Touch perception reveals the dominance of spatial over digital representation of numbers

We learn counting on our fingers, and the digital representation of numbers we develop is still present in adulthood [Andres M, et al. (2007) J Cognit Neurosci 19:563–576]. Such an anatomy–magnitude association establishes tight functional correspondences between fingers and numbers [Di Luca S, et al. (2006) Q J Exp Psychol 59:1648–1663]. However, it has long been known that small-to-large magnitude information is arranged left-to-right along a mental number line [Dehaene S, et al. (1993) J Exp Psychol Genet 122:371–396]. Here, we investigated touch perception to disambiguate whether number representation is embodied on the hand (“1” = thumb; “5” = little finger) or disembodied in the extrapersonal space (“1” = left; “5” = right). We directly contrasted these number representations in two experiments using a single centrally located effector (the foot) and a simple postural manipulation of the hand (palm-up vs. palm-down). We show that visual presentation of a number (“1” or “5”) shifts attention cross-modally, modulating the detection of tactile stimuli delivered on the little finger or thumb. With the hand resting palm-down, subjects perform better when reporting tactile stimuli delivered to the little finger after presentation of number “5” than number “1.” Crucially, this pattern reverses (better performance after number “1” than “5”) when the hand is in a palm-up posture, in which the position of the fingers in external space, but not their relative anatomical position, is reversed. The human brain can thus use either space- or body-based representation of numbers, but in case of competition, the former dominates the latter, showing the stronger role played by the mental number line organization.

[1]  Luigi Cattaneo,et al.  Numbers within Our Hands: Modulation of Corticospinal Excitability of Hand Muscles during Numerical Judgment , 2007, Journal of Cognitive Neuroscience.

[2]  S. Dehaene,et al.  A Magnitude Code Common to Numerosities and Number Symbols in Human Intraparietal Cortex , 2007, Neuron.

[3]  M. H. Fischer,et al.  The Future for Snarc Could Be Stark… , 2006, Cortex.

[4]  Giovanni Galfano,et al.  Breaking Ranks: Space and Number May March to the Beat of a Different Drum , 2006, Cortex.

[5]  Guilherme Wood,et al.  Crossed Hands and the Snarc Effect: Afailure to Replicate Dehaene, Bossini and Giraux (1993) , 2006, Cortex.

[6]  Y. Rossetti,et al.  Interaction between space and number representations during motor preparation in manual aiming , 2006, Neuropsychologia.

[7]  Silke M. Göbel,et al.  Parietal rTMS distorts the mental number line: Simulating ‘spatial’ neglect in healthy subjects , 2006, Neuropsychologia.

[8]  Xavier Seron,et al.  Finger–digit compatibility in Arabic numeral processing , 2006, Quarterly journal of experimental psychology.

[9]  Marco Zorzi,et al.  Explicit versus Implicit Processing of Representational Space in Neglect: Dissociations in Accessing the Mental Number Line , 2006, Journal of Cognitive Neuroscience.

[10]  Brian Butterworth,et al.  Dexterity with numbers: rTMS over left angular gyrus disrupts finger gnosis and number processing , 2005, Neuropsychologia.

[11]  Paola Guariglia,et al.  Dissociation between physical and mental number line bisection in right hemisphere brain damage , 2005, Nature Neuroscience.

[12]  S. Dehaene,et al.  Interactions between number and space in parietal cortex , 2005, Nature Reviews Neuroscience.

[13]  Patrik Vuilleumier,et al.  The Number Space and Neglect , 2004, Cortex.

[14]  D. Boisson,et al.  Does Action Make the Link Between Number and Space Representation? , 2004, Psychological science.

[15]  Philippe Pinel,et al.  Distributed and Overlapping Cerebral Representations of Number, Size, and Luminance during Comparative Judgments , 2004, Neuron.

[16]  Vincent Walsh A theory of magnitude: common cortical metrics of time, space and quantity , 2003, Trends in Cognitive Sciences.

[17]  T. Landis,et al.  Pure Global Acalculia Following a Left Subangular Lesion , 2003, Neurocase.

[18]  Michael D. Dodd,et al.  Perceiving numbers causes spatial shifts of attention , 2003, Nature Neuroscience.

[19]  K. Priftis,et al.  Brain damage: Neglect disrupts the mental number line , 2002, Nature.

[20]  B. Mazoyer,et al.  Neural Correlates of Simple and Complex Mental Calculation , 2001, NeuroImage.

[21]  S. Dehaene,et al.  Understanding dissociations in dyscalculia: a brain imaging study of the impact of number size on the cerebral networks for exact and approximate calculation. , 2000, Brain : a journal of neurology.

[22]  M. Thioux,et al.  Neuroanatomical Substrates of Arabic Number Processing, Numerical Comparison, and Simple Addition: A PET Study , 2000, Journal of Cognitive Neuroscience.

[23]  T. Simon,et al.  The foundations of numerical thinking in a brain without numbers , 1999, Trends in Cognitive Sciences.

[24]  R. J. Seitz,et al.  A fronto‐parietal circuit for object manipulation in man: evidence from an fMRI‐study , 1999, The European journal of neuroscience.

[25]  B. Butterworth,et al.  A Head for Figures , 1999, Science.

[26]  Peter Brugger,et al.  Stimulus-response compatibility in representational space , 1998, Neuropsychologia.

[27]  J. Grafman,et al.  Visualizing Cortical Activation during Mental Calculation with Functional MRI , 1996, NeuroImage.

[28]  Morris Moscovitch,et al.  Object-Centered Neglect in Patients with Unilateral Neglect: Effects of Left-Right Coordinates of Objects , 1994, Journal of Cognitive Neuroscience.

[29]  S. Dehaene,et al.  The mental representation of parity and number magnitude. , 1993 .