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LLN, le 28/09/05 Dear Leandro, >I have a basic question, let say I have tow conditions: activation >and rest. (100 scans). >Vector onsets for the activation condition is: 10 30 50 70 90. Duration: 10 >Vector onsets for the rest condition is: 20 40 60 80. Duration: 10 > >Is it the same to specify only the activation condition (contrast >[1]) than specifing both conditions (contrast [1 - 1])? No, it's not the same: - [1 -1] tests for positive differences between Activation and Rest; - [1] tests for positive differences between Activation and "Anything that is not declared", i.e., your scans 0 to 9 that are not declared in your vectors. Hope this helps, Mauro. -- _____________________________________ Help fighting hunger: http://www.hungersite.com Just click your mouse and sponsors of The Hunger Site donate a serving of food to a person in need - at no cost to you. ______________________________________ Mauro PESENTI Research Associate, National Fund for Scientific Research (Belgium) Unite de Neurosciences Cognitives Departement de Psychologie Universite Catholique de Louvain Place Cardinal Mercier, 10 B-1348 Louvain-la-Neuve tel.: +32 (0)10 47 88 22 fax: +32 (0)10 47 37 74 E-mail: [log in to unmask] http://www.nesc.ucl.ac.be http://www.nesc.ucl.ac.be/mp/pesentiHomepage.htm