  It is argued that Feynman's rules for evaluating probabilities, combined with
von Neumann's principle of psycho-physical parallelism, help avoid
inconsistencies, often associated with quantum theory. The former allows one to
assign probabilities to entire sequences of hypothetical Observers'
experiences, without mentioning the problem of wave function collapse.The
latter limits the Observer's (e.g., Wigner's friend's) participation in a
measurement to the changes produced in material objects,thus leaving his/her
consciousness outside the picture.
