visual and depth perception

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perception: visual and depth perception

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Front page TOPIC: VISUAL PERCEPTION AND DEPTH PERCEPTION PRESENTED BY- GURLEEN NANRA

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Key Concepts- INTRODUCTION TO VISUAL PERCEPTION PERCEPTUAL CONSTANCIES SHAPECONSTANCY SIZE CONSTANCY BRIGHTNESS AND COLOUR CONSTANCY GESTALT APPROACH

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An Introduction to Visual Perception! Perception is the mental process of organizing sensations into meaningful patterns. “Perception is an individual’s awareness aspect of behaviour, for it is the way each person processes the raw data he or she receives from the environment, into meaningful patterns.” -By R.E. Silverman “Perception is the experience of objects ,events or relationships obtained by extracting information from and interpreting sensations .” - By O.Desiderato, D.B. Howieson & J.H. Jackson “Visual perception is the end product of vision” It can be described as the way the brain interprets what the eyes see.

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SHAPE CONSTANCY Shape constancy refers to the tendency of perceiving the shape of familiar objects as relatively stable, constant and unchanging despite the fact that the retinal images may vary greatly depending on the viewing angles. SIZE CONSTANCY Size constancy refers to the fact that our perceptions of the size of objects are relatively constant despite the fact that the size of objects on the retina vary greatly with distance. BRIGHTNESS AND COLOR CONSTANCY Color and brightness constancy are responsible for the fact that a familiar object will appear the same color regardless of the amount of or color of light reflecting from it.

herman:

Hermann Von Helmholtz , seen as the founder of visual perception studies believed vision was a form of unconscious inference , (Inference is the act or process of deriving a conclusion based solely on what one already knows) Two well known assumptions are that light comes from above and that objects are viewed from above , not below. Visual illusions are where this process goes wrong e.g… Hermann Von Helmholtz herman

The Scintillating grid illusion:

The Scintillating grid illusion Black spots will seem to appear very quickly at the intersections. Optical illusion Focus on the black dot and move your head back and forth

Gestalt Views In Psychology:

Gestalt Views In Psychology Gestalt psychologist’s believe the problem of visual perception should be considered as a whole. Max Wertheimer believes that thinking happens in two ways: Productive thinking - is solving a problem with insight. Reproductive thinking -is solving a problem with previous experiences and what is already known. Other Gestalts psychologist such as Perkins believes insight deals with three processes: 1) Unconscious leap in thinking. 2) The increased amount of speed in mental processing. 3) The amount of short-circuiting which occurs in normal reasoning.

Gestalt Theory:

Gestalt Theory The Gestalt Theory originally came about in the 1890’s. There are 3 main Gestalt psychologists: Max Wertheimer Wolfgang K öhler Kurt Koffka The concept of Gestalts Psychology was originally founded by an Austrian psychologist called Christian Freiherr von Ehrenfels

Gestalt Theory:

Gestalt Theory The Gestalt Principles can be split into 3 groups: Similarity, Proximity, Common Fate and Good Continuity Figure and Ground Closure

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Figure and Ground explains how we put different elements together to make one scene or a whole image. “Figure” is the more dominant shape. “Ground” can be referred to as the Background. Once you have identified the figure , the rest of the image becomes the ground. FIGURE AND GROUND

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When we have similar objects of size, shape and colour again we form groups. Squares and Circles SIMILARITY

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When objects which are closer to each other we tend to associate them together to form groups. You will see columns rather than You will see rows rather than rows columns Real life example. MTV Music awards. We group this image into 2 parts, the top left this shows us this is the MTV music awards, and the bottom right which groups together the sponsors of the awards. PROXIMITY http://1.bp.blogspot.com/_e8-FIzavQEE/SS4efco7aUI/AAAAAAAAA1E/kjNIB_tJBl4/s1600-h/gestalt_law_of_symmetry_and_of_proximity.gif

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Objects which are facing the same direction or appear to be travelling in the same direction are usually grouped together. The arrows which are pointing in a Again the lines facing upwards tend common direction are usually grouped to be grouped together. together. COMMON FATE

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Seeing things as a whole is important however seeing in a whole is not necessarily what we are meant to see. What do you see here? CONTINUITY

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Seeing things as a whole is important however seeing in a whole is not necessarily what we are meant to see. What do you see here? Well there are two answers. Continuity makes us see 2 lines crossing BUT Is it actually 4 lines, A-O, O-D, C-O and O-B CONTINUITY

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If we have a large pattern with missing components we tend to fill in the missing parts to create the image we actually see. When joined you can see a triangle. This image can be seen as an “S” shape Real Life example.: WWF Logo / IBM Logo CLOSURE

DEPTH PERCEPTION:

DEPTH PERCEPTION Why have depth perception? Why is depth perception difficult? How do we see depth?

Why is depth perception difficult?:

Why is depth perception difficult? The world is three-dimensional Our initial visual representation is two dimensional Somehow, we need to recover the third dimension (depth)

HOW DO WE SEE DEPTH ?:

HOW DO WE SEE DEPTH ? Monocular cues : these are the cues that only require the use of one eye. Binocular cues : these are those cues that involve both eyes being used together.

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MONOCULAR CUES : Linear perspective Aerial perspective Texture Interposition Shading Motion parallax BINOCULAR CUES : Convergence Retinal disparity Accommodation Stereopsis

Monocular depth cues:

Monocular depth cues

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Linear perspective : Lines that are parallel in the real world appear to converge in a drawing. The greater the distance, the greater the convergence. At infinity, lines meet at the vanishing point.

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In this painting from the 16th century, the artist made use of linear perspective to indicate that the Church is somewhere in the distance. The lines of squares are parallel in the real world, so they appear to converge in this painting. Note that there is one spot in the upper left of the painting where the artist did not draw the lines converging -- instead they are parallel. This lack of linear perspective makes it look as though there is an incline just to the left of the church.

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Aerial perspective : More distant objects are perceived less clearly than closer objects. The further the light must travel to reach the eye, the more likely that light will be interfered with in some way by matter. Aerial perspective sometimes is called atmospheric perspective because the effect is due to the atmosphere interfering with light.

(Source : internet, Google images):

(Source : internet, Google images)

Interposition : Still another monocular cue is interposition, which occurs when one object obstructs our view of another. When one object is completely visible while another is partly covered by it, the first object is perceived as nearer. :

Interposition : Still another monocular cue is interposition, which occurs when one object obstructs our view of another. When one object is completely visible while another is partly covered by it, the first object is perceived as nearer.

Source : internet (google images):

Source : internet (google images)

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Shading : Three-dimensional objects cast shadows, so 3D objects tend to have luminance gradients. In perceiving depth from shading, we make certain default assumptions about lighting There is only one light source. Light comes from above. "Above" is defined retinally, not environmentally (i.e., the light seems to come from the same direction as the top of your head, even when you turn your head on its side). Some animals have evolved a camoflauge strategy called counter-shading to counteract the effects of shading. For example, fish are lighter on their undersides and darker on their top sides. This way, when light hits them from above, they'll minimize the luminance gradient, and look as flat (and unappetizing) as possible.

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Motion Parallax Refers to the movement of an object’s image over the retina. It is also involved if there two stationary objects at different distances from the observer, and it is the observer’s eyes that move. Interesting properties of motion parallax can be observed through the window of a moving train : objects that are closer to you than the fixation point appear to be moving in the opposite direction to the train, whereas objects that are beyond the fixation point appear to be moving in the same direction as the train.

Source : internet (google images):

Source : internet (google images)

Binocular cues:

Binocular cues

Convergence ::

Convergence : It refers to the fact that the eyes turn inwards to focus on an object to a greater extent with a very close object than with one that is somewhat further away. In other words, you converge your eyes when looking at close objects you diverge to look at distant objects

Retinal disparity:

Retinal disparity Although humans have large binocular visual fields, each eye is getting a slightly different view of the world because the two eyes are in slightly different positions. Retinal disparity is the difference between the lateral position of object in the left and right eyes

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These images illustrate how the same scene might look to the left and the right eyes. Notice that objects are different distances from one another in the two pictures. The difference in the lateral positions of an object in the left and right eyes' image defines the retinal disparity for that object. The disparity in this scene is particularly easy to see in the arrangement of the champagne glasses and pointing hand on the right side of each scene.

Accommodation ::

Accommodation : Accommodation refers to the variation in optical power produced by a thickening of the lens of the eye when focusing on a close object. In other words, you accommodate more to focus on closer objects.

Stereopsis : :

Stereopsis : Finally and most importantly, there is, stereopsis, which is stereoscopic vision depending on the disparity in the images projected on the retinas of the two eyes. Our minds are able to perceive the world in three dimensions primarily because we have binocular vision. Binocular vision occurs when two eyes look at the same thing at a slightly different angle, resulting in two slightly different images. It's simple to confirm that we have binocular vision: place your hand a foot in front of your face and alternate closing each eye. Your hand will appear to jump back and forth.

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CONCLUSION Vision is not necessarily what we see but how our brain interprets the world around us, our own experiences can shape how we perceive this world.

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REFRENCES Goldstein , E. B. (2002). Sensation and perception (6th edition.). Pacific Grove CA: Wadsworth. O’Shea, R. P., Blackburn, S. G., & Ono, H. (1994). Contrast as a depth cue. Vision Research, 34,( 595-604) Baron R. A., Psychology 5th Edition (2007 ) Morgan C. T., Introduction to psychology 7 th edition (2007 ) Mangal S.K, General Psychology (1998), 16 th edition (2011), Sterling Publishers Pvt. Ltd. (104-120)

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THANK YOU FOR YOUR TIME AND PATIENCE..!! HAVE A NICE DAY.!! 

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