ers ▁could ▁not ▁eth ically ▁indu ce ▁rod ▁and ▁cone ▁loss ▁either ▁gen et ically ▁or ▁with ▁chemical s ▁so ▁as ▁to ▁directly ▁study ▁the ▁gang l ion ▁cells . ▁For ▁many ▁years , ▁only ▁infer ences ▁could ▁be ▁drawn ▁about ▁the ▁re ceptor ▁in ▁humans , ▁though ▁these ▁were ▁at ▁times ▁pert inent . ▁ ▁In ▁ 2 0 0 7 , ▁Za idi ▁and ▁colle agues ▁published ▁their ▁work ▁on ▁rod less , ▁con eless ▁humans , ▁showing ▁that ▁these ▁people ▁retain ▁normal ▁responses ▁to ▁non visual ▁effects ▁of ▁light . ▁The ▁identity ▁of ▁the ▁non - rod , ▁non - con e ▁phot ore ceptor ▁in ▁humans ▁was ▁found ▁to ▁be ▁a ▁gang l ion ▁cell ▁in ▁the ▁inner ▁ret ina ▁as ▁shown ▁previously ▁in ▁rod less , ▁con eless ▁models ▁in ▁some ▁other ▁m amm als . ▁The ▁work ▁was ▁done ▁using ▁patients ▁with ▁rare ▁dise ases ▁that ▁w ip ed ▁out ▁classic ▁rod ▁and ▁cone ▁phot ore ceptor ▁function ▁but ▁preserved ▁gang l ion ▁cell ▁function . ▁Despite ▁having ▁no ▁ro ds ▁or ▁con es , ▁the ▁patients ▁continued ▁to ▁exhib it ▁circ ad ian ▁photo ent rain ment , ▁circ ad ian ▁behaviour al ▁patterns , ▁mel aton in ▁supp ression , ▁and ▁pup il ▁re actions , ▁with ▁peak ▁spectral ▁sens it iv ities ▁to ▁environmental ▁and ▁experimental ▁light ▁that ▁match ▁the ▁mel an ops in ▁phot op ig ment . ▁Their ▁bra ins ▁could ▁also ▁associate ▁vision ▁with ▁light ▁of ▁this ▁frequency . ▁C lin