Lecture 4 Cortex and Beyond

Question 1

What is center-surround antagonism?

Answer 1

intermediate responses when both inhibitory and excitatory regions of a visual center-surround receptive field is stimulated

Question 2

Describe the visual pathway.

Answer 2

1. optic nerve
2. LGN
3. V1 (striate cortex)
4. temporal/parietal lobe (dorsal/ventral streams)
5. frontal lobe

Question 3

What is the role of the superior colliculus in the visual pathway? What percentage of the nerve fiberes leaving the eye does it account for?

Answer 3

control eye movements’ 10%

Question 4

What is the role of the LGN in the visual pathway? What percentage of the nerve fibers leaving the eye does it account for?

Answer 4

• center-surround receptive fields (like in the retina)
• may regulate or filter info passed along to V1
• 90%

Question 5

Describe the feedback mechanism of the LGN in the visual pathway.

Answer 5

• LGN receives more info FROM the cortex than it sends to the cortex

Question 6

What are feature detectors?

Answer 6

neurons that fire in response to specific features of a stimulus

Question 7

TRUE or FALSE: receptive fields of neurons in the visual cortex are centre-surround

Answer 7

FALSE: feature detectors

Question 8

What are the major types of feature detectors in V1?

Answer 8

• simple
• complex
• end-stopped

Question 9

What are orientation tuning curves?

Answer 9

they plot the response of a simple cortical cell to line stimuli of varying orientations

Question 10

What are the characterisitcs of the simple cortical cell?

Answer 10

• excitatory and inhibitory areas arranged side-by side
• responds best to bars of a particular ORIENTATION

Question 11

What are the characteristics of the complex cortical cell?

Answer 11

• response best to MOVEMENT of a correctly ORIENTED bar across the receptive field

Question 12

What are the characteristics of an end-stopped cortical cell?

Answer 12

responds to corners, angles, or bars of a particular LENGTH moving in a particular DIRECTION

Question 13

What is the absolute threshold?

Answer 13

smallest amount of energy needed to detect a stimulus

Question 14

What can be used to determine the absolute threshold?

Answer 14

Method of Limits

Question 15

What is the Method of Limits used to determine? What are the steps?

Answer 15

• determine absolute threshold
  1. present stimuli of different intensities in ascending and descending order
  2. record whether the stimulus can be perceived in each trial
  3. average the cross-over point

Question 16

What is selective adaptation?

Answer 16

phenomenon in which neurons tuned to specific stimuli properties fatigue with prolonged exposure to stimuli containing those properties

Question 17

fatigue or adaptation to stimulus causes a decrease in both:

Answer 17

1. baseline firing of those neurons
2. the response of those neurons to repeated presentation of the stimuli they have been adapted to

Question 18

Provide an example of selective adaptation.

Answer 18

feature detectors tuned to respond to vertical lines will fatigue when shown lots of vertical lines, but other feature detectors should be unaffected

Question 19

What are gratings?

Answer 19

the typical stimuli used for selective adaptation, made of alternating light and dark bars

Question 20

How are gratings used to test selective adaptation?

Answer 20

1. angle relative to vertical can be changed to test for sensitivity to ORIENTATION
2. difference in intensity can be changed to test for sensitivity to CONTRAST

Question 21

What is the general experimental procedure for testing selective adaptation?

Answer 21

1. measure sensitivity to range of one stimulus property (baseline); determine contrast THRESHOLD by decreasing intensity of grating until person can just see it, and SENSITIVITY (reciprocal)
2. adapt neurons with extended exposures of stimuli that have the property being tested
3. remeasure the sensitivity to range of the same stimulus property

Question 22

Describe the relationship that allows us to make causal claims about how neural activity affects perception.

Answer 22

we can observe a change in perception (contrast threshold) that we have experimentally demonstrated is caused by a change in physiology (selective adaptation)

Question 23

What is selective rearing?

Answer 23

raising animals in environments that contain only certain types of stimuli (while depriving exposure to other kinds)

Question 24

Describe Blakemore and Cooper’s 1970 experiment? What did they test?

Answer 24

• assessed selective rearing and how that affects perception
• manipulated whether kittens were raised in environments with (only) either horizontal or vertical lines
• kittens raised in an environment of all vertical lines couldn’t perceive horizontals (and vice versa)
• effects apparent in both behavioural and neural responses

Question 25

What is the oblique effect?

Answer 25

vertical and horizontal lines are more easily identified than oblique lines by most humans

Question 26

What is the rationale behind the oblique effect?

Answer 26

because horizontal and vertical lines are more common in our environment, this should promote the development of more feature detectors that respond to those kinds of stimuli

Question 27

What is the main difference between selective rearing and selective adaptation? What accounts for this discrepancy?

Answer 27

• selective rearing = total lack of response if never exposed to a stimuli
• selective adaptation = reduced response if exposed to a stimuli
• discrepancy due to long-term vs short-term effects

Question 28

Explain the steps of lesioning/ablation experiments.

Answer 28

1. an animal is trained to indicate perceptual capacities
2. a specific part of the brain is removed or destroyed
3. animal is retrained to determine which perceptual abilities remain
4. the results reveal which portions of the brain are responsible for specific behaviours

Question 29

What is the object discrimination problem?

Answer 29

monkey is trained to look in the food well UNDER a specific object

Question 30

What is the landmark discrimination problem?

Answer 30

monkey is trained to look in the food well NEXT TO a specific object

Question 31

Explain Ungerleider and Mishkin’s experiment.

Answer 31

• using ablation, part of the parietal lobe was removed from half the monkeys and part of the temporal lobe was removed from the other half
• temporal lobe removal –> problems with OBJECT DISCRIMINATION –> ventral stream/what pathway
• parietal lobe removal –> problems with LANDMARK DISCRIMINATION –> dorsal stream/where pathway

Question 32

The dorsal and ventral pathways demonstrate a classic _____________________.

Answer 32

double dissociation

Question 33

What is meant by double dissociation in terms of the visual stream?

Answer 33

it has two functions that involve different mechanisms and operate independently

Question 34

What is an example of double dissociation besides the visual stream?

Answer 34

broca’s and wernicke’s area

Question 35

What are three similarities of the ventral and dorsal pathways?

Answer 35

1. originate in the retina and continue through 2 different types of ganglion cells in the LGN (magnocellular and parvocellular)
2. have some INTERCONNECTIONS
3. receive FEEDBACK from higher brain areas

Question 36

What is the main difference between magnocellular and parvocellular ganglion cells?

Answer 36

PARVOCELLULAR neurons are more sensitive to COLOUR and FINE DETAIL