Abstract:

When randomly and centrally presenting different numbers on the display and asking participants to classify the probe numbers by pressing specified key of keyboard according to numerical magnitude or parity or numerical other natures, participants invariably respond faster to small numbers with the left key pressing than the right key pressing. However, participants respond faster to large numbers with the right key pressing than the left key pressing. This phenomenon was the spatial-numerical association of the response code (SNARC) effect. Although previous studies believed that the SNARC effect was the product of the spatial representation of numbers in individuals’ brains, it is unclear whether the spatial representation of numbers takes place in individuals’ long-term memory or their working memory. The spatial representation of numbers in long-term memory was caused by individuals’ early cultural experience, especially their reading and writing direction, and even influenced by genetic factors; however, the spatial representation of numbers in working memory was influenced by situational factors such as the provisional order of numbers, cognition tasks, interferential stimuli and was constructed online. When randomly presenting the numbers and other symbols in one experiment and asking participants to classify the numbers and other symbols depending on specific natures, the spatial representation of numbers in long-term memory was not influenced by the randomly presented context. However, the spatial representation of numbers in working memory was influenced by it. Therefore, it can be inferred that the SNARC effect was induced by other spatial representations of numbers in long-term memory or the spatial representation of numbers in working memory in the numbers and symbols randomly presented context.
Therefore, this study randomly presented numbers and letters or Chinese characters and explored the rapid presentation stimulus classification paradigm, in which participants were asked to classify numbers depending on the numerical magnitude and classify letters depending on the letters’ sequence in the alphabet or classify Chinese characters depending on the Chinese characters’ composition among the two experiments to investigate the encoding mechanism of the SNARC effect in processing numbers in the numbers and letters or Chinese characters randomly presented context to reveal whether the SNARC effect was caused by either the spatial representation of numbers in the mental number line of long-term memory, or the spatial representation of numbers in working memory. In addition, both the ratio of numbers to letters and to Chinese characters were manipulated in this study to investigate whether the SNARC effect on processing numbers in interferential situations was moderated by either the ratio of numbers to letters or to Chinese characters. The results show that (1) when both the ratio of numbers to letters were equal, no SNARC effect was captured in the processing of numbers in interferential situations; however, when both the ratio of numbers to letters were “6 to 1” and “1 to 6, ” the SNARC effect appeared in the processing of numbers in interferential situations. That is, an inverted U-shaped relationship existed between the alphanumeric ratio and SNARC effect. (2) The inverted U-shaped relationship between the alphanumeric ratio and SNARC effect can also extend to the processing of numbers in mixed number and Chinese character situations.
In conclusion, these results show that (1) randomly presenting the interference stimulus and numbers in one experiment can influence the SNARC effect in processing numbers by task switching. (2) The SNARC effect in processing numbers was moderated by the ratio of numbers to interference stimuli in interferential situations, regardless of the interference stimulus used. These results imply that spatial representations of numbers are constructed online by humans through statistical learning, and the results support the working memory account for the SNARC effect.

Key words: SNARC effect, numbers, letters, spatial representation, mental number line, working memory