Astereognosis is an inability to recognize objects by touch when they are placed in one hand – even though there is no defect of sensation in the fingers or any difficulty holding objects.
Testing for astereognosis is part of any examination of the central nervous system. Astereognosis is either left-sided or right-sided; tactile recognition is normal on the other side.
Agnosia results when both sides of the brain are affected.
Astereognosis and tactile agnosia are caused by damage to parts of the cerebrum (main mass of the brain) concerned with recognition by touch.