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Abstract:
Abstract: We examined number processing using patients with
Alzheimer Dementia (AD). On the basis of neuropsychological tests
and SPECT imaging, we distinguished two groups of patients: 1) 10
patients in whom the disease was predominantly located in the
anterior part of the brain [frontal lobes (FL)], and 2) 13 patients
in whom the disease was predominantly located in the posterior part
of the brain [posterior parieto-temporal (PT)]. AD patients and
normal controls evaluated either numerical size or physical size of
stimuli varying along both dimensions (e.g., 3-5). In addition,
each subject performed a math test. FL and PT patients did not
differ in their mathematical abilities. In contrast, patients with
FL produced a larger size congruity effect that was mainly composed
of an enlarged interference component. In addition, while the
healthy elderly and PT patients showed the typical distance effect
(i.e., large numerical distances were being processed faster than
smaller ones), FL patients showed no distance effect. Our results
suggest that AD individuals with a lesion in the FL have more
difficulty suppressing the irrelevant dimensions of a stimulus than
do AD patients with no lesion in this region. In addition, the fact
that PT patients showed a distance effect does not support
suggestions that the temporo-parietal junction is essential for
number comparison.
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