- WELCOME
- ISS EXPERIMENTS
- ISS DATA COLLECTION
- UNDERWATER EXPERIMENTS
- MICROGRAVITY EXPERIMENTS
- GROUND EXPERIMENTS
- THE SCIENCE
- CONTACTS
Deciding “which way is up” involves combining information from more than one sense. It involves the balance senses, vision, the touch senses, as well as our understanding of which way our body’s is lined up. Judging such things as “up/down”, “above/below” is relatively easy when all the senses agree in terms of the direction of ‘up’. This might be when you are standing upright on earth with your feet pressing against the ground and surrounded by visual objects which help your judgement of orientation (e.g. room walls, ceilings, floors, people, the ground plane and sky). If your senses provide conflicting information on which way is up, such as when you lie down, or when the visual information isn’t there or is confusing (or during space when there is no gravity) then the brain must decide which information to use and which to ignore.
The Bodies in the Space Environment (BISE) aims to find out how we combine more than one sense to make judgments of object orientation in space. By testing before going into space, in the early and late periods of long periods of space flight, as well as after returning to earth, we can find out how judgments of orientation change as a result of weightlessness.
Background
The information involved in deciding which way is up can be put into two broad groups: gravity sensors, visual information and your internal representation of your body. We refer to these as ‘gravity’, ‘vision’ and ‘body’.
Information concerning gravity comes from the balance sensors of the ‘inner ear’. Other information comes from your weight pressing down against the floor through your feet, buttocks or back.
You have an internal idea of the structure of your body, with you head at one and your feet at the other. This has been built up by experience and is always with you.
The visual world provides a range of information to help you decide which way is ‘up’. Some objects have a natural right way up e.g. the people have a head at the top and feet at the bottom. Objects naturally sit ‘on top of’ others e.g. a cup on a saucer. Walls are lined up with gravity; the floor and the horizon are 90° to the direction of ‘up’.
Previous research has said that the way in which body, gravity and vision cues to up are combined involves using some information more than others. This means that when different sources of information disagree on which way is up we have to decide which information to rely on most. Although there are considerable differences between people in how they treat the importance of different sources of information, a specific person tends to always rely on the same information: for example, if you mostly rely on your body’s orientation to say which way is up, then this emphasis doesn’t change very much from day to day.
The problems in measuring ‘up’ during weightlessness
For over a hundred years the perceived direction of up has been found through adjusting a line or rod to match the direction of gravity. The method is known as the ‘luminous line’ test. This is a basic test that directly measures where you think gravity is. However this test requires you to have an idea of gravity with which to align the line so you can’t do it in space.
The shape-from-shading test was designed to try and find a way of measuring up without thinking about gravity. You are asked to judge which of a number of actually flat, shaded disks appears most convex. In general your brain assumes that light comes from ‘above.’ This test identifies where you think light is coming from and we can use this to work out where you think up is. This test has been used in both the short periods of weightlessness during special ‘parabolic’ aircraft flight, as well as during longer weightlessness during spaceflight. However it has been found this test may not measure the true sense of ‘up’. The test is also takes a long time to run and is quite difficult to do. In spite of this, it is useful to run this test on the ground to compare the results with other tests like the luminous line test.
The recently developed Oriented Character Recognition Test (OCHART) overcomes the problems of the luminous line and shape-from-shading tests. OCHART is a straightforward and easy to apply test for up’s direction which can be run in both normal gravity and weightlessness. OCHART uses that fact that the letter ‘p’ appears to change into the letter ‘d’ when you rotate it. By finding the angle at which the letter changes from p-to-d and d-to-p we can calculate a direction of up we have called “the perceptual upright”. By putting the letter against a picture background of a room filled with visual information concerning ‘up’, it has been found that OCHART shows how the orientation of the visual background affects the direction of the perceptual upright. OCHART is also sensitive to the body orientation of the observer. By applying OCHART in various body orientations, against visual backgrounds of differing orientations, and in differing gravity, we can calculate the way in which each individual uses the three cues of gravity, body and vision when deciding the direction of up. During parabolic flight the perceptual upright, measured using OCHART, has been found to change towards being more lined up with the body during short periods of decreased gravity.
The science question
Our results from applying OCHART in parabolic flight were surprising. We had expected that when gravity was removed the influence of the background picture’s orientation on the perceived upright would increase. But we found the opposite: the effect of vision decreased during weightlessness. We wondered whether the very short period of weightlessness created by parabolic flight might not be long enough to allow the brain to take into account the fact that gravity had been removed.
To check this idea we are looking at how astronauts use vision to decide which way is up during long periods of weightlessness. We will test astronauts before flight, early in their mission in space, late in the mission and then on their return to earth.
We expect that during early flight there will be a decrease in the influence of vision - as happened during our parabolic flight experiment. We expect that this change will then reverse to an increase in vision’s influence once astronauts are fully adapted to weightlessness. On return to earth an early testing of vision’s influence should show evidence for how this increased reliance on vision is still present, with the influence of vision returning to how it was before the space mission after a longer period on earth.
We will also check that the results which we obtain through OCHART broadly correspond to those from the luminous line and shape-from-shading tests in the ground-based testing.
The procedure
In order to answer our science question, and to ensure proper controls for our testing, a minimum of five sessions are required for each astronaut. These consist of three testing sessions on earth (one pre-flight, two post-flight) and two in-flight (one early and one late in the orbiting mission).
The ground-based testing sessions involve running the three protocols, OCHART, luminous line and shape-from-shading, each in two body orientations: sitting upright and lying right side down. From the results of these six tests we can calculate the influence of gravity, body and vision under normal gravity conditions, before flight for each person. The test all involve judging simple patterns: letter recognition (OCHART); line orientation judgments (luminous line test); and curvature judgments (shape-from-shading). The patterns are all presented on a laptop computer screen seen through a special viewing tunnel. Responses are made using buttons attached to the viewing tunnel. Each ground-based-testing session takes approximately two and a half hours.
The in-flight testing involves using only OCHART. The testing early in the space mission will measure the influence on vision on ‘up’ judgments before the astronaut has adjusted to weightlessness; testing later will measure this after adapting to life in space. The laptop and viewing tunnel will be identical to the one used for ground-based testing. Each of the two in-flight testing sessions lasts approximately 65 minutes.
Publications
2008
Jenkin, H., Barnett-Cowan, M., Dyde, R., Jenkin, M., Harris, L. Left/right asymmetries in the contribution of body orientation to the perceptual upright. Proc. VSS, Naples, FL, 2008.
Dyde, R. T., Jenkin, M., Jenkin, H., Zacher, J. and Harris, L. R. The role of visual background orientation on the perceptual uprihgt during parabolic flight. Proc. 7th Symposium on the role of the vestibular organs in space exploration, Noordwijk, The Netherlands, 2006.
Harris, L. R., Jenkin, M., Jenkin, H., Dyde, R. T. and Oman, C. M. Visual cues to the direction of the floor: implications for spacecraft design. Proc. 7th Symposium on the role of the vestibular organs in space exploration, Noordwijk, The Netherlands, 2006.
2004
Dyde, R. T., Sadr, S., Jenkin, M. R., Jenkin, H. L. and Harris, L. R. The perceived direction of up measured using a p/d letter probe. [Abstract]. J. of Vision, 4: 385a, 2004. http://journalofvision.org/4/8/385.
Harris, L., Dyde, R., Sadir, S., Jenkin, M. Jenkin, H. Cross-modal contributions to the perceived direction of "up". International Multisensory Research Form 2004, June 2-5, Barcelona, 2004.
Jenkin, H. L., Dyde, R. T., Jenkin, M. R. and Harris, L. R., The perceived direction of up measured using shape-from-shading in a virtual environment [Abstract]. J. of Vision, 4: 384a, 2004. http://journalofvision.org/4/8/381.
Oman, C. M., Howard, I. P., Smith, T., Beall, A. C., Natapoff, A., Zacher, J. E. and Jenkin, H. L., The role of visual cues in microgravity spatial orientation. In J. Bucky and J. Momick (Eds.) Neurolab Spacelab Mission: Neuroscience Research in Space NASA SP-2003-535, pp. 69-81, 2003.
