4: Organization in the Visual System

Question 1

In the lateral geniculate nucleus, what layers have magnocellular cells, parvocellular, and koniocellular? How large are these cells?

Answer 1

Magnocellular: layers 1, 2 (big cells)

Parvocellular: layers 3-6 (small cells)

Koniocellular: interlaminar zones (very small cells)

Question 2

What layers process the ipsilateral eye? Contralateral?

Answer 2

Ipsilateral: layers 2, 3, 5

Contralateral: layers 1, 4, 6

Question 3

What are retinotopic maps? How do they relate to receptive fields?

Answer 3

Form “location columns” about ~1mm wide.

Receptive fields smaller near fovea, and larger in periphery. Location columns tile entire visual field.

Question 4

What is the cortical magnification factor? What is its benefit?

Answer 4

Fovea accounts for 0.01% of retina, signals account for 8-10% of visual cortex.

Provides extra processing for high-acuity tasks.

Question 5

What are orientation columns?

Answer 5

Within location columns. Each include simple, complex, end-stopped cells.

Question 6

If a cell in the right visual cortex’s response to the right eye is 11 spikes/second and the response to the left eye is 6 spikes/second, what does that make it?

Answer 6

Ipsilateral dominant.

Question 7

What is the pattern of activity that might be introduced by a simple stimulus?

Answer 7

Retinotopic map, magnification factor, orientation columns.

Question 8

Regarding objects, what happens if you remove the temporal lobe? The parietal lobe?

Answer 8

Remove temporal: cannot judge WHAT objects are.

Remove parietal: cannot judge WHERE objects are.

Question 9

What is the dorsal stream? The ventral stream?

Answer 9

Dorsal stream: parietal, “where” pathway.

Ventral: temporal, “what” pathway.

Question 10

What occurred with patient “D.F.”?

Answer 10

Damage to ventral stream. Cannot recognize objects, but can interact with them.

Question 11

What occurred with patient “V.K.”?

Answer 11

Damage to the dorsal/parietal stream. Can identify objects, cannot interact with them appropriately.

Question 12

Which pathway is fooled by the Ponzo illusion? Why?

Answer 12

“What” pathway. Measures distance in a relative sense.

Question 13

A brain structure specialized to process information about a specific type of stimulus is called what?

Answer 13

Module.

Question 14

fMRI studies have identified what area to recognize faces in humans? Where is it located?

Answer 14

Fusiform face area (FFA). Located in inferotemporal cortex.

Question 15

Difficulty recognizing faces of individual people, but can still identify a face as a face, is what disorder?

Answer 15

Prosopagnosia.

Question 16

List two other modules described using fMRI studies.

Answer 16

Parahippocampal place area (PPA): activated by outdoor and indoor photos.

Extrastriate body area (EBA): activated by pictures of bodies and body-parts, but not faces.

Question 17

Distributed coding within a specific module increases _____.

Answer 17

Information capacity.

Question 18

A single scene or object activates _____.

Answer 18

Multiple modules.

Question 19

A single stimulus activates _____.

Answer 19

Large area of cortex.

Question 20

Why should it not be surprising that stimuli are presented in a distributed manner?

Answer 20

They are multidimensional.

Question 21

What is the medial temporal lobe (MTL) important for? What is an example of an individual with damage to it? What does it contain?

Answer 21

Important for memory formation.

Patient H.M.

Contain neurons that respond to “concepts.”