Biomedical Engineering Reference
In-Depth Information
XX
s
n
−
t
=
A
B
(13.20)
2
2
s
n
p
p
+
A
B
The results of the previous statistical analysis can be represented on a realistic
model of the cortex of the subjects for each of the frequency bands of interest. The
model will show only the statistically significant cortical activations, pointing out
the differences between the characteristic activations during the tasks being consid-
ered (see Figure 13.2).
The figure represents statistically significant spectral cortical activations repre-
sented on the model of the cortex related to the average head model provided by
McGill University. The figure shows the areas of statistically significant spectral
cortical activity occurring in the brain of a representative subject during the execu-
tion of task
A
as compared to the brain activity elicited by the execution of task
B
.
Usually, task
B
is related to some “rest” state, whereas task
A
is related to the for-
mal experiment being conducted. Generally, these statistical brain pictures could be
generated for each frequency band investigated. In the different views of the cortical
surface, grayscale is used to highlight the cortical zones in which the brain activity
during task
A
is statistically significantly different from the cortical activity during
task
B
. In contrast, the cortical areas that are activated in a similar way during tasks
A
and
B
for the particular subject are presented in gray. The dark gray indicates the
maximum of the statistical differences between the cortical power spectra estimated
during tasks
A
and
B
in the particular subject investigated, after the Bonferroni cor-
rection for multiple comparisons. The black is at the lowest level of statistical
significance at 5% Bonferroni corrected.
Until now, the assumptions of the normality and homoscedasticity of the esti-
mated spectra were assumed in order to perform the statistical analysis with the Stu-
dent's test. It might be argued which test could be used in the case in which such
Figure 13.2
Statistically significant spectral cortical activations represented on the model of the cor-
tex related to the average head model provided by McGill University.
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