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Abstract:
The present work examined possible damage in number concepts
in Alzheimer's disease (AD) patients and healthy individuals. The
parieto-occipito-temporal junction in the brain of healthy adults
is associated with number comparisons and with the distance effect,
i.e., large semantic distances are processed faster than smaller
ones. Since the parieto-occipito-temporal junction is damaged in AD
patients, we surmised that the distance effect and number
comparisons would be affected. AD patients, and young and elderly
healthy individuals, were asked to perform a size comparison task.
In one experimental block numeric values were relevant and physical
size irrelevant, and in another block the reverse, i.e., irrelevant
numeric values and relevant physical sizes. Numeric values and
physical sizes affected performance even when they were irrelevant
(reflected by a size congruity effect), regardless of group. This
indicates that AD patients, and elderly individuals, have no
deficiency in automatic processing of digits. In healthy subjects,
we found the typical distance effect. In contrast, under certain
circumstances, AD patients did not show this effect. We suggest
that healthy individuals and AD patients can automatically process
the semantic and physical aspects of a digit. The current pattern
of results notwithstanding, AD patients seem to have a lesion in
neuro structures that is involved in numeric processing, which
brings about some deficiency in their performance (reflected by the
reduced distance effect).
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