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Binocular depth perception and the optic chiasm
Vkon
Rrr.
Vol. 10. pp. 4347.
BINOCULAR
Pergamon Press 1970. Pnatcd in Great Britain
DEPTH
PERCEPTION
AND THE OPTIC CHIASM
COLINBLAKEMORE~ The Neurosensory Laboratory. School of Optometry, University of California, Berkeley. California 94720, U.S.A. (Received
4 August
1969)
OX THE basis of neurophysiological experiments on the cat. BARLOW,BLAKEMORE and PETTIGREW(1967) have speculated that binocular depth discrimination depends upon signals from binocularly-driven neurones of the visual cortex which receive input from specific regions in the two retinae. The horizontal disparity varies widely from cell to cell. In other words, different neurones are optimally stimulated by objects lying at different distances from the eyes. There is a great problem for such a simple system in the centre of the visual field. The image of an object lying beyond the fixation point. and directly behind it. falls upon nasal retina in both eyes. Because of partial decussation in the optic chiasm. the two images should project separately to the two hemispheres (see point B in Fig. 1). Clearly. if partial decussation exactly splits the retinal projection to the brain. there is no chance of direct convergence of information about such an object upon a single binocular neurone. The same difficulty holdsfor an object directly in front of the fixation point which projects upon temporal retina in both eyes (see point A in Fig. 1). However. there is no doubt that the normal observer can in fact interpret the relative distances of objects briefly ,exposed in the midline of the visual field, even with very large disparities (VONHELMHOLTZ. 1866; OGLE, 1952, 1953; WESTHEIMER and TANZMAS.1956). This qualitative depth localization with double images may not be comparable with true ‘patent’ stereopsis for fused targets (OGLE. 1952) but it must involve some mechanism for the recognition of the disparity of images falling on opposite sides of the central vertical meridian in the two eyes. Somehow and somewhere the aberrant binocular messages must be combined. BLAKEMORE (1969) has suggested that neurones of the visual cortex, receiving input from near the central edge of the ipsilateral hemiretina of one eye, send axons across in the corpus callosum to contact similar cells in the visual cortex of the other hemisphere. The binocularly-driven cells formed by this kind of linkage will be optimally stimulated by objects directly in front of, or behind, the fixation point. Figure 1 shows this arrangement. Follow through the neural representation of point A which projects to both optic tracts, and hence to both occipital lobes. A fibre crossing in the corpus callosum allows the formation of a binocularly-driven neurone (marked A) in the left hemisphere. There is a similar arrangement for object B. beyond the fixation point (F). If this model, for which there is a wealth of evidence in the cat, also apphes to man, then damage to the optic chiasm or corpus callosum should have certain consequences for depth perception in the middle of the visual field. The question of the callosum is discussed in the following article and the chiasm if the subject of this study. If the opticchiasm is sagitally 1Present address: The Physiological Laboratory. University of Cambridge, Cambridge. England. 43
44
COLIN BLAKEWIRE
CALLOSUM FIG. 1. The eyes are ftxating point F. The image of object A: directly in front of F. fails on temporal
retina in both eyes. Follow through the neural connections for the retinal images of point A. The solid circIes represent active neurones. The large solid circle, marked A, in the left hemisphere, is a cell which receives an input from both eyes. The input from the right eye is delivered by a fibre crossing in the corpus callosum. The left eye‘s connection is direct, through the ipsilateral optic tract and radiation. (LGN = lateral geniculate nucleus). There is a similar set of connections with a fibre crossing in the callosum for object B. directly behind F. The appropriate cells are shown as open diamonds, the axons as interrupted lines. There is a binocularImit marked B which would represent the disparity of object B. However, the sagittal transection of the optic chiasm has interrupted the decussating fibres and object B is invisible.
sectioned, as shown in Fig. 1, the nasal retina should be completely blind in both eyes and therefore it should be totally impossible to see an object (B in Fig. 1) lying directly beyond the fixation point. On the other hand, it should be possible not only to see an object (A) immediately in front of fixation but also to recognize that it is in front, as long as the disparity is not too great. I have confirmed this simple prediction. EXPERIMENT
The subject of this study, D.W., fell from his bicycle on 12 ApriI, 1966, when he was 14 years old, and fractured the right side of his skull. FISHER,JAMPOLSKYand Scorr.(1968) have described his case in detail and the single important consequence of the injury seems to be a total and perfect section of his optic chiasm. They plotted his visual field defect and he has no residual vision whatever within the temporal hemifield of either eye. The field loss exactfy splits the fovea. In normal viewing conditions he can no longer fixate binocularly and an outward deviation (exotropia) of the right eye, by about 15”, has developed. Consequently, he usually has double vision. The apparatus used to test D.W.‘s depth perception was a modified haploscope. Transill~ated targets, mounted on the arms of the haploscope, could be presented
Binocular Depth Perception and the Optic Chiasm
4s
separately to the two eyes. Each eye saw two, vertical, thin bright slits, one above the other. (The slits subtended 2.25’ in length, 2.25’ in width. They were all at a viewing distance of 437 mm. Their luminance was 1 ft Lambert and that of the dim background 10-Z ft Lamberts.) The upper slit was illuminated continuously in both eyes and the subject learned to manipulate the arms of the apparatus until the diplopic images came close to fusing into a single slit: in other words he practically fixated the upper slit with both eyes. Immediately he obtained fusion of the upper slit’s images, the lower slit was simultaneously exposed in both eyes for about 100 msec, too brief a period to allow him to direct his gaze towards the flashed targets during their presentation. The horizontal disparity of the lower slit, relative to the upper, was set by the experimenter to produce a cue to depth. It was moved to the right of the upper slit in the right eye, and to the left by the same amount in the left eye, to mimic an object immediately behind the fixation slit, with images of divergent or uncrossed disparity. Offsets in the opposite directions produced an object in front of the upper slit, with images of convergent or crossed disparity. On the first trial the lower slit was set at a convergent disparity of 0.5’ relative to the upper. After it had been flashed, D.W. was asked to describe what he had seen. He immediately volunteered the observation that ‘it seemed’s little closer to me’. On subsequent trials the disparity of the lower slit was randomly varied in magnitude (0.5, 1, 2, 3, 5,6 and 7”) and in direction (convergent or divergent) and D.W. was asked to comment on its apparent depth, compared with the upper slit. In all, two exposures were given at each setting. Since both nasal retinae were totally blind, he never saw the lower slit when its disparity was divergent, even for only 0.5” disparity, showing that his fixation on the upper slit was quite exact. On the other hand, he was confident and spontaneous in his judgements that all the convergent settings from 0.5” to 6’ of disparity seemed closer than the upper slit. His comments included: ‘I’m pretty sure it was in front’, (1”); ‘much closer’, (2’); ‘I think it was nearer’, (5’). He was definitely unsure, however, about the largest convergent disparity of 7”. The first time that it was shown he thought that it was behind and the second time he guessed that it was in front. He also spontaneously commented for this and only this setting that there seemed to be two unrelated diplopic lower slits. These results could, of course, be explained by a simple response bias on D.W.‘s part, but this is rather unlikely. For one thing, he could easily be made to produce a judgement of ‘further away’ by asking him to describe the depth relationship of the upper slit to the flashed, convergent lower slit. DISCUSSION
It seems likely, then, that there is an interhemispheric pathway for binocular integration in man, as shown in Fig. 1. In D.W.‘s case it seems to integrate information falling up to 3” into the temporal retina in both eyes. This 6” disparity limit for D.W.‘s convergent qualitative stereopsis is entirely compatible with previous measures of the limit of depth localization with diplopic images in normal subjects using a similar experimental procedure (WESTHJZIMERand TANZMAN, 1956). Fusional vergence eye-movements, in which the eyes change their angle of convergence to tixate an object, are dependent upon the disparity of that object. In the normal observer convergence and divergence can be triggered by objects with large disparities in the midline
46
COLINBLAKE~~ORE
of the visual field (RASHBASS and W~THEI~~R. 196 1) and this must require the recognition of those disparities. It is of interest that D.W. still seems to possess fusional movements in a convergent direction. If the lower slit was switched on. and left on, D.W. reported that when he paid attention to the lower slit the diplopic images ‘moved together automatically and the top one went out (disappeared)‘. This is a magnificent description of the sensation of a vergence movement to fixate the lower convergence slit. shifting the upper slit on to the blind nasal retina of each eye. The interhemispheric pathway for disparity analysis may be used for the control of vergence eye-movements as well as for depth perception. HEINE(1900) was the first to recognize the problem of fusion and stereopsis in the midline of the visual field and he suggested a pathway for binocular integration crossing from the lateral geniculate nucleus to the opposite visual cortex. There is some anatomical evidence for such a projection (~LICKSTEIN, MILLER and SYITH, 1964) but the overwhelming anatomical and physiological evidence points to an intercortical link.2 L~NKSZ(19.52) proposed an alternative theory for midline stereopsis that demanded no interhemispheric connection. He said that the nasotemporal division might not be sharp and exact. A few ganglion cells in the temporal retina might send their fibres to the opposite optic tract, and some in the nasal retina might project to the ipsilateral tract. But if that were the case then transection of the chiasm should abolish stereopsis completely, even for convergent disparities, and the field defect should spare a little of the nasal retina in each eye. Since neither of these predictions is confirmed one must conclude that inexactitude of partial decussation is not an important factor in man. In conclusion, it should be noted that a neurophysioiogica1 experiment has provided an exact analogue of the present study. BERLUCCHIand R~zzo~~~~1.(19~8) found that, after sagittal section of the cat optic chiasm, there were still a few binocularly-driver neurones present in the visual cortex. They had typical cortical receptive fields (HUBELand WIESEL, 1962) and the two fields for a single unit invariably lay just within the temporal hemiretina in both eyes. These neurones would, therefore, be optimally stimulated by objects in front of the fixation point, exactly like cell A in Fig. 1. The following article (MITCHELLand BLAKE~~ORE. 1970) shows that section of the corpus callosum, as expected. disrupts depth perception entirely in the middle of the visual field. Acknowledgements--I am gratefuf to AM.FLOMand A. JAMPOLSKY for arranging the meeting with D. W. and, of course, D. W. himself for co-operating so willingly in these experiments. The investigation was conducted under a Fight For Sight Research Fellowship of the National Council to Combat Blindness. Inc., and a Fellowship from the Woman s Auxiliary to the American Optometric Association. The research was supported by a grant (No. Nf NDB 052 15)to H. B. BARLOWfrom the United States Public Health Service.
REFEREN.CES BARLOW,H. B.. BLAKEMORE. C. and PETTICREW,J. D. (1967). The neural mechanism of binocular depth discrimination. J. Physiol. 193, 327-342. BERLUCCHI,G. and RIZZOLAIX G. (1968). Binocularly driven neurons in visual cortex of split-chiasm cats. Science, V. I’. 159, 308-310. BLAKEYORE, C. (1969). Binocular depth discrimination and the nasotemporai division. J. Physiol. 205,47 l-497. GLICKSTE~N, M., MILLER,J. and SMITH,0. A. (1964). Lateral genicuiate nucleus and cerebral cortex: evidence for a crossed pathway. Science, N. Y. 145, 159-161. FISHER.N. F., JA%IIPOLSKY, A. and Scot-r, A. B. (1968). Traumatic bitemporaf hemianopsia. Part I. Diagnosis of macular splitting. Am. J. Ophthuf. 65, 237-242. HEW, L. (1900). SehschPrfe und Tiefenwahrnehmung. A&e& Y.Graefes Arch. Uphfhnl. 31, IS-173. ZThe
evidence.
reader is referred to the following article (MITCHELLand BLAKEMORE, 1970) for a fuit review of this
41
Binocular Depth Perception and the Optic Chiasm
Handbuch der physiologischen Optik. Voss, Hamburg. (Helmholrz’s Treati.s.e on Physiological Optics. 3rd. edn., translated by SOUTHALL,J. P. C. (1925). Optical Society of America. Menasha,
VON HELMHOLTZ, H. (1866).
Wisconsin, Vol. 3. pp. 43&I31.). H. and WIESEL,T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. J. Physiol. 160, lO$-154. LINK% A. (1952). Physiology of The Eye, vol. 2, p. 345 ff. Grune and Stratton, New York. HUBEL, D.
MITCHELL,D. E. ~~~.BLA=Mo~&
C. (1970). Binocular depth perception and the corpus callosum. Vision Res.
10,49-54. OGLE. K. N. (1952). On the limits of stereoscopic vision. J. exp. Psychol. 44, 253-259. OGLE, K. N. (1953). Precision and validity of stereoscopic depth perception from double images. J. opt. Sot. Am. 43.906-913. RASHBASS, C. and WESTHEIMER, G. (1961). Disjunctive eye movements. J. Physiol. 159, 339-360. WESTHEIMER, G. and TANZMAN, I. J. (1956). Qualitative depth localization with diplopic images. J. opr. Sot. Am.
46,116-i
17.
Abstract-After sagittal transection of the optic chiasm, a human can still recognize the depth of an object briefly exposed in front of his fixation point. even though its images fall upon temporal retina in both eyes and therefore project separately to the two hemispheres. There might be an interhemispheric link for binocular integration in central vision.
R&u&-Apr&s section sagittale du chiasma optique. un sujet humain continue g percevoir le relief d’un objet exposi britvement en avant du point de fixation, mZme si les images tombent sur les r&tines temporales des deux yeux et sont done separtment projetees dans les deux hemisph&res. II y aurait done une liaison entre les htmisphkres pour I’intCgration binoculaire en vision centrale.
Zusammenfaastmg-Ein Mensch kann die Tiefe eines vor seinem Fixationspunkte kurz dargebotenen Gegenstandes nach Sagittaltrennung seines Chiasmas erkennen, obwohl die Bilder in beiden Augen auf die Scheitelseite der Netzhaut und daher separat auf die zwei Halbkugeln projiziert werden. Es w&de zwischen den beiden Halbkugeln wohl eine Verbindung fiir die Binokularsummierung im Zentralsehen geben.
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CBSI3b,KOTOpaIiCJl)'XK‘I~JUl6HHOKYJlRpHO~
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3pCHHW.
Rrr.
Vol. 10. pp. 4347.
BINOCULAR
Pergamon Press 1970. Pnatcd in Great Britain
DEPTH
PERCEPTION
AND THE OPTIC CHIASM
COLINBLAKEMORE~ The Neurosensory Laboratory. School of Optometry, University of California, Berkeley. California 94720, U.S.A. (Received
4 August
1969)
OX THE basis of neurophysiological experiments on the cat. BARLOW,BLAKEMORE and PETTIGREW(1967) have speculated that binocular depth discrimination depends upon signals from binocularly-driven neurones of the visual cortex which receive input from specific regions in the two retinae. The horizontal disparity varies widely from cell to cell. In other words, different neurones are optimally stimulated by objects lying at different distances from the eyes. There is a great problem for such a simple system in the centre of the visual field. The image of an object lying beyond the fixation point. and directly behind it. falls upon nasal retina in both eyes. Because of partial decussation in the optic chiasm. the two images should project separately to the two hemispheres (see point B in Fig. 1). Clearly. if partial decussation exactly splits the retinal projection to the brain. there is no chance of direct convergence of information about such an object upon a single binocular neurone. The same difficulty holdsfor an object directly in front of the fixation point which projects upon temporal retina in both eyes (see point A in Fig. 1). However. there is no doubt that the normal observer can in fact interpret the relative distances of objects briefly ,exposed in the midline of the visual field, even with very large disparities (VONHELMHOLTZ. 1866; OGLE, 1952, 1953; WESTHEIMER and TANZMAS.1956). This qualitative depth localization with double images may not be comparable with true ‘patent’ stereopsis for fused targets (OGLE. 1952) but it must involve some mechanism for the recognition of the disparity of images falling on opposite sides of the central vertical meridian in the two eyes. Somehow and somewhere the aberrant binocular messages must be combined. BLAKEMORE (1969) has suggested that neurones of the visual cortex, receiving input from near the central edge of the ipsilateral hemiretina of one eye, send axons across in the corpus callosum to contact similar cells in the visual cortex of the other hemisphere. The binocularly-driven cells formed by this kind of linkage will be optimally stimulated by objects directly in front of, or behind, the fixation point. Figure 1 shows this arrangement. Follow through the neural representation of point A which projects to both optic tracts, and hence to both occipital lobes. A fibre crossing in the corpus callosum allows the formation of a binocularly-driven neurone (marked A) in the left hemisphere. There is a similar arrangement for object B. beyond the fixation point (F). If this model, for which there is a wealth of evidence in the cat, also apphes to man, then damage to the optic chiasm or corpus callosum should have certain consequences for depth perception in the middle of the visual field. The question of the callosum is discussed in the following article and the chiasm if the subject of this study. If the opticchiasm is sagitally 1Present address: The Physiological Laboratory. University of Cambridge, Cambridge. England. 43
44
COLIN BLAKEWIRE
CALLOSUM FIG. 1. The eyes are ftxating point F. The image of object A: directly in front of F. fails on temporal
retina in both eyes. Follow through the neural connections for the retinal images of point A. The solid circIes represent active neurones. The large solid circle, marked A, in the left hemisphere, is a cell which receives an input from both eyes. The input from the right eye is delivered by a fibre crossing in the corpus callosum. The left eye‘s connection is direct, through the ipsilateral optic tract and radiation. (LGN = lateral geniculate nucleus). There is a similar set of connections with a fibre crossing in the callosum for object B. directly behind F. The appropriate cells are shown as open diamonds, the axons as interrupted lines. There is a binocularImit marked B which would represent the disparity of object B. However, the sagittal transection of the optic chiasm has interrupted the decussating fibres and object B is invisible.
sectioned, as shown in Fig. 1, the nasal retina should be completely blind in both eyes and therefore it should be totally impossible to see an object (B in Fig. 1) lying directly beyond the fixation point. On the other hand, it should be possible not only to see an object (A) immediately in front of fixation but also to recognize that it is in front, as long as the disparity is not too great. I have confirmed this simple prediction. EXPERIMENT
The subject of this study, D.W., fell from his bicycle on 12 ApriI, 1966, when he was 14 years old, and fractured the right side of his skull. FISHER,JAMPOLSKYand Scorr.(1968) have described his case in detail and the single important consequence of the injury seems to be a total and perfect section of his optic chiasm. They plotted his visual field defect and he has no residual vision whatever within the temporal hemifield of either eye. The field loss exactfy splits the fovea. In normal viewing conditions he can no longer fixate binocularly and an outward deviation (exotropia) of the right eye, by about 15”, has developed. Consequently, he usually has double vision. The apparatus used to test D.W.‘s depth perception was a modified haploscope. Transill~ated targets, mounted on the arms of the haploscope, could be presented
Binocular Depth Perception and the Optic Chiasm
4s
separately to the two eyes. Each eye saw two, vertical, thin bright slits, one above the other. (The slits subtended 2.25’ in length, 2.25’ in width. They were all at a viewing distance of 437 mm. Their luminance was 1 ft Lambert and that of the dim background 10-Z ft Lamberts.) The upper slit was illuminated continuously in both eyes and the subject learned to manipulate the arms of the apparatus until the diplopic images came close to fusing into a single slit: in other words he practically fixated the upper slit with both eyes. Immediately he obtained fusion of the upper slit’s images, the lower slit was simultaneously exposed in both eyes for about 100 msec, too brief a period to allow him to direct his gaze towards the flashed targets during their presentation. The horizontal disparity of the lower slit, relative to the upper, was set by the experimenter to produce a cue to depth. It was moved to the right of the upper slit in the right eye, and to the left by the same amount in the left eye, to mimic an object immediately behind the fixation slit, with images of divergent or uncrossed disparity. Offsets in the opposite directions produced an object in front of the upper slit, with images of convergent or crossed disparity. On the first trial the lower slit was set at a convergent disparity of 0.5’ relative to the upper. After it had been flashed, D.W. was asked to describe what he had seen. He immediately volunteered the observation that ‘it seemed’s little closer to me’. On subsequent trials the disparity of the lower slit was randomly varied in magnitude (0.5, 1, 2, 3, 5,6 and 7”) and in direction (convergent or divergent) and D.W. was asked to comment on its apparent depth, compared with the upper slit. In all, two exposures were given at each setting. Since both nasal retinae were totally blind, he never saw the lower slit when its disparity was divergent, even for only 0.5” disparity, showing that his fixation on the upper slit was quite exact. On the other hand, he was confident and spontaneous in his judgements that all the convergent settings from 0.5” to 6’ of disparity seemed closer than the upper slit. His comments included: ‘I’m pretty sure it was in front’, (1”); ‘much closer’, (2’); ‘I think it was nearer’, (5’). He was definitely unsure, however, about the largest convergent disparity of 7”. The first time that it was shown he thought that it was behind and the second time he guessed that it was in front. He also spontaneously commented for this and only this setting that there seemed to be two unrelated diplopic lower slits. These results could, of course, be explained by a simple response bias on D.W.‘s part, but this is rather unlikely. For one thing, he could easily be made to produce a judgement of ‘further away’ by asking him to describe the depth relationship of the upper slit to the flashed, convergent lower slit. DISCUSSION
It seems likely, then, that there is an interhemispheric pathway for binocular integration in man, as shown in Fig. 1. In D.W.‘s case it seems to integrate information falling up to 3” into the temporal retina in both eyes. This 6” disparity limit for D.W.‘s convergent qualitative stereopsis is entirely compatible with previous measures of the limit of depth localization with diplopic images in normal subjects using a similar experimental procedure (WESTHJZIMERand TANZMAN, 1956). Fusional vergence eye-movements, in which the eyes change their angle of convergence to tixate an object, are dependent upon the disparity of that object. In the normal observer convergence and divergence can be triggered by objects with large disparities in the midline
46
COLINBLAKE~~ORE
of the visual field (RASHBASS and W~THEI~~R. 196 1) and this must require the recognition of those disparities. It is of interest that D.W. still seems to possess fusional movements in a convergent direction. If the lower slit was switched on. and left on, D.W. reported that when he paid attention to the lower slit the diplopic images ‘moved together automatically and the top one went out (disappeared)‘. This is a magnificent description of the sensation of a vergence movement to fixate the lower convergence slit. shifting the upper slit on to the blind nasal retina of each eye. The interhemispheric pathway for disparity analysis may be used for the control of vergence eye-movements as well as for depth perception. HEINE(1900) was the first to recognize the problem of fusion and stereopsis in the midline of the visual field and he suggested a pathway for binocular integration crossing from the lateral geniculate nucleus to the opposite visual cortex. There is some anatomical evidence for such a projection (~LICKSTEIN, MILLER and SYITH, 1964) but the overwhelming anatomical and physiological evidence points to an intercortical link.2 L~NKSZ(19.52) proposed an alternative theory for midline stereopsis that demanded no interhemispheric connection. He said that the nasotemporal division might not be sharp and exact. A few ganglion cells in the temporal retina might send their fibres to the opposite optic tract, and some in the nasal retina might project to the ipsilateral tract. But if that were the case then transection of the chiasm should abolish stereopsis completely, even for convergent disparities, and the field defect should spare a little of the nasal retina in each eye. Since neither of these predictions is confirmed one must conclude that inexactitude of partial decussation is not an important factor in man. In conclusion, it should be noted that a neurophysioiogica1 experiment has provided an exact analogue of the present study. BERLUCCHIand R~zzo~~~~1.(19~8) found that, after sagittal section of the cat optic chiasm, there were still a few binocularly-driver neurones present in the visual cortex. They had typical cortical receptive fields (HUBELand WIESEL, 1962) and the two fields for a single unit invariably lay just within the temporal hemiretina in both eyes. These neurones would, therefore, be optimally stimulated by objects in front of the fixation point, exactly like cell A in Fig. 1. The following article (MITCHELLand BLAKE~~ORE. 1970) shows that section of the corpus callosum, as expected. disrupts depth perception entirely in the middle of the visual field. Acknowledgements--I am gratefuf to AM.FLOMand A. JAMPOLSKY for arranging the meeting with D. W. and, of course, D. W. himself for co-operating so willingly in these experiments. The investigation was conducted under a Fight For Sight Research Fellowship of the National Council to Combat Blindness. Inc., and a Fellowship from the Woman s Auxiliary to the American Optometric Association. The research was supported by a grant (No. Nf NDB 052 15)to H. B. BARLOWfrom the United States Public Health Service.
REFEREN.CES BARLOW,H. B.. BLAKEMORE. C. and PETTICREW,J. D. (1967). The neural mechanism of binocular depth discrimination. J. Physiol. 193, 327-342. BERLUCCHI,G. and RIZZOLAIX G. (1968). Binocularly driven neurons in visual cortex of split-chiasm cats. Science, V. I’. 159, 308-310. BLAKEYORE, C. (1969). Binocular depth discrimination and the nasotemporai division. J. Physiol. 205,47 l-497. GLICKSTE~N, M., MILLER,J. and SMITH,0. A. (1964). Lateral genicuiate nucleus and cerebral cortex: evidence for a crossed pathway. Science, N. Y. 145, 159-161. FISHER.N. F., JA%IIPOLSKY, A. and Scot-r, A. B. (1968). Traumatic bitemporaf hemianopsia. Part I. Diagnosis of macular splitting. Am. J. Ophthuf. 65, 237-242. HEW, L. (1900). SehschPrfe und Tiefenwahrnehmung. A&e& Y.Graefes Arch. Uphfhnl. 31, IS-173. ZThe
evidence.
reader is referred to the following article (MITCHELLand BLAKEMORE, 1970) for a fuit review of this
41
Binocular Depth Perception and the Optic Chiasm
Handbuch der physiologischen Optik. Voss, Hamburg. (Helmholrz’s Treati.s.e on Physiological Optics. 3rd. edn., translated by SOUTHALL,J. P. C. (1925). Optical Society of America. Menasha,
VON HELMHOLTZ, H. (1866).
Wisconsin, Vol. 3. pp. 43&I31.). H. and WIESEL,T. N. (1962). Receptive fields, binocular interaction and functional architecture in the cat’s visual cortex. J. Physiol. 160, lO$-154. LINK% A. (1952). Physiology of The Eye, vol. 2, p. 345 ff. Grune and Stratton, New York. HUBEL, D.
MITCHELL,D. E. ~~~.BLA=Mo~&
C. (1970). Binocular depth perception and the corpus callosum. Vision Res.
10,49-54. OGLE. K. N. (1952). On the limits of stereoscopic vision. J. exp. Psychol. 44, 253-259. OGLE, K. N. (1953). Precision and validity of stereoscopic depth perception from double images. J. opt. Sot. Am. 43.906-913. RASHBASS, C. and WESTHEIMER, G. (1961). Disjunctive eye movements. J. Physiol. 159, 339-360. WESTHEIMER, G. and TANZMAN, I. J. (1956). Qualitative depth localization with diplopic images. J. opr. Sot. Am.
46,116-i
17.
Abstract-After sagittal transection of the optic chiasm, a human can still recognize the depth of an object briefly exposed in front of his fixation point. even though its images fall upon temporal retina in both eyes and therefore project separately to the two hemispheres. There might be an interhemispheric link for binocular integration in central vision.
R&u&-Apr&s section sagittale du chiasma optique. un sujet humain continue g percevoir le relief d’un objet exposi britvement en avant du point de fixation, mZme si les images tombent sur les r&tines temporales des deux yeux et sont done separtment projetees dans les deux hemisph&res. II y aurait done une liaison entre les htmisphkres pour I’intCgration binoculaire en vision centrale.
Zusammenfaastmg-Ein Mensch kann die Tiefe eines vor seinem Fixationspunkte kurz dargebotenen Gegenstandes nach Sagittaltrennung seines Chiasmas erkennen, obwohl die Bilder in beiden Augen auf die Scheitelseite der Netzhaut und daher separat auf die zwei Halbkugeln projiziert werden. Es w&de zwischen den beiden Halbkugeln wohl eine Verbindung fiir die Binokularsummierung im Zentralsehen geben.
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