In reply to Mike Redmayne:
I'm coming at this partly from the point of view of teaching in universities, where there has been a lot of research on how well people assimilate information.
The evidence is that if people sit there while information is presented to them (e.g. a lecture) then when tested only an hour or so later their recall can be as low as 5% to 10%. Thus to teach effectively you need to include lots of "active" exercises, such as them doing tasks, writing essays, solving problems, etc.
We know this because we frequently assess how much they have actually assimilated, by use of tests and exams. From this perspective, the idea that they can have months and months of listening to "lectures", in a largely passive way, and then assimilate and recall any significant fraction of it is rather ludicrous.
Has there been any decent research on this for juries? Not about interpretation or verdict, but simple factual recall. As in, "two weeks ago X gave 2 hrs of evidence, please answer these factual questions as to what he said, you may use your notes if you took any".
From the point of view of university teaching where we regularly do exactly this, I think people generally would be pretty surprised at how bad humans in general are at this. What people do tend to do is form and retain is a "general impression", but it would seem to me that one could form a general impression just as well from a time-limited 10 days.
You say: "if there are complex issues to be explored, and the defence wants to challenge them, it's going to take a long time" -- how much of that complexity is the jury following, as oppose to just forming a general impression?