What's "left"? Hemispheric sensitivity to predictability and congruity during sentence reading by older adults.

A number of studies have found that older adults' sentence processing tends not to be characterized by the prediction-related effects attested for young adults. Here, we further probed older adults' sensitivity to predictability and congruity by recording event-related brain potentials (ERPs) as adults over age 60 read pairs of sentences, which ended with either the expected word, an unexpected word from the same semantic category, or an unexpected word from a different category. Half of the contexts were highly constraining. Consistent with patterns attested when older adults listened to these same materials (Federmeier et al., 2002), N400s, on average, were smaller to expected than to unexpected words, but did not show constraint-related reductions for unexpected words that shared features with the most predictable completion (an effect well-attested in young adults). This pattern resembles that seen in young adults for right-hemisphere-biased processing. To assess whether older adults retain young-like hemispheric asymmetries but recruit right hemisphere mechanisms more, we examined responses to the target words using visual half-field presentation. Whereas young adults show an asymmetric pattern, with prediction-related N400 amplitude reductions for left- but not right-hemisphere-initiated processing (Federmeier and Kutas, 1999b), older adults showed no reliable processing asymmetries and no evidence for prediction with left hemisphere-initiated presentation. The results suggest that left hemisphere mechanisms important for prediction during language processing are less efficacious in older adulthood.