view easily explains how our experience can seem unified as one whole despite all of these individual parts. however, it remains unspecified which kinds of information are integrated in a conscious manner and which kinds can be integrated without consciousness. nor is it explained what specific causal role conscious integration plays, nor why the same functionality cannot be achieved without consciousness. obviously not all kinds of information are capable of being disseminated consciously (e.g., neural activity related to vegetative functions, reflexes, unconscious motor programs, low-level perceptual analyses, etc.) and many kinds of information can be disseminated and combined with other kinds without consciousness, as in intersensory interactions such as the ventriloquism effect. hence it remains unclear why any of it is conscious. for a review of the differences between conscious and unconscious integrations, see the article of ezequiel morsella. as noted earlier, even among writers who consider consciousness to be well-defined, there is widespread dispute about which animals other than humans can be said to possess it. edelman has described this distinction as that of humans possessing higher-order consciousness while sharing the trait of primary consciousness with non-human animals (see previous paragraph). thus, any examination of the evolution of consciousness is faced with great difficulties. nevertheless, some writers have argued that consciousness can be viewed from the standpoint of evolutionary biology as an adaptation in the sense of a trait that increases fitness. in his article "evolution of consciousness", john eccles argued that special anatomical and physical properties of the mammalian cerebral cortex gave rise to consciousness (" psychon ... linked to dendron through quantum physics"). bernard baars proposed that once in place, this "recursive" circuitry may have provided a basis for the subsequent development of many of the functions that consciousness facilitates in higher organisms. peter carruthers has put forth one such potential adaptive advantage gained by conscious creatures by suggesting that consciousness allows an individual to make distinctions between appearance and reality. this ability would enable a creature to recognize the likelihood that their perceptions are deceiving them (e.g. that water in the distance may be a mirage) and behave accordingly, and it could also facilitate the manipulation of others by recognizing how things appear to them for both cooperative and devious ends. other philosophers, however, have suggested that consciousness would not be necessary for any functional advantage in evolutionary processes. no one has given a causal explanation, they argue, of why it would not be possible for a functionally equivalent non-conscious organism (i.e., a philosophical zombie) to achieve the very same survival advantages as a conscious organism. if evolutionary processes are blind to the difference between function f being performed by conscious organism o and non-conscious organism o*, it is unclear what adaptive advantage consciousness could provide. as a result, an exaptive explanation of consciousness has gained favor with some theorists that posit consciousness did not evolve as an adaptation but was an exaptation arising as a consequence of other developments such as increases in brain size or cortical rearrangement. consciousness in this sense has been compared to the blind spot in the retina where it is not an adaption of the retina, but instead just a by-product of the way the retinal axons were wired. several scholars including pinker, chomsky, edelman, and luria have indicated the importance of the emergence of human language as an important regulative mechanism of learning and memory in the context of the development of higher-order consciousness (see neural correlates section above). altered states a buddhist monk meditating there are some brain states in which consciousness seems to be absent, including dreamless sleep or coma. there are also a variety of circumstances that can change the relationship between the mind and the world in less drastic ways, producing what are known as altered states of consciousness. some altered states occur naturally; others can be produced by drugs or brain damage. altered states can be accompanied by changes in thinking, disturbances in the sense of time, feelings of loss of control, changes in emotional expression, alternations in body image and changes in meaning or significance. the two most widely accepted altered states are sleep and dreaming. although dream sleep and non-dream sleep appear very similar to an outside observer, each is associated with a distinct pattern of brain activity, metabolic activity, and eye movement; each is also associated with a distinct pattern of experience and cognition. during ordinary non-dream sleep, people who are awakened report only vague and sketchy thoughts, and their experiences do not cohere into a continuous narrative. during dream sleep, in contrast, people who are awakened report rich and detailed experiences in which events form a continuous progression, which may however be interrupted by bizarre or fantastic intrusions. thought processes during the dream state frequently show a high level of irrationality. both dream and non-dream states are associated with severe disruption of memory: it usually disappears in seconds during the non-dream state, and in minutes after awakening from a dream unless actively refreshed. research conducted on the effects of partial epileptic seizures on consciousness found that patients who have partial epileptic seizures experience altered states of consciousness. in partial epileptic seizures, consciousness is impaired or lost while some aspects of consciousness, often automated behaviors, remain intact. studies found that when measuring the qualitative features during partial epileptic seizures, patients exhibited an increase in arousal and became absorbed in the experience of the seizure, followed by difficulty in focusing and shifting attention. a variety of psychoactive drugs, including alcohol, have notable effects on consciousness. these range from a simple dulling of awareness produced by sedatives, to increases in the intensity of sensory qualities produced by stimulants, cannabis, empathogens–entactogens such as mdma ("ecstasy"), or most notably by the class of drugs known as psychedelics. lsd, mescaline, psilocybin, dimethyltryptamine, and others in this group can produce major distortions of perception, including hallucinations; some users even describe their drug-induced experiences as mystical or spiritual in quality. the brain mechanisms underlying these effects are not as well understood as those induced by use of alcohol, but there is substantial evidence that alterations in the brain system that uses the chemical neurotransmitter serotonin play an essential role. there has been some research into physiological changes in yogis and people who practise various techniques of meditation. some research with brain waves during meditation has reported differences between those corresponding to ordinary relaxation and those corresponding to meditation. it has been disputed, however, whether there is enough evidence to count these as physiologically distinct states of consciousness. the most extensive study of the characteristics of altered states of consciousness was made by psychologist charles tart in the 1960s and 1970s. tart analyzed a state of consciousness as made up of a number of component processes, including exteroception (sensing the external world); interoception (sensing the body); input-processing (seeing meaning); emotions; memory; time sense; sense of identity; evaluation and cognitive processing; motor output; and interaction with the environment. each of these, in his view, could be altered in multiple ways by drugs or other manipulations. the components that tart identified have not, however, been validated by empirical studies. research in this area has not yet reached firm conclusions, but a recent questionnaire-based study identified eleven significant factors contributing to drug-induced states of consciousness: experience of unity; spiritual experience; blissful state; insightfulness; disembodiment; impaired control and cognition; anxiety; complex imagery; elementary imagery; audio-visual synesthesia; and changed meaning of percepts. medical aspects the medical approach to consciousness is scientifically oriented. it derives from a need to treat people whose brain function has been impaired as a result of disease, brain damage, toxins, or drugs. in medicine, conceptual distinctions are considered useful to the degree that they can help to guide treatments. the medical approach focuses mostly on the amount of consciousness a person has: in medicine, consciousness is assessed as a "level" ranging from coma and brain death at the low end, to full alertness and purposeful responsiveness at the high end. consciousness is of concern to patients and physicians, especially neurologists and anesthesiologists. patients may have disorders of consciousness or may need to be anesthetized for a surgical procedure. physicians may perform consciousness-related interventions such as instructing the patient to sleep, administering general anesthesia, or inducing medical coma. also, bioethicists may be concerned with the ethical implications of consciousness in medical cases of patients such as the karen ann quinlan case, while neuroscientists may study patients with impaired consciousness in hopes of gaining information about how the brain works. assessment in medicine, consciousness is examined using a set of procedures known as neuropsychological assessment. there are two commonly used methods for assessing the level of consciousness of a patient: a simple procedure that requires minimal training, and a more complex procedure that requires substantial expertise. the simple procedure begins by asking whether the patient is able to move and react to physical stimuli. if so, the next question is whether the patient can respond in a meaningful way to questions and commands. if so, the patient is asked for name, current location, and current day and time. a patient who can answer all of these questions is said to be "alert and oriented times four" (sometimes denoted "a&ox4" on a medical chart), and is usually considered fully conscious. the more complex procedure is known as a neurological examination, and is usually carried out by a neurologist in a hospital setting. a formal neurological examination runs through a precisely delineated series of tests, beginning with tests for basic sensorimotor reflexes, and culminating with tests for sophisticated use of language. the outcome may be summarized using the glasgow coma scale, which yields a number in the range 3–15, with a score of 3 to 8 indicating coma, and 15 indicating full consciousness. the glasgow coma scale has three subscales, measuring the best motor response (ranging from "no motor response" to "obeys commands"), the best eye response (ranging from "no eye opening" to "eyes opening spontaneously") and the best verbal response (ranging from "no verbal response" to "fully oriented"). there is also a simpler pediatric version of the scale, for children too young to be able to use language. in 2013, an experimental procedure was developed to measure degrees of consciousness, the procedure involving stimulating the brain with a magnetic pulse, measuring resulting waves of electrical activity, and developing a consciousness score based on the complexity of the brain activity. disorders medical conditions that inhibit consciousness are considered disorders of consciousness. this category generally includes minimally conscious state and persistent vegetative state, but sometimes also includes the less severe locked-in syndrome and more severe chronic coma. differential diagnosis of these disorders is an active area of biomedical research. finally, brain death results in possible irreversible disruption of consciousness. while other conditions may cause a moderate deterioration (e.g., dementia and delirium) or transient interruption (e.g., grand mal and petit mal seizures) of consciousness, they are not included in this category. disorderdescription locked-in syndromethe patient has awareness, sleep-wake cycles, and meaningful behavior (viz., eye-movement), but is isolated due to quadriplegia and pseudobulbar palsy. minimally conscious statethe patient has intermittent periods of awareness and wakefulness and displays some meaningful behavior. persistent vegetative statethe patient has sleep-wake cycles, but lacks awareness and only displays reflexive and non-purposeful behavior. chronic comathe patient lacks awareness and sleep-wake cycles and only displays reflexive behavior. brain deaththe patient lacks awareness, sleep-wake cycles, and brain-mediated reflexive behavior. medical experts increasingly view anosognosia as a disorder of consciousness. anosognosia a greek-derived term meaning "unawareness of disease". this is a condition in which patients are disabled in some way, most commonly as a result of a stroke, but either misunderstand the nature of the problem or deny that there is anything wrong with them. the most frequently occurring form is seen in people who have experienced a stroke damaging the parietal lobe in the right hemisphere of the brain, giving rise to a syndrome known as hemispatial neglect, characterized by an inability to direct action or attention toward objects located to the left with respect to their bodies. patients with hemispatial neglect are often paralyzed on the left side of the body, but sometimes deny being unable to move. when questioned about the obvious problem, the patient may avoid giving a direct answer,