Visual Perception at the Threshold
Optical technologies have been transformative for our current understanding of structure and function of neuronal circuits underlying behavior and are in many cases the limiting factors for pushing our understanding of the brain forward.
In vision science despite of investigations for over seventy years, the absolute limits of human vision have remained unclear. Rod cells have been shown to respond to individual photons, yet whether this information is processed by the brain and is accessible on the behavioral level has remained a fundamental open question. We have recently been able to show that humans can report a single photon incident on the eye with an above chance probability . This was achieved by combining a two-alterative forced choice psychophysics procedure with a single photon source base on Type-I Spontaneous Parametric Down-Conversion (SPDC), a tool that allows to eliminate the irreducible variability of photon numbers in previous experiments. Furthermore, we found that the probability for reporting a single photon is modulated by the presence of an earlier photon. Our results and other applications of this tool may open up fundamentally new avenues for investigating yet undiscovered retinal pathways using quantum technologies and may find applications in fundamental tests of quantum mechanics using human observers.
1.Tinsley, J. et al. Direct Detection of a Single Photon by Humans, Nature Communications, (2016)7, 12172