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Perceptions are the process whereby information is attained from the environment. Information of objects and events; it involves the process of recognising and interpreting the information received (Farthing, G 1992). Perception is best described as a voluntary process in that one chooses what environmental objects and so forth is identified by any or all of the five senses (touch, smell, taste, sight, and hear), thus interpreting and remembering information perceived. Hallucinations on the other hand are better explained as an involuntary process, whereby one is unable to fully control their perception and is unable to identify the true nature of their perceptual hallucination.
Hallucinations defined by the DSM-IV, as a 'sensory perception that has the compelling sense of reality of a true perception but that occurs without external stimulation of relevant sensory organ (American psychiatric association, 2000). Thus, this suggested that when one experience a hallucination they are not fully in control of their sensory perception and it seems one does not recognise clearly that what they are experiencing is unreal, as it seems to mirror reality so well. Instead the hallucinations tend to occur spontaneously. It is important to realise that hallucinations are not the same as illusions or delusions which very often get put into the same category. Illusions are an 'external stimulus is misperceived or misinterpreted' (DSM-IV, American psychiatric association, 2000). Delusions are described by the DSM-IV as being a 'false belief' which is due to 'incorrect external reality', regardless of what others are saying and regardless of any apparent evidence, (American psychiatric association, 2000).
The nature of hallucinations, have been found to occur due to many different situations and factors. They are widely known and recognised as a sign of madness and pathology, and are mostly related to the psychiatric illness of schizophrenia. Hallucinations can occur in many different forms, for example hypnogogic hallucination, where they experience hallucination whilst falling asleep or even pseudo hallucination whereby one is aware that the perception they are experiencing is not real, in addition they can be of a visual nature or auditory and so forth, although many studies have found that visual hallucination is a lot more likely to occur than auditory hallucination (Gurney, 1886).
Hallucinations have been thought to have a close relationship with normal perception. In that the occurrence of hallucinations are due to errors of perception (Arnold, 1806). Some believe it to occur due to disruption of the input of information to memory, from perceptual senses, which are part of the 'perceptual release theory', (Jackson, 1888). In addition as it has been suggested that the process has been distorted and disrupted along the way it would propose that it is occurring internally. As external stimuli are recognised the information is getting disarrayed when being processed into memory. Arnold (1806) proposed that hallucination of a pathological level occurred due to a 'defect in the bodily organs' where the information being transmitted is 'incorrect' and processed wrong into the brain, causing hallucinations to occur. However this theory was based only on pathological hallucinations, so therefore does not fully account for other types of hallucination of a simple nature, such as seeing lines or dots for example (Collerton et al. 2005).
The idea that perception and hallucination have a type of relationship, has also been supported by Collerton et al 2005, where he considered hallucination to be a type of 'visual reality' of everyday life. Thus all the information taken in by the senses build up the content of hallucinations which an individual may have. Hallucinations thus are similar to normal perception, especially in terms of the origin and structure as Solmon (1916) suggests. Moreover, Solmon (1916) also suggests that they both (hallucination and normal perception) have a similar underlying process in which there is an absence and presence of primary sensory elements. She proposes there to be a relationship between both phenomenons, where they both derive from the same place, origin, through a similar process.
The relationship between hallucination and normal perception is a complex one to fully understand. It has been found that a lack of normal perception or deprived sensory can cause hallucinations (Vosberg et al, 1960). Thus it is the missing of a real sense which can cause hallucinations. As Fflytche & Howard (1999) support and argue, that the visual loss can lead to a positive perceptual disorder which are experienced as hallucinations. Positive hallucination is the idea that the individual perceives what is not really there, in contrast to negative hallucination which is the notion that one is unable to perceive something that is there. Impaired perception thus seems to be suggested to cause the mind to replace missing information causing hallucination. There are many supporting studies for the idea that a lack of normal perception can cause hallucination however, there is no real explanation to how it is that hallucination actually occurs with any actual normal perceptual system. Although Collerton et al. (2005) supports this idea and explains his findings which suggest that the cause of hallucination is due to disturbances in the lateral frontal cortex-ventral visual stream system, thus affecting visual perception, causing hallucinations of a positive nature to occur.
The question of whether there is a relationship between hallucination and normal perception has so far suggested a direct relationship however other theories would suggest otherwise. Although normal perception seems to play a role in hallucination other theories suggest otherwise. The fact it has been proposed that hallucinations are a random occurrence, suggests that hallucinations must be occurring due to internal factors. As Dennett (1993) suggested, the content in which is hallucinated to the hallucinatory is usually in relation to concerns they may currently be having. Thus Dennett (1993) further explain that the system of perception only falls into a state of hallucination when the 'expectation driven side' of the system is functioning normally and thus when the 'confirmation side', the 'data-driven side' falls into a muddled indecisive cycle of approval and disapproval. Hence hallucinations seem to occur due to underlying factors of the individuals, and thus suggest factors such as stress or even isolation (Siegel, 1984) as a cause for hallucination. On the other hand, although it seems that a factor of stress could cause hallucination initially feeling of stress is likely to be caused by perceptual senses, thus leading back to the idea the initial input of information from normal perception leads to hallucinations.
The relationship between normal perception and hallucination seems to be undetermined. The true reasoning and occurrence of hallucinations is unknown, and seems to be caused due to many different factors, caused on many different levels. However the idea that there is a relationship can be identified. To some extent at least, there is a link where perception, whether it be a lack of it, or too much of it can cause a type of hallucination to occur, thus is a secondary effect. Solmon (1916), 'Hallucinations are of the nature of secondary perception', thus are essentially 'secondary precepts'. The relationship is existent therefore; rather like a cause and effect in some sense. In any case a certain level of perception can lead to a certain form of hallucination or vice versa.