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21 Cards in this Set
- Front
- Back
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How does the brain make up for eye movement problems? |
1. Sends back an efferent copy from the eye movement motor command 2. Selective processing of certain image location or relevant features/informations |
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What are problems that come from eye movements? |
1. Limited computational resources in the brain, but massive amount of input 2. Eye movements are the most obvious sign of attention --> foveal attention 3. For saccadic eye movements, image moves very fast - Each saccade causes a massive change to the retinal image 4. You lose any kind of information about space - Retina does not know where you are looking, just knows about image features (another form of correspondence problem: feature is there, but after eye movement it is in another location. But it is still the same object) |
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How may the brain use eye movement information? |
1. Images move on the retina 2. Proprioception & Corollary discharge allow sense of muscle position 3. Can thus predict motion by knowing the motor command |
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How does response to a stimulus vary on temporal scale? |
Response to the same stimulus is very different if the stimulus appears near the time of a microsaccade (reduced) |
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How can knowledge of eye movement or position solve the challenges produced by eye movement? |
1. Saccadic suppression - Receptors are not that sensitive to rapid image motion - Either stimulus comes with saccade or after/before it - Does stimulus reduce its sensitivity at time of the saccade? - Corollary discharge (efferent command) inhibits the response to new incoming stimuli briefly during moment of saccade (during saccadic movement, response is much lower) - Evidence from the fact that you can't see your own saccades in a mirror |
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What are 2 maps used in vision? |
Spatiotopic vs Retinotopic |
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What are spatiotopic maps? |
Representation in which neurons represent specific location in space regardless of eye/head/body position Spatial representation + retinotopic information (allocentric) |
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What are retinotopic maps? |
Representation in which neurons represent a specific location relative to the current eye position - Numerous retinotopic maps in the brain |
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How can retinotopic maps solve thesudden displacement problemcaused by eye movements? i.e. need to know where objects are in space, even though they move on the retina |
Retinotopic information & info on position of the eye give us spatiotemporal information Retinotopic position of objects changes by eye movements. - If an object is to the right on the retina, it can move to the left after an eye movement Shifting receptive fields in principle allow predicting what should be seen after each eye movement Visual system changes its response properties in anticipation of the retinal consequences of eye movements |
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What are eye position gain fields? What do they allow? |
They allow a spatiotopic representation - Gain fields exist in several areas related to both vision & eye movement (e.g. SC & parietal cortex) - Eye position is not ambiguous - Neural activity varies between eye positions (e.g. increasing firing as eye looks left -> straight -> right) Object location is available using this representation since position relative to retina & position of retina itself are known |
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How can gain fields be implemented? |
By using proprioceptive information about the position of the eye in the orbit |
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What does it mean that the visual system is recursive? |
Needs to calculate things again with every new saccade - Saccade ends at a new location - Correspondence between pre-saccadic & post-saccadic sensation |
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What are features of the classic receptive field? |
1. Moves with the eye 2. Moves to a new target location before eye movement then is recovered after the movement 3. Shifting receptive fields have been found in numerous visuomotor (SC, FEF, LIP) & visual areas |
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What is peri-saccadic perception? How was it measured? |
Receptive fields don't just shift, they converge - Receptive field measured relative to fovea before & after movement - Same neuron responds to different parts of the world - Area V4 receptive fields change properties around the time of saccades - It is no longer retinotopic for a small time around the time of saccades - There is a shift before eye movement and after - Convergence of receptive fields after eye movements - Allocate more neural tissue to where you want to go, then when you process it & perform eye movement, there is convergence. (e.g. soccer players moving for corner kick then moving back to original positions) |
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Where is attention at the time of the saccade? |
- Neurons that shift to the saccade target are essentially acting like "attention" - When we make a saccade, attention seems to be obligatorily attached to the saccade target - More neurons now dedicated to processing the saccadic target - Explains link between saccades and attention |
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Who termed the saccadic compression of space? What does it mean? |
Morrone & Burr Saccade target is most important It "attracts" perceptual resources - Biased object perception is located closer to the saccade target The brain alters response properties of the visual system to give us perceptual stability despite eye movements |
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What is the "stopped clock" illusion? What is this phenomenon called? |
e.g. a clock with a 'seconds' arm that jumps every second but silently If you make a saccade to the clock right at the time of arm movement, may feel that the seconds arm has frozen for slightly longer than 1 second This phenomenon is called Chronostasis |
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What is chronostasis linked to? |
Linked to spatial constancy (visual system extends duration of a stimulus back in time to the pre-saccadic time at which the receptive fields shift) If the receptive field shift gives the percept of "stability", the brain attributes a longer time to the stimulus to account for the "perceptual gap" during the saccade itself |
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What was the experiment investigating chronostasis? |
Method: 1. Subjects asked to make eye movements & show them a counter 2. Manipulate the duration of a second 3. Ask the subject "Was the first second faster than the second?" - Gives a subjective estimate of time - Studies point of subjective equality: how long a second should be to be perceived as a second Result: 2nd second needs less time to be perceived as a second since the first second seems longer due to chronostasis from the saccade |
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In conclusion, how does the brain make up for saccades causing changes to retinal images? |
Sudden change in position 1. Eye position gain fields to recover spatiotopic representation 2. Shifting receptive fields to update retinotopic maps Extremely fast retinal image motion 1. Saccadic suppression |
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How may receptive fields change around the time of saccades? |
Computational model - Hamker et al., - Oculomotor feedback signal acts as a gain modulation |
