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The Relation of Accommodation to the Suppression of Vision in One Eye
T H E RELATION OF ACCOMMODATION TO T H E SUPPRESSION OF VISION IN ONE E Y E GLENN A. FRY, P H . D . SAINT LOUIS
The present work is a continuation of that undertaken by McDougall and represents an attempt further to differentiate the factors involved in the voluntary suppression of vision in one eye. The rate of rivalry between afterimages induced in the two eyes, and between images produced by direct stimulation, can be affected by changes in accommo dation. These effects can be obliterated by paralyzing the ciliary muscles with homatropine or by using a small artificial pupil which minimizes the effect upon the blurredness of the retinal image. From the Department of Ophthalmology, Oscar Johnson Institute, Washington University. This investigation was made possible by a grant from the American Academy of Ophthalmology and Otolaryngology.
The present paper deals with a con tinuation of the type of work under taken by McDougall in 1903.1 McDou gall showed that if one of the eyes is paralyzed with atropine, the ability to favor one of the monocular impressions in binocular rivalry is partially lost. This type of work was resumed by W. R. George and the writer while they were working together under Professor McDougall's supervision in 1932, and to Dr. George belongs the credit for a considerable amount of the prelimin ary work which forms the basis for the present paper. The difficulty lies not so much in demonstrating that accommodation provides the basis for the voluntary suppression of vision in one eye, or the favoring of vision in the other, but in determining the exact manner in which this effect is accomplished. It might be produced in three w a y s : (1) through changes in the blurredness of the optical image, (2) through changes in intraocular pressure, and (3) through facilitating or inhibitory ef fects produced by proprioceptive im pulses from the accommodation mus cles upon the impressions from the retinae. The use of afterimages instead of images produced by direct stimulation presents a situation in which optical blurredness is not involved. Under these conditions one is still able to re tard or accelerate the rate of alter nations between the dextrocular and sinistrocular impressions, as is demon strated by the following experiment: The subject fixated the center of a bright horizontal bar ( 1 " x 3") in a
dark field with the right eye for 20 sec. and after a lapse of 10 sec. fixated the center of a vertical bar with the left eye for 20 sec. The positive after images were observed in complete darkness, the dextrocular and sinis trocular impressions appearing alter nately. These fluctuations were record ed on a kymograph drum by letting the subject press a key controlling a signal marker. Six separate observa tions were made with the eyes normal, the subject trying to retard and ac celerate the rate of fluctuations in al ternate observations.* The eyes were then paralyzed with homatropine and six similar observations were made. The results are given in table 1. Each Table 1. SHOWING THE EFFECT OF THE VOLUNTARY CONTROL OF ATTENTION UPON THE RATE OF ALTERNATION BETWEEN MONOCULAR IMPRES SIONS PRODUCED BY AFTERIMAGES IN THE TWO EYES. (ALTERNATIONS PER MIN.)
135
Eyes Normal
Eyes Paralyzed.
Attempted Attempted Accelera Retarda tion tion
Attempted Attempted Accelera Retarda tion tion
23+2.66
15.4±1.8
13 ± . 6 6
13.4+.8
value represents an average for three one-minute periods of observations. The bright bars used to induce the * In trying to prolong the visibility phase of one eye the subject tries to concentrate his attention on the impression which is visible at the moment, but if he wants to make it disappear and_ bring on the other impression, he tries to imagine the other im pression.
136
GLENN A. FRY
afterimages had a brightness of 3600 c. per sq. ft.,2 and were observed through ficial pupils 2.33 mm. in diameter. As the tabulated results show, one can by voluntarily controlling his at tention change the rate of alternations from 13 to 23 per minute, but this ef fect is practically abolished when the eyes are paralyzed. Although the use of afterimages rules out optical blurredness, the above ex periment does not differentiate between the parts played by changes in intra ocular pressure and proprioceptive im pulses. In order to demonstrate that
the right eye when the right-eye image was present, and on the left eye when its image was present one could retard the rate to 14 alternations per minute. Afterimages differ from primary images in this respect, that they pe riodically disappear even when ob served with one eye. For example, if an afterimage similar to those used in the above experiments is induced in one eye only, every 8 or 10 seconds it will disappear for a short period of about 2 to 4 seconds. Fry and Robertson 2 have shown that these disappearances depend upon the obliteration of the im-
]
Front View
% Cardboard Screen
Containing Stimulus Pattern
Relative Positions of the Two Monocular Patterns in the. Binocular Field
First Surface Mirrors Opol-flashed. Glass
A
FronA View Cardboard Screen Containing Stimulus Pattern
rlificial Evt»
Opal-flashed 6 lass
Fig. 1 (Fry). Apparatus for investigating the binocular rivalry of bars crossing each other. The images of the two stimulus patterns are seen reflected in the two first surface mirrors. The dots in the center bars serven as nfixation marks and the mirrors are adjusted to compen sate phoria. The bars are 1J4 i - l° g, one-fourth in. wide, and one-fourth in. apart. The stimulus patterns are 13 in. from the mirrors, and the mirrors 2.5 in. from the corneas.
changes in intraocular pressure alone are capable of changing the rate of al ternations, the following experiment was performed. Afterimages of horizon tal and vertical bars were used as in the previous experiment and the eyes were paralyzed. By pressing on the closed eyelid of the left eye with the fingers when the image of the right eye appeared, one could make the image of the right eye quickly give way to the image of the left. The appearance of the right-eye image could then be made to reappear by pressing on the right eye. In this way a rate of about 26 alternations per minute could be ob tained. When, however, one pressed on
pression at the retinal level and that by controlling his attention one can in crease or decrease the frequency of these disappearances when the eyes are normal, but not if the eyes are para lyzed with homatropine. To what ex tent the binocular rivalry is affected by the periodic obliteration of the impres sions at the retinal level has not been carefully investigated, but the facts are plentiful enough to make one suspect that the changes in intraocular pres sure produce their primary effect upon the periodic obliteration of the impres sions at the retinal level, and that this in turn affects the rate of alternation in binocular rivalry.
ACCOMMODATION AND SUPPRESSION OF VISION
Even in the case of impressions pro duced by direct stimulation, if an object differs only slightly in brightness from its background, the retinal impression will be obliterated periodically. But the difference can be made great enough so that the retinal impression will be stable, and periodic obliterations at the retinal level cannot be involved in the alternations in binocular rivalry. Although changes in intraocular pressure affect the binocular rivalry of afterimages, this factor can be demon strated to play little or no role in the suppression of vision in the case of im pressions produced by direct stimula tion. For investigating the rivalry of
137
eter, and six other records were ob tained with the eyes paralyzed and artificial pupils 3.94 mm. in diameter. The results are shown in table 2. Although one is able to change the rate of alternations from 48.6 per min ute to 28.4 per minute when the artifi cial pupils have a diameter of 3.94 mm., this ability is almost completely abol ished when the pupil diameters are re duced to 2.06 mm. The most plausible explanation for this is that the small artificial pupil prevents changes in ac commodation from producing marked effects upon the blurredness of the opti cal image, but it does not interfere with the changes in intraocular pressure or
Table 2 SHOWING THE EFFECT OF THE VOLUNTARY CONTROL OF ATTENTION UPON THE RATE OF AL TERNATIO BETWEEN MONOCULAR IMPRESSIONS PRODUCED BY DIRECT STIMULATION OF THE TWO EYES (ALTERNATIONS PER MINUTE)
Eyes Paralyzed
Eyes Normal Art. Pupil 3.94 mm. in Diameter Attempted Acceleration 48.6±4.8
Attempted Retardation 28.4 + 2.8
Art. Pupil 2.06 mm. in Diameter Attempted Acceleration 42.6 + 7.8
impressions produced by direct stimu lation, the apparatus in figure 1 was used, which makes it possible to pre sent a group of three horizontal bright bars in a dark field to the left eye, and a similar group of vertical bars to the right eye. The brightness of the bars was set at .75c. per sq. ft. The two groups of bars are seen alternately, and a record of the alternations for oneminute periods can be made on a ky mograph drum. With the eyes normal and artificial pupils 3.94 mm.* in diam eter placed before them, records for six separate observation periods were obtained. In alternate observations the subject attempted to accelerate and re tard the rate of fluctuations. Six similar records were obtained with normal eyes and artificial pupils 2.06 mm. in diam* U n d e r the conditions of the e x p e r i m e n t the size of the natural pupil is about S m m . in diameter by actual m e a s u r e m e n t .
Attempted Retardation 39.6+.4
Art. Pupil 2.06 mm. in Diameter Attempted Acceleration 45.4+.8
Attempted Retardation 40 + 2
the proprioceptive impulses, so that it cannot be assumed that these factors play an essential role. As can be seen in the tabulated results, the ability to change the rate of alternations is also abolished to a large extent by the use of homatropine. Summary and conclusions The voluntary suppression or favor ing of vision in one eye has been demonstrated to be mediated through changes in accommodation by showing that the voluntary control is abolished by paralyzing the ciliary muscles with homatropine. In the case of afterimages the control is brought about through changes in intraocular pressure because optical blurredness is not involved, and because it can be shown that applying pressure to one of the eyes causes the impression of that eye to predominate over that of the other eye. In the case
138
GLENN A. FRY
of the rivalry of impressions produced by direct stimulation, the voluntary control is mediated through changes in the blurredness of the optical image, because voluntary control is abolished by use of a small artificial pupil, which minimizes the effects of changes in ac commodation upon optical blurredness but does not interfere with proprioceptive impulses or changes in intraocular pressure. The demonstration that the volun tary suppression or favoring of vision in one eye is mediated through the ciliary muscles is of theoretical impor tance because Helmholtz 3 used this phenomenon as evidence against Miiller's doctrine that paths from cor responding points of the two retinae converge upon common cerebral path ways. He believed that the paths from corresponding points of the two eyes remain separate up to the point to which consciousness is adjunct and that the integration of the two monocular impressions is a psychic affair, and the suppression of one of the impressions
is simply a matter of the mind's ignor ing it. Now if the voluntary control is effected through peripheral mecha nisms, this vitiates Helmholtz's objec tion to the doctrine of common cerebral centers. The discovery of the particular mech anisms involved in the voluntary sup pression of vision and of methods for controlling suppression should be of practical importance in the treatment of squint, but procedures utilizing this knowledge have not as yet been worked out. The demonstration that voluntary control of binocular rivalry can be abol ished by such means as mydriatics and artificial pupils is of practical impor tance to those who are interested in the investigation of binocular phenomena, because if proper precautions are taken they need no longer fear that uncon trolled changes of attention will lead to spurious results. Dept. of Physics, Ohio State Univ., Columbus.
References McDougall, W. Physiological factors of the attention process, III. Brain, 1903, v. 12, pp. 473-488. 2 Fry, G. A., and Robertson, V. M. The physiological basis of the periodic merging of an area into its background. Amer. Jour. Psych., In press. 3 Helmholtz, H. von. Physiological optics. American ed., 1925, v. 2, p. 499. 1
The present work is a continuation of that undertaken by McDougall and represents an attempt further to differentiate the factors involved in the voluntary suppression of vision in one eye. The rate of rivalry between afterimages induced in the two eyes, and between images produced by direct stimulation, can be affected by changes in accommo dation. These effects can be obliterated by paralyzing the ciliary muscles with homatropine or by using a small artificial pupil which minimizes the effect upon the blurredness of the retinal image. From the Department of Ophthalmology, Oscar Johnson Institute, Washington University. This investigation was made possible by a grant from the American Academy of Ophthalmology and Otolaryngology.
The present paper deals with a con tinuation of the type of work under taken by McDougall in 1903.1 McDou gall showed that if one of the eyes is paralyzed with atropine, the ability to favor one of the monocular impressions in binocular rivalry is partially lost. This type of work was resumed by W. R. George and the writer while they were working together under Professor McDougall's supervision in 1932, and to Dr. George belongs the credit for a considerable amount of the prelimin ary work which forms the basis for the present paper. The difficulty lies not so much in demonstrating that accommodation provides the basis for the voluntary suppression of vision in one eye, or the favoring of vision in the other, but in determining the exact manner in which this effect is accomplished. It might be produced in three w a y s : (1) through changes in the blurredness of the optical image, (2) through changes in intraocular pressure, and (3) through facilitating or inhibitory ef fects produced by proprioceptive im pulses from the accommodation mus cles upon the impressions from the retinae. The use of afterimages instead of images produced by direct stimulation presents a situation in which optical blurredness is not involved. Under these conditions one is still able to re tard or accelerate the rate of alter nations between the dextrocular and sinistrocular impressions, as is demon strated by the following experiment: The subject fixated the center of a bright horizontal bar ( 1 " x 3") in a
dark field with the right eye for 20 sec. and after a lapse of 10 sec. fixated the center of a vertical bar with the left eye for 20 sec. The positive after images were observed in complete darkness, the dextrocular and sinis trocular impressions appearing alter nately. These fluctuations were record ed on a kymograph drum by letting the subject press a key controlling a signal marker. Six separate observa tions were made with the eyes normal, the subject trying to retard and ac celerate the rate of fluctuations in al ternate observations.* The eyes were then paralyzed with homatropine and six similar observations were made. The results are given in table 1. Each Table 1. SHOWING THE EFFECT OF THE VOLUNTARY CONTROL OF ATTENTION UPON THE RATE OF ALTERNATION BETWEEN MONOCULAR IMPRES SIONS PRODUCED BY AFTERIMAGES IN THE TWO EYES. (ALTERNATIONS PER MIN.)
135
Eyes Normal
Eyes Paralyzed.
Attempted Attempted Accelera Retarda tion tion
Attempted Attempted Accelera Retarda tion tion
23+2.66
15.4±1.8
13 ± . 6 6
13.4+.8
value represents an average for three one-minute periods of observations. The bright bars used to induce the * In trying to prolong the visibility phase of one eye the subject tries to concentrate his attention on the impression which is visible at the moment, but if he wants to make it disappear and_ bring on the other impression, he tries to imagine the other im pression.
136
GLENN A. FRY
afterimages had a brightness of 3600 c. per sq. ft.,2 and were observed through ficial pupils 2.33 mm. in diameter. As the tabulated results show, one can by voluntarily controlling his at tention change the rate of alternations from 13 to 23 per minute, but this ef fect is practically abolished when the eyes are paralyzed. Although the use of afterimages rules out optical blurredness, the above ex periment does not differentiate between the parts played by changes in intra ocular pressure and proprioceptive im pulses. In order to demonstrate that
the right eye when the right-eye image was present, and on the left eye when its image was present one could retard the rate to 14 alternations per minute. Afterimages differ from primary images in this respect, that they pe riodically disappear even when ob served with one eye. For example, if an afterimage similar to those used in the above experiments is induced in one eye only, every 8 or 10 seconds it will disappear for a short period of about 2 to 4 seconds. Fry and Robertson 2 have shown that these disappearances depend upon the obliteration of the im-
]
Front View
% Cardboard Screen
Containing Stimulus Pattern
Relative Positions of the Two Monocular Patterns in the. Binocular Field
First Surface Mirrors Opol-flashed. Glass
A
FronA View Cardboard Screen Containing Stimulus Pattern
rlificial Evt»
Opal-flashed 6 lass
Fig. 1 (Fry). Apparatus for investigating the binocular rivalry of bars crossing each other. The images of the two stimulus patterns are seen reflected in the two first surface mirrors. The dots in the center bars serven as nfixation marks and the mirrors are adjusted to compen sate phoria. The bars are 1J4 i - l° g, one-fourth in. wide, and one-fourth in. apart. The stimulus patterns are 13 in. from the mirrors, and the mirrors 2.5 in. from the corneas.
changes in intraocular pressure alone are capable of changing the rate of al ternations, the following experiment was performed. Afterimages of horizon tal and vertical bars were used as in the previous experiment and the eyes were paralyzed. By pressing on the closed eyelid of the left eye with the fingers when the image of the right eye appeared, one could make the image of the right eye quickly give way to the image of the left. The appearance of the right-eye image could then be made to reappear by pressing on the right eye. In this way a rate of about 26 alternations per minute could be ob tained. When, however, one pressed on
pression at the retinal level and that by controlling his attention one can in crease or decrease the frequency of these disappearances when the eyes are normal, but not if the eyes are para lyzed with homatropine. To what ex tent the binocular rivalry is affected by the periodic obliteration of the impres sions at the retinal level has not been carefully investigated, but the facts are plentiful enough to make one suspect that the changes in intraocular pres sure produce their primary effect upon the periodic obliteration of the impres sions at the retinal level, and that this in turn affects the rate of alternation in binocular rivalry.
ACCOMMODATION AND SUPPRESSION OF VISION
Even in the case of impressions pro duced by direct stimulation, if an object differs only slightly in brightness from its background, the retinal impression will be obliterated periodically. But the difference can be made great enough so that the retinal impression will be stable, and periodic obliterations at the retinal level cannot be involved in the alternations in binocular rivalry. Although changes in intraocular pressure affect the binocular rivalry of afterimages, this factor can be demon strated to play little or no role in the suppression of vision in the case of im pressions produced by direct stimula tion. For investigating the rivalry of
137
eter, and six other records were ob tained with the eyes paralyzed and artificial pupils 3.94 mm. in diameter. The results are shown in table 2. Although one is able to change the rate of alternations from 48.6 per min ute to 28.4 per minute when the artifi cial pupils have a diameter of 3.94 mm., this ability is almost completely abol ished when the pupil diameters are re duced to 2.06 mm. The most plausible explanation for this is that the small artificial pupil prevents changes in ac commodation from producing marked effects upon the blurredness of the opti cal image, but it does not interfere with the changes in intraocular pressure or
Table 2 SHOWING THE EFFECT OF THE VOLUNTARY CONTROL OF ATTENTION UPON THE RATE OF AL TERNATIO BETWEEN MONOCULAR IMPRESSIONS PRODUCED BY DIRECT STIMULATION OF THE TWO EYES (ALTERNATIONS PER MINUTE)
Eyes Paralyzed
Eyes Normal Art. Pupil 3.94 mm. in Diameter Attempted Acceleration 48.6±4.8
Attempted Retardation 28.4 + 2.8
Art. Pupil 2.06 mm. in Diameter Attempted Acceleration 42.6 + 7.8
impressions produced by direct stimu lation, the apparatus in figure 1 was used, which makes it possible to pre sent a group of three horizontal bright bars in a dark field to the left eye, and a similar group of vertical bars to the right eye. The brightness of the bars was set at .75c. per sq. ft. The two groups of bars are seen alternately, and a record of the alternations for oneminute periods can be made on a ky mograph drum. With the eyes normal and artificial pupils 3.94 mm.* in diam eter placed before them, records for six separate observation periods were obtained. In alternate observations the subject attempted to accelerate and re tard the rate of fluctuations. Six similar records were obtained with normal eyes and artificial pupils 2.06 mm. in diam* U n d e r the conditions of the e x p e r i m e n t the size of the natural pupil is about S m m . in diameter by actual m e a s u r e m e n t .
Attempted Retardation 39.6+.4
Art. Pupil 2.06 mm. in Diameter Attempted Acceleration 45.4+.8
Attempted Retardation 40 + 2
the proprioceptive impulses, so that it cannot be assumed that these factors play an essential role. As can be seen in the tabulated results, the ability to change the rate of alternations is also abolished to a large extent by the use of homatropine. Summary and conclusions The voluntary suppression or favor ing of vision in one eye has been demonstrated to be mediated through changes in accommodation by showing that the voluntary control is abolished by paralyzing the ciliary muscles with homatropine. In the case of afterimages the control is brought about through changes in intraocular pressure because optical blurredness is not involved, and because it can be shown that applying pressure to one of the eyes causes the impression of that eye to predominate over that of the other eye. In the case
138
GLENN A. FRY
of the rivalry of impressions produced by direct stimulation, the voluntary control is mediated through changes in the blurredness of the optical image, because voluntary control is abolished by use of a small artificial pupil, which minimizes the effects of changes in ac commodation upon optical blurredness but does not interfere with proprioceptive impulses or changes in intraocular pressure. The demonstration that the volun tary suppression or favoring of vision in one eye is mediated through the ciliary muscles is of theoretical impor tance because Helmholtz 3 used this phenomenon as evidence against Miiller's doctrine that paths from cor responding points of the two retinae converge upon common cerebral path ways. He believed that the paths from corresponding points of the two eyes remain separate up to the point to which consciousness is adjunct and that the integration of the two monocular impressions is a psychic affair, and the suppression of one of the impressions
is simply a matter of the mind's ignor ing it. Now if the voluntary control is effected through peripheral mecha nisms, this vitiates Helmholtz's objec tion to the doctrine of common cerebral centers. The discovery of the particular mech anisms involved in the voluntary sup pression of vision and of methods for controlling suppression should be of practical importance in the treatment of squint, but procedures utilizing this knowledge have not as yet been worked out. The demonstration that voluntary control of binocular rivalry can be abol ished by such means as mydriatics and artificial pupils is of practical impor tance to those who are interested in the investigation of binocular phenomena, because if proper precautions are taken they need no longer fear that uncon trolled changes of attention will lead to spurious results. Dept. of Physics, Ohio State Univ., Columbus.
References McDougall, W. Physiological factors of the attention process, III. Brain, 1903, v. 12, pp. 473-488. 2 Fry, G. A., and Robertson, V. M. The physiological basis of the periodic merging of an area into its background. Amer. Jour. Psych., In press. 3 Helmholtz, H. von. Physiological optics. American ed., 1925, v. 2, p. 499. 1