Print

Print


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

-- 
_________________________________
_________________________________
Elsa Baena
Graduate Student
Clinical Neuropsychology Program
Cognitive Neuroscience Laboratory
University of Arizona
[log in to unmask]