Spatial accuracy demand in aiming movements: kinematic analysis of subtended angle and tolerance width

Subtended angle has been assumed to be an important factor in both response programming time and kinematic characteristics of aiming movements. Support for this assumption has come mainly from studies in which circular targets have been used. However, with circular targets, the subtended angle covaries with the size of the target in the principal direction of the movement (tolerance width). The purpose of this study was to examine the effects of tolerance width and subtended angle on aiming movement with multiple targets. Participants first hit a 5-cm-diameter circular target located 8 cm to the left of a starting position and then moved another 8 cm left to hit either a 5-cm diameter circular target or a 5- x 1-cm rectangular target oriented either horizontally or vertically, depending on the condition. Analysis showed that reaction times and movement times were longer for the vertical rectangular target, which had a smaller tolerance width than the other two targets. In addition, the vertical rectangular target also showed a greater percentage of secondary-submovement trials, lower movement velocity, and higher peak vertical displacement. Overall, the results indicate that the tolerance width of the target may impose more constraints on aiming movements than subtended angle.