No abstract

Event-related brain potentials (ERPs) were recorded from 13 scalp electrodes while subjects read sentences, some of which contained either a verb that disagreed in number with the subject noun (syntactic anomaly) or a word in uppercase letters (physical anomaly). Uppercase words elicited the P300 complex of positivities, whereas agreement violations elicited a late positive shift with an onset around 500 msec and a duration of several hundred msec. These effects differed in their morphology, temporal course, amplitude, and scalp distribution. Furthermore, manipulations of the probability-of-occurrence and task relevance of the anomalies had robust effects on the response to uppercase words, but not on the response to agreement violations. Finally, these anomalies had additive effects when agreement-violating uppercase (doubly anomalous) words were presented. These results are taken to be an initial indication that the positive shift elicited by agreement violations is distinct from the P300 response to unexpected, task-relevant anomalies that do not involve the violation of a grammatical rule.

No abstract

No abstract

Older adults have difficulty when executive control must be brought on line to coordinate ongoing behavior. To assess age-related alterations in executive processing, task-switching performance and event-related potential (ERP) activity were compared in young and older adults on switch, post-switch, pre-switch, and no-switch trials, ordered in demand for executive processes from greatest to least. In stimulus-locked averages for young adults, only switch trials elicited fronto-central P3 components, indicative of task-set attentional reallocation, whereas in older adults, three of the four trial types evinced frontal potentials. In response-locked averages, the amplitude of a medial frontal negativity (MFN), a component reflecting conflict monitoring and detection, increased as a function of executive demands in the ERPs of the young but not those of the older adults. These data suggest altered executive processing in older adults resulting in persistent recruitment of prefrontal processes for conditions that do not require them in the young.