ABSTRACT
Performance of a discrete 2D aiming task under transformed visual-motor mappings (rotations of 45 deg, 90 deg, 135 deg, and 180 deg, and reflections about the horizontal, vertical, and oblique midlines) exhibits target axis effects. That is, the magnitude of aiming error varies with the axis in 2D space on which the aiming target lies. In our experiments, eight aiming targets corresponded to four target axes: horizontal (right, left), vertical (up, down), right oblique (up-right, down-left), and left oblique (up-left, downright). Observed target axis effects are of two varieties. The first is higher aiming error along the left oblique axis than along the right oblique, observed previously under nontransformed mappings and tentatively attributed to biomechanical factors (Keele, 1968). Our transformation paradigm allows examination of biomechanical and other “motor” factors independently of vision, cognition, and other “non-motor” factors, by decoupling the motor (manual input device) and non-motor (display feedback) representations of the axes. The second variety of target axis effects are reflection-specific effects observed here for the first time. We characterize reflection-specific target axis effects in terms of a vector sum process (Cunningham and Vardi, in press) that interacts with the formal properties of reflections so as to produce qualitatively different behavior along different target axes.
