Registering Eye Movements During Reading in Alzheimer’s Disease
Reading requires the fine integration of attention, ocular movements, word identification, and language comprehension, among other cognitive parameters. Several of the associated cognitive processes such as working memory and semantic memory are known to be impaired by Alzheimer’s disease (AD). As a result, a study published online in the Journal of Clinical and Experimental Neuropsychology (28 February 2014) analyzed eye movement behavior of 18 patients with probable AD and 40 age-matched controls during Spanish sentence reading.
Results showed that controls focused mainly on word properties and considered syntactic and semantic structures. In addition, the controls’ knowledge and prediction about sentence meaning and grammatical structure were quite evident when considering some aspects of visual exploration, such as word skipping, and forward saccades. Saccades are quick, simultaneous movements of both eyes between two phases of fixation in the same direction. By contrast, in the AD group, the predictability effect of the upcoming word was absent, visual exploration was less focused, fixations were much longer, and outgoing saccade amplitudes were smaller than those in controls.
According to the authors, the altered visual exploration and the absence of a contextual predictability effect might be related to impairments in working memory and long-term memory retrieval functions and that these eye movement measures demonstrate considerable sensitivity with respect to evaluating cognitive processes in AD. As a result, these measures could provide a user-friendly marker of early disease symptoms and of its posterior progression.