Problem:
Tyler is a young boy who is rapidly developing. His mother is quite proud of his accomplishments and tells you updates weekly. Today, this is her update:
Tyler used to just pick up his rattle and shake it gently. But, now he is shaking it and then hitting it on his belly and leg to make a slightly different sound. He also is no longer tricked when I hide his pacifier under the blanket. He's just beginning to crawl, but I can't wait for him to start walking.
What sub-stage of Piaget's Sensorimotor stage is he in? How do you know? Give evidence to support your answer.