Researchers working between the Research Institute of Molecular Pathology in Vienna and Rockefeller University built a source that could fire exactly one photon at a time toward a person's eye, then asked whether the person could consciously detect it.
Across thousands of trials, volunteers picked out a single photon 51.6 percent of the time against 50 percent by chance, with a clearer margin on trials they felt most sure of. The researchers also found a priming effect, in which detecting one photon briefly raised the chance of detecting another within the next few seconds.
The result gave the first direct evidence on a question vision scientists had debated for decades, suggesting the human visual system can work at the absolute physical limit of sensitivity. The effect was small and borderline on its own, and it has yet to be independently replicated.
Read the original study
Tinsley et al., Nature Communications, 2016 · doi.org/10.1038/ncomms12172
The eye may register a single photon.
Source
- Tinsley, J. N., Molodtsov, M. I., Prevedel, R., Wartmann, D., Espigulé-Pons, J., Lauwers, M., & Vaziri, A. (2016). Direct detection of a single photon by humans. Nature Communications, 7, 12172. https://doi.org/10.1038/ncomms12172