▁delivered ▁when ▁the ▁animal ▁press es ▁a ▁lever . ▁The ▁animal ▁is ▁then ▁tested ▁by ▁being ▁played ▁an ▁intermediate ▁stim ulus ▁C , ▁e . g . ▁a ▁ 1 5   Hz ▁tone , ▁and ▁obser ving ▁whether ▁the ▁animal ▁press es ▁the ▁lever ▁associated ▁with ▁the ▁positive ▁or ▁negative ▁reward , ▁thereby ▁indicating ▁whether ▁the ▁animal ▁is ▁in ▁a ▁positive ▁or ▁negative ▁m ood . ▁ ▁This ▁might ▁be ▁influenced ▁by , ▁for ▁example , ▁the ▁type ▁of ▁housing ▁the ▁animal ▁is ▁kept ▁in . ▁ ▁Using ▁this ▁approach , ▁it ▁has ▁been ▁found ▁that ▁r ats ▁which ▁are ▁subject ed ▁to ▁either ▁handling ▁or ▁tick ling ▁showed ▁different ▁responses ▁to ▁the ▁intermediate ▁stim ulus : ▁r ats ▁exposed ▁to ▁tick ling ▁were ▁more ▁optim istic . ▁The ▁authors ▁stated ▁that ▁they ▁had ▁demonstrated ▁"... for ▁the ▁first ▁time ▁a ▁link ▁between ▁the ▁directly ▁measured ▁positive ▁affect ive ▁state ▁and ▁decision ▁making ▁under ▁uncertainty ▁in ▁an ▁animal ▁model ." ▁ ▁C ogn itive ▁bi ases ▁have ▁been ▁shown ▁in ▁a ▁wide ▁range ▁of ▁species ▁including ▁r ats , ▁dogs , ▁r hes us ▁mac a ques , ▁sheep , ▁ch icks , ▁star lings ▁and ▁h oney be es . ▁ ▁Self - med ic ation ▁with ▁ps y cho active ▁dru gs ▁Hum ans ▁can ▁suffer ▁from ▁a ▁range ▁of ▁emot ional ▁or ▁m ood ▁dis orders ▁such ▁as ▁de pression , ▁anx iety , ▁fear ▁and ▁pan ic . ▁ ▁To ▁treat ▁these ▁dis orders , ▁scient ists ▁have