There are many situations that clearly demonstrate that our visual perception is less than entirely accurate. These situations are called illusions. For example, when looking at a picture, or a television screen, the brain assumes that we are seeing objects and spaces that have depth. As a result, we are accepting a set of signals or cues that create an illusion of three-dimensional space. The vast majority of human beings experience the same illusion, suggesting that its origin lies in the physiological mechanisms of perception.
A clear demonstration of the interpretive nature of visual perception comes from ambiguous figures (optical illusions), i.e., single images that can give rise to two or more distinct perceptions. These are two-dimensional images that are perceived as three-dimensional objects. Due to gravity constraints some configurations are more often present than others. The objective of the Iris (Image Reversal in Space) experiment designed by a team of students from the International Space University was to investigate whether the perception of three-dimensional ambiguous figures was affected when the observer is in a reduced gravity environment.
In order to conduct the experiment, a series of 20-25 ambiguous figures were displayed on one of the International Space Station laptops using an interactive presentation. Some ambiguous figures were three-dimensional while others were two-dimensional objects. For each ambiguous figure, the astronaut-subject were asked to identify which form he saw first and then indicate when he saw the second. The time delay between the occurrence of the first and the second form will then be calculated.
Tests were performed with Canadian Astronaut Dr. Bob Thirsk before and during the flight. The same tests were also conducted on a population of subjects on Earth. The students' hypothesis is that for three dimensional figures, there will be a significant difference when observed both on Earth and in space, but not for two-dimensional figures. The images used for this student research as well as the project results are available on the Canadian Space Agency website.