Visual Perception

Question 1

What are the key parts for vision and the brain?

Answer 1

Eye
Lateral Geniculate Nucleus (LGN)
Visual cortex - V1, V2, V3, V4, V5 (MT = medial temporal lobe)

Question 2

What in the eye helps with vision?

Answer 2

Two visual receptor cells in the retina
- cones
- rods

Retinal ganglion cells receive input from a few cones or hundreds of rods

Question 3

What do cones do?

Answer 3

Colour and detail perception
Mostly located in the fovea

Question 4

What do rods do?

Answer 4

Vision in dim light
Located in the periphery

Question 5

What is LGN?

Answer 5

Lateral Geniculate Nucleus

Question 6

What is the retina geniculate-striate system

Answer 6

Parvocellular (P) pathway
- sensitive to colour and fine detail
- most input from cones

Magnocellular (M) pathway
- most sensitive to motion
- most input from rods

Question 7

What are V1 and V2?

Answer 7

Primary visual cortex (V1)
Secondary visual cortex (V2)

Receptive field
- Area sensitive to a visual stimulus

Lateral inhibition
- Increases contrast at edges

Question 8

What is form (shape) processing?

Answer 8

V1, V2, V3, V4 likely all process object shape and form

Neurons in inferotemporal cortex respond to specific semantic categories (e.g., animals, body parts).

And form processing: Yamane et al., 2008 neurons within inferotemporal cortex responded to 3D object shape.

Baldassi et al. (2013) anterior inferotemporal neurons responded on the basis of aspects of form or shape rather than object category.

Question 9

Colour processing in V4?

Answer 9

Bouvier and Engel (2006) achromatopsia cases (no colour perception): found small brain area close to V4 was damaged in nearly all cases.

Goddard et al. (2011). fMRI more activation in V4 with full-colour movie clips (compared to Black & White).
Banissy et al. (2012) found TMS reduced colour processing performance in V4.

V4 important in colour processing network, but not the “colour centre”

Question 10

Motion processing in V5? (MT)

Answer 10

V5 (also known MT: medial temporal cortex) is heavily involved in motion processing.

fMRI show associations.

McKeefry et al. (2008) used transcranial magnetic stimulation (TMS) to disrupt V5/MT, it produced a subjective slowing of stimulus speed and impaired observers’ ability to discriminate between different speeds.

Question 11

Whats the binding problem?

Answer 11

How are features combined and integrated?
1. Binding visual features together?
2. Binding information across multiple eye movements?

Hard to solve

Feature integration theory: selective attention plays a role (Treisman & Gelade, 1980)

Question 12

What are the suggestions for the binding problems?

Answer 12

Suggestion 1: binding-by-synchrony
Features from single object fire in synchrony (e.g., Singer & Gray, 1995).

Suggestion 2: Guttman et al. (2007) suggested patterns of neural activity over time help coordinate binding.

Question 13

What’s the dorsal and ventral visual streams?

Answer 13

These streams of neuron activity flow from V1 and into the parietal and temporal lobe,

One helps identify shapes and names the objects

The other processes spatial and movement

Question 14

What are the two visual streams?

Answer 14

Ventral stream
Dorsal stream

Question 15

What’s the ventral stream?

Answer 15

Vision-for-perception
Identifies objects
Allocentric (labelling of objects without reference to self)
Sustained representation
Usually conscious
Input from the fovea

Question 16

Whats the dorsal stream?

Answer 16

Vision-for-action
Processes spatial information to guide movement
Egocentric (represents object in space relative to self)
Short-lived representations
Usually unconscious

Question 17

What does dorsal stream damage cause?

Answer 17

Poor guided movement

Question 18

Is there a connection between dorsal and ventral networks?

Answer 18

Had damage in the ventral stream and visual form agnosia
However, also made more errors than average on dorsal stream test

Question 19

How can visual illusions help?

Answer 19

Visual illusions can be used to understand visual perception
Including whether they support the dorsal vs ventral streams theory

E.g.,

Bruno et al. (2008) found when pointing (using vision-for-action system), the illusion size was 5.5%

When verbalising a response (using vision-for-perception system), the illusion size was 22.4%

Question 20

Evaluation of dorsal and ventral systems?

Answer 20

Independence of the dorsal and ventral systems is not absolute
The dorsal stream is appears to be only required for rudimentary actions
Double dissociation between optic ataxia and visual form agnosia is not clear cut

Question 21

Whats the trichromatic theory?

Answer 21

Three types of colour receptors or cones identified by microspectrophotometry

Question 22

Whats opponent process theory?

Answer 22

But what about negative afterimages, that are not well explained by trichomatic theory?
- Green - Red
- Yellow - Blue
- White - black

There is strong physiological evidence for the existence of opponent cells (Shevell & Martin, 2017).

the theory claims it is impossible to see blue and yellow together or red and green, but the other colour combinations can be seen. Abramov and Gordon (1994) found evidence for this.

Question 23

What’s the dual process theory?

Answer 23

Combination of trichromatic and opponent process theory

Question 24

Whats colour constancy?

Answer 24

The tendency for a surface or object to appear to have the same colour despite a change in the wavelengths contained in the illuminant

Question 25

What’s size constancy?

Answer 25

The tendency for objects to appear the same size whether their size in the retinal image is large or small

Size perception of objects depends on memory of their familiar size rather than on perceptual information

Question 26

What does perception without awareness mean?

Answer 26

Responding appropriately to visual stimuli in the absence of conscious visual experience

• Associated with severe brain damage to V1
• Impairments largely due to knock-on effects due to V1 damage (Silvanto, 2008)

Intact abilities rely upon a neural tract linking lateral geniculate nucleus to the human visual motion area (V5/MT) that bypasses V1