In what circumstances will an expert be allowed to testify in a criminal case?

In Frye v. United States, supra, 293 F. 1013, from which this state's Kelly/ Frye rule is derived, the court was called upon to determine the admissibility of expert testimony that is based on a new scientific technique. The test in question was a "systolic blood pressure deception test," which might be described now as a form of lie detection test. It was based on a theory that systolic blood pressure rises when a subject experiences fear, rage, or pain, and that because a person who consciously lies or conceals facts about, or guilt of, crime fears detection when under examination, there will be a rise in blood pressure corresponding to the extent of the subject's fear and attempt to control that fear. The defendant in a murder prosecution had offered an expert to testify to the result of this test. The trial court sustained the prosecutor's objection and excluded the evidence.