Study published in July 2016 concludes human vision can detect a single photon.
The most amazing thing is that its not like seeing light. Its 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 article here: https://www.nature.com/articles/ncomms12172
and
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.
The most amazing thing is that its not like seeing light. Its 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 article here: https://www.nature.com/articles/ncomms12172
and
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.