5.6 Perceiving objects requires organization of visual information

Question 1

Optical illusions

Answer 1

• Optical illusions are among the tools psychologists have for understanding how the brain organizes and interprets information
• Illusions illustrate how we form accurate representations of the three-dimensional world
• Researchers rely on these tricks to discover automatic perceptual systems that, in most circumstances, result in accurate perception

Question 2

Figure and ground

Answer 2

• In order to simplify the visual world, we automatically divide visual scenes into objects and background
• Determining that a collection of lines, shapes, and colors composes one figure or object in turn changes how we perceive those visual cues moving forward
• In this illusion, the figures periodically reverse, and the visual system strives to make sense of the stimulation. In ways like this, visual perception is dynamic and ongoing.
• At times, there is not enough information to distinguish the figure from the background and we have to rely on experience to make this judgment (dalmatian illusion). Thus, experience can inform how we identify figures and distinguish them from the background.

Question 3

Gestalt principles of perceptual organization

Answer 3

• Gestalt perceptual laws help explain how we group together some visual cues to perceive objects
• These Gestalt grouping laws include proximity, similarity, good continuation, closure, and common fate

Question 4

Gestalt principle: Proximity

Answer 4

The closer figures are to each other, the more likely we are to group them and see them as part of the same object

Question 5

Gestalt principle: Similarity

Answer 5

We tend to group figures together according to how closely they resemble each other, whether in shape, color, or orientation

Question 6

Gestalt principle: Good continuation

Answer 6

We tend to group together edges or contours that are smooth and continuous as opposed to those having abrupt or sharp edges

Question 7

Gestalt principle: Closure

Answer 7

• We tend to complete figures that have gaps
• The principles of good continuation and closure sometimes can result in seeing contours, shapes, and cues to depth when they do not exist, as is the case with illusory contours

Question 8

Gestalt principle: Common fate

Answer 8

• We tend to see things that move together as belonging to the same group
• For example, you would have no difficulty seeing the Dalmatian in the scene if the subset of black dots that represent the Dalmatian all began moving in the same direction

Question 9

Object constancy

Answer 9

• Once we perceive a collection of sensory information as belonging to the same object, object constancy leads us to perceive the object as unchanging, despite changes in sensory data that compose the objects
• What you see in the mirror might look like it is your actual size, but the image is much smaller than the parts of you being reflected
• For the most part, changing an object’s angle, distance, or illumination does not change our perception of that object’s size, shape, color, or lightness.
• But to perceive any of these four constancies, we need to understand the relationship between the object and at least one other factor. For size constancy, we need to know how far away the object is from us.
• For shape constancy, we need to know what angle or angles we are seeing the object from.
• For color constancy, we need to compare the wavelengths of light reflected from the object with those reflected from its background.
• Likewise, for lightness constancy, we need to know how much light is being reflected from the object and from its
• In order to see objects as constant despite changes in size, shape, color, or lightness, the brain computes the relative magnitude of the sensory signals it receives rather than relying on each sensation’s absolute magnitude
• The perceptual system’s ability to make relative judgments allows it to maintain constancy across various perceptual contexts

Question 10

Prosopagnosia

Answer 10

• Some people have particular deficits in the ability to recognize faces - a condition known as prosopagnosia - but not in the ability to recognize other objects.
• People with prosopagnosia cannot tell one face from another, but they are able to judge whether something is a face or not and whether that face is upside down or not.
• This specific impairment in recognizing faces implies that facial recognition differs from nonfacial object recognition.
• Prosopagnosia can be present from birth or can be acquired following a brain injury. Certain brain regions appear to be dedicated solely to perceiving faces, and damage to these regions results in prosopagnosia.
• As part of the ‘what’ stream, a region of the fusiform gyrus in the temporal lobe is critical for perceiving faces.
• This brain area responds most strongly to upright faces, as we wold perceive them in the normal environment.