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C T Hall Oct 12
Replying to @AliceProverbio
Wow! What are V5 and V4 tho?
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Alice Proverbio Oct 12
Replying to @ChThH
V5 (or MT) is the cortical area devoted to motion processing, while V4 is devoted to color and shape (like the pentagon) processing. V4 neurons are saturated so much that the basal/rest firing rate of MT neurons is interpreted as an actual sensory signal
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Kriegeskorte Lab Oct 12
Replying to @AliceProverbio @ChThH
The illusion is amazing. Not sure I understand that explanation, though. Not every colorful texture elicits illusory motion and the perceived direction appears to depend on the shading.
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Alice Proverbio Oct 12
Replying to @KriegeskorteLab @ChThH
Your right, it strictly depends on receptive field sizes (the illusion changes as a function of viewing distance), V4 preference for spirals and spheres, MT involvement in 3D and stereopsis: it is a very complex interaction, rarely leading to such illusions!
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Kevin Mitchell Oct 12
I'm still deeply confused... Is there some kind of interaction between V4 and V5?
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Alice Proverbio Oct 12
yes! a lot of feedback and feedforward interactions!
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Gregory Katsoulis Oct 12
Replying to @AliceProverbio
Astounding — and the clearest explanation I've heard for this phenomenon. I recently created an illusion that it much more straightforward, but reference the original illusion of this type, the rotating snakes. Would love to hear your thoughts.
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Kevin Mitchell Oct 12
Interesting! So, does this illusion illustrate the existence of some normal perceptual function of that interaction between V4 and V5? What is it normally doing?
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Alice Proverbio Oct 12
Replying to @gregkatsoulis
I actually use the snake illusion picture as a slide for teaching!! :-) it is very nice. The neural explanation is the same
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Alice Proverbio Oct 12
It basically represents an example of Competition within the visual cortex, whenever a signal is attenuated or suppressed for whatever reason other inputs get the chance to be represented at higher cognitive levels, thus accessing percipient awareness
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Kevin Mitchell Oct 12
Hmm... Okay, but why would you want to have form/color information competing for awareness with motion information? (As opposed to being integrated with it?)
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Alice Proverbio Oct 12
Magnocellular inputs have a special status for primates (in order to detect motion, low spatial freq. shades even if not paying attention); ventral stream information (color, shape) require attention in order to reach awareness. This asymmetry start at retinal gangliar cell level
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MarketCashCapital Oct 12
Replying to @AliceProverbio
Why can I make the illusion stop by focusing (staring intently) at the center but restart the illusion by not focusing?
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Minutemen Oct 12
Replying to @AliceProverbio
Very nice! Thanks for sharing this insight into our cognitive processing. Do you know if this illusion and interaction between V4/V5 is related to the sensory perception of movement from psychedelic drugs such as LSD?
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Kevin Mitchell Oct 12
Okay..., but what I am wondering is why the cross-modal interaction between color and motion...?
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Sofia Deleniv Oct 12
Out of curiosity - why do you think the illusion only occurs when you move your eyes? It seems to me if this was a question of response saturation in V4, we might expect to it happen regardless of eye movements.
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Deb Hepplestone Oct 12
Replying to @AliceProverbio @ChThH
A fascinating and very useful explanation thanks! I’m an Art teacher so it is great to have the science behind the illusion! I can’t stop staring at it 🙂
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That Pesky Pooch Oct 12
it seems that extended viewing lessens the effect. making the effect strongest at first viewing after pauses. does that mean the visual cortex "learns" to correct the error to some degree after extended viewing?
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Christopher Brown Oct 12
I have figured out how to pause it - concentrate in one place and keep the mind very still
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