Chapter 4 - The Visual Cortex and Beyond

Question 1

1- Explain the visual pathway to the brain.

Question 2

2- Explain receptive fields of neurons in the visual cortex. Distinguish simple cells from complex cells and end-stopped cells.

Question 3

3- Explain the role of feature detectors in perception.
Explain selective adaptation and selective rearing.

Answer 3

Feature detectors
* Stimulus–physiology
relationship
* Demonstrating a link
between physiology and
perception
* Requires measuring the
physiology–behavior
relationship

Selective Adaptation
* When we view a stimulus with a specific property, neurons tuned to
that property fire.
* Selective adaptation
-This firing causes neurons to eventually become fatigued, or adapt.
-Two physiological effects:
1- the neuron’s firing rate decreases
2- the neuron fires less when that stimulus is immediately presented again.
Selective Adaptation to Orientation
* Contrast threshold:
A grating’s contrast threshold is the minimum intensity difference between two adjacent bars that can just be detected.

Selective Rearing:
Selective rearing experiments
If an animal is reared in an environment that contains only certain types of stimuli, then neurons that respond to these stimuli will become more prevalent.
Neural plasticity or experience dependent plasticity:
The idea that the response properties of neurons can be shaped by perceptual
experience.
Oblique effect?

see all graphs and images

Question 4

4- Explain spatial organization in the visual cortex.

Answer 4

• The Neural Map in the Striate Cortex (V1)
• Determine this by stimulating various places on the retina and noting where neurons fire in the cortex.
• Retinotopic map
  -Map of the retina on the cortex.
• Cortical magnification
  -Apportioning of a large area on the cortex to the small fovea.
• Cortical magnification factor
  -The size of this magnification

Magnification factor in the visual cortex (see all images)

Question 5

5- Explain the column organization of the visual cortex.

Answer 5

Location and Orientation Columns:
* Hubel and Wiesel (1965) experiments.
* Inserted an electrode perpendicular to the
surface of a cat’s cortex.
* Every neuron they encountered had its
receptive field at about the same location on the retina.
* Neurons all preferred stimuli with the same
orientation.

Orientation columns and hypercolumns.

Question 6

6- How V1 Neurons and
Columns Underlie
Perception of a Scene

Answer 6

• The cortical representation of a stimulus does not have to resemble the stimulus; it
  just has to contain information that represents the stimulus.
• The representation of the tree in the visual cortex is contained in the firings of neurons in separate cortical columns.

Tiling

Question 7

7- Extrastriate cortex (what and where)

Answer 7

• David Milner and Melvyn Goodale
  -Dorsal stream:
  -Vision for action
  -Provides information about where and how

Patient D.F.
* Damage to her ventral pathway from carbon monoxide poisoning.
* Damage to ventral stream.
* Had trouble orienting a card to match the orientation of the slot.
* Could mail the card in the slot.
* Performed poorly in the static orientation-matching task but did well as soon as action was involved.
* Double dissociation.
* Patients with dorsal stream
damage.

No brain damage length estimation task

Question 8

8- Higher level neurons

Answer 8

• Inferotemporal (IT) cortex
• Receptive fields of neurons in the visual system become larger as we move to higher levels.
• Increase in receptive field size continues through the what stream so that neurons at the apex of this stream in IT cortex have the largest receptive fields— large enough to encompass whole
  objects in one’s visual field.