Term
| Why do we study eye movements when we want to study planning? |
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Definition
Complex behavior, but no language processing
Tight output, easy to measure
Input is easily controlled
Few Degrees of freedom
Good animal models |
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Term
| What are the three key areas associated with neural control of eye saccades? |
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Definition
Superior Colliculus (SC)
Frontal Eye Fields (FEF)
Lateral Intraparietal lobe (LIP) |
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Term
| What is the main difference in the receptive fields of SC, FEF and LIP compared to Primary Visual cortex |
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Definition
| SC FEF and LIP have movement fields as well as visual receptive field |
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Term
| What is the difference between a movement field and a visual receptive field? |
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Definition
Visual receptive fields are a region of space where visual stimuli activate a cell.
Movement fields are a region of space for which the neurons respond prior to a saccade there (primed to respond before moving) |
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Term
| Which of the 3 main areas associated with neural control have topographic maps? |
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Definition
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Term
| What happens when we microstimulate SC or FEF? |
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Definition
| saccade to center of movement field. Independent of starting position! |
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Term
| Describe the Memory Saccade Task |
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Definition
1. Monkey Fixates on central target
2. Peripheral Target in flashes in response field
3. Delay
4. Eye saccade to target |
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Term
| How do LIP neurons behave in a memory saccade task? |
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Definition
| Large increase in firing rate during target flash, increased activity during delay, and return to baseline after eye movement |
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Term
| What are the broad classification for neurons in LIP, SC, and FEF? |
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Definition
Visual neurons -> Respond to visual stimulus
Visual-Movement -> respond to both visual stimulus and movement towards it
Movement -> big burst of activity right around saccade |
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Term
| How are the responses organized in layers in the SC? |
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Definition
Superficial layers -> Vision responses
Intermediate -> Visual/movement responses
Deep Layers -> Primarily movement responses |
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Term
| How do some scientists interpret the delay period activity in LIP? |
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Definition
Motor Plan - Spatial attention (confounded)
There is a difference between covert and overt attention. |
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Term
| What is the evidence for LIP neurons activity being a motor plan? |
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Definition
| Snyder et al showed that the LIP activity was not independent of the effector (worked for eyes, but not for arms), showing that it was not solely paying attention to an area, which would have activated the LIP neurons for both effectors |
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Term
| What is the evidence for LIP neurons activity being spatial attention? |
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Definition
| The Parietal cortex is very heterogeneous! Gottlieb et al showed that most neurons had stronger behavior when shown a light in the receptive field, regardless of moving towards or away from the stimulus. If it were a movement plan, as long as the motion of direction was the same, it should have been strong, but that was not the case for most of the neurons. |
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Term
| How can we tell apart reference frames that use different central points? |
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Definition
| Change the fixation point of the eye/head/limb and see if the neural tuning curve shifts by the same amount. Some are hybrid reference frames. |
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Term
| what do neurons in the Parietal reach region do? |
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Definition
| Encode high level reach planning. Uses an Eye-centered reference frame even though the task might be better suited in hand-centered space. |
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Term
| What sort of reference frames are utilized in the Superior Colliculus? |
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Definition
Visual reference frames (eye centered from retina)
Auditory reference frames (head centered) |
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Term
| What was the primary finding of the Jay and Sparks experiment with reference frames in the SC? |
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Definition
| Most Auditory responses were in an intermediate reference frame (12 degree shift for 24 degree stimulus offset). The visual responses are nearly eye centered, but with a wide distribution! Intermediate frames allow for flexibility! |
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Term
| Describe the current theory on how LIP neurons make a decision during a random coherent motion task. |
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Definition
| Integrate to reach a decision. Longer decision times are a result of lower coherence, and less overall energy in the decision. Fast rampup when easy, slow noisy rampup when hard (<10% coherence) |
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Term
| What did Shadlen call the population of LIP Activity? |
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Definition
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Term
| What is the diffusion-to bound model of LIP activity? |
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Definition
| Neurons in LIP have a certain threshold necessary to reach a decision; more coherent activity means a stronger signal, and thus reaches threshold quicker. |
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Term
| How did Shadlen confirm that decisions are already partially formed in the LIP neurons? |
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Definition
| Microstimulation of FEF while there were sub-threshold decisions showed a bias in saccades toward the decision it was currently heading towards. |
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