What is the most sensitive measure of retention when learning something already committed to memory?

Relearning is indeed considered the most sensitive measure of retention for information that has already been committed to memory. This process involves re-acquiring knowledge or skills that have been previously learned but may not be currently accessible. The key aspect of relearning is that it typically takes less time to learn that information again compared to the initial learning phase, which indicates that some level of memory retention has occurred even if it isn't consciously accessible.

This sensitivity is due to the fact that relearning effectively measures the difference in time or effort taken to learn something when compared to the original learning experience. It highlights the underlying memory traces that remain even when the individual is not able to recall or recognize the information fully, making it a robust indicator of how much has been retained.

The other options, while relevant to memory and retention, do not provide the same level of sensitivity in measuring what has been retained. Recall generally tests the direct retrieval of information without cues, recognition involves identifying previously learned material from a set of options, and retrieval cues are external prompts that assist in remembering. However, none of these methods specifically measure how much information is retained as effectively as the relearning method does.