What is perception by jackshepherd


									                                        Visual Perception:

I. What is perception?

II. Gestalt Laws of Grouping

        A. Proximity
        B. Similarity
        C. Continuity
        D. Closure
        E. Common Fate
        F. Simplicity
        G. Review of Gestalt Groupings

III. Figure and Ground

IV. Perceptual Constancy

        A. Lightness Constancy
        B. Color Constancy
        C. Shape Constancy
        D. Size Constancy
        E. Review of Constancy

V. Depth Perception
       A. Monocular Cues
               1. Interposition
               2. Atmospheric Perspective
               3. Texture Gradient
               4. Linear Perspective
               5. Motion Parallax
       B. Binocular Cues

VI. Illusions
         A. Illusions of Length
                   1. Poggendorff Illusion
                   2. Muller-Lyer Illusion
                   3. Ponzo Illusion
         B. Illusions of Shape: Zollner Illusion
         c. Illusions of Size: Aims Room
         D. Illusions of Contours
         E. Impossible Figures
         F. Reversible Figures

VII. Class Game show: Peril

VIII. Conclusion
What is perception?
The book Psychology: An Introduction defines perception as ―The process of creating meaningful
patterns from raw sensory information‖ More specifically Hugh Foley Associate professor of
Psychology at Skidmore College defines perception as ―process by which organisms interpret and
organize sensation to produce meaningful experience of the world.‖

Perceptual organization
Arranging sensory stimulus into meaningful experience involves thinking, understanding and

Attempt to read the following sentence

Can you read this text upside down?
   1. Easier to read right side up
   2. Knowledge of letters and shapes helps us to read the sentence - For example, look at this
      Chinese character. Without knowledge of Chinese characters this symbol is meaningless
      but to someone with knowledge of Chinese it is the symbol for love.
   3. Read as whole words and phrases – You didn’t read each letter
   4. Context is key – Since the word upside is often followed by down for this reason one
      may overlook that each letter in down is also reversible. U.M.O.P

Gestalt Groupings
   • Proximity
   • Similarity
   • Continuity
   • Closure
   • Common Fate

The closer objects are to one another, the more likely we are to mentally group them together.
(Foley, 2005)

Proximal Random
This random grouping of boxes helps us to perceive them as separate objects.

Proximal Unity
When the squares are close, unity occurs. While they continue to be separate shapes, they are now
perceived as one group. Something else is happening here notice the black circles that are
appearing between the squares. We will explain this phenomenon in more detail

Linking together parts of the visual field that are similar in color, lightness, texture, shape, etc.
(Foley, 2005) This is why despite the likeness in shape of the circles to on the right we perceive
them in two groups because of their size.
The law of similarity is the reason why we perceive rows instead of columns with these circles
and triangles.

Leads us to see a line as continuing in a particular direction rather than making an abrupt turn.
(Foley, 2005)

The viewers eye will naturally follow a line or a curve. The crossbar of the ―h‖ leads the eye to
the maple leaf.

Continuation occurs when the eye is compelled to move through one object and continue to
another object. Gestalt psychologists use this term to describe our tendency to see lines as
continuing, without breaks.
In the drawing on the left below, we see a straight line with a curved line running through it.
Notice that we do not see the drawing as consisting of the two pieces in the drawing on the right.

We are inclined to overlook incompleteness in sensory information and to perceive a whole
object even where none really exist. (Morris and Maisto, 1993) On the right we complete the
lines on the object so we can observe the panda.

We prefer complete forms to incomplete ones which is why in the image below we mentally close
the lines to perceive a duck.

Common fate
The law of common fate leads us to group together objects that move in the same direction.
(Foley, 2005)

Imaging if three of the circles are moving in one direction and the two other circles are moving in
the other we would mental group the circles that moved in the same direction.


The law of simplicity encompasses all the other Gestalt laws of perception. People prefer the
simplest possible organization. According to the principle of simplicity, we likely to describe this
as a spiral rather than nine vertical rows of dots (the spiral is simpler).

Review of Gestalt Groupings

Proximity – Is the grouping of objects because of how close the are together.
Similarity - refers to our tendency to group things together based upon how similar to each other
they are.
Continuity – refers to our tendency to see patterns and therefore perceive things as belonging
together if they form some type of continuous pattern. This is why we see a cross as one object
instead of two distinct intersecting lines.
Closure – We prefer complete forms to incomplete ones.
Common Fate – Objects moving in one direction will be grouped. Like a flock of geese.
Simplicity – People prefer the simplest explanation

Figure and Ground

Distinguishing objects from its surroundings. Dr. Foley says that ―Gestalt psychologists have
devised ambiguous figure-ground relationships—that is, drawings in which the figure and ground
can be reversed—to illustrate their point that the whole is different from the sum of its parts.
Consider the accompanying illustration entitled ―Figure and Ground.‖ You may see a white vase
as the figure, in which case you will see it displayed on a dark ground. However, you may also
see two dark faces that point toward one another. Notice that when you do so, the white area of
the figure becomes the ground. Even though your perception may alternate between these two
possible interpretations, the parts of the illustration are constant. Thus, the illustration supports
the Gestalt position that the whole is not determined solely by its parts.‖

Perceptual Constancy

Is the tendency to perceive objects as relatively stable and unchanging despite changing sensory
information. (Morris and Maisto, 1993)

This is why once we have a stable perception of an object we can recognize it at almost any
distance or level of light.

Types of Constancy: There are essentially four types of perceptual Constancy, Lightness, Color,
shape and size constancy.

Lightness Constancy:
Means that our perception of an object’s lightness or darkness remains constant despite changes
in illumination.

Everyone flip over the packet over so that you see the backside of the last page. With the lights
on you see that the paper appears white. [Turn off two lights] If we turn off two lights then the
paper still appears white. [Turn off all lights except for the projector] Even with very little
light the paper still appears white. [Lights back to normal state]

This illustrates an important perception principle and that is that perception is relative. We
determine the lightness and darkness of the paper relative to other items in the room.

Color Constancy
Perceive the color of an object as the same despite changes in lighting conditions. Dr. Foley
says: ―You have experienced color constancy if you have ever worn a pair of sunglasses with
colored lenses. In spite of the fact that the colored lenses change the color of light reaching your
retina, you still perceive white objects as white and red objects as red. The explanations for color
constancy parallel those for lightness constancy.‖
Shape Constancy
Perceive objects as retaining the same shape despite changes in their orientation.

Take out your book and hold it up with the cover facing you. The book is clearly in the outline of
a rectangle. Now rotate the top of the book forward to a 45 degree angle. The image should now
be trapezoidal with the bottom edge closer it looks larger than the top edge. Despite the
trapezoidal image we still perceive the book as a rectangle.

Size Constancy
Tendency to perceive object as staying the same size despite changes in our distance from them.

For example, we see a person off in the distance we don’t perceive them tiny as they appear. We
perceive them as their normal size. The same goes for seeing a skyscraper or mountain off in the

Review of Constancy
Lightness Constancy – refers to our perception of an object’s lightness or darkness remains
constant despite changes in illumination
Color Constancy - refers to our ability to recognize that color remains the same regardless of how
it looks under different levels of light
Shape Constancy - allows us to perceive that plate as still being a circle even though the angle
from which we view it appears to distort the shape
Size Constancy - refers to our ability to see objects as maintaining the same size even when our
distance from them makes things appear larger or smaller

Depth Perception
The ability to see the world in three dimensions and perceive distance. (Foley, 2005)

Monocular Cues

These are things that we can perceive with one eye. Several animals such as fish, birds, and deer
rely on monocular cues entirely because their eyes are located on the sides of their heads.

When one item overlaps another we discern the covered object to be further away. (Foley, 2005)

Take the two straws we provided you and place one in each hand. Hold your hands out in front of
you so that one straw is a couple of inches in front of the other. Now close one eye. From this
perspective it is difficult to tell which straw is in front of the other. Now move the straws so they
overlap. We know the object that overlaps the other is closer. How we use interposition to tell
depth perception.

Atmospheric Perspective:
Air contains fine particles of water vapor, dust, and smoke. These particles scatter light and
change its direction. The presence of scattering shows distant subjects in pictures as having a
haze. The greater the distance, the more haze one will perceive. (Foley, 2005)

Texture Gradient
Take a look at the ceiling. You will notice that the part of the ceiling directly above you has a
vivid texture where as further away it is less distinct.

Linear Perspective:
Refers to the fact that parallel lines appear to converge with distance eventually reaching a
vanishing point on the horizon. (Foley, 2005)

Artist use linear perspective to create the appearance of three dimensional space. Notice how this
image looks two dimensional. But then if we move the road to the horizon it creates the
appearance of depth.

Motion Parallax:
Objects at different distances from you appear to move at different speeds when you are in
motion. (Foley, 2005)

The next time you are walking in a parking lot walking towards a store. As you are walking turn
your head and look off in the distance. You will see that the closer items, such as the car, appear
to be moving faster than the objects in the distance. When you are driving home look at a light
off in the distance it will appear to be moving slower than the lights near you.

Binocular Cues
According to Morris and Maisto binocular clues are visual cues that requiring the use of both
eyes. Take out one of the straws we provided you. Hold it out in front of you and with both eyes
open line it up with parallel with a line in this room. Close your right eye then open your right
eye and close your left. The straw jumps between our original alignments. This phenomenon is
known as Binocular Disparity.


Occurs when what the brain perceives differs substantially from the actual qualities of and object
or stimulus. (Foley, 2005)

An illusion is a sort of mistake in sensory perception. Dr. Foley says that psychologist study
illusions because they provide important clues about the functioning of perceptual systems.
Lets look at some types of illusions:

Illusion of length:

Illusions of length typically occur when additional line segments interfere with our perception on
an object. For example, these three pillars are the same length.

Poggendorff Illusion

The Poggendorff illusion was discovered in 1860 by physicist and scholar J. C. Poggendorff

The illusion is that the line segment passing behind the rectangle are offset when they are aligned.
Muller-Lyer Illusion

One of most famous illusions is the Muller-Lyer Illusion crated by German psychiatrist Franz
muller-lyer in 1889.

Look at the following animation and when you perceive the lines as being identical in length
remember that number.

Ok what kind of numbers did you pick. Well the correct answer was 6. If you picked 4 or 5 then
your perception tricked by the Muller-Lyer Illusion.

A simple explanation is that the wings provide depth cues. In this situation, our brain incorrectly
interprets the depth cues, resulting in the optical illusion.

Ponzo illusion:

The Ponzo Illusion is named after Itialan psychologist Mario Ponzo. The two lines do not appear
similar in length but in fact they are. We interpret the diagonal lines as indicating depth, because
our mind believes that the top line is farther away we perceive it as longer.

Illusions of Shape:

Zollner Illusion

In the Zollner Illusion a square appears trapezoidal, wider at the top than at the bottom, because
of the horizontal lines in the background.

Illusions of Size:

Look at the following photograph. The girl on the right appears gigantic compared to the women
on the left. This is an illusion of depth that forces us to misperceive the size of objects.

This picture is of an Aims Room named after Albert Aims who first made the room in the 1940s.
And anyone who has seen the Fellowship of the Ring has been tricked by the Abrams Room.

Illusions of Contours:

If you look at the figure most likely you perceive a white trinangle. But if you look closely there
are each side of the triangle is white space. According to Dr. Foley Gestault psychologist
indicate that people prefer a well organized whole rather than individual parts.

Impossible Figures:
This occurs when we perceive objects as reasonable but they are actually impossible. How many
legs does the elephant have?

Reversible figures

Do you see a young woman with her back to you or old women with a wart on her nose?
According to Dr. Foley reversible figures aren’t true illusions because there isn’t an error in the
perception. However they do allow more than one interpretation.


Hopefully our presentation has enhanced your understanding of the human visual perception
system. We have learned about Gestalt groupings like proximity, closure and simplicity. We
have also gained a better understanding of perceptual constancy which is our a tendency to
perceive objects as stable and unchanging despite changing sensory information. We discussed
depth perception and the difference between monocular and binocular clues. Lastly we studied
illusions. We hope that you come away from our presentation with a greater understanding of
human visual perception.

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