The late positive component of the evoked waveform II: Relationship to picture recognition processes

Averaged evoked potentials were collected from Cz, C3', C4', and Pz while subjects made cognitive decisions about pairs of pictures using perceptual and semantic features. Decisions were made at three different levels within the picture recognition process. These levels correspond to feature detection and synthesis, and semantic memory activation at the basic category and superordinate category levels. The late positive component of the evoked waveform systematically varied as a function of the nature of the cognitive decision being made. The late positive component of the waveform was highly correlated with the response times associated with each experimental condition. It would appear that the late positive component of the waveform provides an internal index of the neural processes which accompany cognitive decisions. As such, the late positive component of the evoked waveform serves as a source of converging evidence, along with response latency measures, that the picture recognition process can be successfully tapped at several different levels within the information processing system. This work should be applicable for studying disruptions to the pattern recognition process which accompany stroke, head trauma, and neurological problems associated with learning disorders. It should also be sensitive to any disorder which influences central processing time more than early perceptual and peripheral processes.