Heuristics and biases in mental arithmetic: revisiting and reversing operational momentum

What is it about?

Mental arithmetic is characterised by a tendency to overestimate addition and to underestimate subtraction results: the operational momentum (OM) effect. Here, motivated by contentious explanations of this effect, we developed and tested an arithmetic heuristics and biases model that predicts reverse OM due to cognitive anchoring effects. Participants produced bi-directional lines with lengths corresponding to the results of arithmetic problems. In two experiments, we found regular OM with zero problems (e.g., 3+0, 3¡0) but reverse OM with non-zero problems (e.g., 2+1, 4¡1). In a third experiment, we tested the prediction of our model. Our results suggest the presence of at least three competing biases in mental arithmetic: a more-or-less heuristic, a signspace association and an anchoring bias. We conclude that mental arithmetic exhibits shortcuts for decision-making similar to traditional domains of reasoning and problem-solving.

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Why is it important?

our results suggest the presence of multiple competing sources of bias in mental arithmetic, thus making a first step towards generalising the heuristics and biases view of human cognition into the domain of mental calculation. Future studies could examine extensions of this proposal to other arithmetic operations and the impact of different problem presentation methods on the relative contributions of these powerful heuristics and biases.