Academic journal article Psychonomic Bulletin & Review

Reading Habits for Both Words and Numbers Contribute to the SNARC Effect

Academic journal article Psychonomic Bulletin & Review

Reading Habits for Both Words and Numbers Contribute to the SNARC Effect

Article excerpt

This study compared the spatial representation of numbers in three groups of adults: Canadians, who read both English words and Arabic numbers from left to right; Palestinians, who read Arabic words and Arabic-Indic numbers from right to left; and Israelis, who read Hebrew words from right to left but Arabic numbers from left to right. Canadians associated small numbers with left and large numbers with right space (the SNARC effect), Palestinians showed the reverse association, and Israelis had no reliable spatial association for numbers. These results suggest that reading habits for both words and numbers contribute to the spatial representation of numbers.

The spontaneous association between numbers and space has drawn much attention since its discovery (Dehaene, Bossini, & Giraux, 1993). Well over 100 published experiments have shown that small-magnitude values are associated with the left side and larger values with the right side of space (for a recent meta-analysis, see Wood, Nuerk, Willmes, & Fischer, 2008). The association is typically found by comparing the speed of rightand left-hand responses in a parity classification task. This so-called " spatial-numerical association of response codes" (SNARC) effect has been interpreted as reflecting a "spillover" of directional reading or writing habits.1 Readers in Western cultures progress through each line of text from left to right, and they also seem to place small numbers further on the left side of a "mental number line" than larger numbers when they enumerate objects or think about magnitudes. Supporting this explanation of the SNARC effect as a generalized habitual association, the spatial association for numbers was weaker in Iranians, who habitually read Arabic script from right to left but were only recently immersed into a left-to-right reading culture (Dehaene et al., 1993, Experiment 7). However, that study reported no data from Iranians in their native reading context, and thus no demonstration of the expected reversed association between numbers and space in right-to-left readers.

A field study by Zebian (2005) tried to address this point. She reported that monoliterate Arabic readers were faster to name the side of the larger number in a pair when it was on the left side of a display than when it was on the right, suggesting a reversed association between numbers and space consistent with their right-to-left reading habits. However, the verbal naming task is not sensitive to the SNARC effect (Keus & Schwarz, 2005); this was evidenced by the absence of a normal effect in Zebian's English-speaking control group. Together, these results cast doubt on whether a reversed SNARC effect was indeed present in Zebian's (2005) study, or whether some other aspect of the task led to a spatial bias in these monoliterate Arabic readers.

Ito and Hatta (2004; see also Schwarz & Keus, 2004) reported a vertical SNARC effect (small numbers associated with lower keys and larger numbers with upper keys) in Japanese readers. This association conflicts with the habitual top-to-bottom reading direction in Japanese and suggests that reading habit and SNARC effect might be independent. Recently, Hung, Hung, Tzeng, and Wu (2008) showed a horizontal mapping for Arabic number symbols, which their Chinese participants typically encountered in horizontally printed English text, and a vertical mapping for Chinese number symbols, which most often appeared in vertically printed Chinese text. Such flexibility in the same group of readers in the association of numbers with space resulting from both the number format and the associated reading context suggests that number concepts might not possess spatial associations in their own right. Instead, it seems possible that separate spatial associations become activated from the number itself and also from the associated reading context, and that their combination determines the resulting SNARC effect.

To test this possibility, we measured the SNARC effect with a parity task in three groups of participants with different combinations of spatial directional habits associated to the processing of words and numbers: Canadians, who habitually read and write both English words and Arabic numbers from left to right; Israelis, who habitually read and write Hebrew words from right to left but Arabic numbers from left to right; and Palestinians, who read and write both Arabic text and Arabic-Indic numbers (also called Eastern Arabic numerals) from right to left. …

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