Final answer:
The person who has lost the ability to form new declarative memories has anterograde amnesia. This is caused by brain trauma and affects the transfer of information from short-term to long-term memory.
Step-by-step explanation:
The person who has lost the ability to form new declarative memories has anterograde amnesia. This type of amnesia is caused by brain trauma, such as a blow to the head, which affects the hippocampus and the ability to transfer information from short-term to long-term memory. A famous example is H.M., who could not remember new information or people he had met after his surgery, but could still form new procedural memories.