read this paper
DESCRIPTION
Read this paper. Chellazi et al. (1993) Nature 363 Pg 345 - 347 . Different Pathways , Different Processes. Retinocollicular vs. Retinostriate. Recall that 10% of optic nerve gets routed through the Superior Colliculus (SC) What does it do? - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/1.jpg)
Read this paper
• Chellazi et al. (1993) Nature 363 Pg 345 - 347
![Page 2: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/2.jpg)
Different Pathways , Different Processes
![Page 3: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/3.jpg)
Retinocollicular vs. Retinostriate
• Recall that 10% of optic nerve gets routed through the Superior Colliculus (SC)
• What does it do?
• SC contributes to control of eye movements (saccade vector maps)
• SC and Pulvinar contribute to orienting of attention
![Page 4: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/4.jpg)
Superior Colliculus
left right
• Superior Colliculus (SC) contributes to control of eye movements
– a saccade is a rapid eye movement
– SC contains a retinotopic map of possible saccade vectors
– Activation of particular cells guides eyes to specific location
Does SC contribute to orienting even when “main” visual pathway is disrupted?
![Page 5: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/5.jpg)
Lesions of Retinostriate Pathway
• Lesions (usually due to stroke) cause a region of blindness called a scotoma
• Identified using perimetry• note macular sparing
X
![Page 6: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/6.jpg)
Retinocollicular Pathway Might Independently Mediate Orienting
• The theory is that the retinocollicular pathway continues to operate despite lesions in the retinostriate pathway
• note this is somewhat counterintuitive in that it predicts people should be able to orient to visual objects that they can’t “see”
![Page 7: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/7.jpg)
Retinocollicular Pathway Might Independently Mediate Orienting
• Weiskrantz (1986)
• subject fixates at centre
• target appears in periphery and subject saccades to target
• in control condition, no light appears
• Importantly, both conditions appear the same to subject!
![Page 8: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/8.jpg)
Retinocollicular Pathway Might Independently Mediate Orienting
• Prediction: subject should be able to orient accurately to the target even when it is in the blind field
![Page 9: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/9.jpg)
Retinocollicular Pathway independently mediates orienting
• Subject was able to orient with relatively good accuracy up to about 25 degrees
![Page 10: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/10.jpg)
Blindsight
• Intact retinocollicular pathway mediates eye movements despite V1 lesions
• Might it also orient attention? The theory is that it does.
![Page 11: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/11.jpg)
Retinocollicular Pathway independently mediates orienting
• Rafal et al. (1990)
• Prediction: visual stimuli in scotoma should interfere with (i.e. distract) orienting to stimuli in the good field
• subjects move eyes to fixate a peripheral target in two different conditions:– target alone
![Page 12: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/12.jpg)
Retinocollicular Pathway independently mediates orienting
• Rafal et al. (1990)
• Prediction: visual stimuli in scotoma should interfere with (i.e. distract) orienting to stimuli in the good field
• subjects move eyes to fixate a peripheral target in two different conditions:– target alone– accompanied by distractor
![Page 13: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/13.jpg)
Retinocollicular Pathway independently mediates orienting
• Rafal et al. (1990) result
• Subjects were slower when presented with a distracting stimulus in the scotoma (359 ms vs. 500 ms)
![Page 14: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/14.jpg)
Retinocollicular Pathway independently mediates orienting
• Blindsight patients have since been shown to posses a surprising range of “residual” visual abilities– better than chance at detection and discrimination of some
visual features such as direction of motion
• These go beyond simple orienting - how can this be?
![Page 15: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/15.jpg)
Retinocollicular Pathway independently mediates orienting
• Recall that the feed-forward sweep in not a single wave of information and that it doesn’t only go through V1
![Page 16: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/16.jpg)
Retinocollicular Pathway independently mediates orienting
• Recall that the feed-forward sweep in not a single wave of information and that it doesn’t only go through V1
• In particular, MT seems to get very early and direct input
![Page 17: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/17.jpg)
Retinocollicular Pathway independently mediates orienting
• The theory is that direct connections from the retinocollicular pathway to MT mediate residual vision for moving stimuli
• Giaschi et al (2003): tested patient with bilateral V1 lesions– since birth– little or no visual awareness (aware of some fast moving
stimuli)– striking “blindsight” capabilities
![Page 18: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/18.jpg)
Retinocollicular Pathway independently mediates orienting
• Prediction:– moving dots compared to stationary dots should show
activation of MT despite ablated V1
![Page 19: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/19.jpg)
Retinocollicular Pathway independently mediates orienting
• Result:– Hemodynamic activity was in various other non-visual areas
![Page 20: Read this paper](https://reader036.vdocuments.us/reader036/viewer/2022081502/568166dc550346895ddb0304/html5/thumbnails/20.jpg)
Retinocollicular Pathway independently mediates orienting
• Interpretation:– Patient’s brain underwent profoundly different development
trajectory early in life
– Functionally “remapped