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Meares R, Horvath T. 
“A Physiological Difference Between Hallucinosis and Schizophrenia”. 
Brit Psychiat. 1973;122:687-688.
Boulton (1971), in an authoritative review, has pointed out that biochemical research into schizophrenia has depended upon the assumption that hallucinogens, such as mescaline and LSD produce a state similar to schizophrenia, and that such research has therefore principally been concerned with attempts to find hallucinogens, or substances closely related to them, in the bodily fluids of schizo- phrenics. Since this model has been criticized on phenomenological grounds, we decided to make a comparison between states of visual hallucinosis and of schizophrenia with thought disorder, using a measure which tests a common hypothesis concerning the origin of schizophrenic symptoms. This hypothesis suggests that the symptoms of schizophrenia are manifestations of failure of a hypothetical sensory 'filter' (Broadbent, 1958). This mechanism determines the individualts 'selective inattention' to the irrelevancies of his environment. Its function can be assessed by a study of habituation, which is the Process whereby a randomly repeated stimulus fails in time to elicit an orienting response. METHOD Habituation rates were determined in 10 schizophrenics, whom three psychiatrists independently considered to be suffering from schizophrenic thought disorder. They were compared with those of normals, and also with those of another 1 l patients No. of Stimull who suffered from visual hallucinosis as part of an acute brain syndrome. LSD was the cause of hallucinosis in two cases. All patients were alert when tested,and none were taking psychoactive medication. The ages were 36 2 years (s.e. 4 o) for the schizophrenics, 42 4 years (s.e. 4 7) for the normals, and 47.1 years (s.e. 5 7) for those with visual hallucinosis. None of these differences reach significance when the t-test is applied. The data were analysed according to standard practice (Lacer, Wing, 1966), so that changes in skin resistance were calculated as change in log skin opposing directions when the parameter is habituation conductance. The mean change in log conductance for each stimulus was plotted against the log stimulus number, and a regression line was drawn, using the method of least squares. RESULTS The regression lines displayed in FIG 1 show that the schizophrenics had no tendency to habituate, while on the other hand the subjects with visual hallucinosis habituated significantly more rapidly than normals. The mean channges in log skin conductance for each stimulus point are displayed in a table, which has been omitted for reasons of space, but can be supplied on request. Using Student¹s t-test, the first significant difference between the schizophrenics¹ and the normals¹ response is at the fourth stimulus point, while the first significant difference between those with visual hallucinosis and the normals is at teh fifth stimulus point.
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