ARE AGE TRENDS IN ADULT HAND PREFERENCE BEST EXPLAINED BY DEVELOPMENTAL SHIFTS OR GENERATIONAL-DIFFERENCES

Hand use in the performance of six everyday activities was analyzed as a function of age in a sample of 654 adults. An unskilled grasping ta sk showed the largest shift toward consistent right-handedness as a fu nction of age; skilled manipulation tasks, such as writing, exhibited weaker age-related trends. Analysis of individual preference patterns showed decreases in mixed right hand use (defined as a right-hander wh o occasionally uses the left hand) and increases in consistent right h and use in older adults. There was also a weaker age-related reduction in mixed left hand use but the numbers of consistent left-handers rem ained a small, constant percentage of the sample across all age groups . These results are congruent with the predictions of two developmenta l hypotheses offered to explain trends in adult hand preference. These are, first, a postulated age trend toward hand preference consistency and, second, a practice effect related to an environment arranged to favor right hand use.