The Effects of Normal Aging, Subjective Cognitive Decline, Mild Cognitive Impairment, or Alzheimer's Disease on Visual Search

Background: To examine the progressively developed visual-search deficiency associated with Alzheimer's disease (AD). Methods: Healthy-younger adults (34), healthy-older adults (normal-aging control, NC, 30), adults with subjective cognitive decline (SCD, 14), amnestic mild cognitive impairment (aMCI, 20), or mild AD (15) participated in this study. To determine whether 1 of 4 letters presented at 4 symmetrically-located positions differed from the other 3, when the 4 letters were masked by either other randomly positioned and oriented letters or random-pixel noise. Meanwhile, eye movements were tracked. Results: In all the participants, with the stimulus-presentation time being longer, the visual-search performance improved, and both the eye interest-area first fixation duration (IFFD) and the interest-area-fixation count (IFC) increased. Particularly under the noise-masking condition, the AD group performed the worst at stimulus-presentation times between 300 and 900 ms. The aMCI group, but not the SCD group, performed worse than the NC group at the stimulus-presentation time of either 300 or 500 ms. The IFC was higher in all the patient groups than that in the NC group, and distinguishable between participants with AD and those with SCD or aMCI. Conclusions: The visual-search performance combined with eye-moment tracking under the noise-masking condition can be used for distinguishing AD from normal aging, SCD, and aMCI.