Perspectives on Number Processing

This special issue pulls together work on how the brain handles number. Hans-Christoph Nuerk, Klaus Willmes and Wim Fias organized the collection, and in their opening editorial they set out why so many separate questions about numerical cognition belong side by side. The papers that follow fall into four groupings, each with its own editor and its own slice of the problem.

The first group, edited by Fias, takes up the spatial side of how we represent number: the idea of a mental number line. Wim Gevers and Jan Lammertyn go after the SNARC effect, the finding that small numbers seem to sit on the left and large ones on the right. Martin H. Fischer and Julia Rottmann push the question further by asking whether negative numbers get a spot on that line at all. Nuerk, together with Frank Bauer, Joseph Krummenacher, Dieter Heller and Willmes, uses an Eriksen flanker task to test how the magnitude of a number you are told to ignore still bleeds into your performance.

A second set of papers, edited by Nuerk, moves to multi-digit numbers, where the story gets more complicated than single digits suggest. Nuerk and Willmes look at how the magnitude of two-digit numbers is held in mind. Maud Deschuyteneer, Stijn De Rammelaere and Fias compare adding two-digit numbers when a carry is needed against problems where it is not. Guilherme Wood, Moritz Mahr and Nuerk take apart the base-10 structure of Arabic numerals and put it back together to see what the system is actually doing.

The third group, edited by Willmes, turns to mental arithmetic. Frank Domahs and Margarete Delazer sort out which claims about stored arithmetic facts hold up and which are assumption. Karin Kucian, Thomas Loenneker, Thomas Dietrich, Ernst Martin and Michael von Aster use brain imaging to examine how activation patterns differ between men and women during mental rotation and number tasks. Tom Verguts and Fias report neighbourhood effects, the way nearby problems influence one another in arithmetic.

The last section, again edited by Nuerk, looks at how numerical cognition develops. Liane Kaufmann and Nuerk survey where the field stands and where it might go. Jan Bachot, Gevers, Fias and Herbert Roeyers study number sense in children with visuospatial difficulties, asking how the orientation of their mental number line holds up. Sandrine Censabella and Marie-Pascale Noël close things out by measuring how practice with multiplication spills over into children's addition.