A question to consider as you read . . .Think about when you get dizzy and what causes it. Why do you think astronauts have this same problem in space?
Vocabulary that will help you understand this section
Astronauts often report a profound sense of spatial disorientation during space flight. This disorientation may arise from conflicting information being provided by the visual and vestibular senses. The major aim of the Vestibular Team, which includes Drs. B. Cohen and G.Clement, is to better understand this phenomenon by investigating the fundamental question of how spatial orientation of the vestibulo-ocular reflex and the optokinetic response are altered in microgravity.
Drs. Cohen and Clement's StudyIn space or on the Earth, the visual and vestibular systems must work together to allow the eyes to maintain a fixed gaze on an object while the body is in motion or the head is moving. The eyes provide the mechanics for seeing an object, and the vestibular system provides the inputs that allow the eye muscles to fixate an object on the retina, the vision instrument of the eye. When the head is moved, signals from the semicircular canals and the otolith, two sensory organs of the ear associated with maintaining body equilibrium, cause the eyes to move in a direction equal and opposite to the motion of the head or body. This is referred to as the vestibulo-ocular reflex. When a person spins in a circle for a sustained period of time, the vestibulo-ocular reflex action alone cannot keep an object oriented in the visual field. In order to maintain fixation of the object on the retina, the eye muscles make quick corrective jumps to reorient the eyes on the object. The repeated rapid movements of refixation are called optokinetic response.
In the Vestibular Team's study, as test subjects spin in a rotation chair, their eye movements and subjective motion and orientation perception are recorded. During one portion of the spin, the subject has no visual stimulation and sees nothing but darkness. Suppression of visual stimulation during this portion of the spin allows responses from the vestibular system to be isolated. During another portion of the spin, the subject is provided visual stimulation in the form of moving objects enabling analyses of the optokinetic response of the eye.
Signals from the vestibular and visual systems are provided to a specific area of the brain that controls spatial orientation. By further exploring the mechanisms that provide input to this area of the brain, basic information can be obtained about spatial orientation. This data can be applied to disorders of imbalance common in the population of age 60 and older.