Hypnosis and Synesthesia
New Scientist ran a recent review article by David Robson that might be of interest to those exploring the nature of hypnosis. It is on the experimental investigation of synesthesia effects using hypnosis. Feb 14-20 2009 issue. Research is reviewed narrowing down the genetic origin of synesthesia, but then research is also reviewed showing that similar sensory cross-over effects can be reproduced with suggestion. The percentage of people who showed a particular cross-over effect under the hypnosis condition was roughly the same as that of people diagnosed with synesthesia, and significantly different from non-hypnosis controls.
This is interesting but not neccessarily something all that new. It doesn't say as much about the nature of hypnosis as a different state of consciousness as Robson's article seems to assume because it is also suspected that synesthesia effects are actually fairly common, and that the diagnostic criteria reveal a matter of degree more than kind. So as in T.X. Barber's famous line of "non-trance" experiments, suggestion rather than hypnosis per se could well be what brings out the cross-over effects. Missing from the hypnosis synesthesia experiment seems to be a non-trance task-motivated or expectancy control, their controls were simply "asked to imagine." The difference between being "asked to imagine" and being motivated or expectant to see results is very different, and this was one of Barber's central contributions to hypnosis research.
On the incidence of synesthesia effects, also see Alison Motluk's article from New Scientist last year: "Do we all have some synaesthetic ability?"
Synesthesia and suggestion both turn out to be fascinating windows into the mind!