Lecture 20 - Visual Perception during saccades (MI)

Question 1

Challenges for visual system

Answer 1

1) Omission of peri-saccadic stimuli - get rid of the big shift that occurs during the saccade
2) Spatial integration

Question 2

Before and during a saccade, what happens to contrast sensitivity? As it happens before a saccade, what does this suggest?

Answer 2

It decreases, suggests that the brain is involved

Question 3

Why are perceptual studies limited?

Answer 3

Good for phenomenology but bad for mechanisms - we must turn to electrophysiology

Question 4

How is the visual response modulated before saccade vs after saccade

Answer 4

BEFORE - saccadic suppression -Response suppressed = no AP -Spontaneous suppression in some cells -Contrast sensitivity reduction AFTER - saccadic enhancement -Spontaneous activity increases (which leads to the decreased latency) -Response amplitude increases -Latency decreases

Question 5

Does PSE improve performance above baseline?

Answer 5

No -it maintains the control level so the system is not disrupted by the sudden image motion- this is why in the red squares, there isn’t a strong enhancement seen as it just brings it back to baseline

Question 6

There is strong post-saccadic enhancement of reflexive ocular following

Answer 6

If you are looking at a fixation spot with a textured screen and you suddenly move the textured screen, there is a delay and your eye chases the moving image. If we suddenly move an image after a saccade, there is an increase in tracking speed (compared to when there isn’t a saccade)

Question 7

T/F -Saccadic suppression is a perceptual term

Answer 7

T

Question 8

If the stimulus e.g bright light is presented only during the saccade - can you see it? If the stimulus is still present 40 ms after the saccade, can you see it?

Answer 8

Yes (as a smeared structure), no - indicates that something happens after a saccade that omits the image

Question 9

Backwards masking

Answer 9

Phenomenon where you present two stimuli, one weak and one strong, people only see the strong one In this case, combined saccadic suppression and PSE lead to omission of the image during the saccade

Question 10

What cortical areas also show the suppression the PSE?

Answer 10

dLGN and PGN (pre-geniculate nucleus) *The point he is trying to make here is that this signal is propagated by the whole brain

Question 11

Perception of time is shorter/longer just before and during saccade

Answer 11

Shorter

Question 12

The top and bottom green stimulus came at different times and they were asked which one flashed first At a long way before the saccade, they get it right all the time Before a saccade, people got it wrong all the time - the obvious implication is that time is going backwards

Answer 12

The top and bottom green stimulus came at different times and they were asked which one flashed first At a long way before the saccade, they get it right all the time Before a saccade, people got it wrong all the time - the obvious implication is that time is going backwards

Question 13

Post-saccadic time expansion is called

Answer 13

Chronostasis

Question 14

Explain how temporal inversion occurs during saccades

Answer 14

-2 stimuli have to be close together in time -One flash occurs then another flash after (during saccade) - the second flash takes lesser time to get to the brain due to the decreased latency during the saccade -Hence because, the second flash gets to the brain first, you have temporal inversion where time appears to be backwards

Question 15

Which cortical area does PSE occur in?

Answer 15

MST