Depth Perception and Cues

Definition

Depth Perception – The process or ability to perceive the world in three dimensions is called depth perception. It is the mental process that leads to formation of perceptual concept of depth and distance between objects in space.

Space – Space is a visual field or surface in which things exist, move or can be positioned.

Introduction

          The concept of perception is also called as distance perception. The ability of ‘depth perception’ is instrumental in judging the distance between objects that are found in space. Space is a three dimensional surface. The image of objects formed on the retina is two dimensional and flat. But our brain perceives objects as three dimensional. This occurs due to presence of two types of cues i.e. Monocular cues and Binocular cues.

Cues

1.       Monocular Cues (Signals) – Monocular means ‘with, for or one eye’. The cues provided by one eye for perceiving depth & distance. They are also called as ‘pictorial depth cues’. They are effective when the objects are seen with only one eye. The artists often uses these cues to show depth in distance in two dimensional paintings. The few monocular cues are described below: -

(i)       Relative Size – The object tends to appear small when it is farther away and bigger when it is closer. This cue is function of size of retinal image.

(ii)      Linear Perspective – This reflects a phenomenon by which distant objects appear to be closer to one another than the nearer objects such as railway tracks appear to converge in the distance. The more the line converge , the farther away the appear.

(iii)     Interposition or Overlapping – These cues are generated when one object overlaps or covers another object. In this case the overlapping object is seen as closer than the overlapped object.

(iv)     Aerial or Atmospheric Perspective – The distant objects are seen as hazy or blurry due to presence of microscopic  particles such as dust and moisture in the atmosphere.

(v)      Light & Shade – The lighter part of an object seen to closer while the darker one is seen to be away. The highlights and shadows provide information about an object’s distance and depth.

(vi)     Relative Height – The distant objects are seen as smaller while the closer one are seen as larger and vice versa despite being of same size.

(vii)    Texture Gradient –  The texture of a surface appears smoother as distance increases the denser area of a visual   field is seen as farther and vice versa.

(viii)   Motion Parallax – It occurs when the distant objects move to appear slowly than the objects that are closer. The rate of movement of an object provides a cue to its distance. When we travel in a vehicle, the far away objects appear to move in direction with the vehicle, whereas closer objects seen to be move in the opposite direction. This is kinetic cue rather than pictorial cue.

2.       Binocular Cues – Binocular means ‘using both eyes’. The cues provided by both eyes for perceiving depth & distance.

(i)       Retinal or Binocular Disparity (असमानता) – It is also known as ‘binocular parallax’. It occurs due to distance between the location of eyes that is 6.5 cm. Due to this distance the image of same object forms differently on both retinas. This difference is called as retinal disparity. Larger the disparity closer the object is seen and vice versa because the disparity is lesser for distant objects and larger for close objects.

(ii)      Convergence – The inward turning of our eyes to see closer objects is called convergence. The convergence occurs to bring the image of the object on the fovea (yellow spot) of each eye. The concerned muscles transmit the message regarding the degree of inward turning of eyes to the brain which are understood as depth perception cues. Closer the object higher the convergence and vice versa.

(iii)     Accommodation – It refers to a process by which we focus the image on the retina with the help of ciliary muscles (changes the thickness of the lens). These muscles are relaxed in the event of object being away by more than 2 meters. The thickness of lens increases when the object is closer and vice versa. The change in the thickness of lens is controlled by ciliary muscles which transmit the    message to the brain. Where these messages are interpreted as depth perception cues.

References:

1.       NCERT, XI Psychology Text book.

2.       Ciccarelli, S. K. & Meyer, G. E. (2016). Psychology. Noida: Pearson India.

3.       Baron, R. (1993). Psychology.

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