title: Shifts of spatial attention underlie numerical comparison and mental arithmetic: Evidence from a patient with right unilateral neglect.
abstract: OBJECTIVE
  Recent findings suggest that mental arithmetic involves shifting attention on a mental continuum in which numbers would be ordered from left to right, from small to large numbers, with addition and subtraction causing rightward or leftward shifts, respectively. Neuropsychological data showing that brain-damaged patients with left neglect experience difficulties in solving subtraction but not addition problems support this hypothesis. However, the reverse dissociation is needed to establish the causal role of spatial attention in mental arithmetic.
  
  
  METHODS
  R.H., a 65-year-old left-brain-damaged patient exhibiting right unilateral visuospatial and representational neglect, was tested with various numerical tasks including numerical comparison, arithmetic problem-solving, and numerical interval bisection.
  
  
  RESULTS
  In numerical comparison, R.H. showed a selective response latency increase when judging numbers larger than the references whereas his performance was normal for numbers smaller than the references. In the arithmetic task, R.H. was impaired in solving addition but not subtraction problems. In contrast, performance in number bisection shows a deviation toward larger numbers.
  
  
  CONCLUSIONS
  These results establish a double dissociation between subtraction and addition solving in patients with left versus right neglect and demonstrate clear evidence that attentional mechanisms are crucial for mental arithmetic. We suggest that attention shifts are involved whenever a number is represented relative to another on a mental continuum, be it during numerical comparison or arithmetic problem-solving. R.H.'s performance in numerical interval bisection indicates that this task involves processes that are distinct from those involved in number comparison and mental arithmetic. (PsycINFO Database Record
authors.affiliation: Institut de Recherche en Sciences Psychologiques, Université Catholique de Louvain.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Masson
authors.affiliation: Institut de Recherche en Sciences Psychologiques, Université Catholique de Louvain.
authors.forename: Mauro
authors.initials: M
authors.lastname: Pesenti
authors.affiliation: Centre de Revalidation Neuropsychologique, Cliniques Universitaires Saint-Luc.
authors.forename: Françoise
authors.initials: F
authors.lastname: Coyette
authors.affiliation: Institut de Recherche en Sciences Psychologiques, Université Catholique de Louvain.
authors.forename: Michael
authors.identifier: 0000-0002-7505-8157
authors.initials: M
authors.lastname: Andres
authors.affiliation: Institut de Recherche en Sciences Psychologiques, Université Catholique de Louvain.
authors.forename: Valérie
authors.initials: V
authors.lastname: Dormal
mesh_terms: D000368:Aged; D001288:Attention; D001922:Brain Abscess / Q000000981:diagnostic imaging / Q000523:psychology / Q000601:surgery; D007839:Functional Laterality; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008433:Mathematics; D009483:Neuropsychological Tests; D010468:Perceptual Disorders / Q000000981:diagnostic imaging / Q000523:psychology*; D011340:Problem Solving; D011597:Psychomotor Performance; D011930:Reaction Time; D013028:Space Perception