▁ref lex ▁and ▁opt ok in etic ▁ref lex , ▁and ▁gaz e - sh ifting ▁mechan isms ▁as ▁s acc ades ▁and ▁purs uit ▁movements . ▁ ▁Ver gence ▁movement ▁or ▁convergence ▁is ▁the ▁movement ▁of ▁both ▁eyes ▁to ▁make ▁sure ▁that ▁the ▁image ▁of ▁the ▁object ▁being ▁looked ▁at ▁falls ▁on ▁the ▁corresponding ▁spot ▁on ▁both ▁ret inas . ▁This ▁type ▁of ▁movement ▁helps ▁in ▁the ▁depth ▁per ception ▁of ▁objects ▁ ▁P urs uit ▁movement ▁or ▁smooth ▁purs uit ▁is ▁the ▁movement ▁the ▁eyes ▁make ▁while ▁tracking ▁an ▁object ' s ▁movement , ▁so ▁that ▁its ▁moving ▁image ▁can ▁remain ▁maintained ▁on ▁f ove a . ▁ ▁S acc ades ▁ ▁The ▁eyes ▁are ▁never ▁completely ▁at ▁rest : ▁they ▁make ▁frequent ▁fix ational ▁eye ▁movement ▁even ▁when ▁fix ated ▁at ▁one ▁point . ▁The ▁reason ▁for ▁this ▁movement ▁is ▁related ▁to ▁the ▁phot ore cept ors ▁and ▁the ▁gang l ion ▁cells . ▁It ▁appears ▁that ▁a ▁constant ▁visual ▁stim ulus ▁can ▁make ▁the ▁phot ore cept ors ▁or ▁the ▁gang l ion ▁cells ▁become ▁un respons ive ; ▁on ▁the ▁other ▁hand ▁a ▁changing ▁stim ulus ▁will ▁not . ▁So ▁the ▁eye ▁movement ▁constantly ▁changes ▁the ▁stim uli ▁that ▁fall ▁on ▁the ▁phot ore cept ors ▁and ▁the ▁gang l ion ▁cells , ▁making ▁the ▁image ▁clearer . ▁ ▁S acc ades ▁are ▁the ▁rapid ▁movement ▁of ▁eyes ▁that ▁is ▁used ▁while ▁sc anning ▁a ▁visual ▁scene . ▁In ▁our ▁subject ive ▁impression , ▁the ▁eyes ▁do ▁not