Effects of hypnotic induction and hypnotic depth on phonemic fluency: A test of the frontal inhibition account of hypnosis

According to the frontal inhibition account of hypnosis, many of the phenomena traditionally associated with hypnosis, such as the suspension of reality testing and loss of planning functions, come about because hypnosis produces decrements in frontal lobe performance. In line with this view, previous studies investigating the frontal inhibition account of hypnosis have found that phonemic fluency performance declines with hypnotic induction, but only for high hypnotizables. However, these studies were limited by their use of small restricted samples and suggestion based measures of hypnotizability. The aim of the present study was to attempt to investigate this effect using a sample which included a full range of hypnotizability, and dividing the phonemic fluency task into its frontal (switches) and temporal (cluster size) components. In addition, depth reports were used to assess the influence of hypnotic induction instead of suggestion based measures of hypnotizability. Results showed that overall, hypnosis had a negative effect on frontal aspects of the fluency task, and a positive effect on temporal aspects of the task; however, whilst the resulting changes partly differentiated those of medium depth from the other groups, they did not differentiate between subjects of high and low hypnotic depth. High hypnotic depth, however, was related to better phonemic fluency performance in the nonhypnotic condition. An explanation in terms of divided attention is proposed, the importance of adequate sampling in neuropsychological studies of hypnosis emphasized, and problems for the frontal inhibition account of hypnosis are identified.