5 ms·

Off-topic, but I'd be really interested in seeing a reference for such a study. A single action potential is usually only 1-3 ms (see https://en.wikipedia.org/

by kkylin 9y ago

Off-topic, but I'd be really interested in seeing a reference for such a study. A single action potential is usually only 1-3 ms (see https://en.wikipedia.org/wiki/Action_potential https://en.wikipedia.org/wiki/Action_potential and references therein), and retina to LGN to V1 (the first two stops in the early visual pathway in mammals) takes seveeral tens of ms (off-hand cannot find a ref, sorry). If a human can react to a visual stim in anything less than that, it would seem to be because (i) they are anticipating the stim based on some prior cue, or (ii) there is some shortcut directly from the eye to motor neurons, and the rest of the brain isn't involved directly. In any case 1-3 ms still seems extremely fast. Also, a child observing a cat continuous for 10 seconds is getting highly correlated samples, not new independent instances. The effective number of samples (which I quite agree would be >1 if the child got to examine the cat from different perspectives, or the cat moves around, etc etc) should still be lower than what a putative sampling rate would suggest.

Phemist 9y ago
The optic nerve is directly connected to the superior colliculus, which directly controls saccades and is sensitive to novel (bright) visual stimuli. If such a stimulus hits the the periphery just outside the fovea the time from stimulus onset to "fixation" should be minimized, without having to go through the "slow" ventral pathway/stream (V1 etc.). This time should still be more than 1-3 ms, but likely is below 100ms. No references, sorry. Edit: First said LGN projects SC, but pathway is even shorter than that. Edit2: The consensus on these fast, superior colliculus-guided "Express" saccade latency seems to be 80-120 ms. See: http://www.scholarpedia.org/article/Human_saccadic_eye_movements http://www.scholarpedia.org/article/Human_saccadic_eye_movem...
- nonbel 9y ago
  Why is there so much expertise being shared without any refs on this topic? Are they hard to find online for some reason?
  - Phemist 9y ago
    One of the issues is this type of neuroscience is becoming too "basic", so it's what gets taught in classes as the truth and professors don't necessarily give references anymore. Also I was typing on my mobile phone, but have switched to my laptop now. The scholarpedia (basically peer-reviewed wikipedia) article on saccades should be pretty interesting.
    - ant6n 9y ago
      If it's very basic, the reference could be a text book.
      - Phemist 9y ago
        Ofcourse, but textbooks are super-broad in scope. I don't think just referencing "Kandel, 5th edition" would be of much help and I don't have these books on hand to actually point you to the right page/section of the book.
      - nonbel 9y ago
        I wouldn't trust a textbook, they usually leave out the nature of the evidence for whatever is being claimed (not even citing sources). You really have to get to the primary literature. For example, this sounds factual enough: "The optic nerve is directly connected to the superior colliculus" But I wonder how this "direct connection" was established. Was it done in humans or only mice/rats? Is it really always a direct connection or only in eg 80% of people, etc.
        Balgair 9y ago
        https://www.amazon.com/Principles-Neural-Science-Fifth-Kandel/dp/0071390111 https://www.amazon.com/Principles-Neural-Science-Fifth-Kande... This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited. That particular connection is straightforward to do in humans. A Golgi stain to the rector muscles/ON and dissection in cadavers would be sufficient to trace the reflex to the SC and then another Golgi stain to that area to get back to the optic nerve. I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive. Also, the visual systems to the brain-stem are remarkably conserved through evolution. I would not be surprised to see this connection in lampreys. That any significant percent of humans lack it would be a hell of paper. Blind individuals usually have these reflexes too (like Stevie Wonder): https://en.wikipedia.org/wiki/Blindsight https://en.wikipedia.org/wiki/Blindsight
- Phemist 9y ago
  So in response to the grandparent, 1-3 ms is way too short, but it kinda of depends on the definition of "react" in this instance. The delay from a photon hitting the retina to triggering neurons in the superior colliculus to spike is likely pretty low (I would guess ~10 ms?), but when ocular motor movement becomes involved (ie stimulus onset -> fixation) things slow down considerably.
- kkylin 9y ago
  Cool, thanks!

by kkylin 9y ago

Phemist 9y ago

The optic nerve is directly connected to the superior colliculus, which directly controls saccades and is sensitive to novel (bright) visual stimuli. If such a stimulus hits the the periphery just outside the fovea the time from stimulus onset to "fixation" should be minimized, without having to go through the "slow" ventral pathway/stream (V1 etc.). This time should still be more than 1-3 ms, but likely is below 100ms. No references, sorry. Edit: First said LGN projects SC, but pathway is even shorter than that. Edit2: The consensus on these fast, superior colliculus-guided "Express" saccade latency seems to be 80-120 ms. See: http://www.scholarpedia.org/article/Human_saccadic_eye_movements http://www.scholarpedia.org/article/Human_saccadic_eye_movem...

nonbel 9y ago
Why is there so much expertise being shared without any refs on this topic? Are they hard to find online for some reason?
- Phemist 9y ago
  One of the issues is this type of neuroscience is becoming too "basic", so it's what gets taught in classes as the truth and professors don't necessarily give references anymore. Also I was typing on my mobile phone, but have switched to my laptop now. The scholarpedia (basically peer-reviewed wikipedia) article on saccades should be pretty interesting.
  - ant6n 9y ago
    If it's very basic, the reference could be a text book.
    - Phemist 9y ago
      Ofcourse, but textbooks are super-broad in scope. I don't think just referencing "Kandel, 5th edition" would be of much help and I don't have these books on hand to actually point you to the right page/section of the book.
    - nonbel 9y ago
      I wouldn't trust a textbook, they usually leave out the nature of the evidence for whatever is being claimed (not even citing sources). You really have to get to the primary literature. For example, this sounds factual enough: "The optic nerve is directly connected to the superior colliculus" But I wonder how this "direct connection" was established. Was it done in humans or only mice/rats? Is it really always a direct connection or only in eg 80% of people, etc.
      - Balgair 9y ago
        https://www.amazon.com/Principles-Neural-Science-Fifth-Kandel/dp/0071390111 https://www.amazon.com/Principles-Neural-Science-Fifth-Kande... This is a good text, at an upper-div/grad level, of fundamental neuroscience with all sources cited. That particular connection is straightforward to do in humans. A Golgi stain to the rector muscles/ON and dissection in cadavers would be sufficient to trace the reflex to the SC and then another Golgi stain to that area to get back to the optic nerve. I'm unfamiliar with the toxicity of Golgi stains, but it may be able to be done alive. Also, the visual systems to the brain-stem are remarkably conserved through evolution. I would not be surprised to see this connection in lampreys. That any significant percent of humans lack it would be a hell of paper. Blind individuals usually have these reflexes too (like Stevie Wonder): https://en.wikipedia.org/wiki/Blindsight https://en.wikipedia.org/wiki/Blindsight
Phemist 9y ago
So in response to the grandparent, 1-3 ms is way too short, but it kinda of depends on the definition of "react" in this instance. The delay from a photon hitting the retina to triggering neurons in the superior colliculus to spike is likely pretty low (I would guess ~10 ms?), but when ocular motor movement becomes involved (ie stimulus onset -> fixation) things slow down considerably.
kkylin 9y ago
Cool, thanks!