Effect of gravity on temporal properties and target selection in vertical pointing movements: a comparison between objective and subjective measures.

This study investigated how gravity affects upper limb movements and the perception of them by evaluating and comparing objectively measured temporal properties of vertical pointing movements with subjectively perceived ones. Sixteen participants performed vertical pointing movements toward upward or downward targets at various distances (simple movement task). Subsequently, participants judged and chose which target could be reached temporally earlier, rather than at a higher movement speed, from upward and downward targets presented simultaneously at various combinations of distances by responding via pointing movements (choice movement task) or by pressing a button without pointing (choice reaction task). The results of the simple movement task showed that the movement times were longer for pointing toward downward targets than those toward upward targets when those distances were equal. In contrast, in both the choice movement and choice reaction tasks under the target conditions with the equivalent distances, participants were likely to judge the downward target as being reachable earlier than the upward one. These findings suggest a discrepancy between the objectively observed effects of gravity on pointing movements and subjectively estimated effects of gravity.