its effect on the defendant’s right under the Confrontation Clause of the Sixth Amendment to cross-examine witnesses against him. The Florida court noted the “‘danger of distortion, delusion, or fantasy,’” as well as “‘the barriers which hypnosis raises to effective cross-examination.’” 471 So. 2d, at 18 (quoting People v. Gonzales, supra, at 627, 329 N. W. 2d, at 748). Furthermore, the court recognized the danger that, after undergoing hypnosis,
“the subject (1) will lose his critical judgment and begin to credit ‘memories’ that were formerly viewed as unreliable, (2) will confuse actual recall with confabulation and will be unable to distinguish between the two, and (3) will exhibit an unwarranted confidence in the validity of his ensuing recollection.” 471 So. 2d, at 17 (quoting People v. Shirley, supra, at 39, 641 P. 2d, at 787).
The Florida Supreme Court concluded, in a holding to which it gave only prospective effect, that “hypnotically refreshed testimony is per se inadmissible in a criminal trial in this state, but hypnosis does not render a witness incompetent to testify to those facts demonstrably recalled prior to hypnosis.” 471 So. 2d, at 18.
II
Since petitioner was convicted and sentenced to death after a trial in which the “crucial link” was supplied by a witness with extremely limited prehypnotic memory who had undergone two hypnotic sessions, the Florida Supreme Court should have overturned his conviction. Instead, the court somehow determined that Anderson’s testimony was refreshed under hypnosis as to only three details: the color of the football jersey the girl was wearing, the numbers on the jersey, and the fact that the man was wearing a pullover sweater and a shirt. Then, purporting to apply the “harmless-constitutional-error rule” of Schneble v. Florida, 405 U. S. 427 (1972), and Fahy v. Connecticut, 375 U. S. 85 (1963), the court concluded: “[Sjufficient evidence does exist, absent the tainted testimony, upon which the jury could have based its conviction of Bundy: There is no reasonable possibility that the tainted testimony complained of might have contributed to the conviction.” 471 So. 2d, at 19.
This review for harmless constitutional error is seriously flawed. First, the Florida court improperly based its enumeration of tainted testimony on Anderson’s own testimony at trial.