Researches in Binocular Vision by Kenneth N.
Ogle, Ph.D. 1950, W.B. Saunders Company, Philadelphia
Introduction
Binocular vision is the coordinated behaviour of the two
eyes by which a single perception of external space is obtained and by which
its greatest achievement, the specific sensation of stereoscopic depth
perception, is made possible.
In trying to understand the processes of binocular vision,
we are concerned in the main with the physiologic and functional organization
of the two eyes – how they work together and how they convey the information
about external space to the higher brain centers.
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Chapter 1
The Structure of the Visual Pathways
Although it has been known for some time that the visual
centers of the brain lie at the occipital lobes, it is only during the past few
decades that research workers have established the fact that the retinas are
projected spatially onto the cortex of the medial surfaces of these lobes.
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The nerve fibres from the left halves of the retinas (concerned
with the right half of the visual field) proceed to the left side of the brain,
and the nerve fibres from the right halves of the retinas (concerned with the
left half of the visual field) proceed to the right side of the brain. The
fibres from the nasal parts of the retinas decussate or cross over at the
chiasm to the opposite (contralateral) lobe, while those from the temporal
parts of the retinas pass to the lobe on the same (ipsilateral) side without
crossing. This division is sharply made along vertical lines through the foveas
of the two eyes.
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Chapter 2
The Theory of Corresponding Retinal Points
Objective and Subjective Spaces
The eyes and the visual processes transform the objective
world through light stimuli into the subjective world of form, spatial
relationships and colour.
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…we assume that an object in objective space may be
displaced without deformation and without changes between related points, and
therefore that the geometric laws of Euclid hold. In visual space, this is not
true. As an object recedes, not only does it appear to become smaller but
its shape appears to change, this change
being greater in depth extent than in height or width.
…there must be a clear understanding of the fact that the
objective world and the subjective world are incommensurate. It is only
important that, whatever relationship exists between objective and visual
space, it should be fairly stable if the individual is to act effectively in
the physical world.
Localization According to Direction
It is an everyday experience that different objects in the
field of view are perceived in different directions with respect to our bodies,
and the differences in these directions certainly are related to the actual
angular separation of those objects referred to the eye. This ability to
discriminate differences in direction is attributed to the discrete character
and arrangements of the receptor elements in the retina – which effectively
comprise a mosaic of separated and insulated light-sensitive elements.
Visual acuity or, more precisely, resolving power, is the
keenest differentiation of this type that can be made. This. of course, depends
not only on the dimensions and density of the receptor cells but also on the
useful optical characteristics of the eye. the so-called “form” sense also has
as its basis the discrimination of separated stimuli and the subsequent
appreciation of extension.
When the eye is directed to a given fixation point, the
image of that point falls on the fovea, and the subjective direction associated
with the retinal elements of this fixation point is called the principal
visual direction (Hering). Objects whose images fall away from that point
are experienced as being in a direction to the right, left, above or below.
Thus every point in the whole visual field has a psychic
counterpoint mediated by the retinal mosaic, which gives rise to a subjective
visual direction always relative to the principal visual direction
corresponding to the point of fixation.
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The foveas, then, when stimulated give rise to the
principal visual direction. Stimulation of adjacent retinal points give rise to
specific subjective directions relative to the principal directions
according to breadth and height, these directions being approximately
proportional to the distance of a given element from the fovea. This
discrimination of direction obviously become less exact toward the periphery of
the retina, because there the discrete makeup of the retina becomes cruder.
The Binocular Visual Field – Corresponding Points
By means of mirrors, Fischer has demonstrated the
correspondence of those peripheral retinal elements that under ordinary
conditions can never be used simultaneously because the nose of the individual
occludes that part of the binocular field of vision.
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Images from object points in space which do not fall on
corresponding elements are said to be disparate, and in terms of
monocular vision each of the images would give rise to two different
subjective primary directions. The farther such points are from the horopter
the greater the disparity. Because the two eyes are arranged in the head
horizontally, the horizontal meridian forms a convenient basis to describe
disparities as horizontal or vertical. Horizontal disparities are the basis for
the stereoscopic perception of depth.
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The Longitudinal Horopter and the Region of Binocular Single Vision
The oldest concept regarding corresponding retinal points
was that when the images from a point in space fell on corresponding points it
would be seen single. Singleness was the criterion for determining the
horopter. Wheatstone, however, found with the reflecting stereoscope that
configurations of unequal separation in the two targets, which could obviously not
stimulate corresponding points, would nevertheless fuse and be seen single.
Panum first systematically studies this problem and showed that an image on a
retinal point of one eye would fuse with a similar image on the retina of the
other eye, anywhere within a small area of the retina. Thus, singleness alone
could not be used as a criterion for determining the corresponding retinal
points.
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Moving the rod still farther away [from a fixation point
where binocular single vision is experienced], one suddenly becomes aware of
uncrossed double images, the apparent separation of which increases as the rod
continues moving away. There exists an interval between Pc and Pu
where no doubling is seen [fixation point where binocular single vision is
experienced]. Such intervals obtained for all visual angles define a region in
space which is designated as the region of binocular single vision. The images
from the two eyes of all points within this region are said to be “fused”.
There is a diagram to go with this.
On each side of this position [single vision fixation point]
the images are either crossed (rod nearer) or uncrossed (rod farther), even
though within a certain region only one image is seen; that is, within this
region the two images are fused, although disparate.
The boundaries of the region of binocular single vision are not well defined…
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The appearance of double images as the disparities
increase is easier to observe when there is movement in the test rods. In the
case of stationary objects, one rarely is aware of double images unless the
disparities are very great and when one consciously looks for the doubling, as
for example, in the apparent doubling of the curtain string on fixating on a
distant object through the window. The greater part of this failure to see
double images in ordinary life is thought to be due to some form of rivalry and
certainly suppression.
Add this to Meinel’s description
of the experience of double images.
The small oscillatory movements of the eyes (physiologic
nystagmus) also are factors in the extent of Panum’s areas. Adler and
Fliegelman showed that for monocular fixation there were three types of these
movements acting at the same time: (1) rapid shifts of fixation of 12 minutes
of arc that occur about once a second; (2) waves, small shifts and recoveries
of about 2.5 minutes of arc at the rate of five per second, and (3) fine
vibratory movements of about two minutes of arc at a rate of 50 to 100 per
second.
This links to something Gibson said about eyes never being stationary
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Chapter 6
The Phenomenon of Fusion
The striking fact of normal vision with the two eyes is that
although there are two retinal images, we as individuals experience only a
single perception of space.
There [in regions of the occipital lobe] fusion
(unification) either takes place locally as a physiologic process or takes
place more diffusely entirely as a psychic response. This unification must
occur prior to the conscious awareness of the images in the perceptional experience.
In either case the emergent sensation is one of singleness. At the present time
we can only conjecture as to the nature of the process involved.
Links to Julesz’ random-dot-stereogram – depth/fusion
occurring before conscious awareness of image.
Much discussion and controversy exists in the literature as
to whether there is ever real fusion, whether fusion centers exist in the
brain, or whether what appears as fusion is the psychic replacement of one part
of the image from one eye by a corresponding part of the image from the other
eye.
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The Fusion Compulsion
The movements of the eyes necessary to cause the images
to fall again as near as possible to corresponding retinal elements, so that
fusion is regained, are known as fusional movements. This phenomenon of
the visual processes is for the purpose of preventing the appearance of double
images (diplopia).
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In ordinary surroundings where there may be many objects
in the field of view at different distances from the observer, then, there are
a multiplicity of horizontal disparities of the images of different objects.
While each of these may exert its influence for a fusional movement, attention
may be a prerequisite before the reflex goes into action. In any event, once
the attention is directed to a given point, although the images are then
disparate, the reflex to fusion so directs the eyes that the images on the two
retinas fall as nearly as possible on corresponding retinal points. These
reflexes cannot be considered as pure reflexes because they first depend upon
an attention factor before they become effective.
Conditions for Fusion and Rivalry
The optical image on the retina is made up of contagious
light and dark areas, the lines of separation being designated as contours. It
is these contours, the demarcations between light and less light areas, that
provide the pattern of the images and the stimuli for fusion when they exist in
both eyes.
Links to Meinels description of
Double Vision
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Chapter 12
Spatial Localization and Stereoscopic Vision
Binocular Spatial Localization
Binocular space perception and the stereoscopic perception
of depth in particular exist by virtue of the fact that the two eyes are
separated in space. Each, therefore, views the three-dimensional world of
objects from a slightly different point of view.
The perspective and the relative alignment of objects in
space will be unlike in the two images, and this dissimilarity will be greater
the nearer are the objects to the observer. As those objects recede into the
distance, the two images gradually become identical.
Direct reference for close-up
perspective of mask
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The subjective appearances of objects in space and their
orientation, whether observed by one eye or by both eyes, are essentially of
the same inherent nature and have the same origin in past experience,
individual and phylogenetic. Both monocular and binocular space perceptions are
based on relationships to an innately fixed organizations in the anatomy of the
retinas.
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Many other factors well known to psychologists exist in the
perception of space. These are especially demonstrable in certain illusions.
Attention is called to the size-constancy phenomenon, by which the
apparent visual size of an object is also dependant on its apparent visual
distance, and not wholly on the size of the retinal image. In fact, there is an
approximate proportionality between apparent size and object distance (Emmert’s
law). For a retinal image of a given size, the apparent size will, within
certain limits, increase with the distance.
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