Please forgive my obtuseness but what is a professional juror?
None exist, but I've advocated their need for many a decade.
I first perceived the need after talking with a person who had been a member of the jury in the first murder trial of Dr. Sheppard -- convicted by stealth jurors and/or jurors who had prejudged his guilt. Many years later, the bountiful and totally asinine convictions that were taking place as a result of the hysteria surrounding the many sexual-abuse, child-care trials in the 80's and early 90's solidified the need in my mind.
At the very least, I would seat them in murder one trials and high-profile trials.
In circumstantial evidence cases, there is an absolute necessity for jurors to be able to derive -- a high percentage of the time -- conclusions developed from inferences that are both valid and true. This should be a judicial imperative.
However, when given an applied logic test that provides a set of five multiple choice answers, test results (late 70's, 80's early 90's) consistently revealed that the average person did not possess the level of reasoning skill to score better than 35% (on average). Obviously, this represents a massive deficiency in the most needed skill.
Objectivity is another key juror need, especially in high-profile, circumstantial evidence cases. For if you look at a piece of evidence from the prosecution's perspective, you may find that it points to guilt, but if you look at the same piece of evidence through the prism of reasonable doubt, it can be entirely exculpatory.
I still believe that we need professional jurors. However, as an alternative, I would accept a process whereby potential jurors must first pass an applied logic test -- 80% correct at a minimum -- before they can go through voir dire.
Net, I think it's absurd that we have a professional behind the bench and a professional representing the prosecution and a professional representing the defendant, but we do not require jurors to even demonstrate that they can validly reason a healthy percentage of the time.
FWIW