Dexterous workspace of human two- and three-fingered precision manipulation

Precision manipulation, in which an object held between the fingertips is translated and/or rotated with respect to the hand without sliding, is used frequently in everyday tasks such as writing, yet few studies have examined the experimental precision manipulation workspace of the human hand. This study evaluates the range of positions over which 19 participants manipulated a moderately sized (3.3-4.1cm diameter) object using either the thumb and index finger (2 finger condition) or the thumb, index and middle fingers (3 finger condition). The results show that the 2-fingered workspace is on average 40 % larger than the 3-fingered workspace (p <; 0.001, likely due to added kinematic constraints from an additional finger. Representative precision manipulation workspaces for a median 17.5cm length hand are shown from multiple views to clearly illustrate the overall workspace shape, while the general relationship between hand length and workspace volume is evaluated. This view of the human precision manipulation workspace has various applications, ranging from motivating the design of effective, comfortable haptic interfaces to benchmarking the performance of robotic and prosthetic hands.