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Three processes underlying the carry effect in addition – Evidence from eye tracking

Authors

  • Korbinian Moeller,

    Corresponding author
    1. Knowledge Media Research Center, Tuebingen, Germany
    2. Department of Psychology, Eberhard Karls University, Tuebingen, Germany
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  • Elise Klein,

    1. Department of Psychology, Eberhard Karls University, Tuebingen, Germany
    2. Department of Neurology, Section Neuropsychology, University Hospital of RWTH Aachen University, Aachen, Germany
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  • Hans-Christoph Nuerk

    1. Knowledge Media Research Center, Tuebingen, Germany
    2. Department of Psychology, Eberhard Karls University, Tuebingen, Germany
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Korbinian Moeller, Department of Psychology, Eberhard Karls University, Tuebingen, Friedrichstrasse 21, 72072 Tuebingen, Germany (e-mail: korbinian.moeller@uni-tuebingen.de).

Abstract

Recent research indicated that processes of unit-decade integration pose particular difficulty on multi-digit addition. In fact, longer response latencies as well as higher error rates have been observed for addition problems involving a carry operation (e.g., 18 +27) compared to problems not requiring a carry (e.g., 13 +32). However, the cognitive instantiation of this carry effect remained unknown. In the current study, this question was pursued by recording participants’ eye fixation behaviour during addition problem verification. Analyses of the eye fixation data suggested a prominent role of the unit digits of the summands. The need for a carry seems to be recognized very early during the encoding of the problem after initial unit sum calculation has established the basis for the no carry/carry detection. Additionally, processes related to the actual carry execution seemed to be associated with the processing of the decade digit of the solution probe but were less unambiguous. Taken together, our findings indicate that unit-based calculations and the associated recognition that a carry is needed as well as its completion determine the difficulty of carry addition problems. On a more general level, this study shows how the nature of numerical-cognitive processes can be further differentiated by the evaluation of eye movement measures.

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