Human infrared vision is triggered by two-photon chromophore isomerization.
Level 5 - mechanism / opinion, no new human data
Mechanistic laboratory study combining basic human psychophysics, ex vivo mammalian tissue assays, in vitro biochemistry, and computational modeling (Level 5 bench research).
PubMed 25453064 · doi:10.1073/pnas.1410162111
What was done
The authors investigated human perception of infrared light using psychophysical testing with pulsed infrared laser emission. They evaluated mammalian photoreceptor activation across near-infrared wavelengths (including >900 nm) and varying laser power levels, conducted biochemical assays using rhodopsin, cone visual pigments, and an 11-cis-retinyl-propylamine Schiff base model, and performed quantum mechanics modeling of two-photon activation.
What was found
Humans perceived near-infrared laser emission as visible light. Mammalian photoreceptors were directly activated by near-infrared light with sensitivity that paradoxically increased at wavelengths above 900 nm and displayed a quadratic dependence on laser power, indicating a nonlinear optical process. In vitro assays and quantum modeling confirmed direct two-photon chromophore isomerization. The abstract reports no specific numerical data, sample sizes, or statistical metrics.
Why it matters
This establishes that human visual perception can detect near-infrared wavelengths via two-photon chromophore isomerization, identifying a non-linear biophysical mechanism of photoreceptor activation.
Limits
The abstract provides no sample sizes or demographic characteristics for the human subjects. The process requires high-intensity pulsed laser stimulation and does not imply visual perception under ambient or continuous low-density infrared illumination.
Cited by
- supports The human eye can perceive light at wavelengths up to 1,050 nanometers in the infrared spectrum as a faint red glow if the light's intensity is sufficiently high.