Contrast polarity affects verification of addition and subtraction problems via conceptual mapping

The extent to which processing of abstract numerical concepts depends on perceptual representations is still an open question. In four experiments, we examined the association between contrast polarity and mental arithmetic, as well as its possible source. Undergraduate psychology students verified the correctness of single-digit arithmetic problems such as 2 + 5 = 7 or 9 - 6 = 5. Problems appeared either in white or black on a grey background, thus creating positive or negative contrast polarity, respectively. When the correct response was Yes (No), participants were faster (slower) in verifying positive than negative addition problems and in verifying negative than positive subtraction problems. Experiment 2 confirmed that the same result also held for written word problems (e.g., SEVEN + SIX = THIRTEEN). However, Experiment 3 found that the effect of contrast polarity observed in Experiments 1 and 2 disappeared in a blocked design where arithmetic operation was a between-participant factor. In addition, Experiment 4 revealed that the effect of contrast polarity does not generalise to multiplication and division. Overall, available evidence suggests that participants spontaneously associate the abstract relation between addition and subtraction (more-less) with a similar relation between contrast polarities (bright-dark).