Excitable cells 20: Extrastriate Cortex and posture

Question 1

Sum up the purpose of the ventral and dorsal visual pathways?

Answer 1

Ventral pathway = what pathway (object recognition)

Dorsal pathway = where pathway (vision processing for action)

Question 2

Describe the progression of both the dorsal and ventral stream from the striate cortex (V1) to their extrastriate cortex areas of processing

• mention what information is processed by each pathway

Answer 2

Ventral stream (What pathway)
V1 -> V2 
- Thin stripes (Colour)
- Interstripes (Edge Detection)
V2 -> V4
- Complex form, Perceived colour
Inferior temporal cortex
- Object recognition and perception (WHAT)

Dorsal (where pathway)
V1 -> V2
- Thick stripes (motion and disparity)
V2 -> MT
- Global motion through space
MT -> Intraparietal complex
- Vision for action + eye movements (WHERE)

Question 3

Damage in the inferior temporal complex leads to what types of agnosia? Properties of each type?

Answer 3

What pathway

Aperceptive agnosia -> cannot copy of match object (cannot integrate visual features)

Associative agnosia -> cannot interpret, understand or assign meaning to objects (problems with recognition)

Question 4

Damage in the intraparietal cortex leads to what? Why?

Answer 4

Where pathway

Damage to left side leads to fairly mild symptoms

Damage to right side -> hemi-neglect of left visual field

This is because the right side sees whole of the visual field through interhemispheric connections
- left side only sees right visual field

Question 5

What is meant by ‘bottom up’ and ‘top down’ processes?

Answer 5

Bottom-up = sensory (exogenous) information

Top-down = internal (endogenous) information
- interpretation heavily influence by expectation, context and learning

Question 6

What is ‘binding’ - and what are the 2 problems with it?

Answer 6

The integration of highly diverse neural information to form a cohesive experience

Problem 1) The segregation problem
- How are complex patterns of sensory input allocated to discrete objects?

Problem 2) The combination problem
- How are various features combined into a single perceptual experience?

Question 7

4 Factors which contribute to balance?

Answer 7

Vision - Parietal (dorsal WHERE) pathway

Vestibular system - otoliths, semicircular canals

Somatosensory system - muscle spindle, golgi tendon organ, joint receptors, pressure sensors on feet

Efference copy - brain has an internal copy of outflowing motor signal

Question 8

Advantages and disadvantages of efference copy?

Answer 8

Adv.

• fast movements, don’t need to wait for sensory feedback
• movements where it is unlikely for external forces to affect movements e.g. eye movements

Dis.

• dont allow for unexpected changes
• no absolute reference, needs sensory updates
• less accurate for slow movements