Literally, human mind is a storehouse of complexity. Major stake-holders of the complexity are the First Signal System and the Second Signal System both of which together or separately are available only to human brain. Other living organisms have the skill of only the First Signal System. Whether First or Second, the system represents means of communication between and or among the living entities.
Sensory centres in the human brain interact with stimuli emanating from the environs with the aid of sense organs. Cognitive ability of the human brain depends upon the interaction of the sensory centres. There are situations where cognition gets refracted and become disorderly due to malfunctioning or improper functioning of the sensory centres.
Brain activity that reflects the objective reality of the outside world begins with Sensations. Brain does not react directly with the outside objects but it acts through receptors called sense organs. Sensation is the primary mental activity and it is the initial stage of cognitive process. The process of reflection of objective reality does not stop at the initial stage. A person gets not only the individual qualities of an object but the object itself as a whole. The mental activity by or through which the entire object is reflected, involving unity and judgment, not only individual properties but the object in its entirety, is known as Perception.
Everything one sees, hears or feels is reflected through Perception. The cognitive ability up to the stage of perception is common for animals as well as humans but the cognitive capability of humans is at a higher level due to the complexity of brain development. The distinction is attributable to Conception. Conception belongs to Second Signal System that is the means of communication through words. It is specifically separate from the First Signal System which is the means of communication of Signs and Symbols.
The transformation of cognitive function of the brain through sensations and perceptions supplemented by Conceptions pass through Evaluation and Judgment which finally ends up in the form of Memory. Memory is human ability to retain traces of past perceptions and sensations and to reproduce them as concepts. This is where the cognitive activities of central nervous system of humans sustain its generality for normal existence. However there arise situations which affect cognitive functions and end up in deflected experiences for the individuals. Such deflections generate experiences which are outside generality. What is commonly known as Illusions, Hallucinations and Delusions belongs to the deflected experiences.
Illusion is a distorted or a false perception of an existing thing or matter. The experience of illusion is deceptive but it need not necessarily be serious derangement. For example, in hot summer season, highway vehicle drivers see a mirage which is an illusion but not a serious one.
Persons who are in affective state of sensory function due to extreme beliefs, fear and anxiety become victims of deranged consciousness. They experience very deep visual, auditory, olfactory or other illusions which are serious in nature. Take the case of mental patients: Cracks on walls, shadows on ceilings, wandering clouds in far away skies may appear to them as monsters, characters in mythology or denizens of heaven. Their experiences are illusions that belong to the serious category. Illusions occur to healthy individuals as well as mentally retarded persons when their cerebral hemispheres and its working are obliterated or reduced due to partial inactivity or inhibition of the sensory centres in their cortex.
Hallucination is an imaginary perception: Complete absence of objects of perception is its peculiarity. The false perception appears as real to the perceiver with external projection. The perception occupies the same position in space as that of real objects and it becomes so certain to the perceiver that the authenticity of what is perceived is never doubted by the perceiver.
Hallucinations take place as a result of disorder or derangement of mind. The disorder or the derangement can be either of elementary nature or it can be complex with high intensity. Elementary hallucination is less serious compared to complex ones. Seeing sparks of light and hearing cracking sounds in the absence of real object of vision or any source of the sound can be cited as examples for elementary hallucination. These experiences take place even while the perceiver is in total wakeful state with normal sensibility. On the other side, complex hallucinations are serious in intensity and nature: Most hallucinations belong to auditory, visual, olfactory and gustatory sensory centres. A serious mental patient may hear voices that command him to do something or not to do something. The command could be that the patient shall kill himself or he shall go out and preach the gospel of god. In other situations, the patient would be seeing landscapes, angels roaming the heavens, god appearing before him to bless, demons chasing to devour him; all according to deep rooted beliefs.
Delusions are false opinions and beliefs which do not correspond with the true position of things and matters in the environs. They have morbid basis and are distorted and perverted reflection of objective reality. Delusions and hallucinations are not of the same stature. Hallucinations are experiences while delusions are false opinions got deep rooted in the memory. Delusions do not correspond with reality. They are always at variance with reality and are not subject to criticism and correction. Delusion is a symptom of serious mental derangement. It is difficult for the sufferers to free themselves out of the influence of delusions.
Illusions and Hallucinations take place when the cerebral cortex is in the transitory state of hypnotic phase. Delusions too belong to this transitory state but the bases of its arousal being strong conditioned nerve connections, the intensity of delusions remain unalterable.
It is necessary in this context to have a general understanding of natural sleep and hypnosis which is induced by idealistic practices.
While awake, the sensory centres in the cerebral hemispheres interact with stimuli from the environs and consequently the nerve cells lose energy due to the process of excitation. Then the cells pass on to restful, inactive state of inhibition. Such inhibitory state of the cells is what is commonly known as natural sleep. The very basis for the reach of the restful, inactive state of inhibition is continuous excitation.
Except for the natural environs, humans have created several other environs by way of beliefs, faiths, rituals, pursuits, societal norms, codes of conduct, behaviour, concepts of rights and wrongs, authority and abeyance and so many other conditions. The man made environs too lead to cerebral inhibition due to excitation provided by the artificial environs. The persons, who are extreme adherents to the man made environs, pass through the artificial inhibition akin to hypnosis in their cerebral hemispheres. They are the ones who become prey to the abnormal cognitive experiences. The partial sleep of hypnosis during its paradoxical phase brings in experiences of illusions and hallucinations. Delusions of patients suffering from serious mental disorders arise either in paradoxical hypnotic phase or in transition of paradoxical and ultra paradoxical hypnotic phases separately or intermittently.
Human mind is complex: The complexity has no idealistic basis. Mind is materialistic and it is the product of brain activity. Brain activity manifests desires and striving to make changes by way of acts and deeds. The manifestations are known as Volitional processes involving active attention. Volitional processes are facilitated by Cognition. Illusions, hallucinations and delusions debilitate cognition: Persons who are victims of cognitive disorders are disgrace for those who are sound and well-set.