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The human vertical optokinetic afternystagmus and the effect of gravity during pitch tilt
1The Naval Aerospace Medical Research Laboratory, Pensacola, FL, USA. stayko.kolev@meteo.bg
Background:
Findings concerning human vertical optokinetic afternystagmus (VOKAN) are often not consistent and in some cases even contradictory.
Method:
VOKAN was studied in nine normal subjects using corneo-retinal potential technique and an infrared video camera detection apparatus (ISCAN). VOKAN responses were measured at three angles of pitch head (and body) tilt: 0 degrees (upright), 90 degrees (supine) and 135 degrees (45 degrees below horizontal). The optokinetic stimulus was stripe movement with a velocity of 60 degrees/s.
Results:
Upward slow phase velocity (SP-Up) VOKAN was evoked in 6/9 subjects (67%) at 0 degrees tilt and at 90 degrees tilt, and in 4/9 (44%) at 135 degrees tilt. Downward slow phase velocity (SP-Down) VOKAN was elicited in 3/9 subjects (33%) at 0 degrees tilt; in 2/9 subjects (22%) at 90 degrees tilt and in 0/9 subjects (0%) at 135 degrees tilt.
Conclusion:
The pitch tilt, as a gravity effect, influences significantly on the appearance and the duration of VOKAN.
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