PROPERTIES OF COMPLEX HALLUCINATIONS ASSOCIATED WITH DEFICITS IN VISION

Complex visual hallucinations are known to occur in individuals with i mpaired vision yet whose emotional and intellectual functions are with in the normal range. These hallucinations, which were first reported b y Charles Bonnet in 1760, have been described in many case studies, bu t have not been analyzed empirically to determine their major properti es. In the present study, sixty complex hallucinators labeled as Charl es Bonnet hallucinators were administered a questionnaire to determine the properties of their hallucinations. Combined use of multiple-corr espondence analysis and hierarchical cluster analysis reveals a set of features that characterize the 'typical' Charles Bonnet hallucinatory experience: the hallucinators' experience occurs while they are alert and with the eyelids open; a sharply focused image appears suddenly, without any apparent trigger or voluntary control; the hallucination i s present for seconds, does not move during this time, then suddenly v anishes. These features are discussed in terms of a 'dimension' of hal lucinatory/perceptual experience, which ranges from discrete perceptua l experiences to multiple, changing experiences. Possible mechanisms t hat underlie the Charles Bonnet hallucinations are discussed.