  We develop a kind of quantum formalism (Hilbert space probabilistic calculus)
for measurements performed over cognitive (in particular, conscious) systems.
By using this formalism we could predict averages of cognitive observables.
Reflecting the basic idea of neurophisiological and psychological studies on a
hierarchic structure of cognitive processes, we use p-adic hierarchic trees as
a mathematical model of a mental space. We also briefly discuss the general
problem of the choice of adequate mental geometry.
