Direct detection of a single photon by humans.
Level 4 - case-series / case-control
Graded by design analogy; laboratory human psychophysics experiment without clinical trial design
PubMed 27434854 · doi:10.1038/ncomms12172
What was done
Investigators tested whether humans can perceive a single photon incident on the cornea by coupling a psychophysics protocol with a quantum light source that generated single-photon states of light.
What was found
Humans detected single photons incident on the cornea with a probability significantly above chance. The abstract reports no numerical values, trial counts, false-positive rates, or effect sizes. The researchers also found that reporting probability was modulated by the presence of an earlier photon on a timescale of seconds, suggesting a priming mechanism that temporarily increases visual system gain.
Why it matters
This provides direct experimental evidence that single-photon events at the cornea can cross the threshold into human conscious awareness, resolving a fundamental 70-year question about the physical limits of vision.
Limits
The abstract omits sample size, participant characteristics, exact statistical parameters, and false-alarm rates. The experiment evaluates detection under specialized, dark-adapted quantum optical laboratory conditions, limiting direct extrapolation to everyday vision or diverse demographic groups.
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