The late positive component of the evoked waveform: relationship to word recognition processes

Averaged evoked potentials were collected from Cz, C3', C4', and Pz while subjects made perceptual and cognitive decisions about pairs of visually presented words. The nature and level of the decision being made was manipulated by varying the relationships between the two words presented Decisions were made at three different levels within the word recognition process. These levels corresponded to feature detection and synthesis, lexical access and naming, and semantic memory access at the superordinate category level. The late positive component of the evoked waveform varied systematically with the nature of the perceptual and cognitive decisions being made. The late positive component of the waveform was highly correlated with the response times associated with each of the three decision types. It would appear that the late positive component provides an internal index of the neural processes which accompany cognitive decisions. Specifically, the late positive component appears to reflect the time course of stimulus evaluation and comparison processes. The response time data and the evoked waveform provide converging sources of evidence in support of the notion that the word recognition process can be selectively tapped at several different levels within the information processing system.