Tone duration discrimination in demented, memory-impaired, and healthy elderly.

In order to assess the diagnostic validity of a new test of tone duration discrimination (TDD), we tested elderly subjects, 32 Alzheimer-type (AD) and 11 vascular-type dementia (VAD) patients, 11 memory-impaired (MI), and 21 healthy controls with a TDD test as well as with 18 standard neuropsychological (NP) tests. The TDD test efficiently discriminated demented patients from MI, and MI from controls. As an index of cognitive impairment, the TDD test was sensitive also in comparison to NP tests. This suggests that processing of auditory duration information is impaired in dementia as well as in MI. Patients suffering from AD and VAD differed in that the VAD but not the AD patients improved their TDD performance when the interstimulus interval was lengthened. This shows that the processing of auditory temporary information involves functions sensitive to dementia diseases as well as to MI. The TDD test could add discriminatory power in diagnosis and differential diagnosis of dementia.