Answer:
neutral stimulus; conditioned stimulus
Explanation:
In Pavlov's classical conditioning, <em>before conditioning takes place, a neutral stimulus does not really elicit a response other than serving to secure attention</em>. The metronome, before conditioning, does not elicit salivation in dogs ordinary, except for focusing of attention. Food naturally elicits salivation in dog, and is referred to as an unconditioned stimulus.
Conditioning takes place when the ticking metronome is paired with an unconditioned stimulus such as food, in order to produce the same response of salivation that food produces. After conditioning, the presentation of the ticking metronome will elicit salivation. <em>After conditioning, we refer to the ticking metronome as a conditioned stimulus</em>.
The ticking metronome is the neutral stimulus before conditioning, and the conditioned stimulus after conditioning.