Figure 2.

Illustration of the bi-directional model where the same-colored points in space-time represent the equidistant locations relative to self, further suggesting they are both acquired at/around the same time/developmental stage irrespective of the direction—past or future. Our bi-directional model adheres to the undifferentiated stage when time is egocentric and not yet unidirectional. We proposed that this undifferentiated time/space concept only lasts until the child replaces it with the more differentiated Newtonian concept of absolute time and space around school age. Before that transition happens, children between 4 and 6 often resort to the sequence of events to intuit duration when they have to, expressed by event density as an estimate of time.