Speech perception
Agnosia is "the loss or diminution of the ability to recognize familiar objects or stimuli usually as a result of brain damage". There are several different kinds of agnosia that affect every one of our senses, but the two most common related to speech are speech agnosia and phonagnosia.
Apperceptive agnosia
Visual apperceptive agnosia is a visual impairment that results in a patient's inability to name objects. While agnosics suffer from severe deficits, patients' visual acuity and other visual abilities such as perceiving parts and colours remain intact. Deficits seem to occur because of damage to early-level perceptual processing. While patients are able to effectively allocate attention to locate the object and perceive the parts, they are unable to group together the parts they see and name the object accurately. This is demonstrated by the fact that patients are more effective at naming two attributes from a single object than they are able to name one attribute on each of the two superimposed objects. In addition they are still able to describe objects in detail and recognize objects by touch.