In my reading of sci-fi I came across a fascinating concept: an alien race called the Chromatics that had a partially photonic nervous system. They were described as having very fast reflexes. Now I am planning on introducing a plant-like race of aliens. (They are actually planimals) Because I find the idea fascinating and it seems that real plants might have a photonic nervous system, albeit a very primitive one, I'd like my aliens to share the trait. What I need to know is if a photonic nervous system would grant this race faster reaction times than a human and if so by how much.
There are a number of issues with fast nerve conduction. Whether this is achieved by photons travelling down organic fibre optic cables, or electrons travelling down organically deposited wires, we get a situation that, over any typical distance found in an organism, a signal takes effectively zero time to be transmitted. This differs from many animals' sodium-channel depolarisation-wave axons, where transmission speeds are in the order of 3-120 metres per second, depending upon myelination.
However, this is not the only part of the problem. In most animals, communication between nerve cells occurs by neurotransmitter/receptor coupling. This, too, is relatively slow, as neurotransmitter released by a neuron takes time to diffuse across the transmitter/receiver gap. However, in a system where axons do not rely on myelination for impulse acceleration, but instead use a wire or optical fibre which results in a much greater conduction speed, faster intra-neuron transmission would be more beneficial.
This could be achieved by implementing some sort of mechanical connection rather than a chemical one. If, on the transmitter neuron firing, a mechanical gate was operated that connected to a mechanical gate in the receiver neuron, the neurotransmitter delay could be significantly reduced.
This leaves only the neuron body's sodium-channel gates as the slowest link in a neuron's reception/firing process. However, this is difficult to overcome, as the voltage threshold of the sodium-channel gates is how a neuron acts as an integrator. Still, removing the axonal delay and the neurotransmitter delay would significantly speed up motor control, sensation and processing.
An alien species will not have the same structures, but the arguments in favour of mechanical connections between neurons and photonic/electrical conduction are the same.
The consequence of greater speeds in neurotransmission and communication would result in significantly faster reaction times. Human visual-motor reaction times (eye-hand) are on the order of 280ms (typically 190ms-410ms). A significant part of this would be axonal pulse propagation and neurotransmitter delays, though some of it is also depolarisation integration that cannot be so simply overcome. I would speculate that if a human was enhanced in this manner, a reaction time on the order of ten times faster should be achievable, i.e. 28ms (typically 19ms-41ms).
This also presupposes that muscular interaction is involved. Just because nerves operate faster does not necessarily mean that muscles do so too, though with faster neurons there would be selection pressure toward more responsive muscles too. With thought processes, which do not involve muscular activity, we could expect more like a twenty-fold increase in processing speed.
So, we have our hypothetical neutrally-boosted creature. If we pitted such a being against a human in hand-to-[whatever] combat, provided that its muscles operated at a similar speed, there would be no contest. It would be able to see the human begin an action, would be able to analyse and predict the probable intention of the action, and before the human's action could be completed, it would be initiating a counter-action. Should it decide to attack, it could see the human's attempt at defence and would be able to think and react fast enough to circumvent that defence.
In missile combat, such a being would be likely to be able to see bullets, though avoiding them entirely would still be very difficult. However, dodging or catching arrows would be as easy as dodging or catching a thrown ball would be for us.
If we were able to experience being such a creature, we would notice that our thoughts flowed much more rapidly compared with our bodies. We would be able to see things moving about us in slow-motion, however our own bodies would seem similarly slow. We'd have more time to think about our actions before having to perform them. It is likely that to a human observer, such a creature could seem abrupt and jerky, but also incredibly precise in its movements. In order to save energy, it would move as little as possible until movement became necessary, at which point it would move as quickly as required. In a combat situation against a slower opponent, that would likely look like a series of almost static poses with very quick attacking movements in between. Defensive manoeuvres might look almost leisurely, as the creature would not need to take as much time to think about the appropriate defensive action, which would as a consequence not need to be executed as quickly.