CS : Conditioned stimulus associated with any material object like bell . if example we provide meat to the dog with the ringing bell then it will be conditioned stimulus and salivation will be CR conditioned response .

if we talk about natural process then while providing meat to the dog salivation will be there UC stimulus without any condition of the bell so it will be UC RESPONSE .

understand this concept with pavlov experiment of dog saliva with the ringing bell and meat .

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M.S.A