Advanced information about target location facilitates movement planning: More evidence using a deadline procedure on movement time

It was recently shown that in a multiple choice aiming task the knowledge of the target location prior to stimulus introduction, even though the trajectory to follow was still uncertain, facilitated movement planning and execution (Girouard et al. 1987). In that particular study, the subjects had, in the first condition, knowledge about the target location prior to the stimulus presentation. In that condition, they started their movements in the direction indicated by one of four possible stimuli. However, they always ended their movements on the same target (single-target condition). In a second condition, there was always a one-to-one mapping between the stimuli and the targets (multiple-target condition). The facilitating effects of knowing target location were found for both the movement planning time or reaction time (RT) and movement time (MT). A possible explanation of the latter effect was that the subjects, somewhere along the movement path, made a check to see if their movement was carried out as expected and corrected it accordingly. The purpose of the present experiment was to see if knowing the target to reach before the stimulus presentation, even though the trajectory to follow is uncertain, could override the well-known effect of stimulus-response uncertainty on RT (Hick 1952) when the possibility of making a check during MT was reduced. To reach that goal the methodology used by Girouard et al. (1987) was modified by limiting the time permitted to execute the required response. The effect of this manipulation was that it almost tripled the target location effect on RT found in the previous study. Furthermore, the significant effect found on MT disappeared for the single-target condition whilst it remained significant for the multiple-target condition. Different interpretations are offered to take into account the latter result.