Compatibility between response position and either object typical size or semantic category: SNARC- and MARC-like effects in primary school children.

In two experiments, we administered two binary classification tasks to third- to fifth-grade students and found that either the conceptual size (Experiment 1) or semantic category (Experiment 2) of the target picture interacted with response position: Participants emitted faster and/or more accurate right- and left-side responses to stimuli referring to typically large and small objects (i.e., a SNARC [spatial-numerical association of response codes]-like effect) or to living and nonliving objects (i.e., a MARC [markedness association of response codes]-like effect), respectively. The effect of either stimulus dimension was present only when this dimension was the task-relevant one. These findings may be accounted for by the polarity compatibility principle. In binary classification tasks, one of the two relevant stimulus values (i.e., the dominant one) and one of the two response values would be coded as having a positive polarity, whereas the other would be coded as having a negative polarity. Response selection would be faster and/or more accurate when stimulus and response polarities are compatible. According to a less parsimonious hypothesis, the polarity principle would only explain the effect of the stimulus semantic category in Experiment 2, whereas the effect of stimulus conceptual size in Experiment 1 might be traced back to the fact that children spatially code the typical size of stimulus referents (even if only when the task requires accessing this stimulus dimension). Small and large objects would be represented relatively on the left and right, respectively, which would result in faster and/or more accurate responses when response position is compatible with the stimulus referent's position in this spatial representation.