Naval Submarine Medical Research Laboratory

NSMRL Report 1164 10 December 1990

IDENTIFICATION OF COLOR CODED TARGET LINES OF

DIFFERENT ORIENTATIONS ON CRT SCREENS

S. M. Luria

David F. Neri

Naval Aerospace Medical Research Laboratory

Matthew J. Shim

Released by:

R. G. Walter, CAPT, DC, USN

Commanding Officer

Naval Submarine Medical Research Laboratory

Approved for public release; distribution unlimited

20031216 193

2- 7s
IDENTIFICATION OF COLOR CODED TARGET LINESOF DIFFERENT

ORIENTATIONS ON CRT SCREENS

S. M. Luria

David F. Neri

Naval Aerospace Medical Research Laboratory

Matthew J. Shim

NAVAL SUBMARINE MEDICAL RESEARCH LABORATORY

NSMRL REPORT 1164

NAVAL MEDICAL RESEARCH AND DEVELOPMENT COMMAND

RESEARCH WORK UNIT 65856N-M0100.001-5003

Approved and released by

R. G. WALTER CAPT, DC, USN

Commanding Officer

NavSubMedRschLab

Approved for public release; distribution unlimited
SUMMARY PAGE

THE PROBLEM

To determine if the ability to match the color of a target line presented on a CRT varies with its orientation.

THE FINDINGS

When the target tracks were one pixel wide, performance was significantly worse for diagonal tracks than for horizontal or vertical tracks. When the target tracks were two pixels wide, there

were no significant differences with orientation. Performance was not affected by the presence of colored distractor lines.

APPLICATION

The use of color coding with target tracks only one pixel wide will result in more errors of color matching for diagonal lines. Designers of color-coded displays should be aware that extensive color coding should be used only with target tracks two or more pixels wide.

ADMINISTRATIVE INFORMATION

This investigation was conducted under Naval Medical Research and Development Command

Research Work Unit 65856N-MO1OO.001-5003. It was submitted for review on 10 October 1990, approved for publication on 10 December 1990, and designated Naval Submarine Medical Research Report 1164.

ii
Abstract

Current passive broadband sonar "waterfall" displays are monochromatic,

but color may be added in the future. One possible use of color would be to

have the operator assign different colors to the different target tracks.

The speed and accuracy of matching a colored target line on a CRT to a

standard set of colors was measured as a function of the orientation of the

target line. With lines one pixel wide, performance was significantly worse

for diagonal than horizontal or vertical lines. There were no significant

differences when the width of the line was doubled. Performance was not

affected by the presence of colored distractor lines.

iii
Current passive broadband sonar "waterfall" displays are monochromatic,

but it is possible that color may be added in the future. One possible use

of color would be to have the operator assign different colors to the

different target tracks.

We assume that in using color, alphanumeric information about the

targets would be displayed in the same color as the relevant target track,

and the operator would want to be able to associate as quickly and

accurately as possible a given track with its alphanumerics. We have

examined the question of how many colors an operator could recognize or

recall without undue confusion (Luria, Neri, & Jacobsen, 1986; Jacobsen &

Neri, 1985; Jacobsen, 1985). In the initial study, only one target track

was displayed (Luria, Neri, & Jacobsen, 1986); subsequently, several target

tracks were displayed to see if they detracted from the ability to focus on

the track of primary interest (Luria, Neri, Shim, & Bivenour, 1990).

In these studies, the target track was always a vertical line on the

display. On actual sonar displays, however, the target track can appear at

various angles and orientations. The question arises, what would be the

effect of variations in the target track orientation on performance? In

displaying target tracks at different orientations, it was immediately

apparent that, despite unchanging "instructions" to the computer, the narrow

(one pixel wide) tracks varied in width depending on their orientation.

They varied in width depending on the color as well. Even if the width were

constant, the color for a narrow stimulus could vary because of the

variations in the pixels which happen to be illuminated at different

orientations (Cf. Merrifield, 1987). This variability according to both

color and orientation appears to be characteristic of shadow-mask CRTs.

Would this variability at supra-threshold luminances have a significant

effect on the operator's ability to respond accurately and quickly to the

different colors?

There is a well known perceptual phenomenon which is related to this

problem: the so-called "oblique effect". The threshold visibility of fine

lines varies with their orientation; horizontal and vertical lines are more

detectable or yield higher visual acuity than oblique lines (Higgins &

Stultz, 1948, 1950; Leibowitz, 1953; Ogilvie & Taylor, 1958; Nachmias, 1960;

Luria, 1963; Campbell, Kulikcwski, & Levinson, 1966; Mitchell, Freeman, &

Westheimer, 1967; Pointer & Hess, 1990; Taylor, 1963). This effect, which

is quite evident at threshold, declines, however, when the visual stimuli

are clearly visible (St. John, Timney, Armstrong, & Szpak, 1987). Moreover,

Kelly (1975) has reported that there is no oblique effect for the detection

of chromatic stimuli. It is, therefore, not likely to play a part in the

present study. Any effects on performance will for the most part be due to

the physical variations in the stimuli with changes in orientation. To

investigate any such effects, we have repeated our previous experiments with

colored lines of different orientations.

1

INTRODUCTION
T

DG

Figure 1. The display. The target line (T), shoin here in the vertical position, was presented either alone or with the other five lines colored dark blue (DB), dark green (DG), light green (LG), purple (PRP), and red (R). The target line was also presented in the horizontal position, at 45 deg to the right, and at 45 deg to the left.

2
MEIHOD

Subjects

Eight staff members of the laboratory volunteered to participate. All

were color normal, according to the Hardy-Rand-Rittler pseudo-isochrcinatic

plates and had 20/20 acuity, with their spectacle corrections, if necessary.

Apparatus

The stimuli were presented on an Advanced Electronics Design, Inc.

Color Graphics and Imaging Terminal, Model 1024, under the control of a

Digital PDP 11/04 minicampter. A series of circular stimuli was arranged

in the pattern of a telephone pushbutton keypad: a 3x3 matrix plus one

additional stimulus centered below these (Figure 1). Each circle was 1 an

in diameter, separated by 0.75 an fram the adjacent stimulus. The total

arrangement measured 4.5 cm wide by 6.2 cm high.

A telephone

of the subject. circular stimuli

pushbutton response keypad was placed on a table in front

The arrangement of its 10 keys was identical to that of the

on the display.

Th e circles were of different colors and brightnesses and were always

present. The C.I.E. coordinates and luminances were measured with a Photo

Research Spectroradiameter, Model PR 703A, and are listed in Table 1 and

shown in Figure 2.

TABLE 1

The chromaticity coordinates and luminances

of the colors

Target

Color

Dark Blue

Yellow

Red

Aqua

Purple

White

Pink

Orange

Green

Light Blue

Distractor

Color

ChrCnraticity

x y

.15

.43

.61

.25

.27

.29

.37

.56

.30

.17

.09

.45

.35

.38

.16

.31

.35

.36

.52

.13

chromaticity

x y

umbinance

cd/m2

2.7

42.7

17.8

9.8

2.2

44.7

13.1

7.0

31.4

12.0

umdinance

cd/m2

Dark Blue

Dark Green

Light Green

Purple

Red

.16

.30

.30

.28

.61

.13

.55

.59

.21

.36

2.1

26.4

44.1

5.9

13.8

3

l
.400

Figure 2. C. I.E. chrczaticity coordinates of the stinuai.

4
The target line was 3 an long and was presented in one of four

orientations: vertical, horizontal, and 45 deg (diagonal right) or 315 deg

(diagonal left). Although the camputer was instructed to produce a line 1

pixel wide, the actual width of the lines varied about a mean of 1 mm,

depending on the color and orientation. The target line was presented in

the center of the display with the top of the vertical line 6 an below the

lowest circle or the horizontal line 7.5 cm below the lowest circle. At the

viewing distance of about 60 an, the circular stimuli subtended .95 deg

visual angle; the vertical line subtended 2.9 deg visual angle in length and

about 0.01 deg visual angle in width.

The target could be presented alone or in the presence of five other

lines which were always in the same arrangement (Figure 1). These

additional lines (referred to as distractors) were red, dark blue, purple,

light green, and dark green (see Table 1).

Procedure

Each subject was first given a series of training runs before starting

the experiment. The outlines of the 10 circles were presented in the

appropriate color but the circles were unfilled. One second after a warning

tone, one of the circles filled with its color. The subject pressed the

button on the keypad that corresponded to the position of the filled circle

as quickly as possible. The button press caused the circle to return to

its original unfilled condition. After a two-second delay, another warning

tone sounded, followed by another circle being filled. No color matching

was involved. The circles were presented in random order until the subject

made 7 correct responses to each circle. One training run thus comprised 70

correct responses and took about three or four minutes. The ccmputer

recorded which button had been pushed and the reaction time (RT). Incorrect

button pushes were not included in the mean RTs. The training runs

continued until the Rr had no longer decreased for three runs. The stable

mean Ras indicated the times required to respond using each button in the

keypad without having to match the colors. The training runs not only gave

the subjects practice in responding, but provided them an opportunity to

learn the positions of the colors.

During the experiment, the target line appeared one second after a

warning tone. It was identical in color to one of the (now filled) circles.

The subject matched the line to the correct color as quickly as possible by

pressing the corresponding button. Each orientation was presented during

the test session. The order of the four orientations was counterbalanced

for the eight subjects.

RESULTS

Experiment 1

In the first study, the target line was presented without the

distractors. To get the RT for the color matching, the stabilized practice

response time for each button was subtracted fron the corresponding color

matching time for each subject. Table 2 gives the mean RI of the color

5
matches for each orientation. There were no differences in RT among orientations, but the reaction times to the different colors varied significantly (F= 14.7, p < .0001).

TABLE 2

Mean Reaction Times (sec) to the Colors

at the Different Orientations

in Experiment 1

Horiz Vert Diag (R) Diag (L)

Dark Blue .54 .48 .62 .55

Yellow .52 .46 .54 .49

Red .71 .64 .58 .65

Aqua .66 .62 .68 .66

Purple .37 .33 .38 .34

White .48 .44 .48 .46

Pink .61 .46 .47 .50

Orange .59 .77 .58 .61

Green .60 .66 .59 .59

Lt. Blue .71 .72 .67 .66

Mean .58 .56 .56 .55

S.E.M. .033 .045 .030 .033

The number of matching errors was significantly greater for the diagonal lines than for the horizontal or vertical lines, according to a Friedman non-parametric analysis of variance (X2 = 12.6, p < .01). Table 3 shows the errors for each color at each orientation. It should be noted that because it was obvious that some of the errors were simply motor errors (e.g., pushing button 8 instead of 10 just below it, or matching orange to blue), any errors which occurred no more than twice when summed over the eight subjects were not counted in preparing this table. Thus the smallest number of errors in a cell in Table 3 is three.

It is clear that the same matching errors are made regardless of the target orientation. The only error consistently made to a light blue target is to match it to dark blue; the difference with orientation is that far more errors were made when the target was a diagonal than when it was horizontal or vertical. It was not always the case, however, that the diagonal target always led to increased errors: the dark blue target was erroneously matched to light blue when it was horizontal or vertical but

not when it was diagonal. Green was matched to aqua equally when it was diagonal or not.

6
TABLE 3

Color Matching Errors

at the Different Orientatios

in Experiment 1*

.zontal Vertical Diag. (R)

Blue Lt. Blue -

'4) (8)

- Pink (4) Pink (9)

orange (19)

Green (9) Green (13)

Diag. (L)

Pink (4)

Orange (16)

Green (16)

Target

Dk. Blue

Yellow

Red

Aqua

Purple

White

Pink

Orange

Green

Lt. Blue

TOTAL

* If there were fewer than three errors in

subjects, they were not included.

a cell summed over the eight

7

Hor!

Lt.

- Red (12) Red (8)

- - Aqua (3)

Dk. Blue Dk. Blue Dk. Blue

(13) (16) (29)

34 69 76

Red (12)

Aqua (4)

Dk. Blue

(9)

29
Experiment 2

In an attempt to reduce the orientation effect, the computer was progranned to produce target lines 2 pixels wide. Again there were obvious differences in the apparent width of the lines with changes in orientation and color. We assumed, however, that the color would be more definite under

any condition. The same subjects again participated. The orientations were again counterbalanced.

RESULTS

Table 4 presents the Rrs to the colors at each orientation. Again the RIs to the different orientations were not significantly different, although the RMs to the different colors once again varied significantly (p < .0001). These RTs were appreciably shorter, indicating that the wider target tracks made the matching task easier.

TABLE 4

Mean Reactions Times (sec) to the Colors

for the Different Orientations

in Experiment 2

Horiz Vert Diag (R) Diag (L)

Dark Blue .38 .43 .44 .35

Yellow .31 .35 .25 .34

Red .41 .40 .51 .43

Aqua .53 .43 .50 .44

Purple .16 .17 .18 .16

White .26 .19 .27 .30

Pink .33 .29 .32 .33

Orange .41 .50 .45 .49

Green .42 .43 .35 .38

Lt. Blue .38 .51 .52 .55

Mean .36 .37 .38 .38

S.E.M. .032 .038 .038 .034

There were now no significant differences in the number of errors for

the four orientations according to a Friedman analysis of variance by ranks

(X2 = 2.43, p < .50). Table 5 shows the breakdown of errors to the different colors as a function of target orientation. Again, those errors which occurred no more than twice when summed over the eight subjects were ignored in this table. Only three matching errors were made with any frequency; light blue was again identified as dark blue; orange was identified as red; aqua was identified as green. These errors were not made systematically with orientation.

8
TABLE 5

Color Matching Errors

for the Different Orientations

in Experiment 2*

Target Horizontal Vertical Diag. (R)

Dk.Blue

Yellow

Red

Aqua

Purple

White

Pink

Orange

Green

Lt. Blue

TOrAL

Green (4)

Red (3)

Dk. Blue

(3)

10

Diag. (L)

Orange (4)

Green (3)

Red (5)

Dk. Blue

(3)

15

* If there were fewer than three errors in

subjects, they were ignored.

a cell sunmed over the eight

9

- Green (3)

Red (7) Red (5)

Dk. Blue - (3)

10 8
Experiment 3

Finally, the target line, again two pixels in width, was presented in the presence of the distractors. Again, the same subjects participated.

RESULTS

Table 6 gives the RTs to the colors as a function of orientation. The RTIs were not significantly different for the four orientations, according to

an analysis of variance. The number of matching errors was not significantly different between orientations, according to a Friedman analysis of variance by ranks (X2 = 0.71, p < .90) for the various orientations. Table 7 gives the breakdown of errors to the colors at the various orientations; again, those errors occurring no more than twice in a cell were not counted. The errors made were similar to those made in the first two experiments; primarily, light blue was identified as dark blue. The large number of errors for the first diagonal was due to one subject. Since a given color was repeated until ten correct matches had been made, this color was repeatedly presented and repeatedly mismatched by this subject.

TABLE 6

Mean Reaction Times (sec) to the Colors for the Different Orientations

with the Distractors

in Experiment 3

Horiz Vert Diag (R) Diag (L)

Dark Blue .38 .38 .38 .37

Yellow .26 .21 .22 .26

Red .39 .38 .47 .55

Aqua .38 .45 .45 .49

Purple .16 .29 .25 .26

White .27 .26 .21 .21

Pink .26 .32 .32 .26

Orange .47 .50 .50 .50

Green .41 .40 .53 .45

Lt. Blue .51 .47 .49 .54

Mean .35 .37 .38 .39

S.E.M. .034 .030 .039 .132

10
TABLE 7

Color Matching Errors

for the Different Orientations

with the Distractors

in Experiment 3*

Target Horizontal Vertical Diag. (R) Diag. (L)

Dk.Blue Lt. Blue

(3)

Yellow -

Orange (5) Orange (8)

Aqua

Purple

White

Pink

Orange

Green

Lt. Blue Dk. Blue

(7)

TOMAL 15

* If there were fewer than three errors in

subjects, they were ignored.

a cell summed over the eight

Finally, the RTs were significantly higher in the first experiment

than in the other two experiments (F = 70.20, p < .0001), but they were not

significantly different in the second and third experiments (F = 0.004, p <

.95), indicating that the distractors did not impair performance.

The error rate was, as expected, significantly higher in the first

experiment according to a Friedman analysis of variance by ranks (X2 = 7.00,

p < .05).

11

Red (6)

Dk. Blue

(5)

11

Red (12)

Dk. Blue

(18)

38

Dk. Blue

(5)

5
DISCUSSION

Using this shadow-mask CaI, varying the orientation of the target line altered its width and its apparent color when it was programmed to be only one pixel wide. This resulted from changes in the excitation of the red- green-blue triads as orientation varied, and these changes affected performance with a very thin target line. When, hwever, the width of the target line was increased to two pixels, the changes in color which resulted from changes in orientation were insignificant. Apparently, if the target line is very narrow, changes in width affect performance; if the target line is two pixels wide, the changes in width do not have a significant effect on performance. It seems reasonable to assume that the same would be true for even wider target tracks. Similarly, Carter and Carter (1988) have reported that colors of symbols subteRding less than 30' are less distinct than those that subtend at least one deg. visual angle.

It should be kept in mind that these stimuli were all well above threshold. Performance might be affected much more seriously if very narrow target lines were close to threshold.

These results confirm previous results (Luria, et al., 1990). First, the distractors did not significantly degrade performance, and, second, the results again show very strongly the lack of symmetry or "transitivity" of the matching errors. Although light blue was repeatedly misidentified as dark blue, the reverse occurred much less frequently; similarly, aqua was often confused with green, but not the reverse; and red was confused with orange ruch more than orange was confused with red.

12
ACENOWLEDMTS

We thank CAPr Paul Weathersby, MSC, USN for suggesting this study and

Ms. Kelly Johnson who collected most of the data.

13
REFAUNCES

Campbell, F.W., Kulikcwsid, J.J., & Levinson, J. (1966). The effect of orientation on the visual resolution of gratings. J. Physiol. (London)

187, 427-436.

Carter, R.C., & Carter, E.C. (1988). Color coding for rapid location of

small symbols. COLOR res. and aplication 13, 226-234.

Higgins, G.C. & Stultz, K. (1948). Visual acuity as measured with various orientations of a parallel-line test object. J. Opt. Soc. Am. 38, 756-758.

Higgins, G.C. & Stultz, K. (1950). Variations of visual acuity with various test-object orientations and viewing conditions. J. 0pt. Soc. Am. 40, 135-137.

Jacobsen, A. R. (1985). Effect of set size on time to recall color coded

information. NSMRL Rep. 1044.

Jacobsen, A.R. & Neri, D.F. (1985). Effect of set size on color

recognition. NSMRL Rep. 1041.

Kelly, D.H. (1975). No oblique effect in chromatic pathways. J. Opt. Soc.

Am. 65, 1512-1514.

Leibowitz, H. (1953). Somie observations and theory on the variation of visual acuity with the orientation of the test object. J. O. Soc.

Am. 43, 902-905.

Iuria, S.M. (1963). The effect of body-position on meridional variations in

scotqpic acuity. Am. J. Psychol. 76, 598-606.

Luria, S.M., Neri, D.F., & Jacobsen, A.R. (1986). The effects of set size

on color matching using CRT displays. Human 29, 49-61.

Luria, S.M., Neri, D.F., Shim, M.J., & Bivenour, R. (1990). Effect of

extraneous color-coded targets on identification of targets on CRT

displays. NMRL Rep. 1154.

Merrifield, R.M. (1987). Visual parameters for color Cafrs. In H. John

Durrett (Ed.) Color and the Caopter, New York: Academic Press, p. 77.

Mitchell, D.E., Freeman, R.D., & Westheimer, G. (1967). Effect of orientation on the modulation sensitivity for interference fringes on

the retina. J. 0pt. Soc. Am. 57, 246-249.

Nachmias, J. (1960). Meridional variations in visual acuity and eye movements during fixation. J. Opt. Soc. Am. 50, 569-571.

Ogilvie, J.C. & Taylor, M.M. (1958). Effect of orientation on the

visibility of fine wires. J. Opt. Soc. Am. 48, 628-629.

14
Pointer, J.S. & Hess, R.F. (1990). The contrast sensitivity gradient across

the major oblique meridians of the human visual field. Vis. Res. 30,

497-501.

St. John, R., Timney, B., Armstrong, K.E., & Szpak, A.B. (1987). Changes in

perceived contrast of suprathreshold gratings as a function of

orientation and spatial frequency. Spatial Vis. 3, 223-232.

Taylor, M.M. (1963). Visual discrimination and orientation. J. Opt. Soc.

Am. 53, 763-765.

15
UNCLASSIFIED CCrl IDITV Ci ACIicrATInrq OF THIS PACGE

19. ABSTRACT (Continue on reverse if necessary and identify by block number)

Current passive braodband sonar "waterfall" displays are monochromatic, but color

may be added in the future. One possible use of color would be to have the operator

assign different colors to the different target tracks. The speed and accuracy of

matching a colored target line on a CRT to a standard set of colors was measured as

a function of the orientation of the target line. With lines one pixel wide,

performance was significantly worse for diagonal than horizontal or vertical lines.

There were no significant differences when the width of the line was doubled.

Performance was not affected by the presence of colored distractor lines.

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NSMRL Report # 1164 NA

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Naval Submarine Medical (If applicable) Naval Medical Research and Development

Research Laboratory Command

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11. TITLE (Include Security Classification) (U) Identification of color coded target lines of

different orientations on CRT screens

12. PERSONAL AUTHOR(S)

S. M. Luria, David F. Neri. and MatthewJ._Shim

13a. TYPE OF REPORT 13b TIME COVERED 14. DATE OF REPORT (Year,Month,Day) 15. PAGE COUNT

Interim FROM TO 1990 December 10 15

16 SUPPLEMENTARY NOTATION

17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)

FIELD GROUP SUB-GROUP Sonar displays; Spatial orientation; Color coding;

CRT displays; Color matching