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311 POST MIDTERM II—FINAL PORTIONTESTING ROLE OF Procedures:
POSTERIOR PARIETAL - Subjects reached with right hand to stationary and displaced objects
CORTEX IN SACCADE - Targets would be displaced during saccadic eye movement
STUDY - TMS applied to posterior parietal cortex (creating virtual lesion)
Results from TMS:
- No significant effect on stationary grasp, because already planned movement
- When no TMS= when target jumped R, able to smoothly correct to R and vice versa (smoothly
integrated correction)
- When TMS fired= when target jumped, had no smooth online correction or if correction occurred,
happened at end of movement
- Effect seen on target jump = went to initially planned target location
2nd part of study:
- TMS to left posterior parietal cortex but point with L hand
- Because L posterior parietal cortex controls the R hand
- No effect seen because effect only on part of brain responsible for controlling movement
Implication of this study:
- Can disrupt on line correction of movement by disrupting dorsal stream (posterior parietal cortex)
OTHER STUDIES ON P.P.C - Looked at patients with lesions in PPC
AND ON LINE - Reach and grasp dowel on turntable as fast as possible
MOVEMENT—DOWEL - On some trials, table would turn
STUDY
Results:
- For controls= even when dowel moved with table turning= were smoothly able to adapt during
movement, seen with smooth velocity profile, integrated correction
- No significant difference b/w controls and patients during stationary condition
- patients= when target jumped, velocity profile showed that initial movement of original target location
was completed first then executed second
**patients used ventral/conscious stream
- For correction= separated into secondary movement, not integrated during movement
- grip aperture would open, close then open again
**still some correction observed in controls
SPACE/POSITION
CONSTANCY - Visual world remains stable when we move our eyes
DOUBLE JUMP - Blanking = during saccade, target briefly disappears and comes back at a new position
TARGET—BLANKING - Takes advantage of saccadic suppression = have reduced sensitivity to visual events during eye
movement —prevents blur in vision during rapid eye movement (also helps maintain space/position
constancy)=visual world remains stable when eyes moved
Procedures:
- Blanking paradigm =target shown, disappears and comes back at a new position (jumped)
Results:
- When blanking used to make target jump and asked subjects whether target jumped= start to notice
target moved (restores ability to discriminate whether target remained stationary or not)
HOW DOES THE VISUAL
SYSTEM USE *if target is continuously visible = brain uses that target as reference to assume stable world (things stay where
INFORMATION WHEN A they are in space)
TARGET IS
CONTINUOUSLY VISIBLE *if target made to disappear= visual system interprets this event as something new happening
VS. WHEN IT - Temporary discontinuity is used as evidence of spatial displacement
DISAPPEARS? -
SCHNEIDER Procedures:
STUDY—WHAT INFO WE - Have fixation point
CAN PROVIDE AT END OF - 2 items come up (1 is actual target, other is distractor item)
MOVEMENT - During eye movement, either distractor or target changes position
- And one of the two or both will blank during eye movement
, - Subject gives verbal report of which they think jumped (target or distractor)
Results:
- If target moved and distractor blamed= performance dropped (influence of perception when blanking vs
continuously visible)
- Reporting whatever blanked/was discontinuous as having moved
- While the one that had continuous vision was used as evidence of constancy (interpreted as part of
stable environment)= illusion made
**perceptual constancy pushed to consciousness
BLANKING VS TARGET Procedures:
JUMP—POINT TO TARGET - 2 items in periphery
- Same procedures as previous study (both blank, one of or neither, either one or toher jumps)
- But told to point to target —act on target movement
- Looked at motor performance with respect to target
- Perceptual vs motor report of target movement
Results:
- Verbal report= replication of previous results (whichever one blanked was reported to have jumped)
- Perceptual/motor report= when distractor jumped forward/backward, no diff in pointing —where you
pointed in reference to target did not jump
- Where you pointed followed the target!
- Despite pointing correct motor performance —cant use for inform conscious awareness
Pointing is unaffected by blanking illusion!
- Because on line control is integrated from conscious visual experience
PART 2:
- Point as fast/accurately as possible, same procedures but told if they think target jumped, inhibit
movement (pull back)
Results:
- The one that blanked again, is the one that was reported to have jumped
- Movement was corrected if target jumped forward/backward
- For movement inhibition if perceived that target jumped= seen to have pulled back when distractor
blanked (wrong perception/action)= indicative that decision to move limb back was influenced by
illusion because it is a conscious decision
Summary:
- Despite doing correct movement, this was not able to inform correct perceptual response
- On line control of movement is independent from conscious visual experience (function of dorsal
stream)= indicative of separation b/w dorsal and ventral stream
METACONTRAST - Large arrow hides/masks little arrow from conscious processing
MASKING - If enough time provided, little/masked arrow will come to consciousness
Visual masking = way to hide visual info from consciousness
- Test conscious perception vs unconscious action with use of simple RT task
VISUAL MASKING
PROCEDURE Procedures:
- Respond to direction of arrow after prime shown!!!
- Neutral prime arrow case= prior to arrow presented, neutral shape was shown (no directional info)
- Neutral shape = no diff between L or R mask rxn time
- When presented with prime (little arrow prior to actual) pointing to a specific direction=show effects
Key point** not consciously aware of this little prime shown prior to the arrow
Results:
- Faster if left prime shown then responding to right mask arrow, and faster when right prime to right
mask arrow
- *Respond faster when masked arrow was in the same direction as the mask subject responded to
implication/summary:
- Motor system is already being influenced unconsciously as evident by faster RTs when prime arrow
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