Bisections in two languages: when number processing, spatial representation, and habitual reading direction interact.

Calabria and Rossetti (2005) demonstrated that spatial biases related to the mental number line can be seen even when bisecting strings of number words. Strings of smaller magnitude number words were bisected further to the left than strings of larger magnitude number words. The current study investigated whether the left-to-right mental number line associated with number processing will result in similar spatial biases despite a habitual, right-to-left reading direction. Monolingual left-to-right readers were compared to bidirectional readers of English and Hebrew. Strings of Arabic numerals and of number words (e.g., THREE, EIGHT) were presented in separate conditions of English and Hebrew. Significant rightward biases were seen among native Hebrew readers, regardless of English reading level; whereas native English readers (both bidirectional and monodirectional) did not show significant biases to either the left or the right. The spatial bias in bisecting either Arabic numeral strings or number words was related to the habitual reading direction of the participant. There was no difference in spatial bias or for frequency of spatial bias based on numerical magnitude for either condition. We discuss the influence of cultural factors, such as reading direction and proficiency, on the representation of spatial and numerical material.