![]() ![]() ![]() The P3b, in contrast, is thought to reflect processes related to working memory (Donchin, 1981). The P3a response is conceptualized as a cognitive “orienting” to unexpected stimuli (Courchesne, 1978 Courchesne et al., 1975). The associated P300 responses have distinct temporal characteristics, with responses to targets (P3b Picton, 1992) being delayed relative to responses to novelty (P3a Courchesne et al., 1975 Friedman et al., 1998 Squires et al., 1975). These attentional systems have been studied using the oddball paradigm with electroencephalography to measure event‐related potentials (EEG‐ERPs), elicited by infrequent (target) stimuli interspersed with novel (distractor) stimuli (Knight and Nakada, 1998 Sutton et al., 1965). © 2006 Wiley‐Liss, Inc.Īttention requires the complementary processes of directed behavior (top‐down control) and response to irrelevant but intrusive novel stimuli that may occur during task performance (bottom‐up). Thus, indices of the HRF can be used to better understand the relationship between hemodynamic changes and performance and can be sensitive to individual differences. Age was associated with reduced peak HRF in left frontal region. Sex differences were observed, with higher HRF peaks for novelty in men in right occipital regions, and longer time to peak in the left hemisphere. Both height of the HRF and longer time to peak in the right cingulate were associated with slower response time. ![]() While robust HRFs characterized most regions, target detection was associated with a negative HRF in the right parietal precuneus and a biphasic HRF in thalamus, basal ganglia, and all occipital regions. Overlapping regions were left thalamus, caudate and cuneus and right parietal precuneus. Activation to novelty was more posteriorly distributed, and frontal activation occurred only on the right, while robust activation was seen in occipital regions bilaterally. Targets were associated with bilateral, albeit leftward predominant changes in frontal‐parietal temporal and occipital cortices, and limbic and basal ganglia regions. We studied 36 healthy participants (17 men) applying a visual oddball event‐related design at 4 Tesla, and performed an unbiased determination of the hemodynamic response function (HRF). Event‐related functional imaging enables characterization of hemodynamic changes associated with these processes. The oddball paradigm examines attentional processes by establishing neural substrates for target detection and novelty. ![]()
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