Sensory illusion

These molecules cause significant changes in the perceptual system, producing sensory illusions and inducing a distortion of reality, the sense of space and time, to the point of hallucination. Natural, synthetic or semisynthetic substances can cause hallucinogenic effects psilocin, psilocybin, mescaline, and LSD. Hallucinogenic effects are also created by phencyclidine and ketamine, but these molecules have a dissociative character. 

Color visions were provoked by doses of 0.36-0.44 g. of mescaline sulfate distributed in several subcutaneous injections. The state of intoxication and the visions lasted for 5 to 10 hours. The effects varied widely in different individuals. The most characteristic symptom is that of wonderful visual color hallucinations. Clear consciousness is generally preserved and the subject is fully aware of his condition. Sensory illusions and transposition of sensorial excitation are the interesting factors in this inebriation. Ordinary objects appear to be marvelous. Sounds and music are seen in color. In comparison, the impressions of everyday life seem pale and inert. Color symphonies and new, unknown colors of unimaginable beauty and brilliancy are perceived. Euphoria is not always present. Hallucinations of hearing, taste, or other senses were reported more rarely. Bradycardia, nausea, a feeling of oppression in the chest, faintness, and headache may also occur. 

Menthol is often thought of as a decongestant, but this effect is a sensory illusion. Burrow et al. (1983) and Eccles et al. (1988) showed that there was no change in nasal resistance to air ow during inhalation of menthol, although the sensation of nasal air ow was enhanced. In the former experiment, 1,8-cineole and camphor were also shown to enhance the sensation of air ow but to a lesser extent than menthol. 

A possible link between the movement of the eyes (which is real) and the hallucinated dream movements (which are fictive) is provided by the PGO system. This is because the neuronal firing patterns associated with each PGO wave encode (at least) the direction of the eye movements and provide that encoded information to (at least) the visual thalamus and visual cortex. This means that in the absence of real sensory input from the eyes, feed forward information about the direction of the (also fictive) gaze is provided to the upper brain, which could (and we think almost certainly must) use it in the elaboration of the convincing visuomotor illusion that is dreaming. 

Although it is a desirable anesthetic in many respects, ketamine has been associated with postoperative disorientation, sensory and perceptual illusions, and vivid dreams (so-called emergence phenomena). Diazepam, 0.2-0.3 mg/kg, or midazolam, 0.025-0.05 mg intravenously, given prior to the administration of ketamine reduces the incidence of these adverse effects. 

Psychologists distinguish between illusions and hallucinations. An illusion is a distorted perception of a real physical stimulus in your environment. A hallucination is a total creation of a perception when nothing is really present. If you walk into a dimly lit room and temporarily mistake a coat on a coat rack for a man lurking in the dark, that s an illusion. If the same nonexistent (as far as the rest of us are concerned) man walks out into the well-lit and empty hall with you, that s a hallucination. We can view illusions and hallucinations as extreme points on the continuum of simulation of the world. In illusion the simulation begins with sensory stimulation, but the simulation is a very poor representation. At the other extreme of hallucination, the simulation process produces a perception, an internal simulation, with no external stimulation involved. 

These findings have strongly influenced current views of color perception, and the study of perception and sensation in general. It is still unknown, however, whether similarly organized receptor cells may exist for, or contribute to, perceptual phenomena such as the constancies and illusions. But their demonstrated existence may indicate that many perceived qualities of the physical world are based on such specific sensory mechanisms. 

Illusions—Visual perceptions that are misinterpreted but have a real sensory stimulus. 

It is surprising that sensory dominance can have such a profound effect on our perceptions. It is even more surprising that the changes in perception due to sensory dominance can be much greater than could be achieved by actual changes (as in the parchment hand illusion). 

Partial seizures, simple Consciousness preserved manifested variously as convulsive jerking, paresthesias, psychic symptoms (altered sensory perception, illusions, hallucinations, affect changes) and autonomic dysfunction... 

Use of this agent is associated with a high incidence of disorientation, sensory and perceptual illusions, and vivid dreams during recovery from anesthesia... 

Kettle hop" aroma is an illusive flavor note reminding one of hops, Imparted to beer by the vigorous boiling of "aroma hops" in the wort for up to a few hours. Brewers and hop flavor researchers currently do not agree on the chemical or sensorial nature of this flavor note. It is commonly described as spicy or herbal. There are no standard compounds used to Illustrate this flavor note to flavor panelists. 

The illusion shown in Figure 10.2 is not an inaccurate perception it is a demonstration of how one perception can be inconsistent with another perception. Recognition of the saxophone player is just as valid as recognition of the young woman. Both are as real and accurate as one another. This example also demonstrates that perception is an active process humans constantly interpret sensory data to produce recognisable objects and events. 

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