uc in ations . ▁In ▁contrast ▁to ▁hall uc in ations ▁experienced ▁in ▁organ ic ▁conditions , ▁hall uc in ations ▁experienced ▁as ▁sympt oms ▁of ▁psych oses ▁tend ▁to ▁be ▁more ▁fright ening . ▁An ▁example ▁of ▁this ▁would ▁be ▁hall uc in ations ▁that ▁have ▁imag ery ▁of ▁bugs , ▁dogs , ▁sn akes , ▁dist orted ▁faces . ▁Visual ▁hall uc in ations ▁may ▁also ▁be ▁present ▁in ▁those ▁with ▁Park inson ' s , ▁where ▁vis ions ▁of ▁dead ▁individuals ▁can ▁be ▁present . ▁In ▁psych oses , ▁this ▁is ▁relatively ▁rare , ▁although ▁vis ions ▁of ▁God , ▁ang els , ▁the ▁devil , ▁sain ts , ▁and ▁f ai ries ▁are ▁common . ▁Ind ividual s ▁often ▁report ▁being ▁surprised ▁when ▁hall uc in ations ▁occur ▁and ▁are ▁generally ▁hel pl ess ▁to ▁change ▁or ▁stop ▁them . ▁In ▁general , ▁individuals ▁believe ▁that ▁vis ions ▁are ▁experienced ▁only ▁by ▁themselves . ▁ ▁C aus es ▁▁ ▁Two ▁ne uro trans mit ters ▁are ▁particularly ▁important ▁in ▁visual ▁hall uc in ations ▁– ▁ser ot on in ▁and ▁ac et yl ch oline . ▁They ▁are ▁concentr ated ▁in ▁the ▁visual ▁th al am ic ▁nuc lei ▁and ▁visual ▁cor tex . ▁ ▁The ▁similarity ▁of ▁visual ▁hall uc in ations ▁that ▁stem ▁from ▁diverse ▁conditions ▁suggest ▁a ▁common ▁path way ▁for ▁visual ▁hall uc in ations . ▁Three ▁path oph ys i olog ic ▁mechan isms ▁are ▁thought ▁to ▁explain ▁this . ▁ ▁The ▁first ▁mechanism