What is the test for determining whether extraneous information on the jury was prejudicial to the jury?

The trial court is required to hold an evidentiary hearing to determine the exact nature of the extraneous information upon learning of a possible incident of juror misconduct. United States v. Bagnariol, 665 F.2d at 885. The trial judge is "uniquely qualified" to appraise the likely effect and prejudicial nature of extraneous information on the jury because he or she observes the jurors throughout the trial and hears the evidence presented. Id. Thus, "the judge's conclusion about the effect of the alleged juror misconduct deserves substantial weight." Id.