Stereognosis is a medical term for the ability to identify objects through touch. When a person handles a material, he or she sends touch signals to the brain, and the brain identifies the object. This ability is present in healthy people but can be affected in people who have lesions in the brain.
The arcane scientific term for touch identification, stereognosis, stems from Greek words. Stereos, for example, means solid in Greek. Gnosis is another Greek word and means knowledge. The entire word, therefore, means the solid is known to the person. If the person cannot identify solids properly, then he or she suffers from astereognosis, or lack of knowledge of the solid.
A human perceives the world through his or her senses. Sight is an important sense, and typically when trying to identify an object, people use their sight. Smell may be somehow useful when identifying scented objects like strawberries or perfumes, and hearing only really applies to objects that make a discernible noise. Tasting objects is useful when distinguishing meal ingredients but is not suitable for many other objects.
Touch is a sense that everybody uses all day, everyday, most of the time without even noticing. Identification through touch comes to the fore when a stone is present in a shoe, a countertop is covered in crumbs, or when, in the darkness of a cinema theater, a moviegoer wants to fish out a gummy candy from the box. Stereognosis is this ability to detect objects when the other senses are not involved.
Healthy people usually have no trouble identifying most of the objects their hands encounter. This is because the touch receptors in their hands receive the information about the texture, temperature, shape, and size of the object and send the information to the brain to be properly interpreted. The brain uses the information signals and previous experience of similar objects to figure out what the object is.
When the brain is damaged, the signals from the hands can be misinterpreted. The person affected with a lesion in the areas of the brain involved, such as the sensory cortex of the parietal lobe, cannot properly recognize the object in his or her hand. For this reason, a stereognosis test is sometimes performed on patients who may have suffered brain lesions in that area.
Neurological exams of this kind simply test the ability of the patient to identify most of the common objects placed in his or her hand. Pens, paperclips, or coins are common enough to use for this test. A patient who cannot identify the common objects suffers from astereognosis, which indicates that a brain lesion is present.