What is a monocular vision?
In Monocular vision, both the functioning of the eyes take place separately and increasing in the net field of view and limits the depth of perception. The word monocular is a originated from the Greek word ‘mono’ means single and the Latin word oculus or eye. Animals like horses have monocular vision, have eyes on opposite sides of their head allowing them to see two oppositely placed objects at the same time.
What are monocular cues?
Monocular cues are responsible for providing depth information when a scene is viewed.
• Motion parallax
– The perceived relative motion of a moving observer with respect to the static objects against a background provides information on the relative distance. When information about a movement’s velocity and direction is known then motion parallax can deliver information about absolute depth.
This type of effect is noticed while driving when the car passes nearby objects quickly and distant objects appear to be relatively stationary. Many animals have a wide eye placement due to which they lack binocular vision and employ parallax more clearly than humans for depth cueing. For example, certain types of birds bob their heads for achieving motion parallax, and squirrels move in orthogonal lines with respect to the object they are viewing for the same.
• Depth from motion
– The kinetic depth perception of an object (another form of depth from motion) is provided by the dynamic change in object size. Objects in motion tend to appear more and more distant as the apparent object size decreases and objects in motion tend to appear closer as the apparent object size increases. The brain is able to calculate time-to-crash or time-to-contact or time-to-collision – TTC for a particular velocity by using the kinetic depth of perception. When a person is driving, they are continually estimating the dynamic change in headway (TTC) with the help of kinetic depth perception.
– Perspective referred to the reconstruction of the relative distance of various part of the scene, or of landscaping structure due to the characteristic of parallel lines that converge at infinity.
• Relative size
– When two similar-sized objects are placed in one scene but their exact size is unknown then the relative size cues of the objects can help in determining the relative depth of the two objects, which subtends greater visual angle on the retina appears closer.
• Familiar size
– The visual angle subtends by an object on the retina decreases with an increase in distance and this information about subtend angle can be joined with the information about the object size for determining the absolute depth of the object. For example, while driving people are aware of the size of a vehicle. This information can be joined with knowledge about the angle subtended on the retina for determining the absolute depth of the vehicle.
• Aerial perspective
– The objects that are placed at a distance have lower color saturation and lower luminance contrast because of the light scattered by particles in the atmosphere. Objects appear to be at different levels of depth when they differ only in their contrast with the background. This is the reason why distant objects like mountains generally appear to be bluish in color.
– Accommodation is a term given to the ability of the eye to adjust its focus according to the object it is viewing. Accommodation is the oculomotor cue for depth perception. This ability of the eye is associated with the contraction and relaxation of the ciliary muscles that flatten the eye lens while viewing distant objects and curve the eye lens while viewing nearby objects. The periodic contracting and relaxing kinesthetic sensations of the ciliary muscles or intraocular muscles are then sent to the visual cortex where it helps in determining distance and depth.
– Occlusion, also termed as interposition refers to blocking the vision of objects by others. This provides information about the relative distance of objects.
• Peripheral vision
– Parallel lines has curved at the outer edges of the visual field as explained below lens of fisheye and cropping the picture usually eliminates this effect usually. However, this effect greatly boosts the viewer’s sense of being placed in a real, 3Dspace.
• Texture gradient
– This refers to the perception of the texture of objects with distance. If you are standing on a gravel road then the part of the road near you would appear to be clear in terms of size, texture, shape, and color. However, the part of the road farther away from your position would be less clear had harder to distinguish in terms of texture.
What is the role of monocular vision in maintaining balance?
Balance and postural control along with vestibular and proprioception function in humans can be heavily linked with vision. The perception of our surroundings by the brain is affected by monocular vision as it impairs peripheral vision on one side of the body, decreases the available visual field, and compromises with depth perception. These factors play a major role in maintaining balance.