This document discusses various types of perceptual deficits including agnosias, ataxias, and color blindness. It notes that agnosia is the inability to process sensory information, and describes types of visual agnosia like object agnosia and prosopagnosia. Optic ataxia is defined as the inability to use vision to guide movements. The specificity of deficits has led researchers to believe perception involves separate modular systems. Evidence for this includes some patients having problems recognizing objects but not faces, or vice versa. Understanding perception is important for improving safety, designing assistive devices, and providing treatments.