An inability to recognize objects by touch when they are placed in the hand, even though there is no defect of sensation in the fingers or difficulty in holding the object.
Astereognosis is either left- or right-sided; tactile recognition is normal on the other side.
If both sides are affected, the condition is called tactile agnosia.
Astereognosis and tactile agnosia are caused by damage to parts of the cerebrum (main brain mass) involved in recognition by touch and may occur as a result of a stroke or head injury.
Astereognosis means the loss of the capacity to recognise the nature of an object by feeling it, and indicates a lesion (e.g. tumour) of the brain.
n. a disorder of the brain whereby the patient cannot interpret sensations correctly although the sense organs and nerves conducting sensation to the brain are functioning normally. It is due to a disorder of the *association areas in the parietal lobes. In auditory agnosia the patient can hear but cannot interpret sounds (including speech). A patient with tactile agnosia (astereognosis) retains normal sensation in his hands but cannot recognize three-dimensional objects by touch alone. In visual agnosia the patient can see but cannot interpret symbols, including letters (see alexia).... agnosia
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