
234 S.E.2d 587 (1977)
292 N.C. 567
STATE of North Carolina
v.
Bobby Lee WILLARD.
No. 34.
Supreme Court of North Carolina.
May 10, 1977.
*591 Atty. Gen. Rufus L. Edmisten by Asst. Atty. Gen. James Wallace, Jr., Raleigh, for the State.
James L. Dellinger, Jr., King, for defendant-appellant.
COPELAND, Justice.
Defendant first contends the court erred when it allowed Sheriff Blalock at the pretrial hearing on defendant's motion to express a personal opinion as to why defendant's mental condition had changed.
The record of the hearing discloses the following testimony by Sheriff Blalock on direct examination:
"When Bobby came back from the hospital the first time back in November, the jailer let him out on different occasions to do small jobs around the jail and he appeared to be a normal prisoner. The unusual something came up right before the last term or right after the last term of Superior Court. That is when I noticed a change in Bobby. There was a change in Bobby's attitude. He started sort of rambling in his talk rather than talking about specific things. I might add that at the time that we had Superior Court we had several prisoners here from Central Prison as we have at this time and my own personal feeling is_____" "MR. DELLINGER: Objection.
"COURT: Overruled.
"A. It is my feeling and my observation that these people talked a lot to Bobby and I feel that is one reason why he changed.
"MR. DELLINGER: Objection.
"COURT: Overruled."
A layman who has had a reasonable opportunity to form an opinion based on observation may testify as to the mental capacity of a defendant in a criminal case. State v. Hammonds, 290 N.C. 1, 224 S.E.2d 595 (1976); 1 Stansbury's N.C. Evidence, § 127 (Brandis Rev.1973); see State v. Thompson, 285 N.C. 181, 203 S.E.2d 781 (1974). Assuming, arguendo, that a lay opinion as to the cause of a change in a defendant's mental state would nevertheless be incompetent, then the latter portion of Sheriff Blalock's testimony would be objectionable. However, we assume that when the court is the trier of fact, as is generally true on a pretrial motion, it will not consider incompetent evidence. Brown v. Boger, 263 N.C. 248, 139 S.E.2d 577 (1965); Bizzell v. Bizzell, 247 N.C. 590, 101 S.E.2d 668 (1958).
In a "`hearing was before the judge on a preliminary motion, the ordinary rules as to the competency of evidence applied in a trial before a jury are to some extent relaxed, for the reason that the judge with knowledge of the law is able to eliminate from the testimony he hears that which is immaterial and incompetent, and consider only that which tends properly to prove the facts to be found.' (Citations omitted.)" State v. Davis, 290 N.C. 511, 540, 227 S.E.2d 97, 115 (1976). Absent affirmative evidence to the contrary, this Court presumes that the trial judge disregarded incompetent evidence in arriving at his decision. State v. Davis, supra; Bizzell v. Bizzell, supra.
With respect to the challenged testimony in the instant case Judge Walker made the following finding of fact:

*592 "That he [Sheriff Blalock] did however notice recently a change in the defendant after he had been placed with several persons from either Central Prison or the Department of Correction System, inmates from the Department of Correction, and that the defendant had started rambling in his talk."
This finding was based solely on Sheriff Blalock's competent testimony. The trial court properly ignored the Sheriff's arguably incompetent statement of opinion which had earlier been admitted over defendant's objection. We note, however, that the safer practice is for the trial judge to adhere to the rules of evidence at a hearing on a pretrial motion. State v. Davis, supra. But where, as here, it does not affirmatively appear that the trial judge based his findings on the incompetent evidence the assignment of error will be overruled.
In his next two assignments of error, defendant contends the trial court erred in finding that he was mentally capable of standing trial.
The test of a defendant's mental capacity to proceed to trial is whether he has the capacity to comprehend his position, to understand the nature and object of the proceedings against him, to conduct his defense in a rational manner, and to cooperate with his counsel to the end that any available defense may be interposed. State v. Cooper, 286 N.C. 549, 213 S.E.2d 305 (1975); State v. Jones, 278 N.C. 259, 179 S.E.2d 433 (1971); State v. Propst, 274 N.C. 62, 161 S.E.2d 560 (1968); State v. Sullivan, 229 N.C. 251, 49 S.E.2d 458 (1948); 4 Strong's N.C. Index 3d, Criminal Law § 29 (1976). The issue may be determined by the trial court with or without the aid of a jury. State v. Cooper, supra; State v. Propst, supra; State v. Sullivan, supra. When the trial judge conducts the inquiry without a jury, the court's findings of fact, if supported by competent evidence, are conclusive on appeal. State v. Cooper, supra; see State v. Thompson, supra.
Defendant assails the court's conclusion that he was capable of standing trial because at the hearing on the motion (1) the most recent expert medical evidence indicated the defendant was mentally incapable of standing trial and (2) uncontradicted medical evidence showed the defendant suffered from amnesia regarding the events of the crime.
The trial court's findings and conclusions as to the defendant's capacity to stand trial were supported by (1) defendant's score of 26 on the Competency Screening Test in November 1975, which was well within the range of competency to stand trial according to standards established by the National Institute of Mental Health; (2) Dr. James Groce's expert opinion that when he examined the defendant in November 1975, defendant was competent to stand trial; (3) the testimony of Sheriff Blalock, who observed the defendant in jail from the time of his arrest until trial (except for the periods he was at Dorothea Dix Hospital), which indicated that defendant was a normal prisoner and carried on normal conversations until recently when he started "rambling in his talk" after he had been placed with some prisoners from Central Prison.
Dr. Groce's examination of defendant preceded Dr. Royal's examination by some nine months. Dr. Groce admitted he could not agree or disagree with Dr. Royal's opinions because they were based on data and a time period unavailable to him, and further admitted that defendant's competency could have changed since his examination. We would be inclined to agree with the defendant that the test data and Dr. Groce's examination were too remote in time to support the trial court's conclusion on defendant's competency to stand trial in light of Dr. Royal's examination but for Sheriff Blalock's observation that defendant's personality changed only after he was placed with other prisoners.
The trial court could reasonably have believed from all the evidence that the defendant decided, after coming in contact with other prisoners, that it was to his advantage to feign the auditory hallucinations and delusions which led to Dr. Royal's *593 diagnosis of simple schizophrenia. It appears from the record that simple schizophrenia, combined with defendant's mild mental retardation and amnesia, were the basis for Dr. Royal's opinion that the defendant was incompetent to stand trial. Dr. Royal testified that schizophrenia, simple type, is a disease that comes on "insidiously or slowly so there is not an acute sudden onset." (Emphasis supplied.) By contrast, Sheriff Blalock's testimony disclosed a sudden change in the defendant's personality. Dr. Royal also admitted that it was possible for defendant to fake the hallucinations. Under these circumstances, we think Judge Walker's findings and conclusions are sufficiently supported by the evidence and therefore, are conclusive on appeal. State v. Cooper, supra.
Defendant's alleged amnesia concerning the events of the crime would not prevent him from comprehending his position and understanding the nature and object of the proceedings against him. Nor would his partial amnesia prevent him from conducting his defense in a rational manner or cooperating with his counsel in presenting any available defenses. Obviously if defendant is unable to recall the events of the crime, his available defenses may be limited. We do not believe this fact alone renders him incompetent to stand trial or denies him a fair trial in view of the fact that the State has the burden of proving beyond a reasonable doubt that the crime charged was committed and that the defendant was the perpetrator. The general rule in other jurisdictions, which we adopt, is that amnesia does not per se render a defendant incapable of standing trial or of receiving a fair trial. Annot., 46 A.L.R.3d 544, 553 (1972). See, e. g., State v. McClendon, 103 Ariz. 105, 437 P.2d 421 (1968); State v. Pugh, 117 N.J.Super. 26, 283 A.2d 537 (1971), cert. denied, 60 N.J. 22, 285 A.2d 563 (1972); Cummins v. Price, 421 Pa. 396, 218 A.2d 758, cert. denied, 385 U.S. 869, 87 S.Ct. 136, 17 L.Ed.2d 96 (1966). Partial amnesia places a defendant in no worse a position than the defendant who cannot remember where he was on a particular day because of the passage of time, or because he was insane, very intoxicated, completely drugged, or unconscious at the time. Cummins v. Price, supra. In each of these cases, the defendant's available defenses may be limited or impaired because of his present inability to reconstruct a past period of his life.
In deciding this same issue, the Arizona Supreme Court noted that, "amnesia `is nothing more than a failure of memory concerning facts or events to which an individual has been exposed' and that `every individual's memory process is marked by some distortion which may occur at any point' and `as a result, no one's memory is in fact complete, even under ideal conditions. . . every one is amnesic to some degree.' (Emphasis supplied.) 71 Yale Law J. 109-111 (1961-62)." State v. McClendon, supra, 103 Ariz. at 107, 437 P.2d at 423. The Pennsylvania Supreme Court, in considering the issue which now confronts us, pointed out that, "[i]f in fact the condition of amnesia is permanent, defendant's contention (1) would require Courts to hold that such amnesia will permanently, completely and absolutely negate all criminal responsibility and (2) will turn over the determination of crime and criminal liability to psychiatrists, whose opinions are usually based in large part upon defendant's self-serving statements, instead of to Courts and juries, and (3) will greatly jeopardize the safety and security of law-abiding citizens and render the protection of Society from crime and criminals far more difficult than ever before in modern history." (Emphasis in original.) Cummins v. Price, supra, 421 Pa. at 406, 218 A.2d at 763.
We find the reasoning of our sister courts persuasive on this issue. We note that nothing in the record suggests that this defendant's alleged amnesia was merely a temporary condition, a fact which might have influenced the court to delay the trial. State v. McClendon, supra. We have previously held on a related issue that amnesia is no defense to a criminal charge. State v. Bock, 288 N.C. 145, 217 S.E.2d 513 (1975); see State v. Caddell, 287 N.C. 266, 215 S.E.2d 348 (1975). The assignments of error *594 relating to defendant's mental capacity to stand trial are overruled.
In his next assignment of error, defendant maintains the trial court erred by excluding certain medical testimony as to the mental condition of the defendant. Defendant argues that because the burden of proving insanity to the satisfaction of the jury rests upon him, he should be allowed to introduce any evidence bearing on his mental condition. We disagree.
True, defendant has the burden of proving to the satisfaction of the jury that he was insane at the time the crime was committed. State v. Harris, 290 N.C. 718, 228 S.E.2d 424 (1976); State v. Hammonds, supra; State v. Caddell, supra. This burden, however, is to show that defendant was insane in a legal sense at the time of the crime. State v. Swink, 229 N.C. 123, 47 S.E.2d 852 (1948). The test of legal insanity asks whether, at the time the accused committed the act, he was laboring under such a defect of reason from disease of the mind as to be incapable of knowing the nature and quality of his act or, if he did know this, incapable of distinguishing between right and wrong in relation to such act. State v. Harris, supra; State v. Cooper, supra; State v. Swink, supra. It follows that a defendant who pleads insanity in bar to a criminal charge is only entitled to introduce evidence relevant to the issue of legal insanity.
Defendant complains that Dr. Royal was not allowed to testify at trial concerning his findings of schizophrenia, simple type, and alcohol pathological intoxication. Dr. Royal was permitted to give the following testimony:
"I am not able to state whether or not he [defendant] knew right from wrong at the time that the crime was committed. . .
"I am not able to state because the charged person indicated and has indicated consistently amnesia for the time of the alleged crime and so that is an area that we were unable to discuss. My thought is that he was operating under a psychotic condition and at times those people are able to determine right from wrong even when psychotic, but unless you interview the person at the time that they are in that condition that is impossible to say with certainty.
"A psychotic condition generally means a deranged mind within which a person has certain thought processes going on that are unrealistic."
Thus, it appears the doctor was allowed to state his opinion that the defendant was suffering from some type of psychosis at the time of the crime. The fact that the doctor was not permitted to place a label on the specific type of psychosis would not be reversible error. We also note that no proper foundation for the doctor's opinions as to simple schizophrenia and alcohol pathological intoxication was laid and thus the objections to this testimony were properly sustained. State v. Bock, supra. The doctor did state that he was unable to form an opinion as to whether the defendant knew right from wrong at the time of the crime, which was the relevant consideration. This assignment of error is overruled.
Defendant next challenges the constitutionality of the test for legal insanity in this State, the so-called "M'Naghten Rule." M'Naghten's Case, 10 Cl. & Fin. 200 (H.L.1843). Defendant concedes that our Court has on many occasions rejected this argument, see e. g., State v. Harris, supra, and that the only United States Supreme Court decision on point is contra to his position, Leland v. Oregon, 343 U.S. 790, 72 S.Ct. 1002, 96 L.Ed. 1302 (1952). Defendant nevertheless asks this Court to reconsider the issue. Suffice it to say, that we have adhered to the "right and wrong" [M'Naghten] test for many years and are not disposed to depart from it now. State v. Harris, supra; State v. Hammonds, supra; State v. Wetmore, 287 N.C. 344, 215 S.E.2d 51 (1975); State v. Cooper, supra. This assignment of error is overruled.
Lastly, defendant claims the court erred when it refused to grant defendant's motion to set aside the verdict as being against the greater weight of the evidence. *595 A motion to set aside the verdict as being contrary to the greater weight of the evidence is addressed to the discretion of the trial court and is not reviewable on appeal. State v. Vick, 287 N.C. 37, 213 S.E.2d 335 (1975); State v. Moore, 279 N.C. 455, 183 S.E.2d 546 (1971); State v. Mason, 279 N.C. 435, 183 S.E.2d 661 (1971). The assignment of error is without merit and overruled.
Due to the serious nature of the offenses charged, we have searched the record for errors other than those assigned and have found none.
In the trial we find
NO ERROR.
