Visual information processing and dementia

Eye fixation durations during complex visual search were compared among groups of idiopathic dementia (presumed Alzheimer's disease), dementia secondary to frontally placed mass lesions, pseudodementia of depression, and elderly normal controls. The idiopathic dementia group showed longer mean fixation durations which reflects a stylistic difference to enhance visual perception. The pseudodementia and frontal lobe lesion groups exhibited briefer than normal mean fixation durations. The dementia group with frontal lesions demonstrated a decrease in eye fixation durations during the latter half of the searching task, suggesting an impulsive searching strategy. The same pictorial stimulus was presented twice under two instructional conditions. Fixation durations increased when comparing the first ten fixation durations to the last ten fixation durations for all groups during the initial viewing period. This pattern was reversed in only the normal group during the second viewing period, suggesting that only normals gained sufficient information early on in the scan to allow for more desultory scanning late in the scan. No meaningful association was found between severity of dementia or depression and average eye fixation durations. The authors conclude that the disease processes studied may have differential effects on the patterns of eye fixation during complex visual search.