Visual Perception

Question 1

What is the Retina?

Answer 1

Layer of photoreceptors at the back of your eyeball (where all of your vision comes from)

Question 2

What are the Photoreceptors in the Retina?

Answer 2

Rods and Cones

Question 3

Rods

Answer 3

• Sensitive to dim light (i.e., low levels of light)
• Lower acuity (fine detail)
• Colour-blind
• None in the fovea

Question 4

Cones

Answer 4

• Cannot function in dim light
• Higher acuity (fine detail)
• Colour-sensitive
• Mostly in or near the fovea; none in the periphery

Question 5

What Does the Optic Nerve Do?

Answer 5

Info from retina to the brain; all of the axons bundle together into a nerve and that nerve passes out through the back of the eyeball into the brain

Question 6

Cornea

Answer 6

The transparent tissue at the front of each eye that plays an important role in focusing the incoming light

Question 7

Lens

Answer 7

The transparent tissue located near the front of each eye that (together with the cornea) plays an important role in focusing incoming light

Question 8

Fovea

Answer 8

The centre of the retina and the region on the eye in which acuity is best; when a person looks at an object, they are lining up that object with the fovea

Question 9

What is Lateral Inhibition?

Answer 9

A pattern in which cells, when stimulated, inhibit that activity of neighbouring cells.
In the visual system, lateral inhibition in the optic nerve creates edge enhancement

Question 10

Bipolar Cells

Answer 10

A type of neuron in the eye; bipolar cells receive their input from the photoreceptors and transmit their output to the retinal ganglion cells

Question 11

Ganglion Cells

Answer 11

A type of neuron in the eye; ganglion cells receive their input from the bipolar cells, and then the axons of the ganglion cells father together to form the optic nerve, carrying info back to the lateral geniculate nucleus

Question 12

What is the Lateral Geniculate Nucleus (LGN)?

Answer 12

An important way station in the thalamus that is the first destination for visual information sent from the eyeball to the brain

Question 13

What is Edge Enhancement?

Answer 13

The neurons in the visual system give exaggerated responses to edges of surfaces

Question 14

What is the Hermann Grid Illusion?

Answer 14

Dark patches at the intersection between two white pathways (only appear in the periphery, not the centre of vision)

Question 15

What are Mach Bands?

Answer 15

A type of illusion in which one perceives a region to be slightly darker if it is adjacent to a bright region, and also perceives a region to be slightly brighter if it is adjacent to a dark region

Question 16

Receptive Field

Answer 16

The size, shape, and location of the area in the visual world to which that cell responds

Question 17

Centre-Surround Cells

Answer 17

A type of neuron in the visual system that has a “donut-shaped” receptive field. Stimulation in the centre of the receptive field has one effect on the cell; stimulation in the surrounding ring has the opposite effect

Question 18

Receptive Fields in Visual Cortex

Answer 18

Simple Cells (primary visual cortex): edge detectors
- these detectors fire when a stimulus within the receptive field contains an edge of a particular orientation
- the less the edge is like the cell’s “preferred” edge, the less often it fires

Complex Cells (secondary visual cortex)
- angles, motion and direction, corners

Question 19

Where vs. What Processing

Answer 19

After processing in early visual areas, information is processed hierarchically in two different pathways

Question 20

“Where” System (top of the brain)

Answer 20

The “where” pathway processes relevant spatial information for the purposes of guiding action

Question 21

“What” System (bottom of the brain)

Answer 21

The “what” pathway extracts shape and texture information to identify objects

Question 22

Parallel Processing

Answer 22

A system in which many steps are going on at the same time

Question 23

Serial Processing

Answer 23

A system in which only one step happens at a time (and so the steps occur in a series)

Question 24

Constancy

Answer 24

We perceive constant object properties (sizes, shapes, etc.) even though sensory information about these attributes changes when viewing circumstances change

Question 25

Shape Constancy

Answer 25

Correct perception of an object’s shape despite changes in its shape on the retina

Question 26

Brightness and Colour Constancy

Answer 26

Objects should not change brightness or colour under different light sources

Question 27

Gestalt Principles

Answer 27

1. Similarity
2. Proximity
3. Good continuation
4. Closure
5. Simplicity

Question 28

Binocular Depth Information

Answer 28

The eyes get slightly different 2D views of the same 3D scene. You can reconstruct the 3D scene by comparing the 2D images

Question 29

What are Monocular Distance Cues?

Answer 29

Features of the visual stimulus that indicate distance even if the stimulus is viewed with only one eye

Question 30

What are Pictorial Cues?

Answer 30

Sources of depth information that can be extracted from static 2D images, such as pictures, even using only 1 eye

Occlusion, Relative height, Relative size, Perspective convergence, Familiar size, Familiar shape, Atmospheric perspective, Texture gradient, Shadows

Question 31

What is a Conjunction Error?

Answer 31

An error in perception in which a person correctly perceives what features are present but misperceives how the features are joined

Question 32

What is a Reversible (or Ambiguous) Figure?

Answer 32

Drawings that can be readily perceived in more than one way (e.g., Necker Cube)

Question 33

Necker Cube

Answer 33

One of the classic reversible (or ambiguous) figures; a two-dimensional drawing that can be perceived as a cube viewed from above or as a cube viewed from below

Question 34

What is the Motion Parallax?

Answer 34

A distance cue based on the fact that as an observer moves, the retinal images of nearby objects move more rapidly than do the retinal images of objects farther away