Visual Perception
Sensation
Stimuli from the outside world is detected
by sensory receptors found in out our
sensory organs.
Sensation is the stimulation of our sensory
organs and the transmission of information
to the central
nervous
system.
Selective Attention
Stimulation of the sense organs is
automatic
 Multiple sense organs are being
stimulated at any time
 We only focus on select stimuli at any
one time- this is known as selective
attention

Perception
While the sense organs gather the
information (sensation), perception is
the name given to the process during
which the brain organises and interprets
the information from the sense organs.
 Perception givens meaning to the
sensations.

Sensation and Perception
Sensation is the same for everyone
(except the visually impaired).
 Perception is not the same for
everyone.
 List the following:

1.
Your favourite colour
2.
Your favourite vegetable
3.
Your favourite muscial instrument
4.
Your favourite perfume/cologne
5.
The temperature at which you like to eat soup
Thresholds
Absolute threshold- the smallest or
weakest level of a stimulus required for
detection
 Differential threshold- the smallest or
weakest change in a stimulus that is
required for the sensory system to detect
a change

Note: The differential threshold is also known as the
just noticeable difference (JND)
The Visual Perceptual System
While there are 5 sensory systems we will focus only on
the visual perceptual system.
The visual sense organ (the eye)
collects information in the form of
electromagnetic radiation- light!
The electromagentic spectrum
The entire range
of electromagnetic
energy is known
as the
electromagnetic
spectrum.
The human eye however can only detect a small
portion of this known as the visible spectrum.
Wavelength, frequency and
amplitude
Electromagnetic energy travels in waves and
therefore has different wavelengths,
frequecies and amplitudes.
We see different wavelengths/freuencies as
different colours.
We see different amplitudes as different
intensities of light.
Structures of the Human Eye
More on the lens…




Ciliary muscles change the shape of the lens
Distant objects = flat and elongated lens
Near objects = round bulging lens
Remember the lens aims to focus the image onto the retina.
More on the lens…
The lens also refracts (bends) light. This allows the image to
converge (come together) on the retina.
 The light bends (refracts) as it passes through the bent
surface of the lens. The light closest to the ends of the lens
are bent the most while the light traveling through the
middle is bent the least.
 The result is an upside-down image.

More on the retina…
The receptor cells of the eye are found in the
retina. They are known collectively as
photoreceptors.
 Photo = light
 There are two types of photoreceptors: rods
and cones.
 The area of the retina where the optic nerve
connects to the retina is known as the blind
spot because it is absent of any rods or cones.

Find your blind spot
Rods
More sensitive to light therefore assist
vision at night
 Present in large numbers on outer
regions are retina. Therefore they play a
large role in peripheral vision.
 Perceive shades of grey
 Approx 120 million in number

Cones
Sensitive to colour therefore involved in
colour vision
 Most effective in bright light
 Concentrated in the centre region of the
retina
 Responsible for visual acuity (high def)
 The fovea is a spot in the retina that
contains only cones. It is on this spot that an
image is focused to enable the best visual
acuity (best detail).
 Approx 8 million in number

Rods
 Night and low light
vision
 Shades of grey
 Found on outside
edge of retina
 Play a large role in
peripheral vision
 More numerous
overall
Cones
• Work best in bright
light
• Colour vision
• Found in centre of
retina
• Fovea used for high
acuity; contains cones
only
Structure of the Retina
From eye to brain- the visual
perceptual process
The Visual Perceptual Process
The visual perceptual process is a six
stage process that describes how we
see and interpret visual stimuli. While
there are six stages, it is a continuous
process
Visual Perceptual Principles
Visual perceptual principles guide the way in
which visual information is organized, grouped
together and given meaning- selection,
organisation and interpretation phase of the visual
perceptual process.
 They are like a set of instructions that enable us
to organize and interpret visual information in a
reliable and meaningful way.
 These principles are used involuntary and
instantly by the brain allowing for efficient
interpretation and understanding.

Visual Perceptual Principles

There are three broad categories of these
principles:
 Gestalt Principles
 Depth perception principles
 Constancies
Gestalt Principles



Suggest that we group individual elements
together to see the whole- we do not
perceive the individual elements
The whole is greater than the sum of its
parts
There are four Gestalt principles:
1.
2.
3.
4.
Figure-ground
Closure
Proximity
Similarity
Figure- ground
The visual system simplifies a scene into a figure- the focus of
out attention- and the ground which is everything else- the
background. This helps us quickly identify the most important
information in scene.
Closure
When a figure is incomplete, our
visual perceptual system will
complete the picture so that we see
a whole.
Proximity
Objects close to each other are perceived as belonging to the
same group.
Similarity
Objects that are similar in appearance are perceived as belonging
to the same group.
Gestalt Principles and Advertising
Depth Perception Principles



Refers to out ability to judge distanceremember that the image projected on the
retina is two dimensional but our world is
three dimensional.
We use cues in the from both our body and
from our environment to judge how near or
far an object is from us
There are two types of depth cues:
1. Primary Depth Cues
2. Secondary Depth Cues
Primary Depth Cues

Internal cues/signals provided by the body

There are three primary depth cues:
1. Retinal disparity
2. Convergence
3. Accomodation
1. Retinal Disparity
Our eyes are positioned
approximately 7 cm apart.
Therefore each eye receives a
different image. The brain merges
the two images together and the
amount of retinal disparity
(difference) acts as a depth cue.
The more different the images, the closer the object. The more
similar the images, the further away the objects are. Beyond 10
meters, retinal disparity does not act as a depth cue because the
images are virtually the same.
2. Convergence
The eyes generally turn in to focus an object on the retina.
Information on the position of the eye and muscle tension acts as
depth cues. If more inward turning of the eye, the closer the
object. Convergence works for objects up to 7m from the eye.
After this, the eyes are parallel.
3. Accomodation
Accommodation refers to the lens changing shape to focus on
an object. The muscles contract and the lens bulges to focus on
near objects. The muscles relax and the lens elongates to focus
on far objects. The information about the shape of the lens and
the action of the muscles is sent to the brain where is assists
depth perception
Accommodation is
effective for objects up
to 3m from the viewer.
Accomodation is the
only monocular (one
eye only) depth cue.
Secondary Depth Cues
Secondary Depth Cues
Secondary depth cues are cues to depth that are
provided by the environment.
There are five secondary depth cues:
1. Linear Perspective
2. Interposition
3. Texture Gradient
4. Relative Size
5. Height in the Visual Field
1. Linear Perspective
Two parallel lines merging together
give the perception of depth.
2. Interposition
Provides a cue for depth when two or more obejcts
overlap each other. The object behind is perceived
as being further away
3. Texture Gradient
Surfaces that are less detailed are perceived as being
further away than objects that include fine detail.
4. Relative Size
An object that projects a large image on the retina is
perceived to be closer than an object that casts a
small image on the retina. Most effective with
familiar objects
5. Height in the Visual Field
Uses the horizon line as a cue for depth and distance.
Objects drawn closer to the horizon are perceived as being
more distant than objects further from the horizon.
Constancy Principles
The images projected onto the retina are
dynamic and changing- as an object
moves, the image on the retina changes
 Even though these images are changing
we perceive the size, shape and
orientation of an object to be constant
using the constancy principles.

Size Constancy
An object has the same size regardless of the
distance from which it is viewed.
We perceive the man in the background as being normal height even though
his image is smaller.
Shape Constancy
The tendency to see an object as the same shape
no matter what angle it is viewed from
The door remains a rectangle even though it is moved and
viewed from other angles.
Orientation Constancy
The tendency to visually perceive the true position
of an object in the environment even though the
retinal image of the object may be at a different
orientation.
The Perceptual Set
Psychological factors influence how to perceive the world. These factors include
past experience, context, culture, motivation and emotion. The way that we
perceive and interpret events is subjective and personal. We have a readiness to
interpret stimuli to meet our expectations. This is known as a perceptual set- a
mental predisposition to interpret stimuli in an expected and predictable way.
How would you interpret this scene? You
interpretation is influenced by your
perceptual set.
Processing
A perceptual set is linked to top-down processing- observing the
whole image first and applying existing knowledge to attribute meaning.
When we proof read an assignment we may not notice simple spelling
mistakes because we are using top-down processing. This is an efficient
way of processing information but is not always accurate.
For more accurate interpretations, we need to use bottom-up
processing. In bottom-up processing, the individual elements of the
stimulus are analyzed and after this a decision is made regarding the
nature of the stimuli. A developing child will use bottom-up processing to
learn about the world around them. We use bottom-up processing to
read a new word.
Past Experience
Past experience refers to the situations and
events we have encountered throughout our life
prior to the present. Each individual’s past
experiences differ and this contributes to our
individual uniqueness. Through experience we
form ideas and expectations about the world.
Past experiences led to the formation of a
perceptual set and hence impact on our
interpretation of the world.
Context
The context is the situation or setting in which we
view a stimulus. The context in which we view a
particular stimulus influences our interpretation of
the stimulus. The context provides a cue to help
your interpretation. With the aid of this cue we can
make quicker evaluations and interpretations of
information. However while correct on most
occasions using cues based on context can lead to
mistakes in interpretation.
What could it be?
Your answer would have been
influenced by your past experience on your
perceptual set
What could it be now?
Your answer shows the influence of
context on the perceptual set.
Visual Illusions
Muller-Lyer Illusion
Explanation of the Muller-Lyer IllusionApparent distance theory
The Ames Room
Explanation of the Ames Room