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

Thanks in advance for the help.


Elsa Baena

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