Intermanual transfer of practice decrements with a haptic illusion

Sixteen subjects were given 8 pre-practice, 80 practice, and 8 post-practice trials with the inverted T illusion figure. Judgements were made haptically with one hand being used on pre- and post-practice trials and the other hand on practice trials. Mean illusion diminshed in magnitude over the practice trials. Inter-manual transfer of the practice decrement was found, but it was partial rather than complete. The illusion after practice was less than before practice, but it was greater than the error found on the last block of practice trials. The bearing of these results on the different theories of illusions is considered.