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

Samuel Shaki, Michal Pinhas, Martin H. Fischer

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


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 sign-space association and an anchoring bias. We conclude that mental arithmetic exhibits shortcuts for decision-making similar to traditional domains of reasoning and problem-solving.

Original languageEnglish
Pages (from-to)138-156
Number of pages19
JournalThinking and Reasoning
Issue number2
StatePublished - 3 Apr 2018


  • Heuristics
  • mental arithmetic
  • mental number line
  • operational momentum
  • problem-solving


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