▁causes ▁movement ▁of ▁the ▁crist a ▁amp ull aris ▁and ▁the ▁hair ▁cells ▁within ▁them . ▁Stim ulation ▁of ▁the ▁ot ol ith ▁org ans ▁occurs ▁when ▁gravit ational ▁forces ▁or ▁linear ▁acceler ations ▁cause ▁movement ▁of ▁the ▁ot ol ith ▁memb rane , ▁the ▁ot ol ith s , ▁or ▁the ▁hair ▁cells ▁of ▁the ▁mac ula . ▁ ▁Som at ogy ral ▁ill us ions ▁occur ▁as ▁a ▁result ▁of ▁angular ▁acceler ations ▁stim ulating ▁the ▁sem ic irc ular ▁can als . ▁Som at og rav ic ▁ill us ions , ▁on ▁the ▁other ▁hand , ▁occur ▁as ▁a ▁result ▁of ▁linear ▁acceler ations ▁stim ulating ▁the ▁ot ol ith ▁org ans . ▁ ▁V est ib ular / som at ogy ral ▁ ▁Ill us ions ▁involving ▁the ▁sem ic irc ular ▁and ▁som at ogy ral ▁can als ▁of ▁the ▁vest ib ular ▁system ▁of ▁the ▁ear ▁occur ▁primarily ▁under ▁conditions ▁of ▁un re li able ▁or ▁un available ▁external ▁visual ▁references ▁and ▁result ▁in ▁false ▁sens ations ▁of ▁rotation . ▁These ▁include ▁the ▁le ans , ▁the ▁gra vey ard ▁spin ▁and ▁spir al , ▁and ▁the ▁Cor i olis ▁ill usion . ▁ ▁The ▁le ans ▁▁ ▁This ▁is ▁the ▁most ▁common ▁ill usion ▁during ▁flight , ▁and ▁can ▁be ▁caused ▁by ▁a ▁sudden ▁return ▁to ▁wings - level ▁flight ▁following ▁a ▁grad ual ▁application ▁of ▁bank ▁that ▁had ▁gone ▁un not iced ▁by ▁the ▁pilot . ▁The ▁reason ▁a ▁pilot ▁can ▁be ▁una ware ▁of