Final answer:
Sonya's inability to recall personal memories from when she was 3 years old and younger is referred to as 'childhood amnesia' or 'infantile amnesia', which is due to the immature state of the hippocampus during early childhood.
Step-by-step explanation:
The inability to recall events from early childhood is known as childhood amnesia or infantile amnesia. This phenomenon is attributed to the incomplete development of the hippocampus, the area of the brain responsible for storing explicit memories. Since the hippocampus has not fully matured in infants and very young children, they often cannot form or retain these explicit memories long-term. Research, including that on patient H.M. who suffered from anterograde amnesia, illustrates that while the hippocampus is crucial for the consolidation of short-term memories into long-term memories, it also plays a role in the formation of episodic memories, which include one's autobiographical events. Due to this developmental aspect, most people are unable to remember personal events that occurred during their earliest years.