Left and right-handed people are watching pantomimes and making up words in the latest Marsden-funded work by the University of Auckland’s Emeritus Professor Michael Corballis. While the study participants are thinking about gestures and language, the research team is watching their brains. Professor Corballis explains why this may help us understand how talking in humans first began.
Do you expect to see any difference between left and right-handed people?
There is very little evidence for systematic differences, although some large-scale studies suggest slight deficits in academic skills (reading, mathematics, memory) in mixed-handers relative to both left- and right-handers. Some studies suggest greater creativity in left or mixed handers, but this is slight, and may be due to nonright-handers being in a minority rather than any difference in brain structure. However nonright-handers are more variable in brain structure than right-handers are, and this variability may mask systematic differences.
Why do you think left-handed people have been given such a hard time?
Historically there has been discrimination against left-handers simply because they are in the minority. Also, many customs and implements favour the right hand, so left-handers may be seen as clumsy or antisocial. For instance scissors are made for use in the right hand, and even simple things like door knobs are placed for the convenience of right-handers. Many societies still have sanctions against eating or writing with the left hand, so left-handers are seen as awkward. There was something of a counter-movement following discoveries in the 1960s that the right brain was dominant for some nonverbal activities, such as spatial awareness of music. Since the right brain controls the left hand, this led to suggestions that left-handers may be more creative. This is flawed logic, because most left-handers show the same brain asymmetries that right-handers do.
Do animals show a predominance towards right-handedness the same way people do?
Great apes show a slight preference for the right hand, but the prevalence is only about 67 percent, compared to around 90 percent in humans. Handedness in humans is probably more obvious than in other animals because humans are bipedal, and therefore use their hands for many more activities than other animals do. Humans have also developed complex manual skills (throwing, writing, tool use, even gesturing) which may have favoured specialisation of the hands.
How can watching brain activity tell us about the origins of language?
We (and other researchers) are finding evidence that the brain areas controlling intentional manual actions, including pantomime and even simple acts like reaching or using a comb, overlap those controlling speech. The corresponding areas in the primate brain also have to do with manual actions, but have virtually no role in the control of vocalisation. Watching brain activity in people using sign language also shows that the same brain areas are involved. And yes, chimps, bonobos, and gorillas come much closer to communicating in language-like ways with gesture than they do by vocalising.
What else do you talk about in your new book?
The book is called The Wandering Mind, and deals primarily with the ability of the mind to escape from the present, and travel mentally into past and future, and into the minds of other people (real or imaginary). The ability of the mind to wander not only allows us to examine our past lives and make future plans, but also allows us to create stories, whether in the form of folk tales, novels, plays, or TV soaps. Creativity seems to depend on activity in a widely dispersed brain network (known as the default-mode network), and not on a single side of the brain, left or right.
Michael Corballis’s new book, The Wandering Mind: What the Brain Does When You’re Not Looking is now available in book stores.
These interviews showcase researchers supported by the Marsden Fund which, since 1994, has been supporting fundamental, investigator-led research in New Zealand.