The effects of task on the modulation of event-related potentials by word repetition.

Event-related potentials were recorded while subjects viewed 3 series of visually presented words. In each series some of the words were repetitions of an immediately preceding word. The subjects' task was to respond to occasional items (‘targets’), the nature of which was varied across the 3 series. Targets were either lower-case words, non-words, or animal names. When the targets were non-words or animal names, event-related potentials to repeated items were characterised by a large, Cz-maximum, positive-going shift with an onset latency of around 300 ms. When the targets were lower-case items, this repetition effect was greatly attenuated, due primarily to an increase in positivity in ERPs to unrepeated items. It is concluded firstly that the modulation of event-related potentials by word repetition is task-dependent. Secondly, the repetition effect seems better interpreted as an attenuation of an endogenous negativity present in ERPs to unrepeated items, than as a positive-going component elicited by repeats.