Effects of chromatic adaptation on color naming

Effects of chromatic adaptation on color naming

Vision Res. Vol. 7, pp. 645-653. Pagamon Press1967. Printed inGreatBritain. EFFECTS OF CHROMATIC ADAPTATION ON COLOR NAMING GERALD H. JACOBSAND HEI...

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Vision Res. Vol. 7, pp. 645-653.

Pagamon Press1967. Printed inGreatBritain.

EFFECTS OF CHROMATIC ADAPTATION ON COLOR NAMING GERALD

H. JACOBSAND HEINZ A. GAYLDRD

Department of Psychology and Defense Research Laboratory, The University of Texas, Austin. Texas 78712 (Received 21 November 1966) THE EFFECTSof

chromatic adaptation have almost always been assessed in the context of some variant of a matching task.* There are several reasons for believing that it might be additionally useful to be able to examine chromatic-adaptation effects in other ways. For instance, in some cases of interest matching becomes very difficult. One such case is where the change is rapid, as the fleeting chromatic changes seen as after effects of intense stimulation. Another involves conditions under which it becomes qualitatively difficult to match precisely; for example, when the change also involves a large shift in spectral saturation. In addition, as BOYNTONand GORDON (1965) have recently emphasized, matching studies fail to provide information about the appearances of stimuli and this feature seems of special interest in a number of cases where chromatic adaptation is involved, as when intense adaptation is used to functionally inactivate one or more receptor mechanisms (BRINDLEY, 1953). For these reasons, in the experiment reported here, we have sought to examine the effects of chromatic adaptation on a color-naming response, utilizing as a basis the recent demonstration (BOYNTON and GORDON, 1965) that direct color naming, used in the appropriate manner, provides a measure as sensitive and reliable as the more traditional matching techniques. APPARATUS AND METHOD

The optical system utilized is shown schematically in Fig. 1. The adaptation beam originated from a tungsten source, Si, passed through a series of lenses and a filter holder, was brought to a focus at a shutter, Sh, and to a final lens, Lr, where it was presented to s2

FIO. 1. Schematic diagram of the apparatus. 1 References to many such studies may be found in MACADAM (1956). 645

646

GERALD

H. JACOBSAND HEINZ A.

GAYLORD

the eye in Maxwellian view subtending 40’ of visual angle. The head of the observer was held firmly in Maxwellian view by means of an adjustable head holder. The test beam originated from a grating monochromator, M, the slits of which were adjusted to yield a stimulus having a spectral bandpass of 15 nm. The beam from the monochromator was also brought to a focus at the shutter and followed the same path as the adaptation beam to the final lens. A third beam originating at Sz was not used in the experiment reported here. The shutter controlled which of the two beams reached the eye. A first-surface mirror was mounted on the shutter arm: when the shutter was in one position the adaptation beam reached the eye; with the shutter in the other position the adaptation beam was blocked and the test beam was reflected onto the final lens and into the eye. The position of the shutter arm was controlled by two sets of opposed relay coils, alternate activations of which drove the shutter arm up and down generating variable length pulses from either beam. This control system provided shutter rise-fall times of about 4 msec as measured by placing a phototube at the position of the eye and monitoring the output on an oscilloscope. Equal-luminance values were calculated for spectral stimuli from 440-650 nm in 10 nm steps and were obtained during the experiment by inserting neutral step filters into the test beam. The adaptation stimuli were produced by inserting various filters into the adaptation beam. Data are reported here on four adaptation conditions: “neutral” for which only neutral density filters were interposed into the tungsten beam, and three conditions of chromatic adaptation produced by using Wratten filters, W92, W74, and W98 (with dominant wavelengths of 646, 538, and 452 nm) in conjunction with various neutral filters. For the observations reported below, the luminance of both the adaptation and test lights was always set at 195 ft L. The color-naming technique was essentially that described by BOYNTONand GORDON (1965). Subjects were instructed to identify the stimulus by utilizing only the color names : blue, green, yellow, and red. They were, in addition, allowed to use two of these names in combination when they felt that more than one was appropriate, indicating in such cases which component was judged primary and which was secondary. Any stimulus was repeated on request of the subject. Preliminary training was given for each adaptation condition although, as pointed out previously (BOYNTONand GORDON,1965), little training appears to be necessary for reliable performance of this task. Only one adaptation condition was examined in any session; each experimental period started with a five-minute adaptation to the appropriate light. Following the initial adaptation period, test stimuli of 300 msec duration were automatically presented once every 18 set throughout the session. Between stimulus presentations the observer viewed the adaptation light. Daily sessions consisted of four presentations of test wavelengths from 440 to 650 nm, in 10 nm steps, with the entire series presented in predetermined random order. Each of the adaptation conditions was run for six daily sessions; thus the results for each are based on 24 responses to each test wavelength. Three adult males with normal color vision served as the observers throughout an extended series of observations, a portion of which constitute the results reported here. RESULTS Color-naming functions for each condition were computed by using the procedure reported by BOYNTONand GORDON(1965). Each stimulus was given a total value of three points; all of these were assigned when a single response was given, e.g. blue. Where

Effects of Chromatic Adaptation on calor Naming

647

both a primary and secondary response occurred, two points were assigned to the primary category and one point to the secondary category, e.g. blue-green would score two points for blue and one for green. The total number of points was then cumulated for each of the four naming categories at each test wavelength. Thus there was a total of 72 points at each test wavelength. The color-naming functions so derived are shown for the neutral condition in Fig. 2 where they are plotted as percentage of total point values.

FIG, 2. Color-naming functions for neutral adapt&ion. Top: observer G; middle: obacrverf;

bottom: observer T. Differences in procedure and stimulus conditions preclude any detailed comparison of the color-naming functions presented in Fig. 2 with the data reported in previous colornaming experiments (THOMSON, 1954; BWIRE,1963; BOYNTON, SCHAFER and NEUN,1964; BOW-KINand GCIRDUN, 1965). Nevertheless, the functions appear muoh as would be expected from these previous descriptions. For the conditions of the present experiment, stimuli below about 490 nm are seldom called anything but blue. Similarly, spectral stimuli beyond about 620 nm produce only the primary response of red. For all observers, a stimulus in the region of 5X-580 nm was nearly always described as containing only yellow. For two subjects, unique green responses were generated by stimuli of about 520 nm whereas for observer T, the maximal green response occurred at somewhat longer ~avelen~s, in the nei~~urhood of 535 nm. It might be noted that the two rather different wavelengths found to produce unique green responses correspond reasonably well to the two spectral locations described by RUBIN (1961) as characterizing unique green in a sample of normal observers.

GERALD H. JACOBS AND HEINZ A.GAYLORD

WAVELENGTH nm FICA3. Color-naming functions for W92 adaptation. Details as for Fig

iii

Y lu

100

r

450

500

550

WAVELENGTH

600 -

-

650

rim

FIG. 4. Color-naming functions for W98 adaptation. Details as for Fig. 2.

Effects of Chromatic Adaptation on Color Naming

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20 -

450

500

t.00

5so

WAVELENG.TH

-

650

nm

FIG. 5. Color-naming functions for W74 adaptation. Top: observer G; bottom: observer J.

Color-naming functions were calculated in a similar manner for the three conditions of chromatic adaptation. They are presented in Figs. 3-5 where the results of the W92 adaptation are given in Fig. 3, the results of the W98 adaptation in Fig. 4, and the results of the W74 adaptation in Fig. 5. For the latter condition, data were obtained from only two of the observers. An examination of these functions shows a number of characteristics of change in spectral appearance under chromatic adaptation. As indicated from the results of numerous matching studies and casual observations, the results of chromatic adaptation are, in general, to cause a loss of the hue normally seen in that part of the spectrum from which the adapting light is taken and to produce a relative enhancement in the complementary hue. This effect is clearly seen for all three adaptation conditions and for all observers. Thus, adaptation with the W92 filter produces a striking increase both in the number of green responses and the spectral range over which they occur, with a coincident loss of red responses. A similar change is seen for the observations under W98 adaptation: an enhancement in the yellow response function and a large loss in the blue function. The same is also true for the W74 condition where both blue and red response functions are enhanced while, at the same time, the response functions for green and yellow are depressed. Indications of the reliability of the color-naming data were obtained by calculating split-half, rank-difference correlations for each color-naming function for every observer under all conditions of adaptation. The correlation coefficients so obtained are given in Table 1. It is apparent that the color-naming task was performed with very high reliability by all three observers. There is some indication that reliability is slightly higher under neutral adaptation than under chromatic adaptation since the mean reliability coefficient for the neutral condition was 0.98 while similar coefficients for the red, blue, and green adaptations were 0.95, O-96, and 0.90 respectively. An indication that there was little change in performance of this task over the extended series of observations was obtained by re-running one of the subjects under neutral adaptation some four months after the original data were taken. The two sets of data thus obtained correlated almost exactly as well as did the split-halves for either set individually. In conjunction with previous reliability measures for this task (BOYNTON,SCHAFERand NEUN, 1964; BO~NTONand GORDON,

650 TABLE 1.

GERALD H. JACOBSAND HEINZ A. GAYLORD SPLIT-HALF,

RANK-DIFFERENCE

COEFFICIENTS OF CORRELATION

FOR EACH OF THE COLOR-NAMING

FUNCTIONS

Adaptation

Observer

Neutral

G

Blue 1.00

J T W92

G

J T W98

G

J T w74

G

J

Color-naming

function

0.99

Green 0.93 0.98 0.97

Yellow 0.97 0.98 0.99

Red 1.00 0.94 0.99

0.96 o-97 0.98

0.90 0.98 0.87

0.82 0.99 0.92

1.00 1.00 I.00

O-94 0.97 0.90

0.97 0.88 0.96

0.98 0.98 0.99

0.99 0.96 0.98

0.79 1.00

0.83 -

0.95 -

I.00 0.80

1.00

1965), it seems clear that color naming, used in the proper manner, is capable of yielding data possessing high reliability. In matching studies of chromatic adaptation the attempt is made to find numerous pairs of wavelengths that produce the same effect under different adaptation conditions. A similar kind of result can also be obtained from the color-naming data of this study. One way to generate such pairs is as follows. Every possible type of response is given an arbitrary scale value. This scale value is then multiplied by the frequency of occurrence of the response and the resulting values cumulated at each of the test wavelengths. In the present case we have considered 12 different responses from blue-red, blue, blue-green, and so on, through the spectrum to red-blue and have assigned scale values running from 0 for the blue-red response to 11 for the red-blue response. We have dropped from this analysis the very infrequent cases in which complementary colors appeared in the same response, e.g. blue-yellow. The values thus cumulated produce a single function for any adaptation condition and, in general, the function goes from a low value in the blue part of the spectrum to a high scale value in the red portion of the spectrum. Such scale functions have been calculated for all observers at each of the adaptation conditions and are shown in Fig. 6. As can be seen in Fig. 6, the functions for the different observers at each adaptation condition are similar in form, reflecting the fact that their color-naming functions are basically alike. There are, however, drastic differences between the functions generated under different adaptation states. The slopes of these derived functions reflect the rate at which the frequencies for the various response classes change from point-to-point in the spectrum. For example, in the neutral functions the frequencies are changing rapidly in the vicinity of 500 nm so the slopes of the scaled functions are steep at this point. In fact, it appears as if the slope of the function corresponds rather well to the acuteness of wavelnegth discrimination at the same spectral points. Some evidence for this was obtained by determining the size of the wavelength change necessary to produce a criterion change in point value at each of the test wavelengths for the neutral functions. This procedure produced a X vs. Dh plot which resembles very much the wavelength discrimination functions obtained in the more usual context. A similar operation might also be performed

Effects of Chromatic

Adaptation

on Color Naming

651

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t

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WAVELENGTH FIG. 6. Scale functions for four adaptation

conditions.

-

nm

See text for details of computation.

Obscrvcrs: *G,oJ,xT.

on the functions obtained under chromatic adaptation. It has not been done because there are apparently few data on wavelength discrimination under chromatic adaptation available for purposes of comparison. From the data presented in Fig. 6, pairs of wavelengths yielding the same point value under different adaptation conditions have been calculated for all observers for neutral against each of the three chromatic-adaptation conditions. The results of these calculations are displayed graphically in Fig. 7. For example, consider the effects of W98 adaptation

g

450

v

-_I 450

500

--z-600

150

650

NEUTRAL

500

550

6OC

b!

ADAPTATION

FIG. 7. Match functions for neutral vs. chromatic-adaptation conditions derived from the scaling procedure. Observer legends as for Fig. 6. Neutral adaptation vs.: A. W92; B. W98; c. w74.

652

GERALD H. JACOBSAND HEINZ

A. GAYLORD

shown in Fig. 7B. In that plot it can be seen that for observer G, 550 nm seen under neutral adaptation produces the same scale value as does 486 nm seen under W98 adaptation. In general, chromatic adaptation moves the point for equal scale values toward the spectral locus of the adaptation light. Thus the W98 condition displaces the effect toward the short-wavelength end of the spectrum while the effect of W92 adaptation is in the opposite direction, i.e. all spectral points producing the same effect have been displaced toward the long-wavelength end of the spectrum. For the W74 condition the displacement is in both directions, toward the longer wavelengths for stimuli from 480-530 nm, and toward the shorter wavelengths for the stimuli in the 530-620 nm range. At about 530 nm there is no shift, so at that point the same effect is obtained under either neutral or W74 adaptation. The analysis of shifts in spectral appearance following chromatic adaptation illustrated in Fig. 7 yield results which can be compared to earlier matching studies. The direction of the shift seen here corresponds to that demonstrated in a number of previous studies EVANSand NEWHALL,1957; MACADAM,1956). It is not possible, (HESS, 1893 ; Bw, however, to compare the magnitude of the adaptation effect in any quantitative manner given the differences in procedure and stimulus conditions among the various studies. Thus the conditions of the present experiment, which include a higher level of adaptation than many of the other studies, a large adaptation and test area which were spatially coincident, and a brief test interval, produce very sizable changes in spectral appearance. It should be re-emphasized that the neutral adaptation used as a comparison here was actually the feeble yellow of a tungsten lamp. There are also considerable resemblances between the results of this experiment and a recent study by AKITA, GRAHAMand HSIA (1964), which used a color-production technique to evaluate chromatic induction effects. In that study it was found that the compensatory shift in wavelength setting necessary to maintain the same color in the presence of an inducing color was always in the direction of the background color much as the shift described here was always toward the adaptation wavelength. DISCUSSION In general, the indices of change in spectral appearance following chromatic adaptation as measured by color naming are as expected. Thus the color responses appropriate to that part of the spectrum complementary to the adaptation light increase both in frequency of occurrence and in their spectral range while, at the same time, the responses normally given in the region of chromatic adaptation become constricted into a narrower spectral zone. Although there is considerable inter-observer variability apparent in the data taken under neutral adaptation, the magnitude of changes seen between that condition and chromatic adaptation are very similar. Indications of the size of the chromatic-adaptation effects can be obtained from color-naming data in a number of ways. The approach utilized here gives information on pairs of spectral wavelengths which produce the same effect under different adaptation conditions and, again, these seem to agree with previous experiments. A few general comments about the color-naming technique seem indicated. This study, in agreement with those of BOYNTONet al. (1964, 1965), shows clearly the high reliability of color naming as a response measure. Not only are these data reliable, but there is strong indication that little practice is necessary to achieve this reliability, suggesting the possibility that the technique would be quite useful with untrained observers. Insofar as the results here are like those obtained in matching studies, it seems likely that the technique also

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produces valid data. Finally, although color naming has been described as being an insensitive measure (GRAHAM, 1965), it is our opinion that the color-naming technique, used in the right way, may indeed prove to be as sensitive as many of the more usual techniques of visual psychophysics. In particular, some unsystematic observations made during the course of this experiment suggest, as has THOMSON (1954), that wavelength discrimination can be measured as sensitively by color naming as by other methods. Acknowledgement-This work was supported by a grant from the National Atronautics and Space Administration (Grant R-129) through U.S. Navy ORice of Naval Research Contract Nom-3579(04) and

the Department of the Navy, Naval Ship Systems Command Contract NObsr-93124. REFERENCES AKITA,M., GRAHAM,C. H., and HSIA,Y. (1964). Maintaining an absolute hue in the presence of different background colors. Vision Res. 4, 539-556. BEARE,A. C. (1963). Color-name as a function of wavelength. Am. J. Psychol. 76, 284-286. B~YNTON, R. M., SCHAFER,W., and NEUN, M. E. (1964). Hue-wavelength relation measured by colornaming method for three retinal locations. Science, N. Y. 146, 666-668. B~YNTON, R.

M. and GORDON,J. (1965). Behold-Briicke hue shift measured by colcr-naming technique.

J. opt. Sot. Am. 55, 78-86. BKINDLEY,G. S. (1953).

The effects on colour vision of adaptation to very bright lights. J. Physiol.,

Lond. 122, 332-350. BURNHAM,R. W., EVANS, R. M., and NEWHALL, S. M. (1957). Prediction cf color appearance with different adaptation illuminations. J. opt. Sot. Am. 47, 3542. GRAHAM, C. H. (1965). Discriminations that depend on wavelength. In Visim and Visaal Perception, pp 350-369, edited by GRAHAM,C. H., Wiley, New York.

HESS, C. (1893). Ueber die Unvereinbarkeit gewisser Ermiidungsercheinungen des Sahorgans mit der Dreifasertheorie. Archs. Opthal., N. Y. 39,45-70. MACADAM, D. L. (1956). Chromatic Adaptation. J. opt. Sot. Am. 46, 500-513. RUBIN,M. L. (1961). Spectral hue loci of liormal and anomalous trichromats. Am. J. Opthal. 52, 166-172. THOMSON,L. C. (1954). Sensations aroused by monochromatic stimuli and their prediction. Opticu Acta 1, 93-102. Abstract-Some effects of chromatic adaptation have been evaluated in the context of a colornaming task. Color-naming responses were obtained from three observers under both neutral and chromatic-adaptation conditions and those data were used to generate indices of the magnitude of change in spectral appearance under various adaptation conditions. A few general comments on the use of color-naming procedures are made. R&&-On &value certains effets de l’adaptation chromatique dans le contexte d’une tiche de noms de couleurs. Les rtponses de noms de couleurs Ctaient obtenues de trois observateurs B la fois dans des conditions d’adaptation neutre et chromatique, et on tirait de ces don& des index de la grandeur du changement dans I’appatence spectrale sous des conditions &adaptation varih. On fait quelques commentaires &n&aux sur l’utilisation des m&hodes des noms de couleur. Zussammenfassung-Mit Hilfe einer Farbbenennungsmethode wurden einige Effekte der chromatischen Adaptation ausgewertet. Die Farbbenennungen wurden von drei Beobachtern sowohl unter neutralen Bedingungen als such im Zustand der Farbadaptation gemacht. Die erhaltenen Werte lieferten Indizes, die die GrliBenordnungsunterschiede in der spektralen Erscheinungsform unter verschiedenen Farbadaptationszustiden angebm. Einip allgemeine Bemerkungen iiber den Gebrauch von Farbbenennungsmethoden werden gemacht. HeKoTopbte OCO~~HHOCTH xpoMaTaqecKolt axanTauIia 6bma 0npeneneHbt B OITblTaXIlO Iia3bIBaHUH)UBeTOB.BTU AaHHbIe6bma ITOJTj”IeIibI Ha TpeX HCIIbITyeMbIX KBK B yCJIOBWIXHefiTpZUIbHOti,TPK H XpOMaTH’ECKOttaAaIITaUUH H IIOTOM 6b1~n.i &%monb3oBaHbI AJIR pa3pa6orsm EHXeKCoB BWIWIHHbI H3MeHe& CITeKTpaJ’IbHbIX nposBneHHtt npa pas= yc.noslllIx axarnaumi. AenaIoTcr HeKoTopbre o6me 3aMe’IaHIfR 06 WCIlOJlb30BaHIiH [email protected]‘AypbI Ha3bIBaHHSI I.IBeTOB.

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