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Inductive brightness depression as influenced by configurational conditions
Vrsion
Hcs.
Vol.
3, pp.
121-130.
Pergamon
INDUCTIVE INFLUENCED
Press
1963.
Printed
m Great
Britain.
BRIGHTNESS
DEPRESSION
BY CONFIGURATIONAL H. W.
AS
CONDITIONS’
HOREMAN
lnstituut voor Perceptie Onderzoek, Eindhoven, The Netherlands (Received 5 Sepretnber 1962) Abstract-In the literature, inductive brightness depression has been described by several authors. They have made use of different configurations of the stimulating fields. Using a haploscopic brightness-matching technique experiments were performed to establish the influence of the luminances and of the configurations of the stimulating fields. Four configurations were tested and compared, one of which had not previously been studied. Two conclusions can be drawn: 1. The configuration in which the test field is completely enclosed by a ring-shaped inducing field results in contrast effects impairing the brightness judgment. Brightness-matching becomes ambiguous in cases where effects such as opposite contrasts occur, when there is a wide separation between the two fields which have to be matched. 2. The amount of the inductive effect is greatly influenced by the extent to which the inducing field encloses the test field. To evaluate inductive brightness depression as it is influenced by retinal distance between test patch and inducing field, for example, it is important to choose a configuration which entails the symmetry of test patch and inducing field and in which the largest possible boundary between test and comparison patch occurs. R&sum&-Dans la litterature, la depression induite de la luminosite a ttt d&rite par divers auteurs. 11sont utilise des configurations differentes du champ stimulant. Des experiences, utilisant une technique d’egalisation de luminosite par le haploscope, ont CtC realisees afin d’ttablir I’influence de la luminance et des configurations des champs stimulants. Quatre configurations ont BtC essayees et comparees, dont I’une avait ete preddemment ttudite. On peut en tirer deux conclusions : I. Si la configuration est telle que le test soit completement enferme dans un champ annulaire inducteur, il en r&he des effets de contraste qui alterent le jugement de luminositt. Les egalisations de luminositt deviennent ambigues s’il se produit des effets de contrastes opposes, lorsqu’il existe une grande separation entre les deux champs a egaliser. 2. L’importance de I’effet inducteur depend beaucoup de I’extension du champ inducteur autour du test. Afin d’evaluer la depression induite de la luminosite pour ttudier par exemple I’influence de la distance sur la retine entre le test et le champ inducteur. il est important de choisir une configuration oh la symetrie du test et du champ inducteur soit telle qu’elle permette une front&e la plus grande possible entre le test et la plage de comparaison. Zusammenfassung-In der Literatur wurde die induktive Helligkeitsunterdrtickung von Sie bedienten sich verschiedener Testfeldformen. Unter mehreren Autoren beschrieben. Helligkeitsvergleichstechnik wurden Experimente Verwendung einer haploskopischen angestellt, urn den Einfluss der Leuchtdichte und der Gestalt des Testfeldes festzustellen. Vier Testfeldformen wurden untersucht und verglichen; von diesen ist eine niemals vorher studiert worden. Zwei Schlijsse konnen gezogen werden: I. Jene Konfiguration, bei der das Testfeld vollstlndig in ein ringformiges Umfeld eingebettet ist, wirkt beziiglich der Kontrasteffekte abschwlchend auf die Helligkeitsbeurteilung. Die zu vergleichende Helligkeit wird uneindeutig in jenen Fallen, in denen Effekte wie die Kontrastumkehr auftauchen, wenn ein grosser Abstand zwischen den beiden zu vergleichenden Feldern besteht. 1 Presented at the 6th I C 0 Congress, Munich, August 1962. 121
I22
H. W. HOK~MAN 2. Der Betrag des induktiven Effekts wird weitgehend davon beeinflusst. in welchem Masse das induzierende Feld das Testfeld einschliesst. Urn die induzierte Helligkeitsverminderung. wie sie beispielsweise durch den Abstand des Testfeldes vom induzierenden Feld auf der Retina hervorgetufen wird, abzuschgtzen, ist es wichtig. eine Anordnung zu wlhlen, die die Symmetrie des Priiffeldes und des induzie~nden Feldes, in dem der ~~sstm~gliche Abstand zwischen Priiffeld und Vergleichsfeld enthalten ist, einschliesst. INTRODUCTION
RY INDUCTIVE brightness depression a phenomenon is meant in which the subjective impression obtained from a luminous test field is depressed by presenting an inducing field to neighbouring places of the retina. In its extreme form with high intensities of the inducing
light source the phenomenon is known as disability glare. The moderate effect can be strikingly demonstrated in a situation in which a subject matches the brightnesses of two patches seen haploscopically.” When presenting an inducing field in one eye only, an initial haploscopic match will no longer hold. In the eye receiving the inducing field the test patch appears dimmer, causing the subject to adjust the test luminance to higher values so as to match again the patch seen with the other eye. In the literature on vision, inductive brightness depression has been described by several authors. Among them SCHOWEN and ORNSTEIN (1939) were the first to suggest haploscopic matching as a tool for measuring the depression. By this means they were able to describe the amount of the depression in terms of the ratio of the luminances necessary to obtain matches with and without the inducing field. Others (FRY and ALPERN, 1953; DIAMOND, 1953; HEINEMANN, 1955) also have used the hapioscopic matching technique, but without evaluating the amount of depression in terms of luminance ratios. Also, some of them allowed the comparison patch instead of the test patch to be adjusted. It should be noted that in this case the depression in the test eye cannot be evaluated. since the reference eye may change as well, and in an unknown way. A direct comparison of the results of these authors has disclosed wide differences. Since the authors used different dimensions and configurations of the patches and the inducing field, the question arises as to whether or not the different results are mainly due to an influence of the configuration on the brightness depression. Therefore, measurements on the brightness depression have been carried out with an experimental design in which different configurations could easily be arranged. METHOD
Test and comparison patches and inducing field were formed by means of diaphragms to which translucent paper was attached and illuminated by three projection lamps (8 V, 50 W). The fields could be seen through an artificial pupil (2 mm) at a viewing distance of 2.10 m. To aid fixation both eyes received red light from two small light spots. An outline of the experimentai design is shown in Fig. 1. The luminances could be adjusted by means of neutral filters and of circular wedges. Since only mirrors were present between the eyes and the field diaphragms, other field configurations could be obtained by a simple exchange of the diaphragms. In all measurements, the inducing field was presented to the right eye. The subject was seated at ease, while his head was kept in the proper position with the aid of a headrest. ? ONLEY (1961) suggested the name “haploscopic matching technique” to distinguish between the fusion of independently presented visual fields as used in this matching technique and the conditions of normal binocular vision.
Inductive Brightness Depression
as Influenced by Configurational
Conditions
123
All the fields were presented continuously and the subject got either of two instructions, viz.: (1) to adjust the right-hand test luminance to match the test field with the constant comparison patch, under different conditions of inducing field luminance; or (2) to adjust CWN
L
SL
S
NI
I I
I
10 ml
-
c/
,’
.. __
E
FIG. 1. Experimental design for haploscopic brightness matching. S sources (Philips 13113 C, 8 V, 50 W); L Lenses; N neutral filters: W circular wedges; M mirrors; G glass plates used as partial mirrors; F fixation spots; P artificial pupils; E subject’s eyes; T, C and I diaphragms for test, comparison and inducing fields.
t
l-
C
. q El non 0. C
T
I
I
C
I
FIG. 2. Configurational conditions tested. (a) Configuration according to Heinemann (b) Configuration according to Diamond (c) Configuration according to Fry and Alpem (d) I.P.O.-configuration.
T
H. W. HOREMAN
124
the left-hand luminance so that the comparison field again matches the depressed brightness impression of the test patch, under various inducing strengths. The results of these experiments are given in terms of the retinal illumination of the inducing field. When the inducing retinal illumination increases one may expect to find adjustments towards higher values for the test patch and towards values for the comparison field. Four configurational conditions, as shown in Fig. 2, have been compared. (a). The conditions as described by HEINEMANN (1955): test and comparison patch are discs F in diam. and about 1” apart. The inducing field is annulus-shaped and surrounds the test patch. (b). The conditions given by DIAMOND (1953): test and comparison patch are squares. about &” in width and 40’ apart. The square inducing field of the same size is along the upper side of the test patch. (c). Conditions like those used by FRY and ALPERN (1953): test and comparison patch are rectangles of about 60’ x 12’. The comparison patch forms the upper extension of the test patch with a gap of 12 in. between them. The inducing field consists of twc rectangles of 60’ x 12’ adjacent to the test patch. (d). Conditions, which will be referred to as I.P.O.-configuration: test and comparison patch are semi-circular discs 40’ in diameter, adjacent to each other. Roth are encircled by the annulus-shaped inducing field of one degree outer diameter.
log
FIG. 3. Adjustment
of the test luminance VT- .Y, and of subject H-n. RESULTS
cl
itroland)
in Heinemann
configuration.
Results of subject
AND DISCUSSION
The different results are shown in Figs. 3-6 for the adjustments of the test field and in Figs. 7-10 for the left-hand adjustments. Common to all these findings is that the curves display an initial section in which the retinal illumination of the adjusted field remains fairly constant. In the case of test field adjustment, each curve represents a line of equal brightness impression. These lines reach a level, after which the curves start upwards. However,
Inductive Brightness Depression as influenced by Configurational Conditions
125
the different curves do not show the same starting points, while the slopes of the rising parts differ widely among the various curves. In detail the different results can be described as follows. Test field adjustments
1. Heinemann conjfguration (Fig. 3). The curves show a very steep rise starting almost at the level at which test and inducing field yield equal retinal illumination. It is striking that curves starting at different levels of the comparison field tend to coincide in the end. Coincidence is quite excluded from the point of view of lines of equal brightness starting at different brightness values. (Coincidence would mean that different brightness values could be attributed to a test field with one specific luminance, depending on the value with which the test field has been compared before. Though complete coincidence has not been found here the results are quite near to this as already described.)
log
(trolond)
FIG. 4. Adjustments of the test luminance in Diamond configuration. Results of subject vT=x, and of subject S= +.
2. ~jamond c~n~gur~t~~n (Fig. 4). The rise in the curves starts again at about equality of test and inducing retinal illumination, but is very moderate. Curves starting at different levels remain fairly parallel throughout the region measured. Thus, no tendency to any coincidence occurs under these configurational conditions; furthermore, in these conditions, an expression of the brightness depression in terms of luminance ratios might be successful. In the case of non-parallel curves, one cannot hope to use such a ratio to evaluate the depression since this ratio is not a constant. SCHOUTEN and ORNSTEIN (1939), who did use the luminance ratio to evaluate the depression, checked the constancy of the ratio for their conjuration by using a point-like inducing field presented near one comer of the test field. In fact Diamond’s configuration is so very similar to Schouten’s that it is tempting to suggest that their findings of a constancy of the luminance ratio was due to an approximate parallelism of the curves, such as is found in the curves with the Diamond configuration. 3. Fry and Alpern configuration (Fig. 5). The curves show steep rises and tend to come very close to each other in the end. Besides there is a shift in the starting points of the rise, for different levels of the comparison field. Though the coincidence situation is not reached,
126
H. W. HOREMA~~;
one may conclude that the brightness discriminability is greatly changed in the end of the curves. The fact of the small separations of the curves may be interpreted in terms of attributing greatly differing brightness values to only slightly differing luminances.
i/ 0
/
1
1
I
2
4
3
log 6X (trolond) FIG. 5.
Adjustments of the test luminance in Fry and Atpern configuration. VA=x, and of subject X= I.
FIG. 6.
Adjustments of the test luminance in l.P.O.-configuration. and of subject H= -.
Results of subject
Results of subject VT-X,
4. i.P.O,-c#~~~r~?i~n (Fig. 6). The rise of the curves is rather steep and the starting point of the rise shifts for different levels of the comparision field. Although the rise is steep the curves become more or less parallel in the end. However+ an evaluation in terms of luminance ratios does not hold since the separations of the curves in the horizontal portions are not equal to those in the rising portions.
Inductive Brightness Depression as Influenced by Configurational
log
cl
I
log 6, FIG. 8. Adjustments of the comparison subject VT= x, and of subject S= + .
127
(troland)
FIG. 7. Adjustments of the comparison luminance in Heinemann subject vT=x, of subject S= +, and of subject H = o.
0
Conditions
2
configuration.
Results of
3
(troland)
luminance in Diamond
configuration.
Results of
I
H. W. HGREMAH
128
Comparison field adjustments
1. Heinemann configuration (Fig. 7). In all curves, starting at the level of equality of test and inducing field (i.e. log er=log Q) a very steep fall sets in. This looks like a complete breakdown of the brightness impression of the test field. Actually HEINEMANN (1955) himself mentions in his article (p. 92) that every setting of the comparison field seems to be brighter than the test field under these conditions, even though the test fiefd can be made still darker by increasing the inducing luminance. 2. Diamond conjiguration (Fig. 8). Ali curves start with the initial constant level and then exhibit a moderate increase. No such sharp breakdown of the brightness impression of the test field can be found here.
log c;
(troland)
FIG. 9. Adjustments of the comparison luminance in Fry and Alpern configumtion. Results of subject VA==x, and of subject K= -f .
3. Fry and Alpern configuration (Fig. 9). The curves do exhibit a steep decrease, but do not seem to show a breakdown. The slope of the decreasing part however is steeper than in the curves of the Diamond configuration. 4. I.P.O.-configuration (Fig. 10). Here the curves possess the same trend, but with no tendency to breakdown. The drop-off of the curves seems somewhat less steep than in the configuration according to Fry and Alpern. CONCLUSIONS
In conclusion we may note that in the configuration in which the inducing field completely surrounds the test field the brightness depression is much more pronounced than if only partly adjacent inducing fields are used. However, in the configuration in which test and comparison patches are separated by the inducing field, the matching becomes uncertain, probably because contrast cues also make themselves felt. In the region where the lines of equal brightness impression tend to coincide, the right-hand part of the stimulus is a dark centre field on a bright surround while the left-hand part is a bright centre field on a dark surround. The hypothesis is that these opposite contrasts of the centre fields with their
Inductive Brightness Depression as Influenced by Configurational
Conditions
129
further impair the brightness-matching which by itself is a hard task because of the separation of the fields which have to be matched. A further indication of this is provided by the fact that with other configurations no breakdown occurs. It is clear that the configuration described by Heinemann is a poor one for measuring inductive brightness depression. surrounds
FIG. 10. Adjustments of the comparison subject vT=x, and of subject H= -+.
luminance
in I,P.O.-configuration.
Results of
In general it can be concluded that the extent to which the inducing field encloses the test field is quite relevant with respect to the amount of the inductive brightness depression. This is expressed, for example, by the steepness of the rising part of the different curves. To measure the influence of other configurational parameters such as the retinal distance between test patch and inducing field one needs the greatest amount of inductive depression. For that reason the configurations used by Fry and Alpern or in the I.P.O. are preferable to the conjuration given by Diamond. An additional disadvantage of Diamond’s partly adjacent inducing field is an asymmetry in the inducing effects. Using the configuration described by Fry and Alpern one may expect that contrast may also influence the results. Although there is no separation between the two fields which have to be matched, the boundary along which the test and comparison patches can be compared is very small. Doubtless the Fry and Alpern configuration gives a symmetrical influence of the inducing field on the test patch. From that point of view it seems to be a good choice, leading to a sort of linearization of the parameters in the configurational conditions. It is doubtful if this linearization is in accordance with the presumptive circular symmetry of the retina. The disadvantage of a small boundary between test and comparison patch is not present in the I.P.O.-conliguration, in which both patches are contiguous within the inducing annulus. In this configuration the brightness-match is not contaminated with other parameters such as contrast. A disadvantage of the I.P.O.~onfiguration remains in that the influence of the inducing annulus on the test patch is not quite symmetrical. Summing up, finally, inductive brightness depression is greatly influenced by the choice of the conjuration of the various fields. It seems worth noting that when measuring the
130
H. W. HoRr~hhi
inductive brightness depression as influenced by the retinal distance between test and inducing field, a proper choice of the configuration must be made in order to avoid introducing irrelevant parameters like contrasts or asymmetry. In this respect both the Fry and Aipern configuration and the I.P.O.-configuratian seem to be good approximations to the ideal. REFERENCES DIAMOND, A. L. ff953).
FoveaI simuftaneous brightness contrast as a function of inducing- and test-field luminances. J. exp. Psychol.45, 304-314. FRY, G. A. and ALPERN, M. (1953). The effect of a peripheral glare source upon the apparent brightness of an object. J. opt. Sm. Amer. 43, 189-195. HEINEMANN, E. G. (1955). Simultaneous brightness induction as a function of inducing- and test-field Iuminances. J. exp. Psychoi. 50,89-96. ONLEY, J. W. (1961). Light adaptation and the brightness of brief fovea1 stimuli. J. opt. Sm. ANT. tit, 667-673. SCN~UTEN, J. F. and ORNSTEIN, L. S. (f939f. Measurements on direct and indirect adaptation by means ofa binocular method. .r. opt. Sot. Amer. 19, 16% I%?.
Hcs.
Vol.
3, pp.
121-130.
Pergamon
INDUCTIVE INFLUENCED
Press
1963.
Printed
m Great
Britain.
BRIGHTNESS
DEPRESSION
BY CONFIGURATIONAL H. W.
AS
CONDITIONS’
HOREMAN
lnstituut voor Perceptie Onderzoek, Eindhoven, The Netherlands (Received 5 Sepretnber 1962) Abstract-In the literature, inductive brightness depression has been described by several authors. They have made use of different configurations of the stimulating fields. Using a haploscopic brightness-matching technique experiments were performed to establish the influence of the luminances and of the configurations of the stimulating fields. Four configurations were tested and compared, one of which had not previously been studied. Two conclusions can be drawn: 1. The configuration in which the test field is completely enclosed by a ring-shaped inducing field results in contrast effects impairing the brightness judgment. Brightness-matching becomes ambiguous in cases where effects such as opposite contrasts occur, when there is a wide separation between the two fields which have to be matched. 2. The amount of the inductive effect is greatly influenced by the extent to which the inducing field encloses the test field. To evaluate inductive brightness depression as it is influenced by retinal distance between test patch and inducing field, for example, it is important to choose a configuration which entails the symmetry of test patch and inducing field and in which the largest possible boundary between test and comparison patch occurs. R&sum&-Dans la litterature, la depression induite de la luminosite a ttt d&rite par divers auteurs. 11sont utilise des configurations differentes du champ stimulant. Des experiences, utilisant une technique d’egalisation de luminosite par le haploscope, ont CtC realisees afin d’ttablir I’influence de la luminance et des configurations des champs stimulants. Quatre configurations ont BtC essayees et comparees, dont I’une avait ete preddemment ttudite. On peut en tirer deux conclusions : I. Si la configuration est telle que le test soit completement enferme dans un champ annulaire inducteur, il en r&he des effets de contraste qui alterent le jugement de luminositt. Les egalisations de luminositt deviennent ambigues s’il se produit des effets de contrastes opposes, lorsqu’il existe une grande separation entre les deux champs a egaliser. 2. L’importance de I’effet inducteur depend beaucoup de I’extension du champ inducteur autour du test. Afin d’evaluer la depression induite de la luminosite pour ttudier par exemple I’influence de la distance sur la retine entre le test et le champ inducteur. il est important de choisir une configuration oh la symetrie du test et du champ inducteur soit telle qu’elle permette une front&e la plus grande possible entre le test et la plage de comparaison. Zusammenfassung-In der Literatur wurde die induktive Helligkeitsunterdrtickung von Sie bedienten sich verschiedener Testfeldformen. Unter mehreren Autoren beschrieben. Helligkeitsvergleichstechnik wurden Experimente Verwendung einer haploskopischen angestellt, urn den Einfluss der Leuchtdichte und der Gestalt des Testfeldes festzustellen. Vier Testfeldformen wurden untersucht und verglichen; von diesen ist eine niemals vorher studiert worden. Zwei Schlijsse konnen gezogen werden: I. Jene Konfiguration, bei der das Testfeld vollstlndig in ein ringformiges Umfeld eingebettet ist, wirkt beziiglich der Kontrasteffekte abschwlchend auf die Helligkeitsbeurteilung. Die zu vergleichende Helligkeit wird uneindeutig in jenen Fallen, in denen Effekte wie die Kontrastumkehr auftauchen, wenn ein grosser Abstand zwischen den beiden zu vergleichenden Feldern besteht. 1 Presented at the 6th I C 0 Congress, Munich, August 1962. 121
I22
H. W. HOK~MAN 2. Der Betrag des induktiven Effekts wird weitgehend davon beeinflusst. in welchem Masse das induzierende Feld das Testfeld einschliesst. Urn die induzierte Helligkeitsverminderung. wie sie beispielsweise durch den Abstand des Testfeldes vom induzierenden Feld auf der Retina hervorgetufen wird, abzuschgtzen, ist es wichtig. eine Anordnung zu wlhlen, die die Symmetrie des Priiffeldes und des induzie~nden Feldes, in dem der ~~sstm~gliche Abstand zwischen Priiffeld und Vergleichsfeld enthalten ist, einschliesst. INTRODUCTION
RY INDUCTIVE brightness depression a phenomenon is meant in which the subjective impression obtained from a luminous test field is depressed by presenting an inducing field to neighbouring places of the retina. In its extreme form with high intensities of the inducing
light source the phenomenon is known as disability glare. The moderate effect can be strikingly demonstrated in a situation in which a subject matches the brightnesses of two patches seen haploscopically.” When presenting an inducing field in one eye only, an initial haploscopic match will no longer hold. In the eye receiving the inducing field the test patch appears dimmer, causing the subject to adjust the test luminance to higher values so as to match again the patch seen with the other eye. In the literature on vision, inductive brightness depression has been described by several authors. Among them SCHOWEN and ORNSTEIN (1939) were the first to suggest haploscopic matching as a tool for measuring the depression. By this means they were able to describe the amount of the depression in terms of the ratio of the luminances necessary to obtain matches with and without the inducing field. Others (FRY and ALPERN, 1953; DIAMOND, 1953; HEINEMANN, 1955) also have used the hapioscopic matching technique, but without evaluating the amount of depression in terms of luminance ratios. Also, some of them allowed the comparison patch instead of the test patch to be adjusted. It should be noted that in this case the depression in the test eye cannot be evaluated. since the reference eye may change as well, and in an unknown way. A direct comparison of the results of these authors has disclosed wide differences. Since the authors used different dimensions and configurations of the patches and the inducing field, the question arises as to whether or not the different results are mainly due to an influence of the configuration on the brightness depression. Therefore, measurements on the brightness depression have been carried out with an experimental design in which different configurations could easily be arranged. METHOD
Test and comparison patches and inducing field were formed by means of diaphragms to which translucent paper was attached and illuminated by three projection lamps (8 V, 50 W). The fields could be seen through an artificial pupil (2 mm) at a viewing distance of 2.10 m. To aid fixation both eyes received red light from two small light spots. An outline of the experimentai design is shown in Fig. 1. The luminances could be adjusted by means of neutral filters and of circular wedges. Since only mirrors were present between the eyes and the field diaphragms, other field configurations could be obtained by a simple exchange of the diaphragms. In all measurements, the inducing field was presented to the right eye. The subject was seated at ease, while his head was kept in the proper position with the aid of a headrest. ? ONLEY (1961) suggested the name “haploscopic matching technique” to distinguish between the fusion of independently presented visual fields as used in this matching technique and the conditions of normal binocular vision.
Inductive Brightness Depression
as Influenced by Configurational
Conditions
123
All the fields were presented continuously and the subject got either of two instructions, viz.: (1) to adjust the right-hand test luminance to match the test field with the constant comparison patch, under different conditions of inducing field luminance; or (2) to adjust CWN
L
SL
S
NI
I I
I
10 ml
-
c/
,’
.. __
E
FIG. 1. Experimental design for haploscopic brightness matching. S sources (Philips 13113 C, 8 V, 50 W); L Lenses; N neutral filters: W circular wedges; M mirrors; G glass plates used as partial mirrors; F fixation spots; P artificial pupils; E subject’s eyes; T, C and I diaphragms for test, comparison and inducing fields.
t
l-
C
. q El non 0. C
T
I
I
C
I
FIG. 2. Configurational conditions tested. (a) Configuration according to Heinemann (b) Configuration according to Diamond (c) Configuration according to Fry and Alpem (d) I.P.O.-configuration.
T
H. W. HOREMAN
124
the left-hand luminance so that the comparison field again matches the depressed brightness impression of the test patch, under various inducing strengths. The results of these experiments are given in terms of the retinal illumination of the inducing field. When the inducing retinal illumination increases one may expect to find adjustments towards higher values for the test patch and towards values for the comparison field. Four configurational conditions, as shown in Fig. 2, have been compared. (a). The conditions as described by HEINEMANN (1955): test and comparison patch are discs F in diam. and about 1” apart. The inducing field is annulus-shaped and surrounds the test patch. (b). The conditions given by DIAMOND (1953): test and comparison patch are squares. about &” in width and 40’ apart. The square inducing field of the same size is along the upper side of the test patch. (c). Conditions like those used by FRY and ALPERN (1953): test and comparison patch are rectangles of about 60’ x 12’. The comparison patch forms the upper extension of the test patch with a gap of 12 in. between them. The inducing field consists of twc rectangles of 60’ x 12’ adjacent to the test patch. (d). Conditions, which will be referred to as I.P.O.-configuration: test and comparison patch are semi-circular discs 40’ in diameter, adjacent to each other. Roth are encircled by the annulus-shaped inducing field of one degree outer diameter.
log
FIG. 3. Adjustment
of the test luminance VT- .Y, and of subject H-n. RESULTS
cl
itroland)
in Heinemann
configuration.
Results of subject
AND DISCUSSION
The different results are shown in Figs. 3-6 for the adjustments of the test field and in Figs. 7-10 for the left-hand adjustments. Common to all these findings is that the curves display an initial section in which the retinal illumination of the adjusted field remains fairly constant. In the case of test field adjustment, each curve represents a line of equal brightness impression. These lines reach a level, after which the curves start upwards. However,
Inductive Brightness Depression as influenced by Configurational Conditions
125
the different curves do not show the same starting points, while the slopes of the rising parts differ widely among the various curves. In detail the different results can be described as follows. Test field adjustments
1. Heinemann conjfguration (Fig. 3). The curves show a very steep rise starting almost at the level at which test and inducing field yield equal retinal illumination. It is striking that curves starting at different levels of the comparison field tend to coincide in the end. Coincidence is quite excluded from the point of view of lines of equal brightness starting at different brightness values. (Coincidence would mean that different brightness values could be attributed to a test field with one specific luminance, depending on the value with which the test field has been compared before. Though complete coincidence has not been found here the results are quite near to this as already described.)
log
(trolond)
FIG. 4. Adjustments of the test luminance in Diamond configuration. Results of subject vT=x, and of subject S= +.
2. ~jamond c~n~gur~t~~n (Fig. 4). The rise in the curves starts again at about equality of test and inducing retinal illumination, but is very moderate. Curves starting at different levels remain fairly parallel throughout the region measured. Thus, no tendency to any coincidence occurs under these configurational conditions; furthermore, in these conditions, an expression of the brightness depression in terms of luminance ratios might be successful. In the case of non-parallel curves, one cannot hope to use such a ratio to evaluate the depression since this ratio is not a constant. SCHOUTEN and ORNSTEIN (1939), who did use the luminance ratio to evaluate the depression, checked the constancy of the ratio for their conjuration by using a point-like inducing field presented near one comer of the test field. In fact Diamond’s configuration is so very similar to Schouten’s that it is tempting to suggest that their findings of a constancy of the luminance ratio was due to an approximate parallelism of the curves, such as is found in the curves with the Diamond configuration. 3. Fry and Alpern configuration (Fig. 5). The curves show steep rises and tend to come very close to each other in the end. Besides there is a shift in the starting points of the rise, for different levels of the comparison field. Though the coincidence situation is not reached,
126
H. W. HOREMA~~;
one may conclude that the brightness discriminability is greatly changed in the end of the curves. The fact of the small separations of the curves may be interpreted in terms of attributing greatly differing brightness values to only slightly differing luminances.
i/ 0
/
1
1
I
2
4
3
log 6X (trolond) FIG. 5.
Adjustments of the test luminance in Fry and Atpern configuration. VA=x, and of subject X= I.
FIG. 6.
Adjustments of the test luminance in l.P.O.-configuration. and of subject H= -.
Results of subject
Results of subject VT-X,
4. i.P.O,-c#~~~r~?i~n (Fig. 6). The rise of the curves is rather steep and the starting point of the rise shifts for different levels of the comparision field. Although the rise is steep the curves become more or less parallel in the end. However+ an evaluation in terms of luminance ratios does not hold since the separations of the curves in the horizontal portions are not equal to those in the rising portions.
Inductive Brightness Depression as Influenced by Configurational
log
cl
I
log 6, FIG. 8. Adjustments of the comparison subject VT= x, and of subject S= + .
127
(troland)
FIG. 7. Adjustments of the comparison luminance in Heinemann subject vT=x, of subject S= +, and of subject H = o.
0
Conditions
2
configuration.
Results of
3
(troland)
luminance in Diamond
configuration.
Results of
I
H. W. HGREMAH
128
Comparison field adjustments
1. Heinemann configuration (Fig. 7). In all curves, starting at the level of equality of test and inducing field (i.e. log er=log Q) a very steep fall sets in. This looks like a complete breakdown of the brightness impression of the test field. Actually HEINEMANN (1955) himself mentions in his article (p. 92) that every setting of the comparison field seems to be brighter than the test field under these conditions, even though the test fiefd can be made still darker by increasing the inducing luminance. 2. Diamond conjiguration (Fig. 8). Ali curves start with the initial constant level and then exhibit a moderate increase. No such sharp breakdown of the brightness impression of the test field can be found here.
log c;
(troland)
FIG. 9. Adjustments of the comparison luminance in Fry and Alpern configumtion. Results of subject VA==x, and of subject K= -f .
3. Fry and Alpern configuration (Fig. 9). The curves do exhibit a steep decrease, but do not seem to show a breakdown. The slope of the decreasing part however is steeper than in the curves of the Diamond configuration. 4. I.P.O.-configuration (Fig. 10). Here the curves possess the same trend, but with no tendency to breakdown. The drop-off of the curves seems somewhat less steep than in the configuration according to Fry and Alpern. CONCLUSIONS
In conclusion we may note that in the configuration in which the inducing field completely surrounds the test field the brightness depression is much more pronounced than if only partly adjacent inducing fields are used. However, in the configuration in which test and comparison patches are separated by the inducing field, the matching becomes uncertain, probably because contrast cues also make themselves felt. In the region where the lines of equal brightness impression tend to coincide, the right-hand part of the stimulus is a dark centre field on a bright surround while the left-hand part is a bright centre field on a dark surround. The hypothesis is that these opposite contrasts of the centre fields with their
Inductive Brightness Depression as Influenced by Configurational
Conditions
129
further impair the brightness-matching which by itself is a hard task because of the separation of the fields which have to be matched. A further indication of this is provided by the fact that with other configurations no breakdown occurs. It is clear that the configuration described by Heinemann is a poor one for measuring inductive brightness depression. surrounds
FIG. 10. Adjustments of the comparison subject vT=x, and of subject H= -+.
luminance
in I,P.O.-configuration.
Results of
In general it can be concluded that the extent to which the inducing field encloses the test field is quite relevant with respect to the amount of the inductive brightness depression. This is expressed, for example, by the steepness of the rising part of the different curves. To measure the influence of other configurational parameters such as the retinal distance between test patch and inducing field one needs the greatest amount of inductive depression. For that reason the configurations used by Fry and Alpern or in the I.P.O. are preferable to the conjuration given by Diamond. An additional disadvantage of Diamond’s partly adjacent inducing field is an asymmetry in the inducing effects. Using the configuration described by Fry and Alpern one may expect that contrast may also influence the results. Although there is no separation between the two fields which have to be matched, the boundary along which the test and comparison patches can be compared is very small. Doubtless the Fry and Alpern configuration gives a symmetrical influence of the inducing field on the test patch. From that point of view it seems to be a good choice, leading to a sort of linearization of the parameters in the configurational conditions. It is doubtful if this linearization is in accordance with the presumptive circular symmetry of the retina. The disadvantage of a small boundary between test and comparison patch is not present in the I.P.O.-conliguration, in which both patches are contiguous within the inducing annulus. In this configuration the brightness-match is not contaminated with other parameters such as contrast. A disadvantage of the I.P.O.~onfiguration remains in that the influence of the inducing annulus on the test patch is not quite symmetrical. Summing up, finally, inductive brightness depression is greatly influenced by the choice of the conjuration of the various fields. It seems worth noting that when measuring the
130
H. W. HoRr~hhi
inductive brightness depression as influenced by the retinal distance between test and inducing field, a proper choice of the configuration must be made in order to avoid introducing irrelevant parameters like contrasts or asymmetry. In this respect both the Fry and Aipern configuration and the I.P.O.-configuratian seem to be good approximations to the ideal. REFERENCES DIAMOND, A. L. ff953).
FoveaI simuftaneous brightness contrast as a function of inducing- and test-field luminances. J. exp. Psychol.45, 304-314. FRY, G. A. and ALPERN, M. (1953). The effect of a peripheral glare source upon the apparent brightness of an object. J. opt. Sm. Amer. 43, 189-195. HEINEMANN, E. G. (1955). Simultaneous brightness induction as a function of inducing- and test-field Iuminances. J. exp. Psychoi. 50,89-96. ONLEY, J. W. (1961). Light adaptation and the brightness of brief fovea1 stimuli. J. opt. Sm. ANT. tit, 667-673. SCN~UTEN, J. F. and ORNSTEIN, L. S. (f939f. Measurements on direct and indirect adaptation by means ofa binocular method. .r. opt. Sot. Amer. 19, 16% I%?.