Human Factors in Engineering and Design1

7/28/2019 Human Factors in Engineering and Design1

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CHAPTER 4. TEXT. GRAPHICS. SYMBOLS. AND CODES 119

frma f par 2 wuld be beer. The cmm percep f par 3 prbably sha he value fr cd b s mre ha wce ha fr . ad ha c s mreha hree mes a because we "see" he vlume f he blck raher ha herhegh. Par 4 crrecs he dsr by shwg he hree heghs ly. Tufe(1983) provides many such examples of perceptual distortions and providesuseful guidelines that would enhance the correct perception of the data dis-played.

SYMBOLSCivilization abounds with a wide assortment of visual symbols and signs thatare intended to convey meaning to us. Examples include symbols for men's andwomen's rest rooms (which often are less distinguishable from one anotherthan we would like them to be); symbols for windshield washers and wipers Q.fIsome automobile dashboard controls; and little icons presented on computerscreens of trash cans, file folders. and filing cabinets tosymboliz.e variouscomputer operations.

Comparison of Symbolic and Verbal SignsWhere there is some question as to whether to use a symbolic or verbal sign, asymbolic sign would probably be preferable if the symbol reliably depictedvisually what it is intended to represent. One argument for this (supported bysome research) is that symbols do not require the that words or shortstatements do. For example, a road sign showing a deer conveys immediatemeaning, whereas use of the words requires the recoding fromwords to concept. Note. however. that some symbols do not visually resemblethe intended concepts very well and thus may require \earning and recoding.A study that supports the possible advantage of symbols conducted by

Ellis and Dewar (1979) where subjects listened to a spoken traffic message(such as "w-way raffc") ad were he shw a slde f a raffc sg (eithera symbolic sign or a verbal sign) and asked to respond yes or no, depending onwhether they perceived the sign as being the same as the spoken message. Thiswas done under both visually "rdegraded" ad "degraded" cds. Themea reac mes, Figure 4-15, show a systemic superiority for thesymbolic signs, especially under the visually degraded conditions.

Objectives of Symbolic Coding SystemsWhen a system of symbols is developed, the objective is to use those symbolsthat best represent their referents (that is, the concepts or things the symbolsare intended to represent). This basically depends on the strength oftion of a with its This association, in turn, depends on either oftwo factors; any already established association [Cairney and Siess (1982) callthis and the ease of learning such an association.


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1000

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PART 2: INFORMATIONINPUT

FIGURE 4-15Mean reaction times of yes and no re-sponses to symbolic and verbal trafficsigns viewed under nondegraded and de-graded viewing conditions. (Source: Ellisand Deward. 1979. Fig. 1. p. 168.)

700'-:----'---,.--,.----- ---::---...--,--Nonoeqraded Degraded

A a mre specfc level. Chaper 3 we dscussed cera gudeles frusg cdg sysems: deecably, dscrmably, cmpably, mea-gfuless, ad sadardza. These gudeles are equally applcable hedesg f symbl sysems. Afer all, symbls are really jus aher frm fcdg.

Criteria for Selecting Coding SymbolsSome coding symbols already exist (or could be developed) that could be usedwith reasonable confidence. If there is any question about their suitability.however, they should be tested by the use of some experimental procedure.Various criteria have been used in studies with such symbols. A few criteria arediscussed below:Recognition On this criterion. subjects usually are presented with experi-

mental symbols and asked to write down or say what each represents.Matching In some investigations. several symbols are presented to sub-

jects along with a list of all the referents represented, and subjects are asked tomatch each symbol with its referent. A variation consists of presenting thesubjects with a complete array of symbols of many types and asking them toidentify the specific symbol that represents each referent. Sometimes reactiontime is measured as well as the number of correct and incorrect matches.


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CHAPTER 4 TEXT, GRAPHICS, SYMBOLS, AND CODES 121

Prefereces ad Ops I her crcumsaces peple are asked ex-press her prefereces r ps abu expermeal desgs f symbls.Examples of Code Symbol StudiesT llusrae he prcedures used I cde symbl sudes, we give a fewexamples.Mandatory-Action Symbols The first example deals with a set of so-called

mandatory-action messages and their respective symbols, illustrated in Figure4-16 (concerning use of protection devices for the ear, eye, foot, etc.) (Cairneyand Siess, 1982). These symbols were shown to a group of newly arrivedVietnamese in Australia, who were first told where the signs were to be usedand then asked to state what they thought each sign meant. A week later thesubjects were given a recall test in the same manner. Figure 4-16 shows, foreach symbol, the percentage of correct responses for both the origina! test (O~and for the second test (R). The results of this particular study show ratherdramatically how well a group of people with a different cultural backgroundcould learn the intended meaning of those particular symbols. (Only the firstsymbol did not come through very well.)This example illustrates the use of a recognition criterion and the desirable

objective of using symbols that are easily learned. even if the symbols are notinitially very recognizable.Comparison of Exit Symbols for Visibility When a -specific symbol has a

poor association with its referent, there can be a problem in selecting ordesigning a better symbol. One approach is to create alternative designs for thesame referent and to test them.Such a procedure was followed by Collins and Lerner (1983) with 18 alter-nate designs of exit signs, particularly under difficult viewing conditions simu-FIGURE 4-16Symbolsofmandatory-actionmessages used ina studyof recognitionand recallofsuch sym-bols.The percentagesbelowthe symbols are thepercentages ofcorrectrecognition,as follows:o = originaltest; R = recan1 week later. (Source: Adapted from Cairney and Siess, 1982,Fig. 1.).O()f)i)O1: Must use ear 2: Mustuseeye 3: Must use foot 4: Must use hand 5: Must use head 6: Must useprotection protection protection protection protection breathing

protection0 10% 20% 30% 50% 37% 13""R - 73 96 100 97 97 97


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122 PART 2: INFORMATION INPUT

lag a emergecy sua. (After all, you would like to be able 10 identifythe exit if a building were on fire!) The subjects were presented with 18designsof exit symbols 'under different levels of viewing difficulty (with very briefexposure time) and asked to indicate whether each was. or was not. an exitsign. Certain of the designs are shown in Figure 4-17. along with their percent-ages of error. (In reviewing the errors. it was found that certain symbols for"N ex" were cfused wh hse fr "Ex.") Cera geeralzas abuhe feaures f he bes sgs ca be made: (1) "flled" fgures were clearlysuperr ' "ule" fgures, (2) circular figures were less reliably identifiedthan those with square or rectangular backgrounds. and (3) simplified figures(as by reducing the number of symbol elements) seem beneficial.

Perceptual Principles of Symbolic DesignMuch of the research regarding the design of symbols for various uses has to beempirical. involving. for example, experimentation with proposed designs.However. experience and research have led to the crystallization of certainprinciples that can serve as guidelines in the design of symbols. Easterby (\967.1970), for example. postulates certain principles that are rooted in perceptualresearch and generally would enhance the use of such displays. Certain of theseprinciples are summarized briefly and illustrated. The.illustrations are in Figure4-18. Although these particular examples are specifically applicable to machinedisplays (Easterby, 1970), the basic principles would be applicable in othercontexts.

Figure to Ground Clear and stable figure-to-ground articulation is essen-tial. as illustrated in Figure 4-18a. In the poor, unstable figure, the direction inwhich the arrow is pointing is ambiguous.

AGURE 4-17Examples of a few of the 18 exitsigns used in a simulated emer-gency experiment. with percent-ages of errors in identifying themas exit signs. (Source: Adaptedfrom Collins and Lerner. 1983.)Green & White

% error -10Black & White Green & White

9 6

Red. White & Black Black & White40 42

Black & White0/0 error -+- 39

.,f'. .

---------------------------~. --.- -- .. -.~. ---


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CHAPTER 4 TEXT. GRAPHICS. SYMBOLS. AND CODES 123

1 (e) UnIty~IeA srmple shape IS readtlylperceived All parts of trns symbol heI wllhin a single boundaryI making a good symbolI

"'(EDGood. stable figure (d) SlmpltcrtyPoor. unstable figure(b) Figureboundary

~Good

(c) Closure

@mi~ .1 Closed figure., readily perceived Bxmimin=1 - Too much detail makes\ x, m/mrn a weak symbol Deiau outside makes aL__ .

-L- I___p_en_fi_gu_r....:e_-'- I rx;o;. symbol _has less impact ~

c::::>Poor

Poor

FIGURE 4-18Examples of certain perceptual principles relevant to the design of visual code symbols. Theseparticular examples relate to symbols used with machines. (Source: Adapted from Easterby,1970.)

Figure Boundaries A contrast boundary (essentially a solid shape) is prefer-able to a line boundary, as shown in Figure 4-18b.

Closure A closed figure, as illustrated in Figure 4-18c, enhances the per-ceptual process and should be used unless there is reason for the outline to bediscontinuous.

Simplicity The symbols should be as simple as possible, consistent with theinclusion of features that are necessary, as illustrated in Figure 4-18d.

Unity Symbols should be as unified as possible. For example, when solidand outline figures occur together, the solid figure should be within the lineoutline figure, as shown in Figure 4-18e.

Standardization of Symbolic DisplaysWhen symbol displays might be used in various circumstances by the samepeople, the displays should be standardized with a given symbol beingassociated with the same referent. One example of such standardization is thesystem of international road signs. A few examples are shown in Figure 4-19.The National Park Service also has a standardized set of symbols to representvarious services and concepts such as picnic areas, bicycle trails, and play-grounds.


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& 6) cg IT] WLIPPERY PEDESTRIAN DON'T BLOWO LEFT MEt:::HANICALROAD CROSSING rELEPHONE(RIGHT) TURN YOUR HORN HEI..P(3) Danger SigM (c) Information signs) Instruction signs

FIGURE 4-19Examples 01 a lew international road signs. These are standardized across manycountries. especially in Europe. Most 01 these signs are directly symbolic 01 their reierents.

CODESAs dscussed Chaper 3, smemes here s a eed have a cdg sysemha defes varus ems f a gve class. Fr example. varus specfcppes a plumbg sysem ca be cded dffere clrs, r varus ypes fhghway sgs ca be cded by dffere shapes. The ems be cded (such asdifferent pipes or different types of highway signs) are called . Thus, aspecific code such as an octagonal (eight-sided) road sign means "stop." Thetypes of visual stimuli used in such circumstances are sometimes called coding

. Some visual coding dimensions are color, geometric and othershapes, letters. numerals, flash rate (of a flashing light), visual angle {thepositions of hands on a clock), size (variation in the size of circles), and even"chart junk" [the term used by Tufte (1983) for the gaudy variations in shadingand design of areas of graphs].

Single Coding DimensionsWhen various coding dimensions can be used, an experiment can be carried outto determine what dimension would be best. One such study done by Smith andThomas (1964) used the four sets of codes shown in Figure 4-20 in a task ofcounting the number of items of a specific class (such as red. gun, circle, orB-52) in a large display with many other items of the same class. (The density ofitems, that is. the total number of items in the display, was also varied.) Theresults, shown in Figure 4-21, show a clear superiority for the color codes forthis task; this superiority was consistent for all levels of density.Although these and other studies indicate that various visual coding dimen-sions differ in their relevance for various tasks and in various situations,

definite guidelines regarding the use of such codes still cannot be laid down.Recognizing this, and realizing that good judgment musteater into the selectionof visual codes for specific purposes, we see that a comparison such as thatgiven in Table 4-5 can serve as at least partial guidance. In particular, Table 4-5indicates the approximate number of levels of each of various visual codesthat can be discriminated, along with some sideline comments about certainmethods.


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xl outhandisk ofIe, orsity of) Thees forirnen-lions,Iown.ections thatile 4-5codesertain

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CHAPTER 4: TEXT. GRAPHICS. SYMBOLS. AND CODES 125

~~~~~~_-; .rC;' _ ~.'S'eFm~lc;-,OrCOle_R-C+,r'C_OI2e,;_1~

r"ongle! Dlom.~nJ StarGMeometriCforms A!.:" I. *

---tt- .. i ! =-:i---~r-----IRadar I' Gun : Alrcrott Missile Shipllitary J I! -- 1

Lymbol:' ~-_.- --~--.--t-i--""'----t-.-- - t-_-.. IIoiMr -1I (~~~o;:11 Green 8lue! White Red YellowI'~ (2SG5/BI lS8G4/51 I (SyB/41 (SR4/9) (10YR6/iO)L~tatIOO) IFIGURE 4-20Four sets of codes used in a study by Smith and Thomas. The notationsunder the color labels are the Munsell color matches of the colors used.(Source: Smith and Thomas, 1964. Copyright 1964 by the American Psy-chological Association and reproduced by permission.)


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TABLE 4-5SUMMARY OF CERTAIN VISUAL CODING METHODS(Numbers refer 10 number of levels which can be discriminated on an absolute basis underoptimum conditions.)Alphanumeric

Color (of surfaces)

Single numerals, 10; single letters, 26; combinations, unlimited. Good;especially useful for identification; uses little space if there is goodcontrast. Certain items easily confused with each other.Hues, 9; hue, saturation, and brightness combinations, 24 or more.Preferable limit, 9. Particularly good for searching and counting tasks.Affected by some lights; problem with color-defective individuals.*t10. Preferable limit, 3. limited space required. Good for qualitativereading.t15 or more. Preferable limit,S. Generally useful coding system,particularly in symbolic representation; good for CRTs. Shapes usedtogether need to be discriminable; some sets of shapes more difficult todiscriminate than others.t24. Preferable limit, 12. Generally satisfactory for special purposes suchas indicating direction, angle, or position on round instruments likeclocks, CRTs, etc.5 or 6. Preferable limit, 3. Takes considerable space. Use only whenspecifically appropriate.6. Preferable limit, 4. Use only when specifically appropriate, such as torepresent numbers of items. Takes considerable space; may beconfused with other symbols.3-4 Preferable limit. 2. Use only when specifically appropriate. Weakersignals may be masked.tPreferable limit, 2. limited applicability if receiver needs to differentiateflash rates. Flashing lights, however, have possible use in combinationwith controlled time intervals (as with lighthouse signals and navalcommunications) or to attract attention to specific areas.

Color (of lights)Geometric shapes

Angle of inclination

Size of forms (suchas squares)Visual number

Brightness of lightsFlash rate of lights

*Feallock et al. (1966).tM. R. Jones (1962).j:Grether and Baker (1972).Muller et al. (1955).

surface clrs. varyg prmarly hue. Hwever. appears ha, wh ra-g. peple ca lear make upward f a cuple f dze such dscrmaswhe cmbas f hue, saura. ad lghess are prepared a re-duda maer (Feallock et al., 1966). When relatively untrained people are touse color codes. however. the better part of wisdom would argue for the use ofonly a small number of discriminable colors.In general. color coding has been found to be particularly effective for"searching" tasks-tasks that involve scanning an array of many differentstimuli to "search out" (or spot). or locale. or count those of a specific class.This advantage presumably is owing to ,the fact that colors "catch the eye"more readily than other visual codes. Examples of searching tasks include theuse of maps and navigational charts. searching for items in a file. and searching


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CHAPTER 4: TEXT. GRAPHICS. SYMBOLS. AND CODES 127

for color-codd lcric wirs of som spcific color. Cris (1975) analyzed theresults of 42 studies in which color codes were compared with other types ofcodes and found that color codes were generally better for searching tasks thanmost other codes (geometric shapes. letters, and digits).Christ also found that color codes were better for' 'identification" tasks than

were certain other codes, but color codes were generally not as good for suchtasks as letter and numerals were. In this sense. an identification task involvesthe conceptual recognition of the meaningfulness of the code-not simplevisual recognition of items of one color from others (such as identifying redlabels-from all other labels). Thus, we can see the possible basis for theadvantage of letters and numerals, since they could aid in tying down themeaning of codes (such as grade A or size 12).In general, then, color is a very useful coding dimension. but it is obviously

not a universally useful system.

Multidimension CodesChapter 3 included a discussion of multidimension codes. indicating some ofthe variations in combining two or more dimensions. Heglin (1973/ recom-mends, however, that no more than two dimensions be used together if rapidinterpretation is required. In combining two visual codes. certain combinationsdo not "go well" together. Some simply cannot be used in combination. Thecombinations that are potentially useful are shown as Xs in Figure 4-22.Although combinations of codes can be useful in many circumstances. they arenot always more effective than single-dimension codes.

FIGURE 4-22Potential combinations of coding systems for use in muJDdimensioncoding. (Source: Adapted from Heglin, 1973, Tables VI-6, VI22.)

~ cQ~ 0o cc ~ '!!0 ~ '" (;~ 0-(; '" c ~ cc Q 2, '" .c (; ~" o, ~ ,E 0 '" "! ' u '" 0'0 , .c N ro 0 ~ cU Z !/l !/l -, U. ...J


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128 PART 2: INFORMA nON INPUT

DISCUSSIONI ur vryday livs. w ar bmbarded wh scads f ex, graphcs. symbls,ad cdes. Ths chaper ly scrached he surface f huma facrs ssuesvlved wh he dsplay f such frma. I he frma age whcreasg use f cmpuers, mre ae wll be pad huma facrsssues vlved he dsplay f frma a frm ha ca be quckly adaccuraely used whu placg a burde he recever. Sofwar packagssuc as word procssors, daa base prgrams, r fle maageme ules fefal r succeed he markeplace based hw well frma, bh hescree ad hardcpy mauals, s preseed. Desg f scree layus adsruc mauals wll cue be areas whch huma facrs wll makebeefcal crbus.

REFERENCESBarfeld, W., ad Robless, R. (1989). The effects of two- or three-dimensional graphicson the problem-solving performance of experienced and novice ~~;on makers.

8, 369-385.Blakemore, C.; and Campbell. F. (1969). On the existence of neurones in the humanvisual system selectively sensitive to the orientation and size of retinal images.

, 203, 237-260.Boff, K., Kaufman, L., and Thomas, J, (eds.) (1986). perception

, vol. I: New York: Wiley.Booher, H. (1975). Relative comprehensibility of pictorial information and printedwords in proceduralized instructions. 17,266-277.

Broadbent, D. (1977). Language and ergonomics. 8, 15-18.Brown, C. (1988). design guidelines. Norwood, NJ: Ablex.Burg, A. (1966). Visual acuity as measured by static and dynamic tests: A comparativeevaluation. 50,460-466.Cairney , P., and Siess, D. (1982). Communication effectiveness of symbolic safety signswith different user groups. 13,91-97.

Christ, R. (1975). Review and analysis of color coding research for visual displays., 17,542-570.

Collins, B. and Lerner, N. (1983). (NBSIR82-2685). Washington, DC: National Bureau of Standards.

Cornog, D., and Rose, F. (1967, February).vol. 2: (NBS Misc. 262-2). Washington, DC:

Government Printing Office.Cushman, W. (1986). Reading from microfiche, a VDT, and printed page and subjectivefatigue. 28(I), 63-73.

Easterby. R. (1967). Perceptual organization in static displays for man/machine sys-tems. 10, 195-205.

Easterby, R. (1970). The perception of symbols for machine displays. , 13,149-158.

Ellis. J . and Dewar, R. (1979). Rapid comprehension of verbal and symbolic traffic signmessages. 21, 161-168.

Human Factors in Engineering and Design1

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