BINOCULAR VISION AND SPACE PERCEPTION
Slide 1
- Location: Position of an object in physical (objective) space
- Localization: Position of the object in visual (subjective) space
- Retinal elements/points/ Areas: The retinocerebral apparatus engaged in elaborating a sensation in response to the excitation of a unit area of the retinal surface
Slide 2
Relative subjective visual direction
- Each retinal element localizes the stimulus as a visual percept in a specific visual direction relative to the visual direction of the fovea
Slide 3-5
Retinomotor values
- It is the degree of movement of the eye to get fixation at the fovea
Slide 6-7
Common relative subjective visual direction
- All object points that simultaneously stimulate the two fovea appear in one and the same subjective visual direction i.e not in the direction of the principal line of direction of either eye but in a direction coinciding with the medial plane of the head
Slide 8-11
Retinal correspondence
- Corresponding retinal elements are those elements of the two retinas that give rise in binocular vision to the localization of objects in one and the same subjective visual direction
- Normal retinal correspondence: Normal retinal correspondence is the normal state in which the visual direction of each fovea is the same
- Abnormal retinal correspondence: This is a binocular condition in which there is a change in visual directional sensitivity such that the fovea of the fixing eye has a common visual directional sensitivity with an area other than the fovea of the deviating eye
- harmonious ARC
- Unharmonious ARC
- Paradoxical
Slide 12
Horopter
- It is defined as the locus of all object points that are imaged on corresponding retinal elements at a given fixation distance
Slide 13
Panum’s fusional space/ area
- It is the region around the horopter where objects are seen as single even though the object points stimulate slightly disparate retinal elements
Slide 14
Fixation disparity
- During binocular fixation, point fixation is rarely ever imaged exactly on the corresponding points of two fovea. The primary line of sight of one eye misses the fixation point very slightly, being under-converged or over converged
Slide 15-17
Diplopia
- Physiological diplopia: As an individual fixes the object of interest, all the objects outside the panum’s fusional space are seen double this is known as physiological diplopia
- Pathological diplopia: Due to pathological disorders of eye like squint
Slide 18
Retinal rivalry
- When dissimilar contours are presented to corresponding retinal areas, fusion becomes impossible Instead, retinal rivalry may be observed. This phenomenon, also termed binocular rivalry
Slide 19
Suppression
- Suppression is the mental inhibition of visual sensations of one eye in favor of those of the other eye when both eyes are open. This may occur in binocular single vision and commonly in manifest strabismus.
Slide 20
Monocular vision (oculocentric visual direction)
Monocular vision is oculocentric because the eye’s visual direction is always located relative to the principle visual direction
Slide 21
Binocular vision (egocentric visual direction):
- In binocular vision, the principle visual direction of the 2 fovea’s are identical.
- An image falling on either foveola will appear to be localized in the same direction- a common principle visual direction
Slide 22-28
Binocular single vision
When a normal individual fixes his visual attention on an object or regards, the image is formed on the fovea of both the eye separately but the individual perceives a single image. This state is called binocular single vision
- Pre-requisites of BSV
- Grade I : simultaneous macular perception (SMP): Simultaneous perception is the ability to perceive simultaneously two images, one formed on each retina
- Grade II: Fusion : It implies the ability of the two eyes to produce a composite picture from two similar pictures each of which is incomplete in one small detail
- Grade III: Stereopsis: Stereopsis implies the ability to obtain an impression of depth by the superimposition of 2 picture of the same object which has been taken from slightly different angles, such as a bucket that is appreciated in 3 dimensions
Slide 29-34
Monocular (Nonstereoscopic) Clues to Spatial Orientation
Stereopsis is restricted to relatively short visual distances and is not the only means we have for spatial orientation. A second set of clues, the monocular or experiential clues, are important in our estimation of the relative distance of visual objects and are active in monocular as well as binocular vision.
- Motion parallax: When one looks at two objects, one of which is closer than the other, and moves either the eyes or the head in a plane parallel to the plane of one of these objects, movement of the objects becomes apparent
- Linear perspective: Object points having a constant size appear to subtend smaller and smaller angles as they recede from the subject
- Overlay of contours: An object that interrupts the contours of another object is generally seen as being in front of the object with incomplete contours
- Distribution of headlights and shadows: Highlights and shadows are among the most potent monocular clues
- Size of known objects: If an object known to be smaller appears to be larger than the other, we judge it to be nearer
- Aerial perspective: objects that are further away look blurry and have a bluish tint
Slide 35
Theories of Binocular Vision
- Correspondence and Disparity: A given retinal element in one retina shares a common subjective visual direction with an element in the other retina. These corresponding elements form the framework or zero systems of binocular vision
- Neurophysiologic Theory of Binocular Vision and Stereopsis: A reasonable assumption is that neuron in the striated cortex responding well to successive stimulation and especially those in which the response can be maximized with simultaneous stimulation are somehow involved with binocular visual processing
- ALTERNATION THEORY OF BINOCULAR VISION: In replacement theory of binocular vision, assumed that corresponding retinal units were represented separately in the brain but that each one of every pair was represented in consciousness by the same single unit
- PROJECTION THEORY OF BINOCULAR VISION: Theory that has now been largely abandoned is the projection theory, which contends that visual stimuli are exteriorized along the lines of direction
