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We assessed delay variability among different cortical sites and between parenchyma and blood vessels. Overall, 81% of all responsive voxels showed activation in phase with the stimulus while the remaining voxels showed antiphase, suppressive responses. Mean delays for activated and suppressed voxels were not significantly different (<jats:italic>P<\/jats:italic>&lt; 0.001). Cortical flat maps showed that the pattern of activated and suppressed voxels was dynamically induced and depended on stimulus size. Mean delays for blood vessels were 0.7\u20132.4 sec longer than for parenchyma (<jats:italic>P<\/jats:italic>&lt; 0.01). However, both parenchyma and blood vessels produced responses with long delays. We developed a model to identify and quantify different components contributing to variability in the empirical delay measurements. Within\u2010voxel changes in delay over time were fully accounted for by the effects of empirically measured fMRI noise with virtually no measurable variability associated with the stimulus\u2010induced response itself. Across voxels, as much as 47% of the delay variance was also the result of fMRI noise, with the remaining variance reflecting fixed differences in response delay among brain sites. In all cases, the contribution of fMRI noise to the delay variance depended on the noise power at the stimulus frequency. White noise models significantly underestimated the fMRI noise effects. Hum. Brain Mapping 13:74\u201393, 2001. \u00a9 2001 Wiley\u2010Liss, Inc.<\/jats:p>","DOI":"10.1002\/hbm.1026","type":"journal-article","created":{"date-parts":[[2002,9,10]],"date-time":"2002-09-10T23:06:08Z","timestamp":1031699168000},"page":"74-93","source":"Crossref","is-referenced-by-count":137,"title":["Analysis and use of FMRI response delays"],"prefix":"10.1002","volume":"13","author":[{"given":"Ziad S.","family":"Saad","sequence":"first","affiliation":[]},{"given":"Kristina M.","family":"Ropella","sequence":"additional","affiliation":[]},{"given":"Robert W.","family":"Cox","sequence":"additional","affiliation":[]},{"given":"Edgar A.","family":"DeYoe","sequence":"additional","affiliation":[]}],"member":"311","published-online":{"date-parts":[[2001,4,18]]},"reference":[{"key":"e_1_2_9_2_1","doi-asserted-by":"publisher","DOI":"10.1088\/0031-9155\/41\/8\/011"},{"key":"e_1_2_9_3_1","doi-asserted-by":"publisher","DOI":"10.1002\/mrm.1910300204"},{"volume-title":"Random data: analysis and 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