Transcript What the colliculus can and can not do in saccade - Smith

What the colliculus can and cannot
do in saccade trajectory control
Ed Keller
Smith-Kettlewell Eye Research Institute
San Francisco, California
My collaborators
• Kuniharu Arai
• Rob McPeek
• Koung-Min Lee
• Population activity in the SC during
saccades with variable trajectories
• Use of a distributed model of the saccadic
system to clarify trajectory control
Types of variations in saccade trajectory produced by a visual search task
Conclusion: if activity remains at two locations when a saccade starts,
its trajectory curves toward the site of smaller activity
A psychophysical observation in humans subjects: Saccade trajectory
curves away from irrelevant visual stimuli (Doyle and Walker 2001)
A hypothesis: active inhibition at the location of the irrelevant stimulus
produces less activity at the SC site representing this location in visual
Space (a hole instead of a mound?)
Trajectories curve away from a lesion in the opposite field SC
Parallel
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signal
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Parallel
Parallel
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signal
signal
Population activity in the monkey
superior colliculus during a 20-deg
horizontal saccade (Anderson et al.
1998)
Population activity in the monkey
superior colliculus during a 20-deg
horizontal saccade (Anderson et al.
1998)
Population activity in the model
SC for a simulated 20-deg
saccade
Population activity in the SC for two
simultaneous visual stimuli, upper is
the target
Highly curved saccade with parallel inputs from the SC and the FN
Conclutions
• Completion between visual stimuli for the goal of a saccade can
result in the presence of multiple loci of activity on the SC at
saccade onset.
• Saccade trajectory variation is associated with these loci of
remaining activity.
• In particular neural recordings and a distributed model of the
saccadic system both indicate that directional errors at saccade
onset, small curvature and end point averaging can be explained by
dynamic changes in spatiotemporal activity in the SC.
• Highly curved trajectories require the additional parallel corrective
signals at the level of the saccadic burst generator.
Distributed model of the saccadic system
Population activity in the model
SC when two identical visual
stimuli are applied simultaneously
Strong intracollicular lateral inhibition