Abstract: Previous studies have shown that mapping of time is represented along horizontal axis. It has been shown that, compared to English speakers, Mandarin speakers were more likely to think about time vertically (top to down) than horizontally (left to right). Time is expressed both horizontally and vertically in Chinese Context. In this study, we examined whether Mardarin speakers employ both the horizontal and vertical representation of time, if so, which kind of representations of time is dominant.
We modified the response-discrimination paradigm employed by Ansorge and Wühr (2004). Participants were asked to categorized words presented centrally as referring to the past or to the future by pressing numerical keys with the index finger of the right hand. Experiment 1 was conducted with a 2 (discrimination: discriminating / non-discriminating) × 2 (response dimension: horizontal / vertical) × 2 (STEARC compatibility: compatible / incompatible) within-subject design, to examine whether the time was represented spatially both in horizontal and in vertical dimensions. Response keys, located on the lower left (key 1), the lower right (key 3), the upper-left (key 7) or the upper-right (key 9) positions of the numerical keyboard, were aligned in either the horizontal or the vertical dimensions. Within the horizontal dimension, participants only selected between upper left and upper right or between lower left and lower right. Likewise, for the vertical dimension, participants only selected between upper-left and lower-left or selected between upper-right and lower-right. Experiment 2 was conducted with a 2 (response location: left-diagonal / right-diagonal) × 2 (STEARC compatibility: compatible / incompatible) within-subject design, to study how the two spatial representations interact. Response keys were assigned in a left-diagonal (lower-right and upper-left) and a right-diagonal (lower-left and upper-right) axes, such that both the horizontal and the vertical direction were manipulated. In both Experiment 1 and Experiment 2, the dependent variable was the response time of the participants in pushing the keys.
In Experiment 1, a STEARC effect was shown in discriminating horizontal dimension. Response was faster with “left-past, right-future” association, than “left-future, right-past” association, but not in the vertical dimension. Similarly, a STEARC effect was also shown in the discriminating vertical dimension (faster responses with “top-past, bottom-future”, than “top-future, bottom-past”), but not in the horizontal dimension. In Experiment 2, for the responses to upper-left vs. bottom-right, a STEARC effect was observed in both the horizontal and the vertical dimension. For responses for bottom-left vs. upper-right, a STEARC effect was observed in the horizontal dimension. The results indicate the horizontal representation is advantageous. A K–S test showed that the distribution of effect sizes was normal, which suggests two spatial representations of time affected each other.
In conclusion, Mandarin speakers possess both horizontal and vertical mental timeline. The horizontal mental timeline is dominant for representations of time. The present results suggest that Chinese linguistic and cultural experience, such as left to right writing/reading direction could play an important role in mental mapping of time.

Key words: mental timeline, STEARC effect, Chinese context, horizontal axis, vertical axis