ELSEVIER Electroencephalographyand clinical Neurophysiology 98 (1996) 294-308 Age-related changes in the electrophysiological response to visual stimulus novelty: a topographical approach Kathleen M. Thomas, Charles A. Nelson *'~ Institute of Child Development, University of Minnesota, 51 East River Road. Minneapolis. MN 55455-0345. USA Accepted for publication: 15 December 1995 Abstract The relationship of task relevance and stimulus probability to P300 morphology, latency and distribution was assessed. Eight year olds and adults completed visual oddball tasks of recognition memory with frequent non-target (60%), infrequent target (20%), and infrequent novel (20%) stimuli. Stimuli consisted of 2 female faces posing neutral expressions, and 40 trial unique novel photographs depicting scenes, animals, objects or abstract patterns. Event-related potentials were recorded from 17 electrodes over frontal, central and parietal scalp, including lateral temporal sites. All stimuli elicited P300 responses at parietal electrodes, with the largest responses to the target stimuli (relevant and infrequent). The P300 responses of adults and children were morphologically dissimilar, with children showing broader peaks and latency shifts across electrodes. In addition, the eight year olds displayed a frontal negativity to novel stimuli which was absent in the responses of adult participants. Results suggest that different anatomical or functional circuitry may be involved in the processing of novelty for adults as compared to eight year olds. Keywords: Visual stimulus novelty; Task relevance; Stimulus probability; Electrophysiologicalresponse; P300 1. Introduction Electrophysiological techniques have long been em- ployed to examine the neurological underpinnings of vari- ous perceptual and cognitive phenomena. For example, Donchin et al. (1986) have described how electrophysio- logical measures permit one to obtain information about human information processing that is not easily or at all available in the traditional subjective and performance measures of psychological research (e.g., mental chronom- etry). Scalp electrical activity is recorded from an individ- ual engaged in some perceptual or cognitive task. The resultant signals are averaged to give an estimate of the proportion of the voltage that is time-locked to a particular event, usually the presentation of an external stimulus (Donchin et al., 1986). This event-related potential (ERP) * Corresponding author. E-mail: CANELSON@VX.CIS.UMN.EDU. Support for this research came from a National Institutes of Health (NIH) training grant to the Center for Research in Learning, Perception, and Cognition, University of Minnesota (HD07151) and grants from the National Institute of Mental Health (MH46860) and the National Insti- tutes of Health (NS32976) to the second author. provides information regarding the temporal sequence of human information processing. The waveforms are exam- ined for predominant components across subjects. Analy- ses of the spatial and temporal information in the averaged ERP may lead to inferences concerning the underlying brain areas which are active during a particular cognitive task. Several robust components have emerged from research employing this technique. The most consistent component described in the ERP literature is the P300, a relatively large positive scalp deflection occurring in adults roughly 300-600 msec after the presentation of a stimulus. This component produces its maximal response over parietal and central scalp locations, with significantly smaller re- sponses over frontal, temporal and occipital areas. The P300 has been observed under many different task circum- stances and is thought by many researchers to reflect some aspect of memory updating (see Donchin, 1981: Donchin and Coles, 1988). It has been suggested by Donchin and his colleagues, as well as other research groups (see Donchin et al., 1986 for review), that the observed charac- teristics of this component depend upon a limited set a parameters which influence the cognitive processes in- volved in completing an assigned task. 0013-4694/96/$15.00 © 1996 Elsevier Science Ireland Ltd. All rights reserved SSDI 00 13-4694(95)00280-4 EEG 95100