In assessing attention, the CPT-IP is administered using MacStim software and MRI compatible audiovisual system. During the fMRI scans subjects are asked to perform the CPT-IP task in a block-periodic design. Participants alternate between two conditions. During the first condition, subjects perform in a control task during which they view a four-digit number repeating at a constant rate (0.75 sec.) and are instructed to simply look at the flashing number without responding in any way. During the second condition, subjects watch a series of high resolution four digit numbers appearing in a random sequence and are instructed to press a response button when they see any number repeat twice in a row during the sequence. Numbers again appear every 0.75 sec.