The development of end- and beginning-state comfort in a cup manipulation task.

End-state comfort (ESC) is the tendency to assume comfortable postures at the end of simple object manipulation rather than at the start; and therefore has been used to assess the behavioral effects of motor planning. Adult-like patterns have been observed at age 9. Observations can extend to joint-action, such that adults consider the beginning-state comfort (BSC) of another, without sacrificing ESC; however, trends in children have yet to be delineated. This study investigated the development of ESC and BSC in a cup manipulation task. Three to 12-year-olds and adults were asked to pick up a cup and (1) pour a glass of water or (2) pass it to the researcher to pour. Paralleling previous findings, adult-like patterns of ESC were observed at age 9. Adding to the literature, adult-like evidence of BSC emerged at the age of 7. Therefore, 7-year-olds consider another's BSC; however, cannot facilitate ESC until age 9.