SUSAN L. AMATO-HENDERSON. Effects of misinformation on the concealed knowledge test. August 1996. Report No. DoDPI97-R- 0001. Department of Defense Polygraph Institute, Ft. McClellan, AL 36205.
Misinformation effects occur reliably in laboratory settings despite disagreement over the mechanism(s) responsible for such effects. Both memory impairment hypotheses (e.g., Lindsay & Johnson, 1987; Loftus 1975, 1977, 1979; Loftus & Hoffman, 1989; Tversky & Tuchin, 1989) and non-impairment hypotheses (e.g., McCloskey & Zaragoza, 1985; Zaragoza, McCloskey, & Jamis, 1987) have been used to explain the phenomenon of misinformation. The present study examined the effects of misinformation on the Concealed Knowledge Test (CKT), a psychophysiological detection of deception technique. Furthermore, the psychophysiological measurements were used to elucidate the controversy surrounding the misinformation effect. Ninety-six subjects watched a videotaped crime used to induce guilt. One week later, subjects were given misinformation about three details of the crime, took a CKT inquiring about the three misled details and three non-misled details of the crime, and took a 20-item recognition memory test concerning the crime. The six details questioned during the CKT were also included in the memory test. Subjects who chose the misinformation on a misled detail were labeled as successfully misinformed regarding that detail. Significant differences in the Lykken (1959) method of scoring the CKT were found between the misled and non-misled CKT series, with misinformation leading to a lower score (i.e., higher probability of being categorized as truthful). A MANOVA demonstrated a significant interaction [Wilks F(18, 3946) = 5.36, p = .000] between type of detail on the CKT (key, misinformation, foil) and information manipulation (non-misled, unsuccessfully misled, and successfully misled) with univariate procedures identifying skin resistance amplitude, skin resistance half- recovery time, and abdominal respiration as significant dependent measures. Follow-up analyses demonstrated that on successfully misled CKT charts, subjects' responses to the misinformation were significantly stronger than were responses to both the original detail and neutral foils (which did not differ). These findings, supportive of memory impairment hypotheses, are discussed in terms of the (un)permanence of memory.
Key-words: forensic psychophysiology, concealed knowledge test, psychophysiological detection of deception, misinformation effect, memory impairment
This project was partially funded as a Department of Defense Polygraph Institute Dissertation Research Grant to the University of North Dakota. There are numerous reports in the literature concerning the validity of psychophysiological detection of deception (PDD) examinations. Very few reports, however, address a psychological manipulation beyond those necessary to manipulate and determine examinee veracity. This study is unusual because it was designed to test theories of forgetting using a PDD paradigm. The project is among the first in the PDD discipline designed to investigate the effect of presenting false information to examinees prior to a PDD examination.
An infrequently used examination format, the concealed knowledge test (i.e., commonly called a guilty knowledge test) was employed, possibly reducing the generalizability of the results. The data, although exploratory and preliminary in nature, clearly suggest that presentation of false information can influence the magnitude of physiological responses recorded during a PDD examination. Further research should be completed to further examine this phenomenon.