Conflicting sources of spatial information in a distance-reproduction task

Previous research has shown that the reproduction of a criterion distance is biased towards previously coded endpoints. The purpose of this research was to illustrate that, in addition to the retention of endpoint information, the presence of conflicting sources of spatial information within a trial causes systematic response biases in distance reproduction. Three experiments were conducted in which participants performed rapid aiming movements on a digitising tablet that translated to movement of a cursor on a computer monitor. The required movement amplitude in all three experiments was 20 cm. In experiment 1, the location of the home and target positions on the monitor was fixed, but the initial position of the hand was varied randomly from trial to trial. In experiment 2, the change in position of the limb was matched by a corresponding change in the location of the monitor display. In experiment 3, the initial position of the limb was fixed, but the location of the display on the monitor varied from trial to trial. The results of experiments 1 and 2 showed that error varied as a function of the initial position of the limb. However, this effect was greater in experiment 1, where the mapping between the location of the monitor display and limb position varied from trial to trial. There was also an effect of varying the location of the monitor display in experiment 3, but this was smaller than varying initial limb position in experiment 1. These findings suggest that both the retrieval of previously specified endpoints and conflicts in the coding of spatial information contributed to the observed response biases in distance reproduction.