A distance effect in a manual aiming task to remembered targets: a test ofthree hypotheses

It has been noted that manual aiming error and variability when pointing to remembered targets increase as a function of target eccentricity. In the p resent study we evaluated which one of three hypotheses (target localizatio n, motor, or movement duration) best explains this 'distance effect'. In ex periment 1, older and younger participants aimed with their unseen hand at the remembered location of targets distributed between 129 and 309 mm from the starting base. Target presentation time was of either 50 or 500 ms and aiming movements could be initiated following either a 100- or a 10,000-ms recall delay. Participants had either no constraints concerning movement ti me or were asked to reach the near target in a longer movement time than th e farther targets. The results revealed a significant distance effect when no time constraints were imposed but showed a significantly reversed distan ce effect when the instructions were to reach the near targets in a longer movement time than the far targets. The same results were obtained regardle ss of target presentation time, recall delay, or age of the participants. T hese results supported a movement duration interpretation of the distance e ffect. In experiment 2, a distance effect was replicated when pointing with one's unseen hand toward a remembered target but did not take place when p ointing to visible targets. Taken together these results suggest that prolo nged movement execution interferes with the stored egocentric target repres entation.