Spatial distortion in chronic pain

Lorimer Moseley has nicely shown us that some people with complex chronic pain problems develop some form of somesthetic distortion, where the spatial characteristics of the painful body part are felt to be missing or sized out of proportion to what they actually are.  So far he's shown this in chronic low back pain and complex regional pain syndrome.  I suspect for those of you reading this post, this is no longer novel to you.

Today I had a chance to listen to a presentation from a driving therapist.  I didn't even know such a discipline exists before this morning.  A driving therapist, at least as far as my very limited knowledge on the subject goes, helps people deal with the anxiety associated with driving after having gone through a motor vehicle accident.  One of the things this guy talked about really struck me as interesting, in light of Lorimer's findings described above.  He mentioned that one of the common triggers of driving anxiety seems to be what amounts essentially to a form of dysmetria (although he didn't use the term).  The example he used was that he would ask his clients to drive up behind a parked car and stop as close to one car length away from the car as they could.  According to this fella, most people are reasonably able to approximate one car length in this exercise.  His clients, highly anxious in terms of driving and most with long term chronic pain problems as a result of the accident, tend to leave anywhere from 2 to 3 actual car lengths.  This despite clients expressing confidence that they were in fact 1 car length back.  In other words, the distortion in distance perception didn't seem to be due to anxiety involved in getting closer.  He says the problem is compouned further when he is driving the car with the client in the passenger seat, and backs up to the parked car from in front of it.  In this case, clients are telling him to stop on average 4 to 5 car lengths away.

This is once again little more than throwing ideas around here, but this story got me thinking that perhaps there is a broader problem of person-environment spatial distortion in some people with complex chronic pain problems, perhaps amplified by co-morbid severe emotional distress.  In fact, maybe this isn't restricted to spatial distortion.  I'm now left to wonder, and am already designing the study in my head, what would happen if we asked a sample of people with complex chronic pain problems to estimate lengths and weights of different objects.  I know from my visit to his lab last fall that Mick Sullivan has a protocol for looking at something very similar, using paint cans of varying weights.  In this case, all items (paint cans) look identical and the weight can't be determined from just looking at them.  I would like to see what would happen if the same type of protocol was run using common everyday objects, the weights of which most people should know.

Would love to hear your comments on this.