Brief articleFlexible spatial mapping of different notations of numbers in Chinese readers
Introduction
The original report of the SNARC effect (Spatial Numerical Association Response Code) (Dehaene, Bossini, & Giraux, 1993) showed that in a parity judgment task, small numbers were responded to faster with the left hand while large numbers were responded to faster with the right hand. It was also found that the SNARC effect was not obtained in sequential stimuli, such as letters, when the ordinal information is not required to perform the task (Dehaene et al., 1993). However, a recent report has demonstrated the association between order (e.g., letters of the alphabet and months of the year) and space (Gevers, Reynvoet, & Fias, 2003). Although it is still under debate that numbers are aligned in the mental space due to their underlying magnitude or order, these and other similar findings (e.g., Fias et al., 1996, Nuerk et al., 2005) have consistently demonstrated that small to large numbers are mapped onto an abstract mental line with the left-to-right orientation.
Despite the clear indication of a close correspondence between numbers and space, the directionality of the mapping seems to be subject to the influence of the reading/writing experience. Dehaene et al. (1993) found that the magnitude of the SNARC effect was modulated by the number of years for which Iranian participants, who were used to reading text from right to left, had been exposed to French, whose text was printed from left to right. Zebian (2005) also demonstrated that the orientation of the mental number line was modified by the cultural artifact of writing. Lebanese illiterates who only read numerals showed no SNARC effect, while the reserved SNARC effect was found in Arabic monoliterates who only read text from right to left and weakened in Arabic-English biliterates. These previous reports imply a general number line underlying different numerical notations, despite the flexibility of its spatial mapping and subjectivity to the influence of the reading/writing experience.
Ito and Hatta (2004) examined the mental alignment of Arabic numbers in Japanese participants by asking them to perform parity judgment. In addition to reporting the typical horizontal SNARC effect, they also observed a bottom-to-top mapping of small to large numbers in the same population. Although this finding is consistent with the spatial metaphor of magnitude being “added up”, the authors did not find the same behavioral pattern in the task of magnitude comparison. Hence, Ito and Hatta argued that it was the information of parity rather than magnitude of numbers being mapped onto space. However, it is not obvious that why the parity information should be aligned both horizontally and vertically with certain orientations. Moreover, the orientation of the vertical number line (i.e., bottom-to-top) is opposite to the dominant writing direction in Japanese participants, which is from top to bottom. Further evidence is needed to resolve the puzzling findings from participants with different cultural experience.
To investigate the influence of a reading/writing system on the spatial component of numbers and to further examine whether such influence applies to all notations of numbers, we employed Chinese numerical words as well as Arabic digits to study the orientation of the mental number line in a parity judgment task. For readers in Taiwan, Arabic numbers are printed horizontally in text. On the other hand, Chinese characters (including number words) appear in vertical text with a top-to-bottom directionality dominantly (i.e., in over 60% of printed books), though horizontal text is also common. If the mapping between space and the concept behind different notations of numbers has an intrinsic, “default” orientation, both Arabic numbers and Chinese number words should be mentally aligned in a similar way. If the mapping between numbers and space is flexible and determined by experience/context, however, we would expect to detect the SNARC effect with different directions for different numerical notations in the same group of participants.
Section snippets
Methods
Thirty right-handed graduate and undergraduate students from National Central University and National Yang-Ming University in Taiwan were tested. All of them were native speakers of Chinese (age range: 19–30) with normal or corrected-to-normal vision. All participants have been exposed to English text no later than age 13 when they entered the high school.
The participants were instructed to make a parity judgment on numbers with their hands aligned horizontally. Numbers (0–9) in three notations
Methods
Thirty new participants were recruited from the same pool as Experiment 1. All of the stimuli and procedures were identical to Experiment 1, except for the following changes. First, the response keys were vertically rather than horizontally aligned. Every participant performed two sessions of parity judgment. In one session, the participants pressed the top (i.e., “7”) and bottom (i.e., “n”) key on a standard keyboard to indicate an odd and even number, respectively. In the other session, the
General discussion
The results from the current study revealed that Chinese participants mentally map Arabic numbers onto a left-to-right line, while Chinese number words (in their simple form) are represented vertically with a top-to-bottom orientation. The different orientations of the mental number lines are consistent with the dominant context in which the numerical materials are often encountered. In line with the previous literature (e.g., Dehaene et al., 1993, Zebian, 2005), these findings support the
Acknowledgements
We are grateful to Dr. Curtis Hardyck (University of California, Berkeley) for his helpful comments on a previous version of this manuscript. This work was supported by the grant from National Central University awarded to DHW, and by NSC95-2752-H-010-001 awarded to DLH and OJLT.
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