Sentence reading in older adults with and without Mild Cognitive Impairment

While language comprehension tends to be well preserved in older adults, the processing and comprehension of syntactically complex sentences might be influenced by age-related changes in Working Memory (WM) and Interference Control (IC). Further, aging can be accompanied by cognitive decline caused by neurological conditions such as Mild Cognitive Impairment (MCI), but its impact on on-line sentence processing has rarely been studied. We report a study of word-by-word reading times and comprehension of sentences with different syntactic complexity in young adults (n = 69) and two subgroups of older adults: healthy older adults (n = 32) and older adults with single- and multi-domain amnestic MCI (n = 21). The experimental protocol was based on a self-paced reading task and a variety of neuropsychological measures including Operation Span (WM) and Stroop (IC) tasks. Syntactic complexity was induced using Spanish embedded relative clauses varying subject-versus object-extraction of the antecedent noun phrase (canonical or non-canonical word order, respectively). Moreover, within non-canonical sentences, we distinguished between those that did or did not contain long-distance dependencies between the extracted object and embedded verb. All these manipulations were expected to lead to a gradual recruitment of IC and WM based on the complexity of the sentence structure. Comprehension was similar across groups, with differences explained by WM capacity. In both subgroups of older adults, the on-line processing of object extracted sentences was modulated by their available IC and WM resources, although older adults with MCI seem to recruit WM to a lesser extent. In conclusion, results suggest that IC and WM have a modulatory role in the processing and comprehension of syntactically complex sentences in older adults. Moreover, older adults with MCI seem to be particularly overwhelmed by WM demands during sentence processing and comprehension.