The input can be external - what is seen is input.no I'm pretty certain that a reaction is an out put , to a stimulus input, if the out put id adrenalin, then that's a reaction, the electrical impulse to the adrenaline grand is an input.
anticipation is your mind trying to predict the future using the past, which is always dodgy, i anticipate that all drivers wearing a hat are automatically homicidal maniac, basically d on a bad experience or five with hat wearing drivers, its saved mY Life
Whether you term something anticipation or early detection is largely a matter of semantics in how you define what movements are part of the punch.