Research report: Space–time interference in action

When you reach out to catch a ball, your brain must simultaneously judge where the object is and when it will arrive. A new study suggests these two judgments do not operate independently: distortions in one dimension leak into the other, even during active, goal-directed movements toward three-dimensional objects. The research, published in Cognitive Research: Principles and Implications, used immersive virtual reality to show that space–time interference, long documented in purely perceptual experiments, extends to the execution of ballistic reaching movements.

The study was motivated by a long-standing gap in the literature. Space–time interference has been reported repeatedly in perceptual paradigms: time feels longer in larger rooms, room size is judged larger when more time is spent inside, and judgments of travel time and traveled distance influence each other during navigation. Similar cross-dimensional biases appear with abstract two-dimensional shapes on a computer screen. Yet researchers frequently illustrate the importance of these mechanisms with action examples such as catching a ball or crossing a busy street, while most experiments measure only perceptual judgments. This discrepancy matters because perceptual biases do not always translate into altered motor behavior. A classic demonstration is the Ebbinghaus illusion: a circle perceived as smaller among large distracters does not reduce the width of a grasping hand.

Only a handful of studies have examined space–time interference in action-related contexts. One key precursor was a 2022 interception experiment in which participants watched three dots appear sequentially from left to right on a two-dimensional display and clicked a mouse at the time and location where an imagined fourth dot should appear. When the spatial interval between dots was larger, participants intercepted later, a space-on-time effect. When the temporal interval was longer, they intercepted further to the left, against the direction of motion, a negative time-on-space effect. But because that study used flat two-dimensional stimuli, its generalizability to real-world interaction with three-dimensional objects remained open. Work on grasping has shown that perceptual biases transfer more readily to motor behavior with two-dimensional than with three-dimensional stimuli.

To close this gap, the researchers adapted the interception paradigm for immersive virtual reality. Forty participants, recruited at the Technical University of Berlin with a mean age of about 27 years, wore an HTC Vive Pro Eye head-mounted display. In the pointing task, three yellow spheres appeared consecutively from left to right along an imaginary horizontal line. Participants then performed a ballistic reaching movement toward the location where, and at the moment when, an imaginary fourth sphere should have appeared, pressing a trigger button on the controller to log both timing and position. In a separate perceptual judgment task, four spheres appeared in sequence, and participants judged whether the final red sphere came too early or too late, or sat too far left or too far right. Spatial intervals of roughly 5, 10 and 15 centimeters and temporal intervals of 0.3, 0.9 and 1.5 seconds were systematically varied across trials.

The pointing task produced clear bidirectional interference. Participants overall reached too late and too far to the right relative to perfect performance, but the critical findings were the cross-dimensional effects. Larger spatial intervals between the spheres led participants to reach relatively later, replicating the positive space-on-time effect in a three-dimensional setting. Conversely, longer temporal intervals attenuated the rightward bias, shifting spatial predictions relatively leftward, matching the negative time-on-space effect seen previously with two-dimensional displays. Statistical modeling confirmed linear relationships for both effects, with no improvement from adding quadratic terms.

The perceptual judgment task told a partially different story. Participants showed a significant positive time-on-space effect: longer temporal intervals increased the frequency of judging the fourth sphere as too far right, implying an expectation of a more leftward position. However, the space-on-time effect did not reach statistical significance, despite a descriptive pattern in the same direction as the pointing task. An unexpected quadratic component emerged in both perceptual effects, suggesting that interference may weaken when the irrelevant spatial or temporal intervals become large, possibly because representational noise in encoding larger magnitudes reduces the influence of the other dimension.

The authors offer two related mechanistic accounts for the negative time-on-space effect. One invokes the tau effect, the classical finding that spatial distance judgments are stretched by longer temporal intervals, which has been linked to an assumption of constant velocity. If participants assumed the spheres moved at constant speed, longer temporal intervals would imply slower motion and therefore less spatial displacement, pulling the anticipated location leftward. The second account invokes representational momentum, the well-studied tendency to remember the final position of a moving object as displaced in the direction of motion. Because this forward displacement shrinks at lower implied speeds, longer temporal intervals would reduce the rightward momentum bias, producing a relative leftward shift rather than a genuine leftward distortion.

A striking dissociation emerged when the two tasks were compared directly. Individual interference effects in the perceptual and pointing tasks were not correlated, neither for the space-on-time effect nor for the time-on-space effect. This absence of correlation leaves open whether perceptual and motor-related space–time interference share a common underlying mechanism. The authors note that motor timing is thought to rely on partly distinct mechanisms from perceptual timing, and that converging evidence points to separate neuronal pathways for processing action-related versus action-unrelated information. Against this backdrop, the demonstration that space–time interference extends to reaching movements toward three-dimensional stimuli carries particular weight.

Several caveats frame the findings. All stimulus sequences moved from left to right, congruent with the learned writing and reading direction of the participant sample, a factor known to shape spatial-temporal associations and representational biases; future studies must test right-to-left sequences and culturally different populations. The paradigm also used explicit timing, with attention directed to the temporal intervals, whereas most real-world movements rely on implicit timing processed without focused attention. Moreover, the design did not allow a strict dissociation of perceptual and motor processes, since both tasks contained components of each. The authors suggest that because perceptual space–time interference has been observed from newborns to older adults, and may increase with age, similar amplification in motor behavior could affect everyday skills such as timing steps while crossing a street or avoiding obstacles while walking, potentially raising fall risk in older adults. As an initial demonstration in immersive virtual reality, the study establishes that cross-dimensional interference between space and time is not confined to the laboratory’s flat screens but reaches into the geometry of action itself.

Subject of Research: Space–time interference in perceptual judgments and goal-directed reaching movements in immersive virtual reality

Article Title: Space–time interference in action

Article References: Jagorska, C., Michel, M., & Riemer, M. (2026). Space–time interference in action. Cognitive Research: Principles and Implications, 11(1), Article 41. https://doi.org/10.1186/s41235-026-00745-7

Image Credits: AI Generated

DOI: 10.1186/s41235-026-00745-7

Keywords: space-time interference, virtual reality, reaching movements, time perception, spatial perception, motor control, representational momentum, kappa effect, tau effect, perception-action, psychophysics, 3D stimuli