▁was ▁no ▁necessary ▁connection ▁between ▁a ▁tact ile ▁world ▁and ▁a ▁sight ▁world — that ▁a ▁connection ▁between ▁them ▁could ▁be ▁established ▁only ▁on ▁the ▁basis ▁of ▁experience . ▁He ▁spec ulated : ▁the ▁objects ▁to ▁which ▁he ▁had ▁h ither to ▁used ▁to ▁apply ▁the ▁terms ▁up ▁and ▁down , ▁high ▁and ▁low , ▁were ▁such ▁as ▁only ▁affected ▁or ▁were ▁in ▁some ▁way ▁perce ived ▁by ▁touch ; ▁but ▁the ▁proper ▁objects ▁of ▁vision ▁make ▁a ▁new ▁set ▁of ▁ideas , ▁perfectly ▁distinct ▁and ▁different ▁from ▁the ▁former , ▁and ▁which ▁can ▁in ▁no ▁sort ▁make ▁themselves ▁perce ived ▁by ▁touch ▁( sect . ▁ 9 5 ). ▁ ▁This ▁thought ▁experiment ▁( it ▁was ▁a ▁thought ▁experiment ▁at ▁the ▁time ) ▁out lines ▁the ▁debate ▁between ▁rational ism ▁and ▁empir ic ism ; ▁to ▁what ▁degree ▁our ▁knowledge ▁of ▁the ▁world ▁comes ▁from ▁reason ▁or ▁experience . ▁ ▁Early ▁cases ▁There ▁are ▁many ▁stories ▁or ▁an ec d otes ▁of ▁the ▁phenomen on , ▁preceding ▁the ▁first ▁documented ▁case , ▁including ▁one ▁from ▁the ▁year ▁ 1 0 2 0 , ▁of ▁a ▁man ▁of ▁thirty ▁operated ▁upon ▁in ▁Arab ia . ▁ ▁Before ▁the ▁first ▁known ▁human ▁cases , ▁some ▁tests ▁were ▁done ▁re aring ▁animals ▁in ▁darkness , ▁to ▁den y ▁them ▁vision ▁for ▁months ▁or ▁years , ▁then ▁discover ▁what ▁they ▁see ▁when ▁given ▁light . ▁A . ▁H . ▁Re isen ▁found ▁severe ▁behaviour al ▁losses ▁in ▁such ▁experiments ; ▁but ▁they ▁might ▁have ▁been ▁due