Approximate quantities and exact number words: dissociable systems.
Numerical abilities are thought to rest on the integration of two distinct systems, a verbal system of number words and a non-symbolic representation of approximate quantities. This view has lead to the classification of acalculias into two broad categories depending on whether the deficit affects the verbal or the quantity system. Here, we test the association of deficits predicted by this theory, and particularly the presence or absence of impairments in non-symbolic quantity processing. We describe two acalculic patients, one with a focal lesion of the left parietal lobe and Gerstmann's syndrome and another with semantic dementia with predominantly left temporal hypometabolism. As predicted by a quantity deficit, the first patient was more impaired in subtraction than in multiplication, showed a severe slowness in approximation, and exhibited associated impairments in subitizing and numerical comparison tasks, both with Arabic digits and with arrays of dots. As predicted by a verbal deficit, the second patient was more impaired in multiplication than in subtraction, had intact approximation abilities, and showed preserved processing of non-symbolic numerosities.
Lemer
Cathy
C
INSERM U562, Neuroimagerie Cognitive Service Hospitalier Frédéric Joliot, CEA/DRM/DSV, 4 Place du General Leclerc, 91401 Cedex, Orsay, France. cathy.lemer@psl.ap-hop-paris.fr
Dehaene
Stanislas
S
Spelke
Elizabeth
E
Cohen
Laurent
L
D000368:Aged; D001037:Aphasia / Q000503:physiopathology; D001927:Brain Diseases / Q000150:complications / Q000503:physiopathology*; D016009:Chi-Square Distribution; D004213:Dissociative Disorders / Q000150:complications / Q000503:physiopathology; D005260:Female; D007839:Functional Laterality; D005862:Gerstmann Syndrome / Q000503:physiopathology; D006801:Humans; D007806:Language Disorders / Q000209:etiology / Q000503:physiopathology*; D008433:Mathematics; D008609:Mental Status Schedule; D008875:Middle Aged; D009483:Neuropsychological Tests; D011340:Problem Solving / Q000502:physiology*; D011930:Reaction Time; D014705:Verbal Behavior / Q000502:physiology*; D014706:Verbal Learning / Q000502:physiology*; D014894:Weights and Measures