(a) At the trial. A member of the jury may not testify as a witness before that
jury in the trial of the case in which the juror is sitting. If the juror is
called so to testify, the opposing party shall be afforded an opportunity to
object out of the presence of the jury.
(b) Inquiry into validity of verdict in civil action. Upon an inquiry into the
validity of a verdict in a civil action, a juror may not testify as to any matter
or statement occurring during the course of the jury's deliberations or to the
effect of anything upon that or any other juror's mind or emotions as influencing
the juror to assent to or dissent from the verdict, or concerning the juror's
mental processes in connection therewith, except that a juror may testify on the
question whether extraneous prejudicial information was improperly brought to the
jury's attention or whether any outside influence was improperly brought to bear
upon any juror. Nor may a juror's affidavit or evidence of any statement by the
juror, concerning a matter about which the juror would be precluded from
testifying, be received for these purposes.