How has the hearsay rule been interpreted in the context of expert testimony?

[32] Thus, Justice Dickson, as he then was, in the case of The Queen v. Abbey, to which I have referred, at page 408 [C.C.C.] of the decision, said: The main concern of the hearsay rule is the veracity of the statements made. The principal justification for the exclusion of hearsay evidence is the abhorrence of the common law to proof which is unsworn and has not been subjected to the trial by fire of cross-examination. Testimony under oath and cross-examination have been considered to be the best assurances of the truth of the statements of facts presented. It would certainly seem plain, for example, that, if an engineer were called to give evidence with respect to the reason for the collapse of a bridge, and during his testimony were to refer to statements made to him by the bridge tender and which either by implication or by expression he believed to be true, such evidence should not be considered as tending to prove the reliability or truth of the bridge tender’s statements. The engineer, after all, is not put forward as having any expertise related to assessing the reliability of the statements that he received. The accuracy, truth and reliability of the statements could not be tested by cross-examination of the engineer. Likewise, a doctor in giving expert evidence pertaining to the diagnosis and prognosis of an injury may, in the course of his testimony, make reference to statements that he heard from the patient and that he accepted and took into account in arriving at his opinion. Although the doctor may refer to such statements in the course of his opinion and may even express his belief in the statements, such statements elicited through the doctor are no evidence as to the reliability or truth of the patient’s statements. Again, the doctor is not held out as having any particular expertise with respect to the ability to assess the reliability of the patient’s statements and again the truth and reliability of his statements cannot be tested through cross-examination. A psychiatrist may give evidence, as was the case in certain of the decisions to which I have referred, with respect to the mental capacity of an accused in relation, for example, as to whether he was capable of appreciating the nature and quality of his acts. In the course of that testimony, the psychiatrist may mention statements that the accused made to him. He may express that he accepted and believed the statements in the course of arriving at his opinion. As is the case with the previous examples, however, the evidence of the psychiatrist qualified to assess the mental state of the accused at the date of the crime, cannot be taken as evidence of the reliability or truth of the statements.