Apperceptive agnosia

Apperceptive agnosia is failure in recognition that is due to a failure of perception. In contrast, associative agnosia is a type of agnosia where perception occurs but recognition still does not occur. When referring to apperceptive agnosia, visual and object agnosia are most commonly discussed; This occurs because apperceptive agnosia is most likely to present visual impairments. However, in addition to visual apperceptive agnosia there are also cases of apperceptive agnosia in other sensory areas.

Auditory apperceptive agnosia are impairments in audition take place despite intact audiogram. In some cases the deficit is in the ability to recognize spoken words and in other cases unable to recognize environmental sounds. In all cases individuals are able to read, write, name objects, and converse intelligently. Similar to visual impairments, the deficit arise because of damage in the primary sensory cortex. In the case of auditory agnosia, lesions are present in the superior temporal gyrus bilaterally or in the posterior temporal lobe of the language-dominant (typically left) hemisphere.

In addition to verbal and nonverbal auditory agnosia, there are cases of auditory apperceptive agnosia where patients are unable to recognize music in the absence of sensory, intellectual, and verbal impairments. In these cases there may be a melodic or a memory basis established in the brain and damage to those areas lead to music agnosia. Agnosia occurs because of failure to re-encode melodic information properly. This associated with right-sided lesions interrupting the melodic route in the brain.

Tactile apperceptive agnosia result in the inability of shape representations specific to tactile modality. The impairment is restricted to the hands even though sensation is not impaired. This is similar to visual apperceptive agnosia in that it is basic level processing that is impaired. Some individuals are unable to recognize objects by touch because of a small cerebral infarction.

Visual apperceptive agnosia is a visual impairment that results in patients 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.

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