 Absolute amnesia for unattended items, or thoroughgoing agnosia for them, may be indistinguishable from inattentional blindness, both behaviourally and from the point of view of retrospective introspection. For that reason it is not a straightforward matter for the advocates of any of these interpretations of the inattentional blindness and change blindness effects to rule out the alternative interpretations. Subpersonal sources of data (such as experiments using neuroimaging) may be the only sources of data that we have to go on. (See Rees, et al. 1999, for an example in which fMRI data is used to argue against the amnesia interpretation of inattentional blindness effects involving written words).