Rule 606 Competency of juror as witness. (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 member is sitting as a juror.

(b) Inquiry into validity of verdict or indictment. Upon an inquiry into the validity of a verdict or indictment, a juror may not testify concerning the effect of anything upon the juror's or any other juror's mind or emotions as influencing the juror to assent to or dissent from the verdict or indictment or concerning the juror's mental processes in connection therewith. Nor may the juror's affidavit or evidence of any statement by the juror indicating an effect of this kind be received. [L 1980, c 164, pt of §1; gen ch 1985]