Numerous studies revealed effects of some linguistic properties like inversion or reading/writing direction on number processing. However, it remains more controversial, whether influences at a syntactic level, such as singular vs. plural form associated with certain numbers, can also influence magnitude and place-value processing and vice versa. In this study, we investigated for the first time in a classical two-digit number comparison task whether grammatical number also affects magnitude and place-value processing (and vice versa). To do so, we used a peculiarity of the Polish language, where the inflection of a verb depends on the unit digit of a number (singular for 25-29, 35-39, etc. and plural for 22-24, 32-34, etc.). This systematic pattern allows the manipulation of congruency between grammatical number and magnitude information, both on an item and a response level (i.e., the grammatical number is either compatible or incompatible to the magnitude information or the response side). We observed no significant interference effects, neither between grammatical number (i.e., associated singular/ plural inflection of the number) and magnitude information, nor between grammatical number and the response side. Model comparisons revealed that models without grammatical number, could explain our data best. Hence, grammatical number did not contribute to the explanation of the data beyond unit-decade compatibility, distance effect and SNARC effect and, thus, seems to be negligible in two-digit number comparison. Task characteristics, which might contribute to this finding are discussed.
No Evidence for an Influence of Grammatical Number in Two-Digit Magnitude and Place-Value Processing in Adults
