In classical conditioning, a stimulus that does not initially elicit any response is called:

1. The four labels in classical conditioning are defined by what a stimulus does before and after training. 2. An unconditioned stimulus already elicits a reflex with no training at all. 3. A neutral stimulus is one that does not initially elicit a response; Pavlov's tone began as exactly this. 4. Once the neutral stimulus has been repeatedly paired with the unconditioned stimulus, the same stimulus is renamed the conditioned stimulus. _Source: OpenStax Psychology (1st ed., CC BY 4.0), Ch 6 "Learning", §6.2 Classical Conditioning_