Agnosia is the general term given to a variety of
recognition disorders thought to occur at later stages of processing; in
other words, beyond the level of basic sensory mechanisms such as vision
The disorder can occur at the level of the
perception of a stimulus, or at the level at which meaning is assigned
to a correctly perceived cue.
Although these disorders often overlap with each
other as well as with other disorders such as aphasia, and are often
hard to distinguish in an absolute manner, there are basic
characteristics that have been established for each subtype.
Several of these subtypes are
apperceptive agnosia, the inability to correctly perceive objects,
associative agnosia, the inability to assign meaning to a correctly perceived
stimulus, and mirror agnosia, the inability to differentiate between
real and reflected objects.