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Direct detection of a single photon by human vision reported

Encap

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Study published in July 2016 concludes human vision can detect a single photon.

“The most amazing thing is that it’s not like seeing light. It’s almost a feeling, at the threshold of imagination,” says Alipasha Vaziri, a physicist at the Rockefeller University in New York City, who led the work and tried out the experience himself."

"Despite investigations for over 70 years, the absolute limits of human vision have remained unclear. Rod cells respond to individual photons, yet whether a single-photon incident on the eye can be perceived by a human subject has remained a fundamental open question. Here we report that humans can detect a single-photon incident on the cornea with a probability significantly above chance. This was achieved by implementing a combination of a psychophysics procedure with a quantum light source that can generate single-photon states of light. We further discover that the probability of reporting a single photon is modulated by the presence of an earlier photon, suggesting a priming process that temporarily enhances the effective gain of the visual system on the timescale of seconds."
From complete article .pdf here: http://vaziria.com/wp-content/uploads/2016/07/ncomms12172.pdf

See also: Direct detection of a single photon by humans | Vaziri Lab

Previously it was thought that sensors in the retina can respond to a single photon. However, neural filters only allow a signal to pass to the brain to trigger a conscious response when at least about five to nine arrive within less than 100 ms. If we could consciously see single photons we would experience too much visual "noise" in very low light, so this filter is a necessary adaptation, not a weakness.
 
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paul1598419

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I think that rather than a single photon priming the visual ability of rods and cones of the eye, it is perhaps more likely that the visual cortex of the brain is primed by the event.
 

Encap

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I think that rather than a single photon priming the visual ability of rods and cones of the eye, it is perhaps more likely that the visual cortex of the brain is primed by the event.
Yes. Off the bat, I think so as well. I don't imagine that retinal isomerization "lag" is a reasonable explaination. Isomerization occurs in a few picoseconds. Absorption of a photon leads to isomerization about half the time; in contrast, spontaneous isomerization in the dark occurs only once in 1000 years. The isomerization event actually causes the proteins to change their shape ultimately leads to the generation of a nerve impulse---
but what do you or I know?:crackup:

I expressed that feeling/considered opinion to the author/principal investigator Dr. Vaziri today, this AM And asked if any follow up work had been done to determine if the observed "delay"was a result of eye, visual cortex or both. Dr. VAziri replied that "further studies while discussed and preliminary experimental desgins have been imagined, the necessary work has yet to be done."
~ From: personal telecon with the author/principal investigator Prof. Dr. Alipasha Vaziri, Vaziri Lab, Rockfeller Univ, NYC, NY of today 11 May 2017

Will follow up with Vaziri on this issue when time permits and report additional information findings here.

from the article/paper.
"The explanation of the corresponding psychophysics data required either assuming unrealistically low-quantum efficiencies or the assumption of an additional multiplicative noise. However,our single-photon data show that the subjects’ performance(Fig. 3d–f) can be readily accounted for by physiological values of the overall quantum efficiency of the eye (Supplementary Table 1)and a Poisson distributed dark isomerization rate suggesting single-photon perception is not limited by further down-stream inefficiencies of the visual system and the brain.

Our light source and experimental protocol allowed us to further discover a single-photon-induced priming effect that is characterizedby a temporal modulation of the gain of the visual system. It is well established that the extreme dynamic range (approximately nine orders of magnitude)20 and sensitivity of the visual system is mediated by a light-dependent modulation of the system’s gain.
Although over a wide range the sensitivity of the visual system is inversely proportional to the average light level, our data show that at the single-photon level, a higher transient detection probability for a photon is obtained if another photon was absorbed previously. This phenomenon is conceptually reminiscent of coincidence detection, although at timescales orders of magnitude slower and likely involving a different physiological mechanism from the known retinal circuit computations.

The retinal and brain-circuitry mechanisms underlying our above observations remain the scope of future work. Further studies aimed at different scales and combining different methodologies such as electroencephalography15 or magnetoencephalography with psychophysics might allow to elucidate possible role of top–down cortical effects, including visual attention or brain oscillations, in the subjects’ performance and choice of confidence ratings. In addition, post-mortem physiological studies on the human retina would be likely required to elucidate any involved retinal circuits mechanisms on the cellular level."
From .pdf of paper, see: http://vaziria.com/wp-content/uploads/2016/07/ncomms12172.pdf
 
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Benm

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I'm not really surprised by this.

I don't really believe the 'noise filtering' theory to be responsible for not being able to see only one photon. The reason for this is that in nature, in rarely gets this dark. Even on a cloudy moonless night some starlight usually makes it through the clouds. We would consider this very dark, probably not venture out because of limited visibility, but there would be no 'use' for a filter that blocks the signal from a signal photon if it really was -that- dark.

Being able to see a single photon every 100 ms or so is not -useful- either since it will not give you an image of your surroundings, but the rod cells just take one photon to trigger.

If accidental triggering would be a realistic problem some neurological mechanism to supress that would make sese, but this seems not to be there. Such accidental triggering does occur outside the protection of the atmosphere and astronauts have reported seeing odd flashes of light even with their eyes closed, possible due to cosmic rays triggering the photosensitive cells in the retina (going right through their vessel and possibly much of their head since there is no way to tell if the photon came from the front or the back of your head in such a scenario).
 

Encap

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Very good find, thank you Encap for sharing! :)

-Alex
Thanks for looking, is interesting work Dr. Vaziri did--pushing/expanding knowledge of human visiual ability limits to a new level.

Human visual perception is quite an abiity/tool --the eyes and how the brain uses the input from them is an amazing thing -- the whole visual perception system-sense and how it interfaces with the rest of the brain.

The visual cortex is the largest system in the human brain and is responsible for processing/creating the visual image.
 
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