Answer:
Tone
Explanation:
The conditioned stimulus is a term that is used in classical conditioning by Pavlov. Conditioned stimulus plays a vital role in classical conditioning. When the tone is sounded, and the right cheek is touched of an infant. When a baby right cheek is touched, the baby reflexively turns the face towards the touch.
When pairing is conducted, the baby turns the head towards tone. So that the tone is conditioned or paired by touching cheek. The conditioned stimulus is tone due to which baby turns its head.