How can we tell what information is represented in each voxel or region? Even if the mean response of the voxel is the same to the two kinds of stimuli, different neural populations in the voxel may respond to the two stimuli, and if so those populations of neurons can represent the difference between those stimuli. This talk explains a method called fMRI adaptation, which provides a way to determine whether a region or voxel can tell the difference between stimulus A and stimulus B.