Week 9- Sensation and Perception 2

Question 1

Define perception

Answer 1

The process of interpreting sensory information

Question 2

What are the two key factors in perception?

Answer 2

• Bottom-up, based on sensory input
• Top-down, driven by knowledge, expectation etc

Question 3

Outline the process of bottom-up processing

Answer 3

Bottom-up processing
|
Detect features of sensory data
|
Analyse specific features and combine component parts into more complex form
|
Form perception

Question 4

Outline top-down processing

Answer 4

Top-down processing
|
Use prior knowledge and experience to organise and interpret sensations
|
Select specific features that meet expectations about stimulus
|
Form perception

Question 5

Outline how the Adelson Figure uses different types of processing

Answer 5

• Bottom-up processing- the cones signal two identical colours (sensation)
• Top-down processing- the brain takes the shadow into account
• Result- we see two different colours (perception)

Question 6

Outline how the Ponzo Illusion uses different types of processing

Answer 6

• A function of both bottom-up and top-down processing
• Top-down processing- understanding of depth, viewing distance, knowledge, expectation, relationship to other objects
• Bottom-up processing- the size of the bars on the retina

Question 7

Outline how the rotating mask illusion uses different types of processing

Answer 7

• Why? Regardless of whether we look at the convex or concave side of the mask, our brain interprets the neural signals such that we see a protruding face
• Based entirely on our knowledge of real faces (always convex

Question 8

Give examples of top-down factors that drive perception

Answer 8

Numerous but include:
* Context
* Schemas (enduring knowledge structures)
* Experience or learning
* Motivation
* Your knowledge of the world
* Your expectations

Top-down factors are very powerful and can dominate perception

Question 9

What are Gestalt’s laws of perceptual organisation?

Answer 9

• A group of German and Austrian researchers in the 1920s and 1930s were particularly interested in how sensations were organised into percepts, what we call perceptual organisation
• These researchers were called Gestalt psychologists
• Gestalt= form/shape
• Argued that in perception, the whole, the percept is greater than the sum of its sensory parts. Attributes of the whole are not deducible from analysis of the parts in isolation
• A small number of basic perceptual rules that the brain automatically and unconsciously uses to organise sensory input into meaningful wholes

Question 10

Outline Gestalt’s Laws (6)

Answer 10

Laws of Similarity
* Things that are similar are grouped together

Law of Proximity
* Things near each other appear grouped together

Law of Good Continuation
* Stimuli tend to be organised into continuous lines or patterns rather than being perceived as discontinuous elements

Law of Closure
* Every stimulus pattern completed such that any gaps are seen as closed, complete, whole figure

Law of Familiarity
* Things are more likely to form groups if the groups appear familiar or meaningful

Law of Common Fate
* Things moving in the same direction appear to be grouped together

Question 11

How do Gestalt’s principles exemplify the way the brain organises perceptual experience?

Answer 11

• To reflect the regularities of nature
• They are ‘rules of thumb’ or heuristics
  -Reflect experience
  -Used unconsciously
  -Occasionally misleading

Question 12

What dimensions is perception organised into?

Answer 12

• Depth
• Distance

Question 13

What kinds of information are essential for depth perception?

Answer 13

• Binocular cues (visual input from two eyes)
• Monocular cues (visual input from one eye)

Question 14

Define convergence in relation to binocular depth perception cues

Answer 14

By comparing how much work your eye muscles have to do, your brain can extrapolate how close or far away the object is

Question 15

Define retinal disparity in relation to binocular depth perception cues

Answer 15

The differences between the two retinal images of the same scene

Question 16

Outline monocular depth perception cues (7)

Answer 16

• Interposition (occlusion)- one object blocks another
• Linear perspective- lines converge
• Texture gradient- distant objects appear finer
• Shading- 3D objects cast shadows
• Arial perspective- far objects are fuzzy and appear blue tinted
• Familiar size- familiar objects that appear small are inferred to be distant
• Relative size- the smaller of 2 objects is seen as further away

Question 17

Outline perceptual constancies (3)

Answer 17

• Colour constancy- tendency to perceive object colour as stable, even under conditions of changing illumination
• Shape constancy- we recognise an object as having the same shape although we may view it from a different angle, at a different distance
• Size constancy- objects do not differ in size when viewed from different distances

Question 18

How are illusions caused by perceptual constancies?

Answer 18

Your brain is familiar with the rule that objects that are further away are seen as being smaller than objects that are close to you. If you see an object like this with clear depth cues indicating that the top car is further away than the bottom car, and if the size of the retinal images is the same, the brain will extrapolate this as meaning the top car must be larger than the bottom car.