So it seems that rather than there being a specific issue with self-reporting, those with aphantasia genuinely cannot imagine things in their mind. The next obvious question then is why this is the case, and if anything could be done to help those who have it.
The most commonly accepted explanation is that when we re-run a memory in our mind's eye, we attempt to reactivate the same patterns of activity as when the memory was formed. It is thought that somehow these neurological pathways are disrupted, or that the brain simply cannot reactivate these pathways in the same way.
If researchers are able to figure out if this is indeed the case, then it could be conceivable for a treatment to be developed that could help people imagine things. On the flip side, it could also be used to treat those with over-stimulated activity patterns, which some think might play a role in addiction, as well as some forms of post-traumatic stress disorder.