/Users/andrea/_magisterarbeit/korpus/clean/testkorpus/30/file13.html NN ----------------------------------------- : Why WRB does VVZ the DT illusion NN work NN . SENT The DT visual JJ system NN needs VVZ to TO determine VV the DT color NN of IN objects NNS in IN the DT world NN . SENT In IN this DT case NN the DT problem NN is VBZ to TO determine VV the DT gray JJ shade NN of IN the DT checks NNS on IN the DT floor NN . SENT Just RB measuring VVG the DT light NN coming VVG from IN a DT surface NN the DT luminance NN is VBZ not RB enough JJ . SENT a DT cast NN shadow NN will MD dim VV a DT surface NN , , so RB that IN a DT white JJ surface NN in IN shadow NN may MD be VB reflecting VVG less JJR light NN than IN a DT black JJ surface NN in IN full JJ light NN . SENT The DT visual JJ system NN uses VVZ several JJ tricks NNS to TO determine VV where WRB the DT shadows NNS are VBP and CC how WRB to TO compensate VV for IN them PP , , in IN order NN to TO determine VV the DT shade NN of IN gray JJ paint NN that WDT belongs VVZ to TO the DT surface NN . SENT The DT first JJ trick NN is VBZ based VVN on IN local JJ contrast NN . SENT In IN shadow NN or CC not RB , , a DT check NN that WDT is VBZ lighter JJR than IN its PP$ neighboring JJ checks NNS is VBZ probably RB lighter JJR than IN average NN , , and CC vice NN versa FW . SENT In IN the DT figure NN , , the DT light JJ check NN in IN shadow NN is VBZ surrounded VVN by IN darker JJR checks NNS . SENT Thus RB , , even RB though IN the DT check NN is VBZ physically RB dark JJ , , it PP is VBZ light JJ when WRB compared VVN to TO its PP$ neighbors NNS . SENT The DT dark JJ checks NNS outside IN the DT shadow NN , , conversely RB , , are VBP surrounded VVN by IN lighter JJR checks NNS , , so RB they PP look VVP dark NN by IN comparison NN . SENT A DT second JJ trick NN is VBZ based VVN on IN the DT fact NN that IN shadows NNS often RB have VHP soft JJ edges NNS , , while IN paint NN boundaries NNS like IN the DT checks NNS often RB have VHP sharp JJ edges NNS . SENT The DT visual JJ system NN tends VVZ to TO ignore VV gradual JJ changes NNS in IN light JJ level NN , , so RB that IN it PP can MD determine VV the DT color NN of IN the DT surfaces VVZ without IN being VBG misled VVN by IN shadows NNS . SENT In IN this DT figure NN , , the DT shadow NN looks VVZ like IN a DT shadow NN , , both CC because IN it PP is VBZ fuzzy JJ and CC because IN the DT shadow NN casting NN object NN is VBZ visible JJ . SENT The DT paintness NN of IN the DT checks NNS is VBZ aided VVN by IN the DT form NN of IN the DT X NP junctions NNS formed VVN by IN 4 CD abutting VVG checks NNS . SENT This DT type NN of IN junction NN is VBZ usually RB a DT signal NN that IN all PDT the DT edges NNS should MD be VB interpreted VVN as IN changes NNS in IN surface NN color NN rather RB than IN in IN terms NNS of IN shadows NNS or CC lighting NN . SENT As RB with IN many DT so RB called VVN illusions NNS , , this DT effect NN really RB demonstrates VVZ the DT success NN rather RB than IN the DT failure NN of IN the DT visual JJ system NN . SENT The DT visual JJ system NN is VBZ not RB very RB good JJ at IN being VBG a DT physical JJ light NN meter NN , , but CC that DT is VBZ not RB its PP$ purpose NN . SENT The DT important JJ task NN is VBZ to TO break VV the DT image NN information NN down RB into IN meaningful JJ components NNS , , and CC thereby RB perceive VVP the DT nature NN of IN the DT objects NNS in IN view NN . SENT Back RB to TO the DT illusion NN . SENT