LAUSR

A major source of errors in decimal magnitude comparison tasks is the inappropriate application of whole number rules. Specifically, when comparing the magnitude of decimal numbers and the smallest number has the greatest number of digits after the decimal point (e.g., 0.9 vs. 0.476), using a property of whole numbers such as "the greater the number of digits, the greater its magnitude" may lead to erroneous answers. By using a negative priming paradigm, the current study aimed to determine whether the ability of seventh graders and adults to compare decimals where the smallest number has the greatest number of digits after the decimal point was partly rooted in the ability to inhibit the "the greater the number of digits, the greater its magnitude" misconception. We found that after participants needed to compare decimal numbers in which the smallest number has the greatest number of digits after the decimal point (e.g., 0.9 vs. 0.476), they were less efficient at comparing decimal numbers in which the largest number has the greatest number of digits after the decimal point (e.g., 0.826 vs. 0.3) than they were after comparing decimal numbers with the same number of digits after the decimal point (e.g., 0.981 vs. 0.444). The negative priming effects reported in seventh graders and adults suggest that inhibitory control is needed at all ages to avoid errors when comparing decimals where the smallest number has the greatest number of digits after the decimal point.