Title

Immediate and persisting effects of misleading questions and hypnosis on memory reports: An extension and replication

Date of Completion

January 2004

Keywords

Psychology, Clinical

Degree

Ph.D.

Abstract

Post-hypnotic testimony by witnesses is subject to a per se exclusion in approximately 2/3 of the US states. This ruling is based upon a lack of evidence that hypnosis promotes increases in accurate recall, and that it promotes confabulation and increased confidence in inaccurate recall. However, little work has been done comparing the effects of hypnosis with other memory distorting techniques. Scoboria, Mazzoni, Kirsch and Milling (2002) recently reported that misleading questions had a greater negative effect upon memory than did hypnosis. This paper extends the theoretical discussion of these issues, and presents a study designed to replicate and extend the previous findings. These extensions include use of a videotaped stimulus, examination of error sub-types, examination of “don't know” responses, and the application of signal detection methods to explore hypothesized mechanisms that misinformation results in decreased stimulus discrimination, whereas hypnosis results in shifts in response bias. Eighty three undergraduate students watched a videotape of a crime. Following a distractor period, half were hypnotized. Half were then asked misleading questions about the video, and half were asked objective questions. Hypnotized participants were inducted, and following a second distractor period all participants responded to objective questions. Finally, participants answered forced choice questions about the narrative for use in signal detection analyses. Results demonstrated strong immediate and persisting effects of misleading questions upon accuracy rates, and immediate effects of misleading information upon “don't know” responses. No overt effects of hypnosis were found. After recoding “don't know” responses, the three treatment groups had lower accuracy rates than the control group. Signal detection predictions were not upheld; marginally significant results of hypnosis and misinformation upon response bias were observed. Signal detection analyses did demonstrate a strong within subjects effect by which questioned material was discriminated less accurately than material not subjected to questioning. These findings demonstrate that misinformation produces a more overt effect upon memory than does hypnosis, but that hypnosis produces more subtle negative changes in the quality of recall. Implications for the per se exclusion of post-hypnotic testimony, as well as the use of questioning during interviews are discussed. ^