Dear SPMers,
There seems to be much confusion about what a negative contrast value means.
My understanding is that a negative contrast value indicates that
significant activation is elicited by the a condition for which a -1
was assigned to in a contrast, not the condition that a 1 was assigned
to. For example, if a contrast comparing semantic memory retrieval and
a control condition yielded a -3 contrast value for a particular brain
region, this brain region would show enhanced activation during the
control task compared to the semantic memory task. Is this correct?
Additionally, what does a negative contrast value mean when performing
a parametric modulation examining the linear increase in activation
given two conditions (e.g. easier vs. hard)? Does it hold the same
principle?
Thanks in advance for the help.
Best,
Elsa Baena
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Elsa Baena
Graduate Student
Clinical Neuropsychology Program
Cognitive Neuroscience Laboratory
University of Arizona
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