Evidence for a hybrid model in moving target interception

When walking to intercept a moving target, people take an interception path that appears to anticipate the target’s trajectory. However, existing literature offers conflicting accounts of whether interception paths are guided by an internal model of the target’s motion (model-based control) or guided only by immediately available visual information (online control). To address this, we asked 18 participants (7 female, 11 male; 19.8 +/- 1.18 years of age) to intercept a moving target that could randomly move along one of two predefined paths (linear or zigzag) and appear under one of three visibility settings (fully visible, initially visible but then disappearing, or disappearing and then reappearing) in an immersive virtual environment. On half of the trials, participants were asked to start walking towards the target before it started to move (walk-first), as opposed to observing the moving target before starting to walk (observe-first). For targets moving on the linear path, and consistent with model-based control, participants achieved an interception rate of 100%, 96%, and 86% on visible, reappearing, and disappearing trials, respectively. On the other hand, interception rates for the zigzag path were more consistent with online control: 97% on the visible setting, but dropping to 69% on reappearing and to 15% on disappearing trials. Although the observe-first condition did not lead to better interception rates, it made walking trajectories more linear, in contrast to curved trajectories in the walk-first condition consistent with previous literature. In a post-session questionnaire, 15 of 18 participants indicated that they thought they knew where the target was going when it disappeared, eight of which tried to actively predict the target’s trajectory during interception. Overall, these results support a hybrid model of moving target interception, where participants are able to switch between model-based and online control based on experimental conditions.