心理学百科 The Psychology Book (Big Ideas Simply Explained)
Pavlov concluded that the food offered to the dogs was an unconditioned stimulus, U.S., because it led to an unlearned or unconditioned response, U.R., in this case, salivation.
However, a famous expert in language pointed out that although children do learn some words by imitation and association, they also combine words to make meaningful sentences in unique and unlearned ways.