Astronauts who flew on the Skylab missions of the early 1970s have reported in various personal communications that, during space flight, with eyes closed or with the lights out, they lost the sense of where everything was in relation to them. There are three possible explanations for why the astronauts might have felt this way.

1. It may be that the central nervous system requires some sense of "upness" or "downness" before it can begin the complex task of assembling an image of the body's surroundings. The lack of "up" and "down" in space may cause a loss of our external spatial map (loss of our image of the outside world), which could create disorientation.
2. The second possibility is that the proprioceptive mechanisms in our joints, tendons, and muscles do not work properly, and that one cannot move one's limbs accurately when one cannot see them in weightlessness. This would demonstrate a loss of our internal spatial map (loss of our own normal body image), and again, this could cause disorientation.
3. The third possibility is that one loses the sense of one's body image, i.e., the sense of relationship of the body's various parts to one another, and therefore cannot relate the external surroundings to the location or movement of the body. This would demonstrate the lack of both an external spatial map and an internal spatial map, and together this could also cause disorientation.

If these three possibilities could be tested individually, we could come much closer to understanding why astronauts seem to "lose themselves" when their eyes are closed.

Figure 23. An astronaut asked to stand "straight up".

Past experiments related to understanding how an astronaut's awareness of position changes during space flight have shown that our knowledge of limb and body position may be altered in space. Astronauts have had difficulty positioning their legs precisely under themselves during "drop tests" in space. Others have shown an interesting difficulty in maintaining a body position perpendicular to the vehicle floor (an "upright posture") in the absence of vision and while secured by the feet only (Figure 23). Finally, other astronauts have shown great difficulty estimating the angle of their knees and elbows when tested repeatedly in space. Dr. Young and his team of researchers carried out an Awareness of Position experiment that was designed to measure the astronaut's ability to point accurately at memorized targets in the absence of vision. They found some interesting results that may help us answer the question of whether our external or internal spatial maps have been affected in space. Let's first examine how the experiment was carried out and then we will examine some of the results.

The test procedure consisted of three parts. Each part was designed so that the two possible perception losses (that of the internal spatial map and the external spatial map) could be tested separately to see which one dominated the response. The three parts of the experiment are described as follows. All sequences were carried out preflight, inflight, and postflight.

Figure 24. The Awareness of Position experiment.

Figure 25. The target screen and the coordinated system.

1. In the first part, the subjects pointed to five remembered target positions on a target screen with their eyes closed. Target pointing accuracy was demonstrated with a hand held light pointer, recorded both on videotape and by the observer (Figure 24). Each point began with the hand close to the chest. The arm was then extended, directing the beam of the light pointer at the (unseen) target. The observer recorded the actual position of the light beam on a data sheet, and the subject brought the hand back to a position close to the chest in preparation for the next point. This was repeated 25 times. This part examined the accuracy and the strength of the astronaut's external spatial map.
2. For the second part, the subject continued to keep the eyes closed and touched various parts of the body with the right index finger. This was done to test the accuracy of the internal spatial map.
3. The third and final part began with the subject opening the eyes and memorizing the target positions again. Pointing was carried out in the same fashion as in the first part of the experiment, with the significant difference that the eyes were closed only during the actual pointing maneuver of the arm Unlike the first part of the experiment, this allowed the subject to maintain an accurate image of the external world during testing. Since it provided no feedback as to how the astronauts perceived their own body position, this test allowed for an evaluation of the astronaut's internal spatial map perception.

Figure 25 shows the five targets (labelled C, U. D, L, and R referring to center, up, down, left and right) and the coordinate system printed on the target screen. This coordinate system was important to provide detailed information about the location of each point for analysis. For instance, the specific locater information for the red dot on Figure 25 is the coordinate (7,14) in the upper right quadrant. The divisions on the screen are in inches.

Figure 26 shows the pointing results from one astronaut, Subject P. for the two preflight tests. The first one was performed with the eyes closed continually, and the second one, with the eyes open between each point. It is quite clear that a frequent updating of one's mental image of the outside world can improve performance even on the ground.

Figure 26. Subject P's preflight test results.

Figure 27 shows how the same subject performed inflight. Once again, the first results, shown in Figure 27a, are with the eyes continually closed and the second results, shown in Figure 27b, are with the eyes open between each point. As you can see, in weightlessness, the subject exhibited a very pronounced downward pointing bias, and this was true for all five targets, C, U. D, L, and R. In fact, there were attempts to point at target D that fell below the target screen; these are not shown here. The data from Figure 27b shows a marked improvement when the astronaut was able to see the external world between each point, although in this particular example, performance in space was not quite as good as on the ground.

Figure 27. Subject P's inflight test results.

Figure 28. The mean pointing bias for all four subjects.

Finally, the mean pointing bias (mean = an average value, bias = an inclination or tendency toward a certain direction) for all four subjects, before, during, and following flights is illustrated in Figure 28. Each arrow represents the combined and averaged data from all of the pointing events that were performed by each subject. Two subjects (N and P) who were able to point very accurately on Earth demonstrated greatly reduced performance inflight, with a pronounced tendency to point towards the floor. All subjects made greater errors postflight than preflight, but in similar directions. Recovery to the preflight level of performance was nearly complete by seven days after landing.

These results provide evidence that the primary factor causing the pointing errors and the perceptional changes is the loss of the external spatial map since performance was lower when the astronauts did not view the world around them between pointing maneuvers. These data also suggest that, in the absence of vision, the maintenance of a stable external spatial map is highly dependent on the presence of normal gravitational forces. We know this because the astronauts were able to point more accurately when performing the preflight tests. The pattern and time it took for the astronauts to recover after landing also suggest that this phenomenon may be normally influenced by the otolith organs.

In this section, we reviewed some interesting results about how space flight affects our perception of our own bodies relative to the world around us. Using these results, Dr. Young and other researchers have begun to develop an understanding of how our perceptions and senses are influenced by gravity. Such an understanding will help clarify what is happening to the astronaut's sensory and balance systems during space flight and may provide the necessary information for researchers to determine how to deal effectively with space motion sickness. You see, when the astronauts become sick in space, not only is it extremely uncomfortable for them, but it also compromises the mission objectives. If the astronauts are sick, they can't perform the multitude of important experiments that we send them up to do. And if they have to take motion sickness medication, as many of them do, the medication alters their physiology. Therefore, any physiological data collected on medicated astronauts will not represent the "normal" state but, instead, a "medicated" state.

The good news is that space motion sickness is a temporary affliction. The most severe symptoms usually last no longer than about the first three days after arriving in space and may require medication. As time moves on the symptoms become "manageable" without medication. If you think about it, three days is not very long for the balance system to completely relearn how to interpret sensory information and to respond with appropriate body movements. But three days out of a one" or two-week shuttle mission is too much time to waste. Therefore, it is a major goal of researchers like Dr. Young to characterize the physiological changes related to vestibular function and develop countermeasures for space motion sickness.

To study space motion sickness in more detail, crew members wore an accelerometer/recording unit (ARU) to measure and record all head movements and they used a voice recorder to record verbal comments. If they experienced space sickness, the crew members recorded any symptoms of space motion sickness and their time of occurrence. This provided Dr. Oman with a chronological (time) history of the onset and continuation of specific symptoms.⁷ By comparing accelerometer data and reports of symptoms, Dr. Oman was able to link specific and provocative (something that causes feelings of any kind) head movements with periods of discomfort.⁸ By understanding which head movements create the worst feelings of sickness, steps can be taken to help the astronauts develop ways of avoiding such movements early inflight, thereby reducing the magnitude of this problem.

The role of visual cues in causing space sickness was also studied by eliminating or reducing head movements in order to determine the extent to which the eye movements themselves were responsible for causing sickness. This was accomplished by having the subjects wear a collar that restricts head movements in order to find out whether wearing such a collar reduces the occurrence of space sickness symptoms. This experiment gave Dr. Young an indication of the degree to which different signals are participating in the sickness response. All of the research being done to understand how the sensory and balance systems operate in space will help researchers here on Earth understand better how the various sensory signals operate together in an integrated fashion. This is because a laboratory in space is the only place that we can eliminate sensory signals related to gravity for days at a time. It is only by eliminating a signal that one can truly obtain an understanding of how important it is. You know the old saying, "you don't know what you have until you lose it!" Well, that saying is true in this case.

Speaking of integrated, let's pay one last visit to our familiar integrated physiology flow chart (Figure 29). Since we have constantly been reminded in every chapter of this book that all of the systems in the body work together, it is truly fitting that we covered the cardiovascular system in the first major chapter of this book and the nervous system as the last chapter. Together, they represent the two powerful communication networks that allowall of the different parts and pieces of the body to work together, through the flow of nerve impulses and the flow of blood.