In order to study "cosmic illusions", a large-scale experiment was conducted by Institute of Biomedical Problems of the Russian Academy of Sciences, during which the pre- and post-flight state of cosmonauts' body was examined, and everything that happened was recorded on the ISS in microgravity. It turned out that in this unusual for the human body state [the microgravity], orientational, kinetic, coordinative and proprioceptive illusions are manifested.
Orientational illusions were observed in almost all cosmonauts (98%). They were expressed in the loss of perception of space. On the ISS, even after examaning the surrounding space, when the lights were turned off, sometimes there was complete disorientation - a person could not determine which direction and how long he should move to the target.
Kinetic illusion was characterized by [a false] sensation of rotation of one's own body around, as well as moving along an axis.
Some astronauts also noted an illusory sensation of the position of various parts of the body: “it seems that you are sitting bent, but actually you are lying flat in a sleeping bag”, “hands are at the top, but it seems they are at the bottom” - this is how proprioceptive illusions showed themselves.
Along with illusory reactions, 72% of astronauts had difficulty tracking a moving target and fixing their gaze on it, discoordinating manifestations were also noted - misses when trying to grab an object, hitting the head against a panel when “swimming” inside the station.
The article also describes scientific devices and methods used for their neurological study.
- Another relevant article in Russian: "Orientation Illusionns in Weightlessness" by Kornilova L.N., Tarasov I.K. , journal of Aerospace and Environmental Medicine, No.3, 1996,
Below is the annotation:
Results of the ANKETA and OPROSNIK experiments performed by 102 cosmonauts in and post flight were analysed. It is shown that perceptive disturbances (orientation illusions) developed in the period of early adaptation to weightlessness were not an inherent feature of individual persons but regular responses of the body sensory systems. The character, intensity, duration, and the dynamics of illusion responses in space mission are described. Forms of the vestibular disorders, types of adaptation of the sensory systems and classification of spontaneous illusion responses in the weightless environment are presented. Hypothesis for possible mechanisms of the illusion responses in weightlessness is suggested.
Unfortunately, the article is behind paywall
- There was a strange case in 1976 on Salyut-5 space station.
The crew of Soyuz-21 mission (the link is for Russian version of Wikipedia page, hence it contains more information of the issue than the English page) after spending 42 days in space, reported an acrid, toxic smell. One of the crew, Vitaly Zholobov, became seriously ill both physically and psychologically. They returned to Earth on 49th day (the mission was planned for 60 days) Later investigations revealed that there were no problems with toxic environment and some psychologists have suggested that it was a hallucination caused by the pressures of the mission (they had had a major electrical power outage and spent 2 hours fixing it without life support system operating):
Further studies showed that the atmosphere was normal, and problems arose due to physical and psychological overload accompanied by the lack of physical excercise, poor sleep and poor psychological support from the Earth.
- NASA astronaut Scott Kelly describes his own experience:
I was often still disoriented about how my body was positioned: I would wake up convinced that I was upside down, because in the dark and without gravity, my inner ear took a random guess as to how my body was positioned in the small space. When I turned on a light, I had a sort of visual illusion that the room was rotating rapidly as it reoriented itself around me, though I knew it was actually my brain readjusting in response to new sensory input.
Emphasis in all quotes mine.