Chapter 3: Neural Processing + Perception

Question 1

What is Lateral Inhibition?

Answer 1

Inhibition transmitted across the retina

Question 2

Explain the experiment that was used to study Lateral Inhibition (Limulus experiment) (4)

Answer 2

• The Limulus experiment shows that lateral inhibition can cause response in neurons
• Its OMMATIDILIA contain lenses on the surface, directly over a single receptor, allowing recordings from single receptors
• Light shown at a receptor led to rapid firing rate of nerve fiber
• But! light shown at neibouring receptors led to reduced firing rate of initial receptor

Question 3

Define Lightness

Answer 3

Perception of shades

Question 4

What are the 3 illusions that can be explained by lateral inhibition?

Answer 4

1. Hermann Grid: seeing spots at intersections
2. Mach Bands: seeing borders more sharply
3. Simultaneous Contrast: brightness of one area affected by another adjacent
   (perceived lighter when surrounded by a dark area, vice versa)

Question 5

Use the Hermann Grid to explain lateral inhibition (3)

Answer 5

• BIPOLAR CELLS respond to white, sending inhibiting signals to the receptors at intersection
• Bipolar cells inhibit each other by 10%, but at an intersection with 4 surrounding bipolar cells, inhibition is stronger at 40% total
• At a corridor with 2 surrounding white cells of 100 each and 2 black cells of 20, 10% inhibition only sums up to 24%

Question 6

What is White’s Illusion? How can it be explained? (3)

Answer 6

In White’s Illusion, people see light and dark rectangles even though lateral inhibition would cause the opposite effect

Belongingness Theory: an area’s appearance is affected by where we perceive it belongs (gray area on the left appears to belong to the white background, contrasting with the white background SO! grey area on the left appears darker)
- The effect probably occurs in the cortex rather retina (top-down processing)

Question 7

What is Adelson’s demos? How can they be explained?

Answer 7

In Adelson’s demos, 2 horses appear to be 2 different shades. They can be explained by lateral inhibition and top-down processing (additional lightness adjustment because shadows)

Question 8

Define Receptive Field

Answer 8

The area on receptors/neurons that influence firing rate

Question 9

What are Center-Surround Receptive Fields? Where can they be found? (3)

Answer 9

On C-S receptive fields, areas are arranged in a center region that responds one way (excite/inhibit) and a surrounding area that responds the opposite (inhibit/excite)

They can be found at the optic nerve and LGN

Question 10

Explain Center-Surround Antagonism

Answer 10

Output of C-S fields changes depending on area stimulated

• If excitatory-center-inhibitory-surround, firing increases if light stimulates center but decreases if light expands to surrounding area
• If inhibitory-center-excitatory-surround, vice versa
• If both areas are stimulated, intermediate response

Question 11

Outline the pathway signals travel from the optic nerve to the frontal lobe (4)

Answer 11

Lateral Geniculate Nucleus (LGN), Primary Visual Receiving area/Striate Cortex/area V1, temporal lobe + parietal lobe, frontal lobe

Question 12

What is the function of LGN cells?

Answer 12

LGN cells regulate info from the retina to cortex. Signals are received from the retina, cortex, brain stem, and thalamus…then organized by eye, receptor type, and type of environmental info

Question 13

Define Retinotopic Map

Answer 13

A map in which each point on the LGN corresponds to a point on the retina

Question 14

What are Feature Detectors?

Answer 14

Elongated receptive fields in area V1, with side by side excitatory/inhibtory areas
(Receptive field properties become more complex in higher level cortical areas, like in the inferotemporal (IT) lobe and fusiform face area (FFA))

Question 15

What are the 3 Feature Detectors?

Answer 15

1. Simple Cortical Cells: respond best to specific orientation
2. Complex Cortical Cells: respond best to moving shapes with specific orientation, and with direction of movement
3. End-stopped Cortical Cells: respond best to moving lines with specific length or moving corners or angles, with particular direction of motion

Question 16

What is Selective Adaptation?

Answer 16

Phenomenon where if neurons fire too long, they become fatigued/adapt, causing a decrease in neural firing

Question 17

How can you test Selective Adaptation?

Answer 17

To test, measure sensitivity, have subject adopt to a stimulus, when remeasure sensitivity

Question 18

What is Grating Stimuli?

Answer 18

Alternating light and dark bars, used to test for sensitivity to either orientation or contrast

Question 19

What is Selective Rearing?

Answer 19

If animals are reared in environments that contain only certain types of stimuli, neurons that respond to these stimuli become predominant due to neural plasticity

Question 20

Explain Blakemore + Cooper’s experiment related to selective rearing (and kittens)

Answer 20

Kittens were reared in tubes with only horizontal and vertical lines.

• Both behavioural and neural responses showed exceptional development of those neurons
• Experiment provided evidence that the visual cortex could be modified by visual experience
• Experiment led to identification of sensitive periods

Question 21

Define Sensitive Period

Answer 21

Window of time during which neurons that code a function can be altered

Question 22

Define Sensory Code

Answer 22

Representation of perceived objects through neural firing

Question 23

What are the 3 coding theories?

Answer 23

1. Specificity Coding: specific neurons respond to specific stimuli
   - Problem: too many different stimuli to assign specific neurons
   - Problem: most neurons respond to numerous stimuli
2. Distributed Coding: representation of specific objects through patterns of neural firing
3. Sparse Coding: representation of specific objects through firing a few neurons (mid-point between 1 and 2)

Question 24

What is the Grandmother Cell Hypothesis?

Answer 24

A hypothesis related to the specificity coding theory, proposing that there are ells in the hippocampus that respond to images and concepts related to grandmas