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Exploring number space by random digit generation

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Abstract

There is some evidence that human subjects preferentially select small numbers when asked to sample numbers from large intervals “at random”. A retrospective analysis of single digit frequencies in 16 independent experiments with the Mental Dice Task (generation of digits 1–6 during 1 min) confirmed the occurrence of small-number biases (SNBs) in 488 healthy subjects. A subset of these experiments suggested a spatial nature of this bias in the sense of a “leftward” shift along the number line. First, individual SNBs were correlated with leftward deviations in a number line bisection task (but unrelated to the bisection of physical lines). Second, in 20 men, the magnitude of SNBs significantly correlated with leftward attentional biases in the judgment of chimeric faces. Finally, cognitive activation of the right hemisphere enhanced SNBs in 20 different men, while left hemisphere activation reduced them. Together, these findings provide support for a spatial component in random number generation. Specifically, they allow an interpretation of SNBs in terms of “pseudoneglect in number space.” We recommend the use of random digit generation for future explorations of spatial-attentional asymmetries in numerical processing and discuss methodological issues relevant to prospective designs.

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Abbreviations

RNG:

Random number generation

MDT:

Mental dice task

SNB:

Small-number bias

LB:

Line bisection

LVF:

Left visual field

RVF:

Right visual field

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Acknowledgments

We thank the investigators of the original experiments on RNG for having administered the Mental Dice Task. We also acknowledge financial support by the Betty and David Koetser foundation (to PB).

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  1. Neuropsychology Unit, Department of Neurology, University Hospital Zurich, 8091, Zurich, Switzerland

    Tobias Loetscher & Peter Brugger

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  1. Tobias Loetscher
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  2. Peter Brugger
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Correspondence to Tobias Loetscher.

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Loetscher, T., Brugger, P. Exploring number space by random digit generation. Exp Brain Res 180, 655–665 (2007). https://doi.org/10.1007/s00221-007-0889-0

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