Mapping of individual time units in horizontal space

We often refer to space when we talk about time. To support this, studies show that we tend to associate the past with the left and the future with the right, space. However, there is little research that compares the spatial mapping of individual time units within the same methodological framework. Here, we used the same line-bisection paradigm to study horizontal spatial biases in various individual time units (i.e., hours, days, and months). Fifty-four adults processed temporal words and indicated their location on a horizontal line representing a time interval via a mouse click. Each word corresponded to one of the three conditions: left, right, or central position on the line. Our results show a reaction-time facilitation effect for hour and day units in congruent conditions (e.g., left semantic bias + left position on the line). Also, processing hour units shifted the response coordinates in the direction of the presumed spatial bias. Finally, the congruent combination of visual and semantic biases led to a shift in manual responses in the corresponding direction for all time units. We conclude that while left-to-right mapping of time concepts is relatively universal, the horizontal mapping is stronger for hours as compared with days and months.