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Overview
Tactile agnosia is a perception disorder that affects the sense of touch. Agnosias are disorders that impair sensory processing. Most often, brain injuries cause agnosias. Patients diagnosed with tactile agnosia cannot recognize objects through touch alone. However, their sense of touch is usually intact. The sense of touch is considered inferior to other senses such as vision for recognizing objects, though tactile recognition allows people to explore their environment more fully. People diagnosed with tactile agnosia would be unable to perform simple tasks often taken for granted. These daily tasks could include digging through a purse to find a cell phone or keys, and feeling in the dark for a lamp switch.

Types
Tactile agnosia is a disorder that is misunderstood. However, Russell Bauer, breaks down some distinctions among the disorder. He discusses the difference between cortical tactile disorders and tactile agnosia. The biggest difference between the two is that a cortical tactile disorder is an impairment in judging the quality of an object (shape, size, etc.), while tactile agnosia is the inability to identify what an object is using just touch. Those with tactile agnosia can experience it in one or both hands. With tactile agnosia in both hands, objects cannot be indentified through touch or gesture. When the impairment only exists in a single hand, the object will not be recognized by touch, but its use will be clear and can be shown through gesture. Additionally, the unimpaired hand will recognize the object.

History of Tactile Agnosia
In 1918 Josef Gerstmann discovered the first recorded case of pure tactile agnosia. Few people had researched patients with this disorder before. The difference between others and Gertsman were those patients before Gertsman’s patient showed symptoms for other disorders besides tactile agnosia. In 1895, Carl Wernicke wrote a case study on two patients who displayed symptoms of tactile agnosia. Wernicke was probably influencecd by prior work done by Lissauer (1890) on visual object perception. Lissauer studied cases of visual agnosia. Those symptoms likely influenced the way in which Wernicke diagnosed his patients. However, in Gertsmann’s own work, he notes one case that appeared in an ER in 1907. This was a case of true tactile agnosia.

Testing for Tactile Agnosia
Typically when testing for tactile agnosia, objects are placed in a subject’s hand and the subject is then asked to identify the object using his or her sense of touch alone. Since most cases of tactile agnosia appear in only one hand, the unimpaired hand can be used as a control. This is important because the sense of touch is not the most accurate sense to use in order to identify objects, and thus error will occur. A case study looking at a patient, E.C. has many specific examples of deficits in identification of objects through use of touch. When testing for tactile agnosia, researchers typically begin by placing objects in one’s impaired hand and their unimpaired hand. In the patient’s impaired hand they might identified only half of the objects, while in the unimpaired hand they could identify almost all of them. Since, the sense of touch is still intact, a lot of the identification errors may be failure to recognize objects, but not a failure to recognize their texture, or what material they were made of. For instance, when this test was administered to E.C., she gave the answer “plastic” when a disposable razor was placed in her impaired hand.

When identifying tactile agnosia, it becomes obvious quickly if a person is struggling to identify an object using touch. Subjects use exploratory tactics in hoped of identifying objects in their impaired hand. When the same objects are placed in the unimpaired hand, there is almost no need for exploration before identification. In the specific case of E.C., she was able to distinguish weight differences, texture differences, and size differences in objects with a slight impairment in shape perception. This distinguishes her disorder, tactile agnosia, from other cortical tactile disorders.

One specific experiment done on E.C. involved having her identify common objects, and for those she incorrectly identified, she would draw them. This gives some insight into the errors E.C. might be making with object identification. The figure below includes some of the objects she drew after incorrectly identifying them.

This set of drawings may suggest that the components of an object are identifiable, but the overall shape is difficult to identify.