Time is represented along a horizontal mental line with an association between the past (or short duration) and left space as well as between the future (or long duration) and right space. A possible vertical time representation is also supposed to exist, even if results are contradictory depending on the stimuli and response keys used. The aim of the present study was to test the presence of a vertical representation of temporal expressions, overcoming possible methodological limits. In Experiment 1, 167 Italian students had to categorize 20 Italian temporal expressions that appeared at the center of the screen with two analogous vertical response keys ("down" and "up" arrows of a regular keyboard). Specifically, in Experiment 1A participants pressed the down arrow with their left hand and the up arrow with their right hand, whereas in Experiment 1B the key-hand assignment was reversed. In Experiment 2, 25 participants underwent the same procedure using a vertically positioned response box. The same participants also performed a Time-to-Position task, in which they located temporal expressions along a vertical line. In both experiments, a space-time interaction was found, with an association between past expressions and the bottom (or down arrow) response key as well as between future expressions and the top (or up arrow) key. The results suggest a bottom-to-top mapping of time representation, according to the "more-is-up" metaphor.
Public Significance StatementThe present study suggests that a vertical mental timeline representation exists, showing a space--time association from bottom to top. This mental representation is probably influenced by the daily life experience of verticality in the physical world, such as the construction of a building from the ground floor to the attic, according to the "more-is-up" metaphor. The results were confirmed using both an analogous and a literal concept of verticality in a temporal judgment task, and this bottomto-top representation of time was not influenced by the hand used to press the response button. Moreover, we confirmed not only that the past was associated with the bottom space and the future was associated with the top space, but also that the temporal expressions used in this study showed an ordinal pattern when participants performed a Time-to-Position task. Therefore, we can conclude that, even if temporal expressions do not refer to fixed moments in time, they occupy a specific position on the mental timeline with a "specific order."