Attention to a particular sensory modality requires the participation of the sensory cortex, which must simultaneously initiate the perceptive and apperceptive processes discussed later. What are called “modality” and “domain-specific” attentions (e.g., face or object recognition) are more complex, and disorders of these functions result in unique types of inattention, such as agnosia and anosognosia (lack of recognition of a part of the body, as discussed in Chap. 21). These are not derived from the all-encompassing loss of attention that is part of general confusional states but can instead be viewed as a restricted forms of disruption of insight for which reason they are not major components of the global confusional state.
Disturbances of Perception
The process of acquiring through the senses a knowledge of the world or, of one’s self by cohering what is sensed into giving meaning to what is experienced, which we have termed apperception, involves much more than being aware of the attributes of a stimulus. New visual stimuli, for example, activate the striate cortex and visual association areas, wherein are probably stored the coded past representations of these and similar classes of stimuli. Recognition involves the reactivation of this system by the same or similar stimuli at a later time. Essential elements in the perceptual process are the maintenance of attention, the selective focusing on a stimulus, elimination of all extraneous stimuli, and identification and naming of the stimulus by recognizing its relationship to remembered experience.
The perception of stimuli undergoes predictable disruption in disease. Most often there is a reduction in the number of perceptions in a given unit of time and a failure to synthesize them properly and to relate them to the ongoing activities of the mind. Part of this, as stated above, is due to distractibility (pertinent and irrelevant stimuli having equal value), and inability to persist in an assigned task. Together, these deficiencies lead to disorientation in time and place.
Qualitative changes of perception also appear, mainly in the form of sensory distortions, causing misinterpretations of environmental stimuli (illusions) and misidentifications of persons; these, at least in part, form the basis of hallucinatory experience in which the patient reports and reacts to environmental stimuli that are not evident to the examiner. There is an inability to perceive simultaneously all elements of a large complex of stimuli, a defect that has been termed “failure of subjective organization.” More specific partial losses of perception are manifest in the “neglect syndromes.” The most dramatic examples are observed with right parietal lesions, which render a patient unaware of the left half of his body and the environment on the left side. There are numerous other examples of focal cerebral lesions that disturb or distort sensory perceptions, each subject to neurologic testing; these are discussed in Chap. 21. Their close connection to spatial experience makes them understandable as alterations of apperception in the spatial-sensory sphere.
Disturbances of Memory
The retention of learned information and experiences is involved in all mental activities. Memory may be arbitrarily subdivided into several parts: (1) registration; (2) fixation, mnemonic integration, and retention; (3) recognition and recall; and (4) reproduction. As stated above, there is a failure of learning and memory in patients with the global confusional state as a result of impaired attention because the material was never registered and assimilated in the first place. In almost all circumstances, the formation of new memories and the ability to recall old ones are disturbed in tandem.