Objects in the real world frequently move along complex, non-linear trajectories shaped by their environment. As they do, they often pass temporarily out of sight, occluded by the surrounding environment. Yet humans can maintain representations of object position and motion even when objects are no longer visible. Here, we investigate the neural basis of tracking objects undergoing non-linear, environmentally constrained motion during occlusion. We recorded EEG while participants mentally tracked the position of a ball falling through differently curved pipes (Pipe condition). The pipe condition was compared to conditions in which only the ball trajectory was visible (Ball-only condition) or in which the pipe was completely covered by an occluder (Occluder condition). On occasional probe trials, the video was terminated at randomized time points and participants had to indicate the ball's last position using the mouse cursor. Behaviorally, participants systematically reported the ball ahead of its true position, with the strongest forward displacement in the occluded conditions. Neurally, multivariate decoding analysis on the EEG data revealed that alpha-band activity carried direction-specific motion information within and across conditions. Critically, cross-condition decoding revealed shared representations between perceived (Ball-only) and mentally tracked (Occluder) motion with representations in the occluder condition anticipating later representations in the ball-only condition. Together, our behavioral and neural findings provide convergent evidence that during non-linear motion tracking under occlusion, the brain codes object motion ahead of its current position, an 'ahead of time' strategy that may underlie temporal precision when tracking objects in a dynamically changing world.
Ajith, S., Kamis, F. P., Dobs, K., Yeh, L.-C., Kaiser, D.
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