Cross-dimensional interference between time and distance during spatial navigation is mediated by speed representations in intraparietal sulcus and area hMT.

When navigating a straight path, perceived travel time and perceived traveled distance are linked via movement speed. Behavioral studies have revealed systematic interferences between the perception of travel time and distance, but the role of neuronal representations of movement speed for these effects has not been addressed to date. Using a combined fMRI-behavioral paradigm, we investigate the neuronal representations that underlie cross-dimensional interferences between travel time and traveled distance. Participants underwent fMRI while experiencing visual forward movements for either a short or a long duration, and covering either a short or a long distance. At the behavioral level, we found bi-directional interference effects between time and distance perception, which was correlated with greater representational similarity in speed-sensitive brain regions. The strength of the distance-on-time effect scaled with representational similarity in the left human middle temporal complex (hMT+), and the strength of the time-on-distance effect scaled with representational similarity in the right intraparietal sulcus (IPS). In accordance with the idea that the interference is mediated by the perception of speed, distance-on-time and time-on-distance effects were of opposing directions. Increases in traveled distance led to increases in perceived travel time, while increases in travel time led to decreases in perceived traveled distance. Together, these findings support the view that cross-dimensional interference effects between travel time and traveled distance are mediated by neuronal representations of movement speed.