-28-
¥Conjunction Junction: WhatÕs Your
Function?
HThe program 3dcalc is a general purpose program
for performing logic and arithmetic calculations
å Command line is of the format
3dcalc -a Dset1 -b Dset2 ... -expr
Ò(a * b ...)Ó
å Some expressions can be used to select voxels with values v
meeting certain criteria:
íFind voxels where v ³ th and mark them with
value=1
expression
= step (v Ð th) (result is 1 or 0)
íIn a range of values: thmin ² v ² thmax
expression
= step (v Ð thmin)
* step (thmax - v)
íExact value: v = n
expression = equals(v Ð n)
å Create masks to apply to functional datasets
íTwo values both above
threshold (e.g., active in both tasks; ÒconjunctionÓ)
expression
= step(v-A)*step(w-B)
values from Dset1 are
to be called ÔaÕ in -expr
mathematical
expression
combining
input dataset values