Lec 4-3

Question 1

How do eye movements work, how do they follow things

Answer 1

Eyes make saccades rapid movement that shifts your gaze to something. You make larger saccades until you get close to the thing you want to look at then make a smaller saccade to get there. If it is not too far in periphery you can make one saccade.

You can also do slow pursuit eye movement, but can only do when tracking/following something

Question 2

explain how your hand eye coordination works (what happens first)

Answer 2

Eye typically moves first, then hand follows. Eye movement is completed while hand is still moving.

Question 3

Describe the research done by Pelisson et al. on fast ‘unconscious” eye corrections and findings

Answer 3

• Participants were asked to point to a target as quickly and accurately as possible to target in periphery.
• There were some trails where the target jumped further slightly called double step trials. Trials where the target remained stationary were called single strep trials.
• Target movements was tied to eye movement, when the eye started to move, the target moved, and people didn’t notice this due to saccadic suppression (reduction in visual sensitivity during eye movements)
• when compare data from single step and double step trials side by side, you see that there were no accuracy discrepancies from them and looking at hand velocity and acceleration you can see they were also the same.
• This shows the smoothness of the corrections and that people weren’t even aware they made them

Question 4

Saccadic suppression

Answer 4

• Reduction in visual sensitivity during saccadic eye movements
• the makes you less sensitive to visual events during saccade. Also reason why things don’t look blurry and smeared when you do a saccade

Question 5

Describe the study done by Cressman et al. on making corrections to target, and findings

Answer 5

• Asked people to move towards a target with hand.
• Target would then jump (ppl were aware) and would have to move toward new target location. Did separate one where they were asked to stop the movement
• Participants were able to do both situations mostly well
• Did another set of trials where there were two targets shown (one green and one red) with the green one always being the target. For some trials, the colours stayed the same, but for some, the colours swapped.
• Now only about 50% of the time people where able to change to reach new target

Comparison:
- people were more able to reach target with location change as opposed to colour change due to automatic reflex causing them to go towards target with location change. Even when asked to stop, the automatic reflex beats the intention to stop

• With the colour change trials, there was no automatic mechanism so people ended up completing their first movement (to the original target) before going to the second target

Significance:

• shows how reliance on the dorsal stream for location adjusting movements without awareness (hence why they are so quick) and reliance on ventral stream for making adjustments based on colour/identity of target (takes longer and is conscious)

Question 6

Describe the Day & Lyon study on pointing to targets, and findings

Answer 6

• Asked to point to target as quickly and accurately as possible. The target jumps at the start of the movement and you are aware.
• There is a point trial and an anti-point trial. Point trial (+) you reach to target, anti-point (-) you reach to opposite target
• For +, they were able to do automatically
• For -, they started going to + target then conscious system took over and they corrected towards the - target.
• Then they did the same trials, but instead of pointing forwards, they just tracked laterally. Only once the targets appeared did they start their movement.
• Due to this, there was no automatic reaction. Both track and anti-track conditions were slower then in the reaching trials

Significance: Shows that not moving before target moves allows them to ignore the dorsal stream and use their conscious ventral stream to make decision to move other way.

Question 7

what did the study using TMS on the posterior parietal cortex during reaching task show

2 studies

Answer 7

• Used TMS on left posterior parietal cortex to disrupt corrections when target moves.
• Resulted in people completing initial movement to original target place, then doing a separate movement to the new target location.
• To show TMS affects, used left and right hand for experiment, where left acts as control not receiving TMS influence (Left brain hem control right hand so right hand displayed affects)

Also did study where tasked to grab something on tray and the tray rotated causing people to have to change path. Saw same results - ppl with Posterior parietal cortex lesion could not make adjustment on the go.