of Pages

15

22. Price

Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
PRACTICAL COLOR VISION TESTS FOR AIR TRAFFIC

CONTROL APPLICANTS: EN ROUTE CENTER

AND TERMINAL FACILITIES

INTRODUCTION

A medical color vision standard has been established

for Air Traffic Control Specialists (ATCSs) by the U.S.

Office of Personnel Management (1993) due to the

use of color coding of critical information for several

tasks, as verified by job-task analysis (Lahey, Veres III,

Kuyk, Clark, & Smith, 1984). Previous research has

also demonstrated that individuals with normal color

vision rarely make errors in simulated ATCS color

tasks, while many individuals with all levels of color

vision deficiency frequently make errors (Adams &

Tague, 1985; Kuyk, Veres, Lahey, & Clark, 1986,

1987; Mertens & Milburn, 1992a). Several clinical

color vision tests have high predictive validity for

identifying individuals who can perform particular

ATCS color tasks without error (Mertens & Milburn,

1992b). Those tests in general tend to have low miss

(false negative) rates, typically 5% or less. While all of

the approved clinical tests had acceptable miss rates,

false alarm rates tended to be somewhat higher, and

were undesirably high with a few tests (Mertens &

Milburn, 1992b). Some individuals who fail clinical

tests may be able to perform ATCS color tasks as well

as color vision normals. Practical color vision tests are,

therefore, desirable for increasing the predictive efficiency and optimizing the validity of color vision

testing for ATCS selection. The present research concerns the development and validation of practical,

"work sample" color vision tests for secondary screening ofATCS applicants who are seeking employment

at terminal and en route center air traffic control

(ATC) facilities.

Optimally, color vision screening of ATCS applicants should provide both the ability to select all

individuals who can perform safety-critical ATCS color

tasks accurately, whether they have a color vision

deficiency or not, and screen out all individuals who

cannot perform those tasks accurately. A test with high

predictive validity for performance in ATCS colo

tasks must have both a low miss (false negative) rate t

ensure safety, and a low false alarm (false positive) rat

to ensure fairness. The most direct way of accomplish

ing that objective is to create color vision screenin

tests that are "work sample" tests such that they accu

rately simulate the color-coded materials of the tas

and the viewing conditions ofthe work environment

The stimulus characteristics that affect color percep

tion, such as color, color contrast, brightness, bright

ness contrast, and stimulus size, must be reproduce

accurately. Viewing conditions that can affect colo

perception, such as intensity and color of ambien

illumination and the viewing distance, must also b

reproduced accurately. Such tests can be considere

"practical tests" because they involve essentially th

same materials and observation conditions that ar

involved in the actual work tasks (Jewell & Siegal

1990). The practical tests should also: (1) simulat

"normal" work situations, rather than more margina

observation conditions that sometimes occur, sinc

those conditions may also degrade performance o

individuals with normal color vision; and (2) involv

very simple color identification and/or discriminatio

responses so that the tests assess only color visio

ability. In addition to testing color vision appropri

ately for the job, the test's relevance to the job shoul

be explained to the applicant and be sufficiently obvi

ous so as to promote a positive response to the tes

situation.

Two practical color vision tests for en route cente

and terminal ATCS work options, that were develope

in the present research, represent the most importan

safety-critical tasks involving non-redundant colo

coding in each work situation. The practical tests wer

developed with the intention that they should b

implemented for secondary color vision screening o

ATCS applicants who fail clinical color vision testin

during their initial pre-employment medical examina

1
tion by an Aviation Medical Examiner. The two tests

described here have subsequently been implemented,

and the tests are administered at the office of the

Regional Flight Surgeon in each of the nine Federal

Aviation Administration (FAA) Regions. A practical

test for a third ATCS work option involving work in

Automated Flight Service Stations (AFSSs) is under development, but is not addressed in the present report.

Practical Color Vision Test for En Route Center

ATCSs

The most demanding color vision task at en route

centers involves accurately distinguishing between red

and black computer printing and handwriting on

Flight Progress Strips (FPSs). The test for this task is

named the Flight Progress Strips Test (FPST). The

FPSs are frequently referred to during an ATCSs time

"on the boards" (Vortac, Manning, & Rotter, 1992).

Each paper FPS is approximately 8 in wide by 1-5/16

in high, and is typically mounted in a plastic holder

and stacked on a sloping bay located near the large

radar cathode ray tube situation display of air traffic.

There is at least one FPS for each aircraft that is

controlled by the en route ATCS. The FPS contains a

variety ofinformation that is either computer printed

by the ATC system's computers, or handwritten by the

ATCSs. The FPS information describes the type of

aircraft and the aircraft's situation, including altitude,

departure, route, fixes, clearances, approach, and so

forth. The most critical color coding involves the use

of the colors black and red to distinguish between

assigned versus non-assigned (planned) information

concerning altitude, route, departure, approach, fixes,

clearances, and so forth (FAA, 1989). Other uses ofthe

black/red code in FPSs include differentiation between (1) coordination versus incorrect reporting altitude, (2) north versus south flights, and (3) east versus

west flights.

The FPST requires the identification of red and

black colors in reproductions of actual FPSs made by

a photographic color separation process and lithographic reproduction process that is also used for

color-critical fine art printing. The FPS copies were

printed on the same 32 lb pale green ledger paper used

by the FAA for FPSs. The FPST was validated by

comparing color responses to the FPST with color

responses to a test consisting ofthe original strips from

which the copies were made. The criterion test containing actual strips was named the Criterion Flight

Progress Strips Test (CFPST). The FPST and CFPST

test materials were illuminated by a special light source

developed to produce illumination of the color and

intensity typical at actual ATCS work stations.

Practical Color Vision Test for Terminal ATCSs

The second test was designed for testing ATCS

applicants who will work in air traffic control towers at

terminal facilities, and who must, therefore, be able to

identify and discriminate the color of aircraft lights at

night. The color coding of aircraft lights is important

for location of aircraft and determining their direction

or orientation, in flight or on the ground, based on

identification ofred, green, and white position lights.

The test is called the Aviation Lights Test (ALT) and

it makes use of the body and mechanisms of the

Farnsworth Lantern, a well-known clinical color vision test that involves identification ofred, green, and

white light points. Modification of the lantern's red

and green filters was required to make the light points

meet FAA and International Civil Aviation Organization (ICAO) color standards for aviation signal lights,

but the brightness ofsimulated lights is similar to the

Farnsworth Lantern. The administration and scoring

procedures also differ from the Farnsworth Lantern as

follows: (1) the ALT procedure involves a demonstration of each of the three test light colors prior to test

trials; (2) the ALT always involves presenting three

random series of the nine pairs of lights produced by

the lantern, and requires scoring ofresponses to all 27

pairs oflights; and (3) the disposition criterion ofthe

ALT is different and results in failure if two or more

errors are made during the responses of 27 test trials;

and (4) a very dim room illumination is used that

approximates the dim illumination in the ATC tower

cab at night. The ALT is a practical test because it

involves actual red, green, and white point sized lights

that accurately meet colorspecifications, and are within

the range ofintensities of aviation signal lights as seen

at night from the ATC tower.

The basis ofvalidity ofthe ALT is thatthe simulated

lights actually meet the specifications for colored aviation signal lights as determined by colorimetric mea-
surements in the present research. The ALT test was

given to individuals under both the design (dim)

illumination, and under conditions of a normally lit

office to determine the importance of variation in test

room illumination in this study. It was predicted that

test effectiveness would not be affected significantly by

this variation in ambient illumination. That prediction is based on the general similarity of the ALT test

stimuli to stimuli of the Farnsworth Lantern test,

which has been shown to be insensitive to wide variation in ambient illumination (Dain, Honson, & Ang,

1988; Steen, Collins, & Lewis, 1974).

METHODS

Subjects

The tests were evaluated using 106 subjects with

normal color vision and 85 with color vision deficiency. The ages of subjects with normal color vision

ranged from 18 to 58 yr with a mean age of31.2 yr and

a standard deviation of 11.1 yr. The ages of subjects

with color vision deficiency ranged from 18 to 61 yr

with a mean age of 35.0 yr and a standard deviation of

12.5 yr. Normals included 63 men and 43 women.

Color deficients included 84 men and 1 woman.

All subjects had at least 20/30 visual acuity in both

near and distant vision, as measured by the Bausch and

Lomb Orthorater vision tester. Subjects were recruited

through advertisements in newsletters at local colleges

and universities, and through local newspapers of the

Oklahoma City (OK) metropolitan area. All subjects

were paid an hourly wage.

Flight Progress Strips Test (FPST)

The FPST included a copy of each of 30 FPSs

selected from many thousands ofstrips obtained from

six en route centers; a day's output of strips was

obtained from each center. The 30 original strips were

used to make the CFPST. The FPSs were selected to be

representative of the type fonts of the two types of

computer printers that are used, the types of pens and

pencils used for handwriting on strips, and representative ofthe range of darkness/lightness normally found

in both computer printing and handwriting in the

actual work environment.

Each group of computer-printed characters in the

same line and column of an FPS, that did not contain

a blank space and were the same color, were considered

an item on the test section pertaining to computer

printing. Each handwritten altitude in the altitude

column was considered an item on the 21 strips (24

items) testing color vision for handwriting on strips.

The FPS copies and instructions for the test were

assembled in book form to make the FPST. Three of

the 30 strips were used for demonstration and 27

served as test items. Subjects responded by identifying

the colors red and black in computer printing on 6

strips containing 100 items and the color of handwriting on 21 strips containing 24 items. There was no

time limit for responding and performance was assessed in terms oftotal number oferrors and a pass-fail

score. An error consisted in misidentifying the color of

a red or black item on a strip. The failure criterion was

two or more errors.

Criterion Flight Progress Strips Test (CFPST)

Performance of the CFPST served as the criterion

for validation ofthe FPST. The CFPST was identical

to the FPST, with the exception that it involved the

actual FPSs, rather than the lithographic copies of

those same FPSs that formed the FPST. The CFPST

and FPST were essentially identical with regard to

form ofthe test book, administration procedure, illumination, and scoring. The individual strips in each of

the two parts of the FPST and CFPST, the computer

printing and handwriting sections, were presented in

different random orders in the two tests.

FPST Test Stand and Illumination

A test stand was constructed to hold the test books

in a convenient testing position, and to provide consistent and appropriate illumination for both the CFPST

and FPST. The stand is shown in Figure 1. This stand

was designed to provide an illumination level of 59 lux

at the center ofthe test page. That corresponded to the

average workstation illumination as measured at two

facilities, the Ft. Worth (TX) and Kansas City (KS) en

route centers. This illumination level was based on

measurements at four work stations at each facility.

Measurements were taken in the FPS bay at the location
ofthe strip farthest from the task light for the bay, with

the task light adjusted to the highest intensity. The

task light used at en route centers for illuminating

flight strip bays is a part of a standard console common

to all en route centers; it contains a cool white fluorescent lamp. The present task light also used a cool white

fluorescent lamp to make color characteristics of the

test illumination realistic. The specific fluorescent

tube used in the FPST light fixture was General Electric Part No. F4T5/CW. Each new tube was aged 50

hours before being used for testing and was tested to

verify the 59 lux illumination level, with a tolerance of

plus or minus 10 percent. Tubes were replaced after

200 h of usage. Measurements of illumination were

made using a Photo Research Corporation (Chatsworth,

CA) Fast Scan Spectroradiometer Model 702/703AM

and reflectance standard Model RS-1. The 59 lux

illumination level is comparable to illumination at

other centers as reported by Adams and Tague (1985).

Aviation Lights Test

The test for applicants for the terminal work option,

called the Aviation Lights Test (ALT), required the

identification of the color of simulated color-coded

aircraft lights in a dark environment as required for

location and identification of aircraft and their direction in night air traffic control tower operations. The

Aviation Lights Test made use ofthe body and mechanisms of the Farnsworth Lantern (Macbeth Corporation, Newburg, N.Y.), but modification of the

Farnsworth Lantern's red and green lights was required to make the simulated lights meet FAA and

ICAO specifications for aviation signal light colors

[Department of Transportation (DOT)/FAA, 1971;

ICAO, 1988]. White lights ofthe lantern met specifications. Appropriate custom filters were designed and

manufactured by Kopp Glass Company (Pittsburgh,

PA) and installed to modify the Farnsworth Lantern to

produce the chromaticities which are plotted in Figure

1 along with the gamuts, or boundries, specified by the

FAA and ICAO for aviation signal colors, red, green,

and white. The new red and green filters were designed

to make slight alterations in color, but maintain the same

luminous intensity of stimuli, and therefore, retain the

independence of color and intensity oflight points.

The simulated aircraft lights were formed by two

2.5 mm circular apertures arrayed vertically and separated by 13.0 mm. The resulting size oflight points at

the 2.438 m (8 ft) viewing distance was 3.5 arcminand

their separation in the visual field of view between

centers was 18.3 arcmin. The 18.3 arcmin separation

would simulate the case of an aircraft with a 25 ft wing

span at a distance ofapproximately 1,432 m (4,700 ft).

The luminance ofthe surface ofthe small circular light

sources in the lantern varied from 114.4 cd/m2 to

647.5 cd/m2 That range ofluminances oflight points

would approximately simulate aircraft position lights

at distances of 190 m (623 ft) to 1,237 m (4058 ft).

This assumes an aircraft position light luminous intensity of 40 cd for the shortest simulated distance and

300 cd for the longest simulated distance. Kaufman

and Christensen (1987) state that the 40 to 300 cd

range of position light intensities occurs among aircraft ofdifferent size in the U.S.; 40 cd is the minimum

intensity required by FAR. There were 9 pairs oflight

points that simulated aviation lights. The 18 light

points in the 9 pairs included 6 red, 6 green, and 6

white lights. The 9 pairs were presented in random

order three times for a total of 27 trials. The

misidentification of the color of either or both members of a pair constituted one error. The criterion for

failure was two or more errors in 27 trials. That

criterion was based on previous research with a similar

task in which normal trichromats rarely made errors,

and never more than one error (Mertens & Milburn,

1992a).

The illumination for the ALT test room, measured

at the position of the ALT, is approximately 1 lux

which is recommended as the upper limit for illumination at windows in the ATC tower (Illumination

Engineering Society of North America, 1972). This

nominal illumination level was achieved by placing a

small desk lamp fixture with an clear incandescent 7

watt, 120 vac bulb approximately 3 ft behind the

subject, with the lamp pointed toward the ceiling.

As mentioned in the introduction, the ALT test was

also administered in a room with normal office illumination. The illumination at the observer's eye was

1065 lux when measured in a horizontal plane and 500

lux when measured in a vertical plane.
The data for the two conditions will be differentiated by calling the task with low, ATC tower illumination ALT-L, and the task with the high, office

illumination ALT-H.

Diagnostic Color Vision Tests

The procedure used for classification ofdeficiencies

involved the Nagel Type I anomaloscope to classify

individuals with red-green color vision deficiency.

Other tests were used to detect and diagnose the rare

blue-yellow deficiencies that the Nagel anomaloscope

does not detect, but none of the latter were found.

These diagnostic methods were identical to those described by Mertens and Milburn (1992a).

Procedure

The Flight Progress Strips Tests, the Aviation Lights

Test, and diagnostic tests were administered at four

testing stations, each supervised by a trained laboratory technician. All anomaloscope testing was performed by the first author. The tests at each station

took approximately 30-40 minutes to administer. The

order of the two FPS tests was reversed for half of the

subjects, as was the order ofthe two ALT tests. At least

one other, different color vision test was given between

the two FPS tests and the two ALT tests. The testing

of each subject was performed in a three-hour test

session. Within each session the four testing periods

were separated by a 5-10 min break.

RESULTS AND DISCUSSION

Diagnostic Classification of Subjects

The number ofsubjects in each classification oftype

and degree of color vision deficiency are shown in

Table 1. Representation of all categories of red-green

color vision deficiency was obtained. The number of

normal trichromats was 106 and the total number of

deficients was 85. There were 35 deficients who were

protans (pro) and 50 deficients who were deutans

(deu). No individuals were found to have the blueyellow type of color vision deficiency.

Relation of Performance on Flight Progress

Strips Tests to Color Vision Classification

Pass/Fail Performance. The CFPST and FPST tests

permit comparison ofresponses to actual flight progress

strips and color copies of strips that comprise the

practical FPST. The criterion for passing was "no more

than one error" for the CFPST and the criterion was

the same for the FPST. That criterion was based on use

of the similar FPS materials in a previous experiment

(Mertens & Milburn, 1992a) in which no normal

trichromat made more than one error. The relationship of passing and failing to type and degree of color

vision deficiency is shown in Table 2. All individuals

with normal color vision passed both the CFPST and

FPST. Only one individual with normal color vision

made one error on the CFPST; normals made no errors

on the FPST. The probability of failing the flight

progress strips tests increased with degree of color

vision deficiency. No dichromats, who have the greatest reduction in color discrimination ability, were able

to pass either test. Only a few of the extreme anomalous category were able to pass both tests, and all were

deutans. At least halfofboth protan and deutan simple

anomalous trichromats were able to pass both tests.

Overall, the impact of color vision deficiency on color

discrimination in flight progress strips seems comparable in both protans and deutans in terms of pass/fail

scoring (but not in terms of total errors as discussed

below). Simple anomalous trichromats had approxiTable 1

Anomaloscope Classifications of Subjects

Anomalous Trichromat

Normal Simple Extreme

Trichromat Pro Deu Pro Deu

106 11 18 11 21

Dichromat

Pro Deu

13 11
Table 2

Number of Subjects Passing and Failing on the Original FPS

Test and the Copy FPS Test as a Function of

Type and Degree of Color Vision Deficiency

Anomalous Trichromat

Normal Simple Extreme Dichromat

Trichromat Pro Deu Pro Deu Pro Deu

CFPST Pass 106 7 11 0 3 0 0

Fail 0 4 7 11 18 13 11

FPST Pass 106 7 9 0 5 0 0

Fail 0 4 9 11 16 13 11

mately a 55% chance of passing, extreme anomalous

trichromats had approximately a 16% chance of passing, and no dichromats were able to pass.

Error Scores. The mean and standard deviation of

total error scores and 95% confidence intervals for the

mean are shown for the CFPST and FPST in Table 3

as a function of type and degree of color vision deficiency. The confidence intervals are presented for

comparison of means for color deficient groups and

normal trichromats. The low, near zero variance among

normal trichromats makes analysis of variance inappropriate for comparison of the means of color deficient groups and normals (Box, 1954). Error scores for

both CFPST and FPST increase with degree of color

vision deficiency, and the 95% confidence intervals for

the means of all categories of deficients typically did

not include the mean for normal trichromats; the only

exception was the small overlap of the confidence

interval for the simple protanomalous category on the

FPST. Similarly, the mean number oferrors for simple

anomalous trichromats in both CFPST and FPST

tasks is consistently below the 95% confidence interval

for extreme anomalous and dichromat categories for

both protans and deutans. Error scores are considerably higher than scores for the simple anomalous in

both dichromats and extreme anomalous ofboth types.

The mean error scores of the extreme anomalous

groups were lower than the means for the dichromat

groups, but within the 95% confidence intervals for

dichromats for both FPST and CFPST error scores.

Analyses of variance, with normal trichromats excluded, were performed with the MANOVA program

of the SPSS statistical system (SPSS, Inc., Chicago,

IL). The error scores were evaluated with analysis of

variance as a function oftype and degree ofcolor vision

deficiency as "between groups" factors and test (CFPST

versus FPST) as a "within groups" factor. The assumption of homogeneity of variance was rejected by the

Box-M test. Since analysis of variance is robust for

violation of this assumption when the number of

subjects in each group is equal, the method ofcompensating for heterogeneity of variance by randomly discarding cases to achieve equal cell numbers was used

(Tabachnick & Fidell, 1989; Toothaker, 1986). Findings ofthe "equal n" analysis are reported below. Each

of 6 groups formed by the two types and three degrees

of color vision deficiency had 11 cases. The main

effects of both type and degree of color vision deficiency were statistically significant. Protans made significantly more errors than deutans on the FPS tests

[F(l,79)=97.52, p<.001] and errors increased significantly with degree of color vision [F(2,79)=70.88,

/K.001], as discussed above. The interaction of type

and degree was also significant [F(2,79)=28.91,
Table 3

Errors on FPST and CFPST as a Function of Type

and Degree of Color Vision Deficiency

CFPST

Standard

Diagnosis Mean Deviation Low to High

Normal 0.01 0.10 0.01 to 0.03

Protans

Simple 1.91 2.39 0.31 to 3.51

Extreme 26.91 4.93 23.60 to 30.22

Dichro. 29.54 7.58 24.96 to 34.12

Deutans

Simple 3.50 5.83 0.60 to 6.40

Extreme 7.67 4.20 5.76 to 9.58

Dichro. 11.91 7.30 7.01 to 16.81

FPST

Normal 0 to 0

Protans

Simple 2.73 4.94 -0.59 to 6.05

Extreme 24.46 5.94 20.47 to 28.44

Dichro. 27.92 9.12 22.42 to 33.43

Deutans

Simple 2.94 5.35 0.28 to 5.61

Extreme 5.48 5.07 3.17 to 7.78

Dichro. 9.55 7.49 4.52 to 14.58

p<.001]; there was greater difference between protans

and deutans among extreme anomalous trichromats

and dichromats than among simple anomalous trichromats. There was also a significant difference for the

main effect of test, the within groups factor

[F(l,79)=6.65, p=.012]. No interaction involving the

test factor was significant. The significant main effect

of test reflects the fact that error scores tended to be

slightly higher in the CFPST test than in the FPST.

The dichromats and extreme anomalous groups averaged approximately two more errors on the FPST than

the CFPST. Mean errors for the simple anomalous

trichromats, however, were very similar in the two

tests; the simple protanomalous actually had 0.82

more errors on the FPST while the simple deuteranomalous had 0.55 more errors on the CFPST. As

shown below, any small difference in difficulty between the two tests was not reflected in pass/fail

performance. The number passing both tests was exactly the same (127), as shown in the marginal totals of

Table 4.

Validity of the FPST

The validity ofthe FPST was evaluated by comparing pass/fail performance on FPST to pass/fail performance on the CFPST. Cohen's Kappa (K), an index of

7
Table 4

Pass/Fail Performance on the FPST versus CFPST

FPST

CFPST

Pass

Pass 123

Fail 4

Total 127

Kappa=0.91

Fail

4

60

64

Total

127

64

191

agreement, was used to assess the validity ofthe practical test, as recommended by the National Research

Council-National Academy of Science (NRC-NAS)

Committee on Vision (1981). The index can be interpreted as the percentage agreement between test and

criterion variable, with correction for chance. The

relation of passing and failing on the FPST to passing

and failing on the CFPST is shown in Table 4. The

validity ofthe FPST for prediction of pass/fail performance on the CFPST was K = .91. That validity is high.

The miss täte, or probability ofpassing the FPST given

that the CFPST was failed was .06. The false alarm

rate, the probability of failing the FPST given that the

CFPST was passed, was .03. Those error rates are

considered acceptably low, and are comparable to

error rates ofthe better clinical color vision tests when

used to predictthe criterion ofnormal versus abnormal

classification by an anomaloscope test.

Reliability of the FPST

The FPSs of each test were split into two groups for

computation of split-half reliability coefficients, one

with odd and one with even numbered FPSs. The

"raw" correlation between the two forms "halves" of

the FPST was .91. The correlation between "halves" of

the CFPST was .94. Since split-half coefficients can be

affected by the particular selection of items that are

assigned to each half, Chronbach's alpha was computed as a more conservative estimate of reliability.

Chronbach's alpha is based on the average inter-correlation among the items of a test, or internal consistency

of items, and the number of items (Nunnally, 1978).

Since the "item" in this analysis was the error score for

all items on an FPS, there were much larger error scores

on some FPSs than others, thus yielding much different variances. Therefore, the "standardized item alpha" based on standardized item scores is cited for the

FPST and CFPST. The alphas obtained were .93 for

the FPST, and .95 for the CFPST. The alphas obtained

for the six FPSs ofthe computer printing subscale were

.91 for the FPST and .92 CFPST. The alphas obtained

for the 21 FPSs of the handwriting subscale were .89

and .92 for the FPST and CFPST, respectively. It can

be concluded that both FPST and CFPST tests and

their subscales have high estimated reliability.

Aircraft Lights Test

Pass/FailPerformance. The ALT-L and ALT-H permit comparison ofresponses to the ALT when administered in a low illumination similar to the illumination

at night in an ATC tower, and a relatively high illumination characteristic of an office. The number of

subjects passing and failing on the ALT are shown in

Table 5 as a function oftype and degree ofcolor vision

deficiency. The criterion for passing the ALT-L was no

more than one error; the criterion for the ALT-H was

the same. All individuals with normal color vision

passed both ALT-L and ALT-H. Only one error was

made by a normal in an ALT test and that was on the

ALT-L. The probability of failing the ALT increased

with degree of color vision deficiency. No dichromats

or extreme anomalous trichromats were able to pass

the ALT, with the exception of one extreme deutan

who passed the ALT-H test. The proportions passing

among simple protans and simple deutans were less

than 50%.
Table 5

Number of Subjects Passing and Failing on the ASL-L Test and the ASL-H Test as a

Function of Type and Degree of Color Vision Deficiency

Anomalous Trichromat

Normal

Trichromat Pro

Simple

Deu Pro

Extreme

Deu

Dichromat

Pro Deu

ASL-L Pass

Fail

106

0

4

7

7

11

0

11

0

21

0 0

13 11

ASL-H Pass

Fail

106

0

3

8

9

9

0

11

1

20

0 0

13 11

Table 6

Errors on ASL-L and ASL-H as a Function of Type and Degree of Color Vision Deficiency

ASL-L

ASL-H

Diagnosis

Normal

Protans

Simple

Extreme

Dichro.

Deutans

Simple

Extreme

Dichro.

Normal

Protans

Simple

Extreme

Dichro.

Deutans

Simple

Extreme

Dichro.

Mean Deviation

0.01 0.10

4.00 5.12

18.27 4.22

17.69 4.44

6.39 7.13

16.48 6.88

19.00 6.02

0

6.00

19.55

17.54

6.78

16.95

18.00

0

5.02

2.65

4.59

7.99

6.01

4.92

Low

-0.01

0.56

15.44

15.01

2.84

13.34

14.96

0

2.63

17.76

14.76

2.81

14.22

14.70

to

to

to

to

to

to

to

to

to

to

to

to

to

to

to

High

0.03

7.44

21.11

20.38

9.94

19.61

23.04

0

9.37

21.33

20.31

10.75

19.69

21.31

Error Scores for the ALT. The mean and standard

deviation oferrorscores and 95% confidence intervalsfor

the mean are shown in Table 6 as a function oftype and

degree of color vision deficiency. Errors increased with

degree of deficiency and the performance of protans and

deutans was similar. The mean of normals was zero or

near zero for both tests. The 95% confidence intervals of

all color deficiency categories did notinclude the mean of

normals, and the means for both simple anomalous

groups were below the 95% confidence limits for the

extreme anomalous and dichromat groups. Means for the

extreme anomalous were slightly higher than the means
for dichromats among protans and lower than dichromats

among deutans, but in both cases means were not outside

the limits of the other group.

The ALT error scores for color deficients were

evaluated by analysis of variance as a function of type

and degree of color vision deficiency as "between

groups" factors and test, ALT-L versus ALT-H, as a

"within groups" factor; normal trichromats were excluded. The same cases that were dropped in the FPS

analysis ofvariance were again dropped in this analysis

to achieve an equal number of subjects (11) in each

group in order to compensate for heterogeneity of

variance. Only the main effect of degree of deficiency

was significantin this analysis [F(2,60)=4l.l5,p<.001].

The main effects oftype ofdeficiency and test were not

significant, nor were any interactions. This result suggests that ALT performance in individuals with varying type and degree ofcolor vision deficiency is relatively

y

.9

.8

.7

.6

.5

.4

.3

.2

.1

.0

.0 .1 .2 .3 .4 5 .6 .7 8

520

510

500

COLOR LIMITS

ICAO

.9

.8

.7

.6

.5

.4

.3

Figure 1. Chromaticity diagram (CIE 1931) showing chromaticity of lights of the Aviation

Lights Test and the color limits for aviation signal colors as specified by the FAA and

ICAO.

10
insensitive to variation in test room illumination. The

relatively minor variations in test room illumination

normally occurring as a function of room size, lightness of walls and so forth, should not affect performance of individuals taking the test.

Validity ofthe ALT. The light point stimuli of the

ALT were validated physically with the computer

controlled spectroradiometer mentioned above. The

measured chromaticities oftest lights met the physical

color specifications for aviation signal red, green, and

white lighting as given in ICAO regulations and FARs.

The measured chromaticities of the red, green, and

white lights of the ALT are given in Figure 1, and are

plotted along with the gamuts for the three signal

colors as specified by the ICAO.

Reliability ofthe Practical Color Vision Tests. The

raw correlation between halves was .96 for both the

ALT-L and ALT-H tests. Reliabilities, estimated by

Chronbach's alpha, were .98 and .97 for ALT-L and

ALT-H tests, respectively. The three series of nine

light point pairs that were presented in each test were

considered subscales; alphas were .92, .93, and .92 for

the three subscales of the ALT-L. The alphas for the

three subscales ofthe ALT-H were .93, .92, and .92. In

summary, the reliabilities ofthe ALT tests were very high.

CONCLUSIONS

The present research is the third study in a series of

studies on the ATCS color vision standard that addressed three problems (1) whether a color vision

standard was needed (Mertens & Milburn, 1992a), (2)

whether FAA-accepted clinical color vision tests were

valid for screening ATCS applicants (Mertens &

Milburn, 1992b), and (3) the development, evaluation, and validation oftwo practical color vision tests

for the two largest options within ATC work, the en

route center and terminal options. While these studies

have shown that error in simulated ATCS color tasks

is rare in normal trichromats and that many individuals with color vision deficiency are prone to error, the

research has also shown that there are some individuals

with color vision deficiency that can perform the tasks

as well as normals. The research evaluating the validity

ofclinical tests has shown thatthe validity ofsome tests

is high and that the error rate is generally acceptable in

terms of not passing individuals who cannot perform

ATCS color tasks accurately. Those tests have higher

error rates in terms offailing some individuals who can

perform ATCS color tasks as accurately as normals.

The present research has shown that practical, jobsample color vision tests can be constructed that have

high face validity and also high demonstrated validity

in terms of selecting individuals who can perform

ATCS color tasks as accurately as normals, and that

also have very high reliability as required of good

selection tests. These two practical color vision tests

yield effective and fair color vision screening of jobrelevant color vision ability for ATCS applicants, and

have been in use for more than one year.

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12

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