Final answer:
The term 'memories' correctly fills in the blank, as it aligns with the semantic network theory and the associative nature of memory recall discussed in the context.
Step-by-step explanation:
The blank in the sentence "_________ are tricky unless you can connect up when and where you'd seen them." should be filled with the term memories. This is because the context provided is indicative of the semantic network theory, which involves the organization of memories in associative networks within the mind. As we learn from memory research, concepts and experiences are hierarchically arranged and linked in the mind, where the strength of the link depends on the frequency and context of the connections made between them.
When we try to recall information, we rely on these semantic networks for the process of recognition and the subsequent retrieval of the associated data or experiences, which in this case are memories. So, the final answer in a two-line explanation in 300 words, as requested: Memories are tricky to recall unless there is a connection to when and where they were formed, given their organization in associative networks within the mind that depend on the frequency of previous associations.