What do visual hallucinations tell us about the nature of consciousness?

The term ‘hallucination’ is difficult to define. There is a fine line between a ‘hallucination’ and an ‘illusion’. A hallucination differs from an illusion in that illusions are a product of misinterpretations of external stimuli whereas hallucinations need no such requirement making them an entirely internal process. A true hallucination can also be distinguished from a pseudo-hallucination in which the individual can recognise that what they’re seeing or hearing is not real. Hallucinations are also different from voluntary mental imagery, in that the thought has not uncontrollably forced itself onto our minds. Slade and Bentall (1988, cited in Blackmore, 2010) …show more content…

Berrios (1990), through looking at a sample of 46 subjects experiencing musical hallucination, concluded that musical hallucinations were more common in females, and age and deafness seemed to play an important role in their development.

Studies looking at CBS or hearing loss are consistent with the claim that hallucinations can occur as a result of an interruption in sensory input. However, studies have also addressed possible consistencies between hallucinations. There is no limit to the variety of hallucinations, although some common features have been identified suggesting a consistency that reflects underlying sensory processes. Such common features include spirals, concentric patterns, wavy lines, and bright colours. These similarities were investigated through studying the effects of mescaline, a hallucinogenic drug (Kluver 1926, as cited in Blackmore, 2010). It was found that brightly coloured images occurred, with a tendency to take on four forms. The first was gratings and lattices, the second was tunnels, funnels and cones, the third was spirals, and the fourth was cobwebs. These forms seem to be evident in hallucinations caused by drugs, fever, and more. The reason for such consistency lies within the mapping between patterns of the retina and the columnar organisation of the primary visual cortex. Concentric circles from the