Participants were administered a standard tape-recorded version of the Harvard Group Scale of Hypnotic Susceptibility, Form A (HGSHS:A) and then a modified version of the HGSHS:A response booklet that asked each participant to report which suggested behaviors they performed during the procedures. These response booklets were altered to include 3 additional suggestions not offered during the hypnotic procedures. Half the participants were administered the questions in the response booklet in the standard format ("I performed the suggested behavior" versus "I did not perform the suggested behavior"). The remaining participants were offered a third alternative to each question ("I do not remember this occurring"). As predicted, participants offered the 3rd alternative were significantly less likely to report performing actions that were never suggested during the procedures. Further, these participants reported performing fewer suggested behaviors (i.e., reported passing fewer of the true Harvard items) than participants in the standard 2-alternative condition.
Int J Clin Exp Hypn. 2008 Apr;56(2):198-213. Eisen ML, Oustinovskaya M, Kistorian R, Morgan DY, Mickes L. California State University, Los Angeles, California, USA.