Dissociation theories have played an influential role in shaping contemporary thinking about hypnosis. The empirical roots of neodissociation theory can be traced to the hidden observer phenomenon by which a person registers and stores information in their memory, without being aware that the information had been processed. In a typical hidden observer study (see , highly hypnotizable subjects are able to recover concealed experiences or memories of pain during hypnotic suggestions for analgesia when they are informed that they possess a hidden part that can experience high levels of pain during analgesia and that this part can be contacted by the hypnotist with a prearranged cue.
Hidden observer studies and their interpretation have been controversial. For instance, Spanos and his associates (reviewed in have shown that hidden observer reports vary as a function of the instructions that subjects receive about the nature of the hidden observer. Whether the hidden observer reflects a true or pre-existing division of consciousness that is directly accessed by hypnotic suggestions or whether it is a product of suggestion continues to stimulate research and theoretical controversy. Accordingly, I am privileged to have the opportunity to guest edit this issue featuring Green, Page, Handley and Rasekhy's target article and incisive commentaries on it, which highlight sharp theoretical differences and issues that divide prominent researchers and theoreticians in the field of hypnosis.
Importantly, Green and his colleagues' study extends the hidden observer paradigm to a motor response. The authors contend that their research indicates that the phenomenon can be explained by the cues inherent in the hidden observer instructions. Kirsch (this issue) states that this and other 'flexible observer' studies leave the theory 'resting on pure speculation without an evidential base', while he concedes that showing that hidden observer reports vary with instructions does not disprove neodissociation theory. Although Naish (this issue) avers that a neodissociation explanation of the hidden observer is not parsimonious, he contends that hypnosis researchers should focus on cognitive mechanisms that bring about hypnotic experiences, and dispense with efforts to simply show that highly suggestible subjects, like role-playing subjects (i.e. simulators), 'do what they believe they are supposed to do'. The importance of hypnotic experience is echoed by Kallio and Revensuo (this issue), who opine that the most serious problem with the hidden observer phenomenon is that it is 'in conflict with most current models of consciousness arising from psychology and cognitive neuroscience'. In a thoroughgoing methodological critique of Green et al., Kihlstrom and Barnier (this issue) argue that evidence that covert reports are influenced by suggestion wording does not detract from the fact that 'the hidden observer is nothing more than a technique for revealing that, despite the subject's phenomenal experience, the "actual stimulus state of affairs" is processed by the subject -albeit subconsciously'. Woody and Sadler's (this issue) commentary underlines the need for researchers to carefully distinguish between Hilgard's neodissociation theory, and another version of dissociation theory -dissociated 121