The Analysis of Functional NeuroImages (AFNI) software package [47] was used for processing the basic structural and functional image. Changes in echo planar images (EPI) intensity in relation to task characteristics [48] were evaluated using the multivariate regressor approach detailed below. A 3D-coregistration algorithm [49] developed to minimize the amount of image translation and rotation relative to all other images used Echoplanar images that were co-registered. Each subject had six motion parameters obtained, three of which were used as regressors to adjust for EPI intensity changes due to motion artifacts. To ensure that different relationships with the regressors were not due to the acquisition of different slices at different times during the repetition interval, all slices of the EPI scans were temporally aligned following registration.
