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Comment by rcthompson | Hacker News Reader

My understanding is that the "grain" is not necessarily caused by your eyes detecting isolated photons, but rather by the electrons in the light-absorbing molecules of your rods & cones becoming spontaneously excited by ambient heat energy rather than absorption of a photon. Either way, it shows that we can indeed consciously perceive single-molecule excitation events, whatever the cause.

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> but rather by the electrons in the light-absorbing molecules of your rods & cones becoming spontaneously excited by ambient heat energy rather than absorption of a photon

Agree, it's not a digital system so there is always some noise, just like you can never get perfect silence in terms of sensory perception. Your brain has also a way to project some kind of images in your mind even when you don't see anything in complete darkness, so it's far from just being the detection of photons.

> just like you can never get perfect silence in terms of sensory perception.

That's a little different because your body produces lots of noises which are only perceivable in the absence of other background noises, eg when inside an anechoic chamber[1].

[1] https://en.wikipedia.org/wiki/Anechoic_chamber

It's also worth noting that senses may actually take advantage of the inherent noise to improve sensitivity of low level signals using stochastic resonance -- random resonances of noise and actual signal boosts the measured signal to a level that is detectable, thus permitting detection of signals that are actually below the (noise free) detection sensitivity. Such mechanisms have been observed in animal sensory systems, and is believed to have a role in mammalian visual processing.

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