Sensorimotor recovery following spaceflight may be due to frequent square-wave saccadic intrusions.
Square-wave jerks (SWJs) are small, involuntary saccades that disrupt steady fixation. We report the case of an astronaut (approximately 140 d on orbit) who showed frequent SWJs, especially postflight, but who showed no impairment of vision or decrement of postflight performance. These data support the view that SWJs do not impair vision because they are paired movements, consisting of a small saccade away from the fixation position followed, within 200 ms, by a corrective saccade that brings the eye back on target. Since many returning astronauts show a decrement of dynamic visual function during postflight locomotion, it seems possible that frequent SWJs improved this astronaut's visual function by providing postsaccadic enhancement of visual fixation, which aided postflight performance. Certainly, frequent SWJs did not impair performance in this astronaut, who had no other neurological disorder.
Neurosciences Laboratories, NASA-Johnson Space Center, Houston, TX, USA. millard.f.reschke@nasa.gov
Millard
M
Reschke
Jeffrey T
JT
Somers
R John
RJ
Leigh
Jody M
JM
Krnavek
Ludmila
L
Kornilova
Inessa
I
Kozlovskaya
Jacob J
JJ
Bloomberg
William H
WH
Paloski
D018480:Astronauts; D006801:Humans; D008875:Middle Aged; D009043:Motor Activity / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology; D020127:Recovery of Function / Q000502:physiology*; D012438:Saccades / Q000502:physiology*; D012677:Sensation / Q000502:physiology*; D013026:Space Flight; D018489:Space Motion Sickness / Q000503:physiopathology; D013647:Task Performance and Analysis; D014785:Vision, Ocular / Q000502:physiology