▁Simple ▁visual ▁hall uc in ations ▁are ▁also ▁referred ▁to ▁as ▁non - formed ▁or ▁elementary ▁visual ▁hall uc in ations . ▁They ▁can ▁take ▁the ▁form ▁of ▁mult icol ored ▁lights , ▁colors , ▁geometric ▁shapes , ▁ind is crete ▁objects . ▁Simple ▁visual ▁hall uc in ations ▁without ▁structure ▁are ▁known ▁as ▁ph os phen es ▁and ▁those ▁with ▁geometric ▁structure ▁are ▁known ▁as ▁phot op si as . ▁These ▁hall uc in ations ▁are ▁caused ▁by ▁ir rit ation ▁to ▁the ▁primary ▁visual ▁cor tex ▁( B rod mann ' s ▁area ▁ 1 7 ). ▁ ▁Complex ▁visual ▁hall uc in ations ▁are ▁also ▁referred ▁to ▁as ▁formed ▁visual ▁hall uc in ations . ▁They ▁tend ▁to ▁be ▁clear , ▁lif eli ke ▁images ▁or ▁scenes , ▁such ▁as ▁faces ▁of ▁animals ▁or ▁people . ▁Sometimes , ▁hall uc in ations ▁are ▁' L illi put ian ', ▁i . e ., ▁patients ▁experience ▁visual ▁hall uc in ations ▁where ▁there ▁are ▁mini ature ▁people , ▁often ▁undert aking ▁unusual ▁actions . ▁L illi put ian ▁hall uc in ations ▁may ▁be ▁accompanied ▁by ▁wonder , ▁rather ▁than ▁terror . ▁ ▁Content ▁ ▁The ▁frequency ▁of ▁hall uc in ations ▁var ies ▁widely ▁from ▁rare ▁to ▁frequent , ▁as ▁does ▁duration ▁( seconds ▁to ▁minutes ). ▁The ▁content ▁of ▁hall uc in ations ▁var ies ▁as ▁well . ▁Complex ▁( formed ) ▁visual ▁hall uc in ations ▁are ▁more ▁common ▁than ▁Simple ▁( non - formed ) ▁visual ▁hall