The development of the subjective solutions to the problem of measurement in quantum mechanics is presented. It is shown that - already in 1932 - von Neumann faced a dilemma: either quantum mechanics represents the only true physical reality and then the reduction of the wave packet is illusory, or the mind is able to act on the physical world producing a transition that is not allowed by quantum- mechanical laws. We show that the first alternative was followed by the many-world or many-mind interpretation, the second by the school of London-Bauer and Wigner. The difficulties of these two interpretations are also pointed out. Finally a third possibility, proposed by Albert and Loewer, is presented: The evolution of mind is independent from that of the physical world and is subjected to its own laws.