@article{WiemersBekkeringLindemann2014,
  author    = {Wiemers, Michael and Bekkering, Harold and Lindemann, Oliver},
  title     = {Spatial interferences in mental arithmetic: Evidence from the motion-arithmetic compatibility effect},
  series = {The quarterly journal of experimental psychology},
  volume    = {67},
  journal   = {The quarterly journal of experimental psychology},
  number    = {8},
  publisher = {Routledge, Taylor \& Francis Group},
  address   = {Abingdon},
  issn      = {1747-0218},
  doi       = {10.1080/17470218.2014.889180},
  pages     = {1557 -- 1570},
  year      = {2014},
  abstract  = {Recent research on spatial number representations suggests that the number space is not necessarily horizontally organized and might also be affected by acquired associations between magnitude and sensory experiences in vertical space. Evidence for this claim is, however, controversial. The present study now aims to compare vertical and horizontal spatial associations in mental arithmetic. In Experiment 1, participants solved addition and subtraction problems and indicated the result verbally while moving their outstretched right arm continuously left-, right-, up-, or downwards. The analysis of the problem-solving performances revealed a motion-arithmetic compatibility effect for spatial actions along both the horizontal and the vertical axes. Performances in additions was impaired while making downward compared to upward movements as well as when moving left compared to right and vice versa in subtractions. In Experiment 2, instead of being instructed to perform active body movements, participants calculated while the problems moved in one of the four relative directions on the screen. For visual motions, only the motion-arithmetic compatibility effect for the vertical dimension could be replicated. Taken together, our findings provide first evidence for an impact of spatial processing on mental arithmetic. Moreover, the stronger effect of the vertical dimension supports the idea that mental calculations operate on representations of numerical magnitude that are grounded in a vertically organized mental number space.},
  language  = {en}
}
@article{KrauseLindemannTonietal.2014,
  author    = {Krause, Florian and Lindemann, Oliver and Toni, Ivan and Bekkering, Harold},
  title     = {Different brains process Numbers differently: Structural bases of individual differences in spatial and nonspatial number representations},
  series = {Journal of cognitive neuroscience},
  volume    = {26},
  journal   = {Journal of cognitive neuroscience},
  number    = {4},
  publisher = {MIT Press},
  address   = {Cambridge},
  issn      = {0898-929X},
  doi       = {10.1162/jocn_a_00518},
  pages     = {768 -- 776},
  year      = {2014},
  abstract  = {A dominant hypothesis on how the brain processes numerical size proposes a spatial representation of numbers as positions on a "mental number line." An alternative hypothesis considers numbers as elements of a generalized representation of sensorimotor-related magnitude, which is not obligatorily spatial. Here we show that individuals' relative use of spatial and nonspatial representations has a cerebral counterpart in the structural organization of the posterior parietal cortex. Interindividual variability in the linkage between numbers and spatial responses (faster left responses to small numbers and right responses to large numbers; spatial-numerical association of response codes effect) correlated with variations in gray matter volume around the right precuneus. Conversely, differences in the disposition to link numbers to force production (faster soft responses to small numbers and hard responses to large numbers) were related to gray matter volume in the left angular gyrus. This finding suggests that numerical cognition relies on multiple mental representations of analogue magnitude using different neural implementations that are linked to individual traits.},
  language  = {en}
}