May 17, 2013

The Monocular Cues for Perception of Dept

The monocular cues are those which are usefully active when only one eye is seeing. These cues can be seen operative in a painter’s work that can give us effective experience of the third dimension from a flat surface quite successfully. Our eye picks them up and we perceive depth. In fact we do not often see objects with one eye exclusively but each eye individually benefits, from these cues. That is, these cues are the ones from the stimulus pattern, regardless of monocular or binocular vision. Among these are the cues based on distinctness, linear perspective, texture, light and shadow, relative position and the known standards.
(i)  Distinctness or the Atmospheric Perspective:

Generally, the more clearly we see an object, the nearer it seems. Because of the dust and smoke in the air, objects may appear blind and indistinct in outline. Many far off objects seem to be quite near if there is no smoke, fog or mist in between. .A person reared in a smoky industrial environment will underestimate a far off hill on a very clear morning. The extent of determining depends on the distance and we learn to interpret distance in these terms. The fact is that with the change in atmosphere we are liable to make incorrect estimates of distance. A distant mountain appears farther away on a hazy, foggy day than on a clear day. It is because the haze in the atmosphere blurs the fine details, which if we can see clearly, we perceive the objects as relatively closer. But if we see only the outlines we perceive it as far away.

(ii) The Linear Perspective:

The objects will look smaller and closer together as they become more distant from the observer. The perceiver will tend to perceive them as meeting and closing together. Among the examples are railway tracks, highway shoulders and tree lines on both Sides will seem as closing and meeting each other as well as the horizon. Uniformly spaced objects like telephone poles appear to be spaced more closely as they recede into the distance. Artists often display these phenomena of linear perspective to represent distance in picture.

(iii) Texture Gradients:

A gradient is a continuous gradient change in something - a change without abrupt transition. As we look at a mosaic floor or a designed carpet, the near parts will display more details while the farther ones will give lesser details. We can use the continuous gradation of texture in the visual field as a cue for depth (Gibson, 1950).

 The regions closer to the observer have a coarse texture and many details but as the distance increases, the texture is seen finer and finer. The factor of texture is closely related to linear perspective. On any surface not perpendicular the line of sight the texture elements appear denser as the surface recedes. Thus texture is adjacent to linear perspective1 operating in situations where there are no converging parallel lines.
(iv) Light and Shadows:

Distribution of light and shadow is a common cue for perceiver of depth. Shadow or highlight pattern in an object is indicative of depth or distance in front. In an aerial photograph of Quonset huts, it was fond that if turned upside down, the huts would look ‘towers’. The only responsible factor for this phenomenon was light and shadow pattern. Every object especially that having a third dimension will also has at least some of it in the dark. That distribution of dark and light portions is a very strong cue helpful toward perception of depth and distance. When light strikes an irregular surface e.g. the human face, certain parts is lightly illuminated and. others are cast in shadow. The appearance of these shadows tells us a lot about depth of the parts concerned.

Painters and artists commonly use Shading and highlighting to convey this notion of depth on a two-dimensional canvas.

(v) Relative Position:

This is another cue for depth perception. Inter position or relative position occurs when one thing obstructs our view of another. One object is partly covered b, another while the latter is entirely in sight and is perceived to be nearer in distance. Two objects being in the same visual line, for example, the nearer one conceals whole or part of the farther one. The hidden object will seem farther in spite of being just near behind the nearer one but it is the relative position which is providing a cue for perception of depth. Near objects usually appear at the bottom of the two-dimensional field of vision and the distant one at the top.
(vi) Known Standards:

If we hold a fifty paisa coin close to our eyes and move it gradually away, we shall not see the coin smaller and smaller, through the retinal image becomes so every moment. The reason is constancy of size. All the known persons and objects, we perceive of the same size and form even if not seen ‘clearly’ from a given distance. Dependence on known standards can sometimes lead us to see strange things if we ‘see’ critically. This interpretation generally lacks in children who often take a man from a distance for a boy. Gaze at a colored paper of square shape for a minute and project the after sensation on to a plain wall some feet away. The image will seem now larger. The size of the retinal image has not changed as we alter the distance our gaze was directed but its perceived size changes through our interpretation of this.
(vii) Movement:

If you watch closely, you will find that the object nearer to you is looking closer and bid than the spot at which you are looking - the fixation point - move in a direction opposite to the direction in which your head moved. Whenever you move your head you can observe that the objects in the visual field move relative to you and to one another. Objects move distant that the fixation point; on the other hand, move in the same direction as your head movement. Thus, the direction of movement of objects when we turn our heads can be a cue for their relative distance. Further-more the relative amount of movement is less for far objects than for near once: Of course, as is the case with all the depth cues, we do not usually think about this information, we use it automatically.
(viii) Accommodation:

Adjusting the lens to bring the image of an object into focus on the retina is the process called accommodation.. This adjustment is made by muscles which are attached to the lens in the way as to allow it to thicken when they contract. When the lens thickens, nearby objects can be foc4 on the retina. For distant objects, the muscles relax allowing the lens to become thinner so that more distant objects can be focused on the retina. Since’ there are sensory receptors in muscles which signal their tension, we may be able to use this sensory input about muscle relaxation and contraction as a cue to depth. The role of accommodations a cue for depth perception is, however controversial.

John S Lam is an IT Instructor at Examskey. He is CISSP Certified Professional. Take the benefit of our 200-120 material and assure your success. Check out our free demo of all certifications Exams.
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