Brief articleLanguage influences number processing – A quadrilingual study
Introduction
In this quadrilingual cross-cultural study, we examined the impact of reading/writing direction and the formation of number words on performance in a number comparison task. We used a 2 × 2 design involving Arabic-, English-, German-, and Hebrew-speaking participants realizing an orthogonal quasi-experimental manipulation of the two factors. These factors were chosen, because both have been observed to influence number processing when investigated in isolation.
First, it is assumed that numbers are represented in ascending order along a so-called mental number line (MNL; e.g., Dehaene et al., 1993, Restle, 1970; but see Santens & Gevers, 2008 for a differing view). Interestingly, the orientation of the MNL seems to depend on the dominant reading/writing direction. In cultures reading/writing from left-to-right numbers increase in size along the MNL accordingly (e.g., Dehaene et al., 1993). In contrast, in cultures with right-to-left reading/writing a less clear or even reversed right-to-left orientation has been observed (e.g., Shaki et al., 2012, Shaki et al., 2009). Importantly, however, influences of reading/writing direction on number processing have so far been investigated primarily for effects with single-digit numbers (e.g., spatial–numerical associations such as the SNARC effect, Dehaene et al., 1993, indicating faster responses to small numbers by the left hand and to larger numbers by the right hand in left-to-right reading cultures). Yet, it has not been examined whether reading/writing direction also influences place-value integration of tens and units in two-digit number processing.
Second, number word formation influences place-value integration in two-digit number processing. Generally, two methods of number word formation can be distinguished. In most Western languages, the order of tens and units in number words follows the sequence of their corresponding digits in digital notation (e.g., English: 47 → “forty-seven”). However, there are also languages in which this order is inverted (e.g., German, 47 → “siebenundvierzig”, i.e., seven-and-forty). This inversion property influences basic numerical tasks such as magnitude comparison. When separate comparisons of tens and units yield incompatible (e.g., 47_62, 4 > 6 but 7 < 2) rather than compatible decision biases (e.g., 52_67, 5 > 6 and 2 > 7) reaction times are prolonged because the units interfere with the processing of the decision-relevant tens (e.g., Nuerk, Weger, & Willmes, 2001). Interestingly, such unit interference was more pronounced in languages with inversion in which the order of tens and units is incongruent between verbal and digital notation (e.g., Nuerk et al., 2005, Pixner et al., 2011a). Additionally, inversion influences are not limited to magnitude comparison but were also reported for a variety of both verbal and non-verbal numerical tasks such as transcoding (Pixner et al., 2011b; Zuber, Pixner, Moeller, & Nuerk, 2009), number line estimation (Helmreich et al., 2011), and even addition (Brysbaert et al., 1998, Göbel et al., 2014; see Nuerk, Moeller, Klein, Willmes, & Fischer, 2011, for an overview). However, so far, influences of number word inversion were only investigated in left-to-right reading/writing languages.
Thus, to date (main) effects of reading/writing direction and inversion on number processing have only been investigated in isolation. Yet, performance may depend on an interaction of these two cultural factors. This idea has so far never been pursued by comparing appropriate languages. One might hypothesize that the increased unit-decade compatibility effect in a language with inversion is driven by the fact of opposing directions of overall reading habits (from left-to-right) and the sequence of tens and unit in number words (from right-to-left). If this assumption is correct a reversed pattern of results should be found for participants reading from right-to-left. In the current study we realized an orthogonal variation of reading direction (left-to-right vs. right-to-left) and inversion (with vs. without, Fig. 1) by testing four language groups: (i) English participants reading/writing from left-to-right with no inversion for number words, (ii) German participants also reading/writing from left-to-right but tens and units are inverted in number words, (iii) Hebrew participants reading/writing from right-to-left with no inversion in number words and (iv) Arab participants reading/writing from right-to-left but with an inversion of tens and units in number words. Increased unit interference is expected for language groups with spatially opposing directionality of reading/writing and inversion (i.e., German and Hebrew participants see Fig. 1). The main effects of inversion (e.g., Nuerk et al., 2005) and reading direction (Shaki et al., 2009) reported so far may thus only reflect specific sections of the postulated interaction. Note that neither reading direction nor inversion was task-relevant in our study as we studied symbolic number comparison using the same stimulus set of Arabic digits throughout. Interestingly, while text is generally read from right-to-left in Arabic and Hebrew, multi-digit Arabic numbers are nevertheless read from left-to-right because the place-value system is not reversed (i.e., “47” is written as 47, not ). Thus, we only presented Arabic two-digit numbers to participants that are processed following the same place-value coding in all four language groups. Expected differences should be driven by differing reading/writing direction and inversion properties of number words. It is important to note that our hypothesis specifically addresses unit interference as indicated by the unit-decade compatibility effect and not overall differences between the languages per se.
Section snippets
Participants and design
24 English-speaking (7 males, mean age 23.1 years), 18 Arabic-speaking (13 males, mean age 24.4 years), 24 German-speaking (8 males, mean age 23.6 years), and 30 Hebrew-speaking participants (5 males, mean age 22.7 years) were tested in the UK, Palestine, Germany, and Israel, respectively. All participants were native speakers of the respective language, had received the majority of their mathematics education in their native language and were assessed in their native language.
Task and stimuli
All participants
Compatibility effects in the four language groups
In each group the majority of participants showed the expected compatibility effect with faster responses to compatible than incompatible number pairs (English: 23 out of 24 participants, Arab: 16/18, German: 24/24, Hebrew: 28/30). Additionally, t-tests indicated that the compatibility effect was significant for each language group [all: ts > 7.43, all ps < .001; MEnglish = 39 ms; MArabic = 39 ms; MGerman = 46 ms; MHebrew = 49 ms, see Fig. 2].
Differences between compatibility effects across language groups
The ANOVA revealed a reliable effect of reading direction,
Discussion
The current study investigated influences of reading/writing direction and the formation of number words on basic numerical cognition employing a quadrilingual (i.e., Arab, English, German, and Hebrew) 2 × 2 design realizing an orthogonal variation of these two factors. Unit-decade integration was differentially affected in the four language groups depending on the combinations of reading/writing direction and inversion: The unit-decade compatibility effect was significantly larger when the
Acknowledgements
Korbinian Moeller and Hans-Christoph Nuerk are members of the Leibniz-ScienceCampus Tuebingen, the LEAD Graduate School of the University of Tuebingen funded within the framework of the Excellence Initiative via the German Research Foundation as well as the “Cooperative Research Training Group” of the University of Education, Ludwigsburg, and the University of Tuebingen supported by the Ministry of Science, Research and the Arts in Baden-Württemberg.
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