This experiment shows that providing spatial contextual cues can help participants intercept accelerating targets: Participants hit more targets when the rolling wheel that the target was mounted on was visible than when it was invisible (
Figure 2). This finding fits with the idea that goal-directed movements use visual attributes that are relevant for the task (
de la Malla et al., 2019;
Smeets et al., 2002). Specifically, the visible wheel helped participants predict the target's accelerations, thus providing helpful information about the target's motion to facilitate interception. This finding adds to the growing body of evidence against a strict functional segregation between visual pathways for perception and action (
Medendorp, de Brouwer, & Smeets, 2018;
Schenk & McIntosh, 2009): Providing a spatial contextual cue improved interception despite the same real-time egocentric information about the target being available to participants in the two conditions.
Even when the wheel was invisible, participants compensated for some of the acceleration of the target (red dots in
Figure 3 are not centered around the yellow line but biased toward the purple curve). How did they do this? People can visually judge acceleration to some extent (
Benguigui et al., 2003;
Brouwer et al., 2002;
Watamaniuk & Heinen, 2003), so maybe what we observe is the result of relying on such information. They might also recognize regularities in the target's motion and use this to guide their movements (
de Rugy et al., 2012;
Diaz et al., 2013;
Fiahlo & Tresilian, 2017;
Mann et al., 2019;
Zago et al., 2009). It is evident that part of the apparent consideration of acceleration is the result of correcting for earlier errors (
Brenner et al., 2023), because participants performed better if they consistently hit the target at the same phase (
Figure 4B). The consequence of doing so is that the target is accelerating in the same direction just before the hit, so that compensating for the error on the next trial reduces the error on that trial (
Brenner et al., 2016;
Brenner et al., 2023). This benefit was particularly evident in the invisible wheel condition, presumably because participants did not have the spatial contextual cues to help them predict the target's acceleration.
Since the precision of interception is better for slower targets, because any timing errors matter less when the velocity is low (
Brouwer et al., 2000), one might expect participants to use a low-velocity strategy, whereby they aim at a position where the target moves slowly (i.e., when it is close to the surface). This strategy would also lead to participants consistently hitting the target in its same rotational phase. To check whether the advantage of a constant-phase strategy was only a consequence of participants aiming to hit the target at its lowest velocity, we also looked at the relationship between the fraction of targets hit and the deviation from the target's lowest velocity. This relationship was not significant in either condition (
Figure 4C), in contrast to the correlation between performance and the consistency in phase. Indeed, several participants who were quite successful were consistent in the phase of the target at the time of the tap but intercepted the target when it was close to its highest velocity (the participant of the middle panel of
Figure 4A is one of them; this participant is indicated by the central thick line in
Figure 4B and the rightmost thick line in
Figure 4C). So, the advantage of using a constant phase is not simply the consequence of using a low-velocity strategy.
Spatial contextual cues improve interception performance by helping participants predict the complicated accelerations and decelerations of the target. In addition, participants who consistently hit the target at the same phase of its rotational movement hit more targets, presumably because it allowed them to use their errors on previous trials to adjust their movement. We conclude that goal-directed movements use any visual information that is relevant for the task and can be judged well enough to be useful.