Hand/foot - .36
Foot/ear - .36
Foot/eye - .35
Hand/eye - .34
Hand/ear - .26
Eye/ear - .26

To show how confusing this can be when designing to accommodate users' performance and preferences, consider the results of the following study on hearing. In this study, all participants were right-handed. Most participants (86%) exhibited the best listening performance using the right ear. Also, most subjects (71%) preferred listening with their right ear, some with their left ear (17%), and a few had no preference (12%). However, when their hearing loss was measured using an audiometer, about two-thirds of the subjects heard best with their left ear (least hearing loss), while only 15% heard best with their right ear, and 18% showed no differences between ears (Reib and Reib, 1998).

In most systems, simple tasks that require little or no specialized training or practice tend to be carried out equally well by either hand (e.g., reaching for objects). In certain highly skilled activities, where both hands may receive an equal amount of training and practice, both sides can achieve close to the same high level of proficiency (e.g., typewriting and piano playing). It is in activities where there is an advantage for one hand or the other to achieve a high level of competence, that one side tends to be used more consistently than the other (e.g., eating, handwriting, playing the violin or cello).

Some past studies of handedness found a higher incidence of right-handedness in females, and in older people. Recent studies report no differences due to gender or age. The incidence of right-handedness in children is as follows:

Both parents are right-handed - 91%
One parent is right and one is left - 81%
Both parents are left-handed - 74%

Designers should be aware that there is a strong cultural bias in favor of using the right hand in many countries. For example, the incidence of left-handedness in writing is less than 1% in China and Japan. One study reported that in Japan the following percentages of children used the left hand for writing:

1st grade - 5.1% of boys and 2.9% of girls
8th grade - 0.2% of boys and 0% of girls

Another factor that could affect the design of systems relates to using the "right vs. left brain." Most true right-handers (up to 99%) show strong lateralization of speech representation by having speech represented in the left cerebral hemisphere. However, left-handers are more likely to exhibit a bilateral representation of speech. Only about 70% of left-handers have speech represented in the left cerebral hemisphere.

 

References

Corballis, M.C., The genetics and evolution of handedness, Psychological Review, 104 (4), 714-727 (1997).

Morgan, M.J. and Corballis, M.C., On the biological basis of human laterality: II. The mechanisms of inheritance, The Behavioral and Brain Sciences, 2, 270-276. (1978).

Porac, C. and Coren, S., The growth and inheritance of laterality, The Behavioral and Brain Sciences, 2, 311-313 (1978).

Porac, C., Coren, S., Steiger, J.H. and Duncan, P., Human laterality: A multidimensional approach, Canadian Journal of Psychology, 34(1), 91-96 (1980).

Provins, K.A., Handedness and speech: A critical reapparisal of the role of genetic and environmental factors in the cerebral lateralization of function, Psychological Review, 104 (3) 554-571 (1997).

Reib, M. and Reib, G., Ear preference: Association with other functional asymmetries of the ears, Perceptual and Motor Skills, 86, 399-402 (1998).