(a) Mach's Principle: The mass of a particle is determined by its relation to the other particules in the universe. If there was only one particle in the universe, it is meaningless to ask how large its mass is.

(b) Mach's Principle in Pereption: In perception, the significance of a firing neuron is determined by its relation to other firing neurons at that psychological moment. It is meaningless to ask the significance of a firing neuron based on its response selectivity only.