Final answer:
The Atkinson and Shiffrin model of memory suggests that actively thinking about previously learned material involves recalling the memory from Long-Term Memory and placing it into Short-Term Memory (STM) for manipulation and use.
Step-by-step explanation:
According to the Atkinson and Shiffrin model of memory, when we actively think about something that we have previously learned, the process described is C. The memory is recalled from Long-Term Memory (LTM) and is placed in Short-Term Memory (STM). This process allows us to actively work with or manipulate the information. As we think about and rehearse information in our short-term memory, through mechanisms such as active rehearsal or elaborative rehearsal, we help to further consolidate this information into our long-term memory, enhancing its retention and making it easier to retrieve in the future.
It's also important to note that the interaction between STM and LTM is complex and involves both encoding and retrieval processes. When information is retrieved from LTM, it becomes part of our conscious awareness and is temporarily held in STM or working memory, where it can be used for cognitive tasks.