Divided attention, as measured by dichotic speech performance, in dementia of the Alzheimer type
C. L. Grady, A. M. Grimes, N. Patronas, T. Sunderland, N. L. Foster and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, Bethesda, MD 20892.
To determine if impaired dichotic performance in patients with dementia of
the Alzheimer type is due to the inability to divide attention or the
inability to perceive degraded auditory stimuli, we measured performance on
tasks of both dichotic and degraded monotic speech materials. We also
examined whether perception of degraded speech stimuli presented monaurally
is related to abnormalities of temporal lobe anatomy and physiology, as we
have shown for dichotic performance. Although the patients were impaired on
both dichotic and monotic tests, significantly greater impairment was seen
on the dichotic test. Our earlier finding of a significant relation between
dichotic performance and measures of anterior temporal lobe atrophy and
reduced glucose metabolism was replicated, but no significant relation was
found between monotic tests and measures to temporal lobe integrity. We
conclude that the inability to divide attention, rather than abnormal
processing of degraded stimuli per se, is reflected in poor dichotic
performance in patients with dementia of the Alzheimer type, and that
dichotic performance, unlike degraded monotic perception, depends directly
on the integrity of temporal cortex in these patients.
