Stereognosis (also known as haptic perception or tactile gnosis) is the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc. In humans, this sense, along with tactile spatial acuity, vibration perception, texture discrimination and proprioception, is mediated by the posterior column-medial lemniscus pathway of the central nervous system. Stereognosis tests determine whether or not the parietal lobe of the brain is intact. Typically, these tests involved having the patient identify common objects (e.g. keys, comb, safety pins) placed in their hand without any visual cues. Stereognosis is a higher cerebral associative cortical function.:71
Astereognosis is the failure to identify or recognize objects by palpation in the absence of visual or auditory information, even though tactile, proprioceptive, and thermal sensations may be unaffected. It may be caused by disease of the sensory cortex or posterior columns. People suffering from Alzheimer's disease show a reduction in stereognosis. Astereognosis can be caused by damage to the posterior association areas of the parietal, temporal, or occipital lobes, or the postcentral gyrus of either hemisphere. For other types of dementia, stereognosis does not appear to decline.
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