During the approximate 150 years of handedness research, most scientists have concentrated on biological mechanisms to explain why people prefer to use one hand, usually the right hand, for one-handed tasks. However, there are a few researchers, and I am one, who are interested in life experience events that can influence the use of one hand over the other. My interest in this issue started when I was contacted by lawyer specializing in personal injury when I was a faculty member at the University of Victoria in Victoria, British Columbia, Canada. He told me about his client who had injured his preferred right hand in a water skiing accident resulting in a permanent disability. The lawyer asked me if it was possible to switch hand use to the non-preferred hand. If such a switch was impossible, the lawyer wanted to claim a large financial settlement for his client based on the fact of an irreversible catastrophic injury. I told him that, sadly, I could not answer his question. At that time there were no scientific studies exploring the issue of whether or not a person could switch handedness after a disabling injury.
This phone conversation prompted me to contact a group of physiotherapists in Victoria who specialized in treating patients with hand injuries. They confirmed the lack of data on the results of preferred to non-preferred hand switches among hand injury patients. With their help, I contacted close to 500 former patients who had been treated in their clinic for temporary hand injuries. My sample included both right- and left-handers and individuals with preferred and non-preferred hand injuries. The average length of the injury recovery period was around 6 months.
I found that individuals with preferred hand injuries switched their hand use to the non-preferred hand during the injury recovery period. When the recovery was complete, they resumed one-handed activities with their preferred hand. This pattern was the same for pre-injury right- and left-handers. However, post-injury hand use was affected by the switch demands of the injury recovery period. The requirements of switching hand use during a hand injury recovery caused a slight shift in overall hand use toward the non-preferred hand. Practice using the non-preferred hand over several months had a permanent effect on hand use.
Researchers interested in experience effects on hand preference propose 3 possible results when life events require that a person use the non-preferred hand. First, there is a complete switch of all activities from the preferred to the non-preferred hand. Second, some activities shift to the non-preferred hand while other activities remain with the preferred hand. Third, there is a general increase in the performance proficiency of the non-preferred hand. In other words, a person becomes more ambi-handed and less reliant on the complete use of the preferred hand after recovery from the injury. My study supports the third explanation. After months of forced use of the non-preferred hand, people with preferred hand injuries become slightly more ambi-handed when the post-injury handedness scores are compared to those scores seen pre-injury.
Cursive handwriting is one of the most difficult activities to switch to the non-preferred hand after a permanent disability of the preferred writing hand. A group of therapists have developed a program to train individuals with preferred hand amputations or permanent disabilities to write cursively with the non-preferred hand. The program is called Handwriting for heroes. It is intense and takes weeks of daily practice. However, the developers of the program claim successful switches of cursive writing to the non-preferred hand. This is a significant result for people who want to preserve the individuality of their personal signature despite their preferred hand disability. (Heroes)Laboratory research where participants practice writing with the non-preferred hand confirms that the quality of handwriting improves with this practice even without the motivation provided by a serious preferred hand disability.