Cone spectral sensitivity and chromatic adaptation as revealed by human flicker-electroretinography

mk+l Ru, vol. 11, pp. 2742. PorpmoD Pmu 1971.Printedia circa% l?ma&l.

CONE SPECTRAL SENSOR AND CHRO~TIC ADAPTATION AS REVEALED BY HUMAN FLICICERELE~RO~~O~~~ P. PADMOS and D. VANNO~REN Institutefor PerceptionRVO-TNO, Kautpwca5, swstertxx&The N&cdar~ds (Received 19 Mu&r

1969; in revised form 30 March 1970)

INTRODUCTION

IN ms paper we will describe experiments on the effects of chromatic adaptation on the spectral sensitivity function, measured with ERG techniques. Many experiments of this kind have been reported with psychophysical methods (Wxtarrr, 1947; BRINDLBY, 1953; BDYNTON, 1956; STILES, 1959; WALD,1964; WALRA~EN, VANHOXST and LEEBEBK, 1966),but ERG methods have special advantages: one can choose a constant response criterion at various levels rather than being forced to use a threshold technique or a matching method. Moreover the ERG, by its nature, gives information about the early stages of the visual process, Until now, however, experiments conducted with ERG techniques have not been successful in unambiguously demonstrating the effects of chromatic adaptation (GRANDA and BIBRSIWWIF, 1963; CAVOMUS, 1964). We have therefore concentrated on improving stimulation and recording techniques in order to detect small changes in the sensitivity function induced by coloured backgrounds of various intensities. The nature of the adaptation effects found is further analyxed with the help of experiments on the recovery of the response after offset of the background. They give valtile information helping to separate the neural adaptation effects from the bleaching of the photopigments. Finally, to provide a link between psychophsyical and ERG data, some parallel psychophysical experiments were performed. The main problem with ERG experiments is that unless special precautions are taken the response to a single flash is dominated by rod activity. Even at high levels of light adaptation the rod response, caused by stray light, may still be present (ARMINGTON, 1953; AMEN, 1959; G~ANDAand B~RSKX)RF, 1963). The most general method for suppressing rod responses is to use a stimulus flickering at 20-35 Hz (e.g. JOHNSON and Cox~swnnr, 1954; lbUvltNsToNand BIBRSMH~P, 1956; DODT, CoprrrJHnvg~ and Gw, 1958). Go= and Gm (1962) have shown that for rod retinas the response at 25 Hz is not more than 20 per cent of the maximum obtainable value, whereas the responses of cone retinas drop to 20 per cent only at 80 Hz. Experiments on rod monochromats (I~oDT,VAN LWEI and SCHMIDT, 1967; Goun~~ and Gvnxu~, 1964) report Sicker fusion of rods at 15-20 Hz. Using 32 Hz DoDT, Couxuu~vna and GUNKEL(1958) recorded a sensitivity function for normals strongly resembling the extrafoveal cone sensitivity curve of WALD (1945). A productive variation of the flicker technique was developed by CAVOMVS (1964) who alternated two spectral colours at 40 msec, thus producing 50 Hz flicker. By equating the 27

P. PADMOSAND D.

28

VAN NORREN

responses for different wavelength pairs he also obtained a sensitivity curve almost identical to the one measured by Wald. However, the strongest effect of chromatic adaptation that could be achieved in this case was a change of the order of 0.1 log relative sensitivity. This might be attributed to the fact that at higher.stimulus rates the responses to the individual &ours become mixed. An elegant technique used to avoid stray light and to stimulate cones exclusively was developed by JOHNSON, %GCS and SCKICK(1966). By 180” phase alteration of a barred pattern it was possible to get responses which reflected extrafoveal spectral sensitivity. U~o~uuately the response amplitude, even without a background, was only of the order of 1 pV, Chromatic adaptation would then cause such a decrease in response amplitude that reliable detection of sensitivity becomes impossible. Suppression of rod activity by background illumination is possible, of course (e.g. VAN LITHand m, 1968; AIBA, ALPSRN and MMSEIDVJ~AG, 1967),but it cannot be recommended in experiments on chromatic adaptation since the extent to which the photopic sensitivity itself is changed by the background is unknown. In view of these difficulties, it is not surprising that no selective effects have as yet been found with certainty. The selective effect found by ARMMOTON and TIDE (1954), ARMKNGTON (i959), and GRANDA and BIER~DORP (1963) must be attributed to suppression of rod activity with blue adaptation.

TAELEl. cou>vR FILTER9USED Colour

White Red cir?%n Blue

Fifter

(KoCo ‘;“;;

2800°K)

sdrott (double interfemnce) wratten 4sa

FOR ADAPTATION-FIELD

Max. retinal itfumination (trolands) 1.3 3.2 2.0 6-3

x x x x

10’ 10” los 10+

Equivalent wav&ngth*

(urn) 647 506 467

Half-bandpass’ (nm)

33 ::

t Equivalent wavelength is &tined as the median of the EaTAYAcurve; half-bandis defined as the transmission width at half the maximum value. See also BR~NDL~Y (1953). EA = spectral emigsion of lightsource, TA = spectral transmission of filter, VA= spectral sensitivity for the peripheral retina as measured by WALD (1945).

conespectral ,$ial&wy ana-

Adaptation

29

Calilmtionofoptic8

nxaauedatthefocalpointofthe Forerch~~~dltatheanergyofthestimulusbeun~ditsctly output kas by means of a fast, calibrated, vacuum thermocoupb(Hilger&WattsmodelFT17),combined with a lock-in voltmeter @rower model 131, tee below) operated at 13 Hz. For each colour * the trans~nPIaf~~ofWaVClCllOth~~~.Forthefbul&aritivitycurvcaarmJIcarrectionotthe to account for the non-inMtesimal handwidth of the stimulus cMremesoftherpcctrumwas~ filters.Forinterf&wwfUterr\ = 4S6theenergyreadingofthe tbarmocouple needed a small cormction, due toaSlir&amdsid&and. ThsrsttivollXUiI& tythroughthebroadhandcolour5Rersintheadaptingheamwasde&mmed photom&vz mruur&thehu&anceofaLamhextr&ctorillui&atedbytheorrtpptbam.Flkker usedtomakethe maswments.Thevaiueintrolandswasdsannmodby~the~output through the Schott interferencefilter (half-handpass 15 MI) with the c&&ratedthermocoupk. sahject$ D wtthg, H.R.R. and T.M.C. pscudoirochroOmoftheauthot3(Pp)semedasasubjcct. ~tcmi~a2”prychophydat(~)~~~clPveprovadhimtabsanonwl~ mrt.His~~~inthe~~ofthcspsarum,wu~o9glog~tlouortlynthscIE ammabqa etting, H.R.R. (protan, vahms.Tb8otberaut&t(WJQwaaaprotanopeaaxmbgtohia medium), T.M.C (protan third degree) tests, and his psychophysical 2” spectml sensitivity curve (la log uuitdownintheredregion). ’ pcopertiesof subject PP we checked all important TomakesurethatweamnotmporGngidiosyncmw 6ndings qualitatively on another normal trichromat. Durinothe exp&mental sessions the subjectwas lying on a bed in an ekctrically shielded dark room, his head Bxed in a pbster impression. Thcpupilwasdiktedbytheuseofamydriatic(~~).AHsnka’typccontect~elcctrodewPs fixed to the right eye. Two Ag-AgCl &&odes, one glued in the middb of the forehead, the other just above the right eye, served as ground and reference, rupectively.

Recording equipment Electrical response! was recorded by two methods. The fust was by amplification (bandpass g-100 Hz) and averaging in a CAT computer. Depending on the amplitude, 5o-200 responses were suflicient to obtain an acceptable signal-to-noise ratio. The second method employed the principle of “‘phase sensitive rectScation*’ (also called “synchronous detection”), performed by a commercially available lock-in voltmeter (Brewer, model 131). This instrument enables the on-line measurement of the fundamental component of a low-voltage, noise-contaminated, periodic input. By means of a frequency selector card, the instrument drives the light chopper at the desired speed and analyzes the ERG-response at the corresponding frequency. The standard operating frequency for determining spectral sensitivity was 40 Hz. In this way, the lock-in voltmeter gives the amplitude of the ERG-response to 40 Hz flicker as a D.C. voltage, with an amplitude resolution better than 0.5 pV, within a sample time of 6 sec. This method offers the immense advantage of on-line detection of the ERG output, and artefacts such as blinking, eyemovements, and fixation errors can immediately be recognized by the experimenter.

30

P.PADMOSAND D. VAN NORREN

Procedure

As moderate light adaptation before the experimental session appeared not to affect the results, no dark adaptation period had to precede the experimental session. Just before, and 5 min after the experiment a standard stimulus was presented in order to check both stimulus and recording equipment. The response to the standard stimulus showed a variability not more than 15 per cent over the experiment period of more than half a year. With the CAT measurements spectral sensitivity was determined by measuring intensity vs. response for each stimulus wavelength and then taking the intensity required for a criterion peak to peak response. Determination of spectral sensitivity generally took a full session of 45 min. With the lock-in voltmeter spectral sensitivity was measured on line. The experimenter inserted as many neutral density filters as were required to make the response equal to a criterion value. The output was continuously recorded by an inkwriter. After each filter adjustment the phase setting of the instrument was checked and if necessary corrected. In this way the determination of a spectral sensitivity for eight wavelengths took not more than 15 min all together. At least 2 min before the chromatic adaptation experiments started, the coloured background was switched on. The recovery of the response during dark adaptation was measured by recording, by inkwriter, the output of the lock-in voltmeter as a function of time, at a constant stimulus level. It was necemary to do this in two subsequent measurements in which the' phase of the reference signal of the voltmeter was set 90” apart because of the great changes in phase angle between stimulus and response during recovery. By taking the square root of the sum of the squares of the two outputs, the output of the voltmeter at optimum phase setting was reconstructed. The ratio of the two outputs gave the tangent of the phase-angle between stimulus and response. In the psychophysical experiments to measure the spectral sensitivity, care was taken to make the differences in procedure with the ERG measuremen ts as ins@itjcant as possible.The experimenter imerted neutral density filters in the stimulus pathway, asking the subject if he could see the 40 Hz monochromatic stimulus flicker. The t-old crlterlon for determining sensitivity was “just perceptibk fiicker”. The subject ts, even the contact glass remamed inserted. The idea wasinthesamepe&ionaswithtbaERGmeasuremen of using this method came up during pilot expe&ents. In response vs. intensity meaJurcmQI ts, it became clear that the intensity at which the ERG response was completely buried in noise came very close to the intensity at which the subject reported the flicker as no longer visible. For an evaluation of this method see discussion. EXPERIMENTAL

RESULTS

Waveform of the response In experiments with response averaging techniques it is usual to take the peak to peak value of the waveform as a quantitative measure of the response. In fact this method makes most sense if the peak to peak value is the only aspect of the response that changes as a function of the stimulus condition. If one wants to compare measurements of peak to peak values with the output of the lock-in voltmeter, which measures the amplitude of the f&lamental component of the response, one has to be certain that the response does not change with the stimulus conditions. In actual fact the CAT recordings do demonstrate that the shape of the response was fairly constant over the various stimulus conditions. An even better test for constancy of waveform was performed by means of the lock-in voltmeter. The instrument normally measures the fundamental component of the response, but is able, after a slight modBc.ation, to measure the second harmonic as well. The third harmonic can be neglected, since it corresponds to a frequency of 120 Hz, which would require mechanisms in the eye faster than ever reported. The waveform can be considered as the sum of the fundamental and second harmonic. Constancy of waveform requires that the ratio of fundamental and second harmonic is constant and that in the case of a phase change the phase of the second harmonic changes twice as fast as the phase of the fundamental. This was tested by determining the spectral sensitivity curve both on a criterion response of the fundamental and of the second harmonic. No systematic differences could be found between the two luminosity functions (F test, p > O-l).

Cone Spectral Sensitivity and Chromatic Adaptation

31

Check for rod contributionand stray light Although the experiments quoted in the Introduction give good arguments for suppression of rod activity at 40 Hz stimulation we felt that in experiments where chromatic adaptation of the tine mechanism was to be detected, even a small contribution of the rods to the output signal might markedly affect the results. Since scattering of the stimulus outside the adaptation field is effective in stimulating rods, the influence of stray light has been carefully checked. A sensitive test for rod activity is to compare spectral sensitivity for low and high response criteria. The shape of the sensitivity function for 1 PV and 20 PV criteria proved to be the same within O-1log unit sensitivity (corresponding with about O-5PV difference in response amplitude, although the corresponding mean intensities are as far apart as 70 and 1500 trolands). It should be mentioned here that some authors report a relative increase in blue sensitivity at higher adaptation levels (ARMINQTON, 1959; GRANDAand BIBRSDORP, 1963). In these experiments the single flash response is used as a sensitivity criterion, which creates daculties for separating rod and cone responses. Since test and adaptation field were of equal subtense, the adapting background favoured stray light responses and thus rod activity. A second test which should have detected stray light if present in our experiments, is to measure response vs. intensity for a 2” foveal field and compare it with that for a field on the blind spot. For this experiment (Fig. 1) white light was used, making the maximum available intensity 3 log units higher than the maximum intensity used for measuring spectral sensitivity (zero value on the abcissa). If stray light would have contributed measurably to the response there should have been a response for blind spot stimulation. We see, however, that a response appears only at intensities well above the maximum intensity used for determining spectral sensitivity. The second rise of the fovea1 response vs. intensity curve can then be t

I

I

5 --

I

I 4 --

m

Foveal stimulation

l ---•

Blind spot

I

stimulation

f

> 3.

I 3 --

: s P 0 a

I : /*

2.-

/’

: I O-0 5

0

I OS

I IO loo atlmulur

I Kl

I 2.0

I 25

I 3.0

intrnrlty

Fro. 1. Responsevs. inwty farws for a 2” stilnuhm &Id of whim light, 6xation le5pectivcly at thefovea~attheblindspot.An~t~~ofOkyMitriclcompurbkwiththemaximum intensity used in experiments with colouzed stiuli (5 x l@ trolands).

32

P. PADIMSANDD. VANNORREN

attributed to a stray light component superimposed over a saturated cone response. We can assume therefore that below log stimulus intensity zero, the stray light response is negligible with respect to the local response. Another indication, finally, in favour of measuring local response is the sensitivity curve for a 6” centrally fixated field (Fig. 2). The sensitivity in the blue region of the spectrum comes close to the CIE curve for a 10”central field. In order to get a criterion response of 1 PV for this small field, stimulation with nearly the highest available intensities (10’ trolands) was necessary. Even at this high intensity level the response appears to be solely caused by local stimulation. Spectral semitiuity without background Three different response criteria have been used to define spectral sensitivity without an adapting background. Irrespective of a parallel shift of the log sensitivity axis, the three criteria introduced no significant difference in sensitivity (F test, p > O-2).In Fig. 2 the sensitivity is presented as measured in 8 experimental sessions. Together with the experimental

Wavelength,

nm

FIG. 2. Spectral sensitivity functions without adaptbackground measu& with different methodsandrcqxmsccritcria. 0 = 5 PV criterion, 0 and 0 = 1 PV criterion, both with the lock-in voltmeter technique.+ = 5 rV &e&on with CAT computer. The solid-is WALD’S (1945) 8” extra foveal sensitivity function. The dashed curve is the CIE function for a 10”field.

points, WALD’S (1945) extra-fovea1 cone sensitivity and the CIE sensitivity for 10’ central field are given. The measured sensitivity for the 45” field comes closer to Wald’s curve in the blue region of the spectrum. The deviation at 456 nm can probably be explained by the well known individual variations of the luminosity curve at short wavelengths, perhaps due to difl’erencesin the absorption in the ocular media. In the long wavelength region there is a

33

Cone Spectral Sensitivity and Chromatic Adaptation

systematic discrepancy which is in accordance with the 0.08 log unit less 14 sensitivity of the subject as measured by conventional 2” flicker photometry.

AUmeasurements of ERG sensitivity under chromatic adaptation conditions were carried out with the lock-in voltmeter. To check that the selective effects found under chromatic adaptation were not solely an effaot of changing the light adaptation condition the spectral sensitivity measured with an intense white background (colour temperature 28OO’K;intensity, 6 x 104trolands), was compared with the data obtained without background as already.presented in Fig. 2. The two functions (Fig. 3, filled symbois, upper curve) do not differ silty (F test, p > O-05).It should be noted that the absolute difference in sensitivity level is about I.3 log

AAUnadapW(ftumFig.2) 0 ’ wapkdkn whim &W@&ds V VMaprotW qusn 2Mo traknds a SAdaprOtkn blue 22xlo4trolimds \ 0 *LLdqr(atkn rsd 3.7~ IO*trolands -3.0 t

I 4%

I 500

I 550 Wavelength,

0

I 600 nm

650

P. PADMOSAND D.

34

VAN

NORREN

units: the wbite adapted curve is shifted this amount upwards to obtain a fit with the unadapted curve.

The results of the chromatic adaptation experiments are also given in Fig. 3. Both blue and red adaptation give significant depressions in the short and long wavelength regions respectively, compared with the combined results of experiments with white and without adaptation (F test, p < O-05).The adaptation to a 506 nm background has no significant effect on the shape of the sensitivity function. Together with these results, those of the parallel psychophysical experiments are given. The psychophysical determination of spectral sensitivity was based on the fIicker fusion criterion. The differences with the ERG measurements are small, considering the greater variability of the psychophysical experiments. The correspondence of the absolute sensitivity level detected with the two methods is remarkable, since a shift along the log sensitivity scale to obtain a best fit between the corresponding ERG and psychophysical experiments hardly appeared to be nv (less than 0.2 log units in all cases). In the literature, the differences between ERG and psychophysical measurements are reported to be at least 0.5 Iog unit (VANLrrrr, 1966).Gur findings indicate that most of this discrepancy is due to taking higher threshold criteria for the ERG.

.& 0.4 -J 8 ?

.g 0.2-

p .*; :$J:$

o

_

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g:: b 0

-OP.--*

01-O &--+A

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6~7xt03troknds 3.7% 104tfoianUs InOx IO%olands

I

I

I

I

I

400

so0

a50

600

660

Wavelength, b-4.

czanpdm

of log rpr;ctral

nm

MMitivityUndNriSdadaptation(threeinteasitkws) andwhite

To give an indication of how the selective adaptation e&et depends on the intensity of the adaptation field, in Fig. 4 the dilbaa of log spectral sensitivity and log sensitivity under white adaptation is given for three acmes of the red adaptation fieid. The remarkable fact is that for the highest intensity the s&ctive depression is hardly more than for moderate intensities.

Since it is generaliy assuzued that protauo~ d&z from normal trichromats in that they miss the red sen&ive cone nicdanism, WG us8d the opportunity of hav* a protanopic subject (WK) avail&e to study his ERG behaviour during chromate a laptation. Inthcfirst~~thespbetrafscnsitivityf~onwithouta~~ ~w~d~~ Figure 5 indicates that it fits WRIOHT’S (1947) protanope luminosity cur e in the long wave-

35

Cone Spectral Sensitivityand Chromatic A_daptation

._ t

e 0

B

/!

-1.5

-25

I

4s

lunadaplsd Wub@otlanblue AAdqMbnrsd I 500

I

I

!wo

600

wavelength,

6210

nm

length region and WALD’S(1945) curve for normal extra fove8l cone vision in tbe blue R?giOIk. The resultS of the chromatic ad8ptation [email protected] demonstrate that neither red nor blue backgrounds cause a s&ctive depression of tbe scnsitivity function Apart from cerkin other concksion~ (which we refet to tbe Discussion), the constancy of spectml Sensitivity of the protanopa: is another proof that tbe rods are not contributing to the Sensitivity curve.

In order to interpret the effect of chromatic adaptation, it is necessary to decide whether only neural sdaptation e&&s are involved, or wbetber photo&em&al cbange~ in receptorS also umtri~ to the astir pkkomena. Tkrefke ezqknents performed in which the amplitude of the response to a constant stimulus w8s me8~med as a ftmction of time after offset of an 8dapting light. ~Fi~6wep~ottheraooveryoftherearponsttofivs~~t515nmstimuruSlhtmRitics aftar~~tiantO8backe;roundOf506nm,1*9 x lff~S.~e~~~ a rapid and a slow phase of the recovery. Recovery curves akme, however, do not yield

36

P. Pmhios AMY D, VAN NORWN

Stimulus int

:

Cone Spectml Sensitivity and Chromatic Adaptation

. I 0

I ?Ka

I

eP----+

60 Time.

SW

aptatlan red 3% IO4tralands

stiiutus:

Time,

g-i$

X-456nm

0-0

A-664nm

set

Fro. 8. Regeacration of the response to two stimuli (664 tun and 456 am, both rbwt 1600 trolands) a&r bkading with red light.

37

P.

38

PADMOS AND D. VAN

NORREN

(t = 0). Soon after offset of the background the difference between the two curves drops below 15 per cent which means a negligible difference in sensitivity. DISCUSSION The psychophysicul method AU the psychophysical measurements were done as a check on the validity of the ERG results, It should be kept in mind that the experimental conditions for measuring psychophysical sensitivity were not sufEciently precise to allow us to draw firm conclusions from the small discrepancy between the psychophysical results and the ERG. In the literature relatively few data could be found which are comparable to those obtained with our method to define spectral sensitivity. Iincrrr and Sm (1936) determined fIioker fusion for a variety of wavelengths as a function of retinal illumination. Their stimulus subtense was 19”. A comparison with their results shows that the spectral sensitivity based on our method is equivalent to the definition of luminance based on heterochromatic brightness matching. However, GKIRGI(1%3), measuring CFF for foveal i&&is,reported that for a red stimulus the sensitivity at higber frquencies decreases in respect to blue sensitivity. This result is at least qualitatively in accordance with our tiding that the red mechanism is saturated earlier at higher luminance levels. Also the results of our psychophysical measurement of CFF u&r chromatic adaption oannot be compared directly with any literature to our knowledge. The technique of KELLY (1962) is too different from ours to allow comparisons. The data of BRINDLEY, Du CROZand RUIN (1966), and GRIZN(1969) do not cover our data at 40 Hz. The indication from both these papers is that the blue receptor mechanism is muoh slower than the red and green ones. Pigment regeneration and sensitivity d&ring dark aduptation

It is beyond the scope of this paper to discuss extensively the recovery of the ERG response from light adaptation. We have used it here only as a means to obtain some additional information on the cause of the chromatic adaptation effects which we found. We can quantify the interpr&ation of the slow phases of the recovery process in the following way. According to RUS~-XTUN (1963, 1965): P(t) = I-

(I-PO) e-5)

where P(t) is the fraction of IBM pigment as a function of time after offstt of the baokground, P,, is the fraction of unbIea&al pigment during &&ground ilbnnination, and 7 is the time constant of regeneration. Assuming further (WSALl3,1964), a linear relation between p(t) and I (t = 00)/l (t) we find: I(t = a31

= 1 - (1 - PO) e-f

10)

To obtain a best fit with the data points for a green background of I.9 x lo* trolands, the ValUesP, =o-22&t = 143 see are appropriate. This time constant is wnaistent with data obtained in other wrgerimnn& (RuMToN, 1%3,1%5; GoLn@nnMand m, 1969). The site of chromatic adbptation

From the fan it is evident that the chromatic adapt&ion eff’ conditions of neural adaptation and of pigment bieaching.

occur both in

Cone Spectral Sensitivityand Chromatic Adaptation

39

From Fig. 4 it is also clear that a considerable selective effect is caused by a red background of only 6.7 x lo3 trolands. At an intensity of about 1 log unit higher the selective depression is not dramatically increased. Figure 8 shows that at this lowest intensity(6-7 x lo3 trohmds) the depression of the red response relative to the blue response is no longer really sign&ant some 5 set after offset of the background. The selective depression at higher adaptation intensities (3.2 x lo5 trolands) stays up to 40 sec. At the same time, the conclusion from the previous section was that already at 1.9 x 10’ trolands some 80 per cent of the pigment was bleached. Thus during the chromatic adaptation the selective effect is more or less independent of the amount of bleaching; soon after offset of the background, the selective effect is strongly dependent on the amount of bleached pigment present. We should like to tentatively put forward the following explanation. At lower luminance levels there is a neural mechanism which primarily reduces the sensitivity of the most stimulated cone system. Thus the cone systems tend to equal sensitivity at the adapting wavelength (WALRA~BN et uZ., 1966). If the stimulus is strong enough to bleach the photopigments selectively, the situation of (nearly) equal sensitivity at the adapting wavelength does not change. Thus, different background intensities induce the same selective effect. During stimulation it is impossible to label the different mechanisms because, apparently (cf. Fig. 4), the neural mechanism alone suffices to bring the cone system to equal sensitivity. After offset of the adapting field the neural system recovers much faster than the pigment system so that an effect due to the slower recovery of the photo-pigments can eventually become manifest. More insight is needed into the recovery of sensitivity during dark adaptation, as a function of stimulus and adaptation parameters; hence future research will be concentrated upon changes in spectral sensitivity as a function of time after offset of chromatic backgrounds. Fundamentalresponse mechanisms

In the psychophysical literature (Hu~vrcri and JAMESON, 1955; BOYNTON, 1956; WALRA~EJN, 1962; WAL.RA~EN et al., 1966; WALD,1964),much effort has been devoted to deriving fundamental response curves from changes in spectraI sensitivity under chromatic adaptation. In these publications some postulates are adopted concerning the site of adaptation and the way in which the fundamental response mechanisms interact to form the luminosity function. But in view of the present discussion, we feel that we also have to restrict ourselves only to qualitative conclusions. The experiments on the protanope, believed to have only blue and green sensitive cones, revealed that selective depression of the sensitivity function with blue backgrounds was not possible. Hence it is most likely that the selective effects we found in normals could not be caused by the blue mechanisms. In other words, with coiour normal sul&cts selective effects can be attributed only to green and red mechanisms. This is not surprising because there is much psychophysical evidence that the blue mechanism contributes only in a minor way to the luminosity. Moreover, the reports of CFF measurements using chromatic backgrounds (BRINDLEY et al., 1966; GREEN,1969)indicate that the blue mccbnism is much slower than both the red and the green ones, so that its contribution might possibly be suppressed in the 40 Hz condition. Finally, the most sensible explanation as to why we could not find a selective depression of the sensitivity curve with 506 nm adaptation is that the difference in sensitivity of the green and red mechanisms is too small at this wavelength. On the basis of WAtluvlm’s et al.

40

P. PADMOSAND D. VAN NORREN

(1966) fundamental response curves, we did not expect this, but the literature is rather confusing (WRIGHT, 1947). Also, almost all experiments in the literature are based on fovea1 stimulation, whereas we used a 45” field. Still greater accuracy will be required in the future to detect the minor changes in spectral sensitivity which are needed for reliable quantitative statements about the shape of the fundamental sensitivity curves. REFERENCES AIBA, T.

S., ALPW, M. and MMSFZDVAACI~, F. (1967). The electroretinogram evoked by the excitation of human fovea1 cones. J. Physfol. lti!#,43-62. ARMINOTON, J. C. (1953). Eiectricpt responses of the light-adapted eye. J. opr. Sot. Am. 43,450-456. ARMINOT~N, J. C. (1959). Chromatic and short term dark adaptation of the human electroretinogram. J. opt. Sot. Am. 49, 1169-1175. ARWNOTON, J. C. and Bnutsaong, W. R. (1956). Flicker and color adaptation in the human electro-retino gram. J. opt. Sot. Am. 46,393-400. AMINOTON,J. C. and T-E, F. C. (1954). EtTect of stimulus area and intensity upon the light-adapted electromtinogram. J. exptf. Psychol. ‘47,329334. BOWION, R. M. (1956). Rapid chromatic adaptation and the sensitivity functions of human color vision. J. opt. Sot. Am. 46, 172-179. BRINDLEY,G. S. (1953). The effects on colour vision of adaptation to very bright lights. J. Physfof. 122, 332-350. BRINDLEY,G. S., Du CROZ,J. J. and Ruwro~, W. A. H. (1966). The 8icker fusion frequency of the bluesensitive mechardsm of colour vision. J. Physiof. l&3,497-500. C~vomrrs, C. R. (1964). Color sensitive response in the human flicker-ERG. Documenter Opkthuf. 18, lOl113. ihDT, E., COPENHAVER, R. M. attdGUNICEL, R. D. (1958). Photopischer Dominator turd Farbcomponenten im menschhchen Elektroretinogramm. Pfltfgers. Arch. ges. Physiol. 267,497~507. Dow, E., VANLrru, G. H. M. and Saiktm~, B. (1967). Electroretinographic evaluation of the photopic malfunction in a totally colour blind. Vision Res. 7,231-241. GIORGI, A. (1963). El&t of wavelengtb on the relationship between critical flicker frequency and intensity in fovea1 vision. J. opt. Sot. Am. 53,480-486. GOLDSTEIN,E. B. and BEIWN, E. L. (1969). Cone dominance of the human early receptor potential. Nature, Land. 222,1272-1273.

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Cone Spectral Sensitivity and Chromatic Adaptation

41

Ww, G. (1964). The receptors of human colour vision. Science, N. Y. 145,1007-1017. WALRA~BN, P. L. (196;L).On the mechrnisms of &our vision. The&, University of Utrecht. WALRAVBN, P. L., VANHour, A. M. J. ~IKIw H. J. (1966). Fundamental responm curves of a normal and a w m derived from Chromatic adaptation data. J. opt. Sot. Am. S&125-127. WEALE,R. A (1964). Relation between dark adaptation and visual pigment regeneration. J. opt. Sot. Am. 54, 128-129. WRIQHT,W. D. (1947). Researches on Normal and Defective Colour Vision, Mosby, St. Louis. Ah&met-The human ERG response to a 40 Hz stimulus was measured using a synchronous d&c&m tc&nique (lock-in amplifier). Thus it was possible to rc~ord spectral sensitivity quiclrly and easily. CheCk experiments showed that only the ~oncs amtributed to the total responsC. Adaptation to a red baCkground of 3.7 x 10’ trolands, and a blm baCkground of 2.2 x l(r trolands paused s&~tivc depression of spectral sensitivity. Neither green nor white adaptation altered the spcztral sensitivity. The results of parallel experiments on a protanope indicated that no change in ape&al sensitivity took place during his exposure to intense ~olouted backgrounds. Measuremen ts of the influence of chromatic adaptation w~rc also performed using a psychophysical threshold Criterion for sensitivity. The results are in close agmament with the ERG data, The -very of the response after exposure to colourcd baCkgrounds of various intensities indicated that the a&Ctivc deprc&on of the lumhlous speCtra1 sensitivity Can be due to both neural adaptation and to blCB&ng of the photopigments.

RL4labChr mesure par un~ &&nique de d&eCtion sync&one la rCponse de I’ERG hum& g un stimulus de 40 Hz. On peut ainai enregistrer vite et fsilcment la SensibiiitC spuztrale. Dca expcrieMns de contr6le tiontrent que l& ~6ncs Contribuent sculs 8 la &port& totale. L’adaotation h un fond IQURCda 37 000 troland et B uo fond bleu de 22 Oootroland oroduit une d&p&ion &.kctive de la s&sibiliti spstrale. Une adaptation v~rte ou blan&c &It&c pas la scnsibilitc spaztrak. Lu &ultats d’exp&iCnCeuparall&les sur un protanope indiquent qu’auGun changcment de scnsibilitt sp&ralc nc se produit pendant son exposition Bde8 fends color&s intenrss. On mesure ausai Padaptation ~hromatique par un Crit&ium psytzhophyaiquc de s&l. Les r&sultats sent en bon afford avtc I’ERG. La r&up&ation de la r@onse apr& exposition B des fends Color& d’intguritCs divcmcs indique quc la depression a&~tive de la sensibiliti lumineu~ ape&ale peut prove& g la fois d’une adaptation nerveuse et de la d&&oration dcs photopigments. ~~~DiemIlPchlicheERGAntwortaufeinen.Reizvon40Hzwurdemittelseiner Syn~hromcthode (d.h. mit &em Einschl~verstitrkcr) m. Dies erm6gliChte e& die Spc~dliChkcit sdmcll und l&t zu r&s-. KontrollvcrauChC bew&n es, dass nur die Zapfen zur Ganzantwort beitrugcn. Die Umatimmung auf cinen rotan Hintergrund von 3,7 x 10’ Troland und &en blaucn Iih~t~rgnmd von 2,2 x 10’ Troland vcnnsa&tc eine sclektive Erniahigung der Spek UmSthIUIlung PamMvuauChCnane gefarbte Hilltcr~de

unblieb. Der Ehdluss da Farbum&immung wurdc such dunzh eine psyChophysisChe S~hwell~ ermittBlt. Die Ergcbnii decken aich mit den ERG-Rcsultaten. Die Erhohmg dcr Antwort Nash einer Auaacmmg an vendWan .starke farbii Hint-e x&t an. dass die aclektivc Emialrim d~r Snckts eit sowohl durch die ncrv& U&timmung als ouch dutch die A&blei&ng der !&farbstoffe verursacht warden kann.

42

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