Forty 9-year-olds were read the same book by their parents every night for one month. The 9-year-olds were tested about the book after the first reading, and then every week thereafter. They were asked to name characters and describe different parts of the books, as well as read passages of the book for themselves. The researchers saw drastic improvement in their skills with this particular book so the performed the same experiment again, but this time they changed the book after a week and asked the same questions. They did not see the same type of improvement as in the initial study. What was the most likely occurring during the initial study