1. Visual Perception

2. 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.

4. 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
Selective Attention Experiment

5. Perception
While the sense organs gather the information (sensation), perception is the name given to the process during which the brain organizes and interprets the information from the sense organs.
Perception givens meaning to the sensations.

6. Sensation and Perception
Sensation is the same for everyone (except the visually impaired).
Perception is not the same for everyone.
List the following:
Your favourite colour (sight)
Your favourite vegetable (taste)
Your favourite muscial instrument (sound)
Your favourite perfume/cologne (smell)
The temperature at which you like to drink water (temperature)

8. 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)

9. 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!

10. 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.

11. Wavelength, frequency and amplitude
Electromagnetic energy travels in waves and therefore has different wavelengths, frequencies and amplitudes.
We see different wavelengths/frequencies as different colours.
We see different amplitudes as different intensities of light.

12. Structures of the Human Eye

14. 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.

15. 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.

16. 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.

17. Find your blind spot

18. 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

19. 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

20. 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

21. Structure of the Retina

23. From eye to brain- the visual perceptual process

24. 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

26. Visual Perceptual Principles
Visual perceptual principles guide the way in which visual information is organized, grouped together and given meaning- the 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.

27. Visual Perceptual Principles
There are three broad categories of these principles:
Gestalt Principles- allow us to quickly interpret an image and focus our attention on what is important.
Depth perception principles- allow us to interpret the two dimensional image sent from our eyes as three dimensional
Constancies- allow us to perceive an object as remaining the same (constant) despite changes to the image on the retina

28. Gestalt Principles
Suggest that we group individual elements together to see the whole- we do not perceive the individual elements
Gestalt principles allow us to interpret and assign meaning to an image more efficiently- but not always accurately.
“The whole is greater than the sum of its parts”
There are four Gestalt principles:
Figure-ground
Closure
Proximity
Similarity

29. 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 a scene.

31. Can you find 13 faces? Can you explain why there are hidden?

32. Closure
When a figure is incomplete, our visual perceptual system will complete the picture so that we see a whole.

33. Proximity
Objects close to each other are perceived as belonging to the same group.

35. Similarity
Objects that are similar in appearance are perceived as belonging to the same group.

37. Gestalt Principles and Advertising

38. Depth Perception Principles
Refers to out ability to judge distance- remember 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:
Primary Depth Cues
Secondary Depth Cues

39. Primary Depth Cues Internal cues/signals provided by the body
There are three primary depth cues:
Retinal disparity
Convergence
Accomodation

40. 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.

41. 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. The more the 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.

42. 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.

43. Secondary Depth Cues

44. 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

45. 1. Linear Perspective
Two parallel lines merging together give the perception of depth.

46. 2. Interposition
Provides a cue for depth when two or more objects overlap each other. The object behind is perceived as being further away

47. 3. Texture Gradient
Surfaces that are less detailed are perceived as being further away than objects that include fine detail.

48. 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

49. 5. Height in the Visual Field
Uses the horizon line as a cue for depth and distance. Objects closer to the horizon are perceived as being more distant than objects further from the horizon.

50. 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.

51. 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.

52. 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.

53. 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.

54. Perceptual Set
Look closely at the image representing a seal act at a circus. What do you see?

55. If you were actually told that this image was of a costume party what do you now see?

56. The Perceptual Set
The visual information in each diagram has not changed but your expectation of what you will see does.
Perceptual set is a readiness to see something that we expect to see.
How would you interpret this scene? Your interpretation is influenced by your perceptual set.

57. 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.

58. Perceptual Set
Perceptual set can assist visual perception when we actually see what we expect to see.
Perceptual set can also however mislead us. We may expect to see something that does not occur causing us to miss vital information in our environment.
'The Cat Sat on the Map and Licked its Whiskers'

59. Influences on Perceptual Set
Perceptual set may be influenced by many things including context, past experience, culture, motivation and emotion.
We will now have a look at each of these in more detail.

60. 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 the perceptual set and hence impact on our interpretation of the world.

61. The Effect of Past Experience
Toch and Schulte (1961)

62. The Effect of Past Experience
Toch and Schulte (1961)
Showed the below images simultaneously (one to each eye) to participants who were: trained policemen, beginning police training and university students with no police training.

63. The Effect of Past Experience
Toch and Schulte (1961) found that 52% of the policemen saw the violent image but only 26% of the trainees and 22% of the university students saw the violent image.

64. 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.

65. Studying the images that you have been given for 1 minute.

66. What do you see?

67. What could it be? What could it be now? 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.

68. Motivation
Motivation leads our behaviour because we want to achieve a particular goal. It also influences our perceptual set.
Motivation leads us to see what we want to see to aid the achievement of this goal.

69. Motivation
Example: When you watch your favourite football team play you are motivated to see them win. You therefore will explain the events of the game with this motivation in mind. Someone who supports the opposite team may explain the events of the game in much different terms. You both see the same game but your interpretation is influenced by your different motivations and hence your perceptions are different.

70. Emotion
Emotions can influence the way we perceive images of our environment.
For example, if you are scared of spiders you are more likely to perceive an insect as a spider than any other invertebrate. You are more likely to perceive an image as food if you are hungry.

71. Cultural Factors
Culture includes things such as customs, traditions, beliefs, values, attitudes, ethics, music and food.
Culture influences our perception of the world.
E.g. When shown a black and white photo of a dog, members of a Malawi tribe could not recognise the drawing despite the fact that many owned dogs. The researches concluded that this was because the members of the tribe has no experience with photos or two dimensional images of dogs.

72. 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.

73. Processing
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.

74. Visual Illusions
Visual perceptual principles are in place to help us to better understand our world yet these mechanisms can also lead us to misinterpret visual information
When we misinterpret visual information- our perception does not match reality- we see a visual illusion
Visual illusions are unavoidable and even when we know they exist we still see them

75. Herman Grid Illusion

76. Fraser Spiral

78. The Impossible Triangle

84. Moon Illusion

85. Psychologists have identified at least 200 visual illusions
The cause or explanation of why we see many of these is still unknown but they have been able to help psychologists understand the importance of the brain in perception.

86. Muller-Lyer Illusion Which line appears to be longer?
The Muller-Lyer Illusion is one of the most researched visual illusions.

87. Muller-Lyer Illusion
The line with the feather tail is perceived as being longer than the line with the arrow head.
There are several explanations of the Muller-Lyer Illusion
We will explore them from each of the four psychological perspectives

88. Biological Perspective
Eye movement theory
Because the feather at the end extends the length of the line it has been proposed that the extra eye movement interprets the line as being longer. However research has found that even when we do not need to move the eyes we still see the Muller-Lyer Illusion.
Another theory proposes that we see the illusion because we have inherited the ability in our genes.

89. Behavioural Perspective
Learning and past experience influence our perception of the lengths of the lines.
We see the line with the feather top as being longer because it represents the inside corner of the further away room. We see the line with the arrow head as smaller because it represents the outside corner of a room closer up.

90. Behavioural Perspective
When the two lines are presented together, your brain overrides information from the retina and tells you that the line that is further away (the feather tail line) must be longer.

91. Cognitive Perspective
Cognitive psychologists suggest that we use the incorrect mental strategies when processing the visual information
We perceive the smaller line as being closer and incorrectly use the size constancy principle. (If the “corner” is closer and the lines are equal then we must perceive the line further away to be longer than the line closer.)
Further we seen to be interpreting the lines as what they represent and not what they actually are (room corner example).

92. Socio-cultural Perspective
It appears that our culture also plays a role in the Muller-Lyer Illusion.
Zulu people do not see the illusion- they see the lines as equal in length. They live in round huts and are not familiar with our angular world.

93. Criticisms
Critics of the above theories have noted the fact that there are many variations of the Muller-Lyer illusion.
Psychologists from all fields agree that there is no one single satisfactory explanation of the Muller-Lyer illusion

94. The Ames Room

96. The Ames Room
The person on the right appears to be much larger than the person on the left despite the fact they are of equal size.
This is due to the construction of the room. The room which appears to be rectangular is actually a trapezium. One side of the room is both longer and higher than the other.
Helping the illusion is the fact that the room is viewed through a peep hole using only one eye (monocular vision). This reduces some of our cues to depth.

98. Explanation of the Ames Room
The back corners of the rooms produce an identical image on the retina suggesting that the corners are the same size and distance. However one corner is further away and higher. Therefore the person in this corner is twice as far away and therefore looks a lot smaller.
Your brain appropriately applies the relative distance principle but is tricked by the shape of the room into thinking the room is rectangular and therefore each person is the perceived to be the same distance from you.
See Zimbardo youtube.