Final answer:
The infant learned to make specific vocalizations through instrumental conditioning by associating their behaviors with positive reinforcement from the parents.
Step-by-step explanation:
The infant learns to make certain vocalizations in order to elicit laughter and hugs through instrumental conditioning, also known as operant conditioning. This type of learning involves associating a behavior with its consequences. When the infant's vocalizations result in positive feedback such as laughter and hugs, they are more likely to repeat those sounds in the future, reinforcing the behavior.