Video Module 6: Perception

Question 1

Sensation vs. Perception

Answer 1

Sensation: getting sensory information to the brain and encoding it
Perception: interpretation of signals to create a sensory reality

Question 2

top-down processing

Answer 2

using models, ideas, descriptions, and expectations to interpret sensory information
- previous experiences & stored information influences our perception

Question 3

bottom-up processing

Answer 3

assembling and integrating sensory information to create perception
- perception based on the signals we receive from the environment around us

Question 4

Gestalt Principles

Answer 4

Describe some of our top-down expectations about the word and how they guide our interpretation of inherently ambiguous visual input
- Gestalt Principles are not the only form of top-down processing we use, but it is an example of how our expectations can influence our perception
1. similarity
2. proximity
3. good continuation
4. closure
5. simplicity

Question 5

similarity (Gestalt Principle)

Answer 5

we tend to group objects with similar features together (e.g. objects with the same color or shape may be perceived as part of a group)

Question 6

proximity (Gestalt Principle)

Answer 6

we tend to perceive groups of objects
- if objects are clustered together, we tend to perceive them as a group

Question 7

good continuation (Gestalt Principle)

Answer 7

we tend to see forms occluded by other forms as continuous rather than split apart (so long as there is good continuation)

Question 8

closure (Gestalt Principle)

Answer 8

we have a bias toward perceiving closed figures rather than incomplete ones

Question 9

simplicity (Gestalt Principle)

Answer 9

we tend to interpret a form in the simplest way possible

Question 10

bistable images

Answer 10

those which can be interpreted as two different images depending on the viewer
- If perception were only based on bottom-up processing (sensory input), we wouldn’t be able to have two different interpretations of bistable images
- perception requires interpretation

Question 11

binocular depth cues

Answer 11

those which require both eyes
- retinal disparity
- convergence

Question 12

convergence

Answer 12

a depth cue which relies on a muscular signal from the eyes moving inwards to focus on nearby objects
- feedback from muscles around the eyes can indicate how close an object is
- this is a binocular depth cue

Question 13

retinal disparity

Answer 13

the phenomenon in which an image falls on different regions of the retinas, resulting in a “disparity” between the two eyes encoded as depth
- Each eye has a slightly different view
- The closer the object, the greater the disparity between both eyes’ views
- this is a binocular depth cue

Question 14

static monocular depth cues

Answer 14

those which require only one eye and do not rely on movement
1) occlusion
2) linear perspective
3) height in plane
4) relative size of object (farther objects = smaller)
5) texture gradients (farther objects = less visible detail; farther objects = dimmed color)
6) light & shadow

Question 15

motion-dependent monocular depth cues

Answer 15

1) optic flow: as we move forward in space, move our head, or as objects pass us, objects in our visual field will move. Objects that are closer to us will move faster out of our visual field, while objects that are farther will move slower out of our visual field.
2) motion parallax: nearby objects tend to move faster in the visual field when you pass them or when they pass you, than if they were farther away. Nearby objects tend to move opposite to your direction, whereas faraway objects appear to move in the direction you’re moving

Question 16

perceptual constancy

Answer 16

The idea that images that hit our retina change all the time, but we do not perceive the world as constantly changing (we perceive objects in the world as constant)
- We understand from experience that objects don’t change shape, size, or color just because they look different in our visual field (from different perspective, lighting, shadow)

Question 17

shape constancy

Answer 17

the idea that we perceive the shape of objects as remaining constant despite changes in the shape of the object’s retinal projection
- our brain uses contextual information to interpret the shape of objects
- in the tabletop example, the tabletops have the exact same retinal projections, but our brain uses context clues and our prior experiences to infer that they’re different shapes

Question 18

size constancy

Answer 18

the idea that we perceive objects as constant in size despite their retinal projections changing
- we understand that objects in the world don’t spontaneously change, however we know that depth and linear perspective influences how we interpret the size of objects
- objects look smaller when they’re farther away

Question 19

Muller-Lyer illusion (cause)

Answer 19

an example of how previous experiences affect our perception of the world (top-down processing)
- our experiences with vertical edges in the real world causes our brain to think that the two line segments are different sizes

Question 20

luminance constancy

Answer 20

the idea that we perceive the brightness of an object as constant despite lighting and shadow around the object changing
- the luminance signal is the wavelength and amplitude of light an object reflects
- contextual information about light and shadow influences the way we perceive the color of an object

Question 21

colour constancy

Answer 21

the idea that we perceive the colour of an object as constant despite the lighting around it changing
- we understand that objects typically do not change color spontaneously
- the dress illusion occurs because we do not have contextual info from the lighting of the dress in the image
—our brain knows that in very dark lighting, a white and gold dress would appear blue and black; in overexposed lighting, the dress would actually be blue and black

Question 22

How do visual illusions demonstrate top-down processing?

Answer 22

Visual illusions demonstrate that do not simply perceive sensory info directly; we use contextual clues and draw on prior experiences to form an interpretation of objects in our visual field
- Visual illusions rely on context clues and expectations, therefore they demonstrate top-down processing

Question 23

Gestalt Theory of Perception

Answer 23

The mind organises sensations into meaningful perceptions
- The whole is greater than the sum of its parts