The effect of Solaris is the change of mentality, which marked hallucinations, visions in the form of ghosts of dead relatives during times of extreme stress. The first description of the effect within the location in space was described by Yuri Gagarin.
During the flight, astronaut heard unreal sounds, which even could not imagine. At one of the concerts of the ensemble musical instruments Gagarin went to the founder of the group, and said unto him, this is the music he heard in space.
Astronaut Vladislav Volkov told about barking dogs and crying child on a spaceship. These phenomena are difficult to explain from a scientific point of view. Apparently, it was an auditory hallucination. Stress affects the brain and similar temporary change in consciousness is quite likely.
Interesting descriptions of visual hallucinations. Vitaly Sevastyanov saw in the window of a two-storey house in which he lived as a child. Other astronauts talked about cars, flying in space. Scientists have linked vision features of the brain. In space increases the clarity of vision and distorted the scale of interest. While consciousness is not able to properly handle the information possible such deviations.