Stereognosis

STEREOGNOSIS (from the Greek stereos—solid and gnosis—knowledge), stereognostic sense, the ability to recognize objects by touch. It is based on those sensations that are derived from the shape, size, temperature, density, and surface character of the touched object. Stereognosis is built upon a complex perception, a combination of tactile and thermal sensations with deep muscular sense, the sensation of movements of the palpating parts (fingers), and the association of the images arising during palpation with visual and kinesthetic memory images. Thus, stereognosis is a complex function depending not only on the activity of the peripheral and central sensory systems, but connected with the synthetic activity of the cerebral cortex. In the brain, the lower part of the middle third of the central gyri, the gyrus supramarginalis, the gyrus angularis, and the occipital lobe are related to stereognosis. In right-handed individuals, the left hemisphere is of greater importance for stereognosis than the right. Stereognosis is examined in such a way that a patient with closed eyes is given small objects one by one into the hand (a coin, a key, a pencil, geometric figures) and is asked, by palpating them, to describe them as accurately as possible. The disorder of stereognosis is called astereognosis (see). Wernicke in 1895 first pointed out that the disorder of stereognosis does not run parallel with the disorder of elementary sensitivity and has a definite localization in the cerebral cortex. Monakow and others reject the localization of stereognosis, considering it too complex a process. The school of Weizsäcker, which employs finer methods for the study of sensitivity than those hitherto accepted in clinical practice, calls into question "pure stereognosis," i.e., the possibility of a disorder of stereognosis without a disorder of elementary sensitivity.