N4 to spoken sentences in young and older subjects

Event-related potentials (ERPs) to spoken sentences were recorded from young and elderly subjects. Sentences ended in semantically typical or atypical words. Subjects listened to the sentences during two attention conditions. In a semantic attention task, subjects listened to the meanings of the sentences for a subsequent memory test. In a phonemic attention task, subjects counted words beginning with the letter "p". Following these tasks, the sentence-final words were presented in isolation. A conventional auditory oddball paradigm was also presented. The N4 components elicited by semantically atypical sentence-final words were slightly attenuated and delayed in the older group. N4 was not influenced by the attention manipulation. Young but not older subjects' N4s were attenuated by repetition. When the sentence-final words were presented a third time in isolation, the N4s elicited were similar in amplitude and latency to those elicited in sentence context, but were not attenuated by repetition. In young and older subjects, the peak amplitude of the sentence-elicited N4 difference wave form was highly correlated with the number of correct recognitions of typical words, but not atypical sentence-final words. In young but not older subjects, sentence-elicited N4 amplitude was correlated with the amplitude of the P3 elicited in the auditory oddball paradigm.