Abstract
There is a close relation between spatial and numerical representations which can lead to interference as in Piaget’s number conservation task or in the numerical Stroop task. Using a negative priming (NP) paradigm, we investigated whether the interference between spatial and numerical processing extends to more complex arithmetic processing by asking 12 year olds and adults to compare the magnitude of decimal numbers (i.e., the prime) and, subsequently, the length of two lines or the luminance of two circles (i.e., the probe). We found NP effects when participants compare length but not luminance. Our finding suggests that decimal comparison is impacted by a visuospatial bias due to the interference between the magnitude of the numbers to be compared and their physical length. We discuss the educational implications of these findings.
Highlights
The close relationship between number and space can be demonstrated by the spatially organized representations of numbers left by primitive cultures as early as the third millennium BCE1
The current study aimed to determine (a) whether comparing decimal numbers that do not have the same number of decimal places (e.g., 0.6 vs. 0.131) requires one to inhibit the lengths of the numbers to process their magnitude throughout development in both adolescents and adults and (b) whether the inhibition of non-numerical continuous dimensions when comparing decimal numbers is specific to space, consistent with the functional overlap between the areas processing numbers and spatial extent in the intra-parietal sulcus (IPS), or extends to other non-numerical continuous dimensions such as luminance
Consistent with previous studies[30,32,34,46,47,48], we observed that participants required more time to compare the magnitude of two decimal numbers when the smallest one has the greatest number of digits after the decimal point (e.g., 0.6 vs. 0.131) than when the two decimal numbers have the same number of decimal places (e.g., 0.612 vs. 0.157)
Summary
The close relationship between number and space can be demonstrated by the spatially organized representations of numbers left by primitive cultures as early as the third millennium BCE1. Dormal and Pesenti[11] reported similar interference between length and numerical processing using a non-symbolic numerical Stroop task in which adult participants were asked to compare either the number of dots or the length of arrays of dots. The same items were presented in all three comparison tasks, i.e., two digits were displayed on the screen that vary in numerical magnitude, physical size and luminance (e.g., 2 7), and participants were asked to focus on one of the three dimensions (i.e., number, size or luminance). One possible explanation for the privileged relation between spatial and numerical processing could be that dedicated neural circuits for processing non-numerical dimensions of magnitude such as space but not luminance are co-opted during the acquisition of complex mathematical skills such as symbolic number processing[27]
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