Introduction
Thirty years ago researchers began to report that substances found in the urine of some individuals may be metabolites of toxic chemicals in the body, that could cause brain dysfunctions associated with stability of perception (Hoffer, 1966a; Hoffer & Mahon, 1961; Hoffer & Osmond, 1961b, 1962; Irvine, 1961). These urinary substances were given various names, such as unidentified substances (Hoffer & Mahon, 1961), mauve factor (Hoffer & Osmond, 1963), kryptopyrrole (Irvine, et al., 1969), and most recently, 2-hydroxyl hemopyrrolene-5-one or HHPO (Irvine, 1981). (Throughout this paper the term HHPO shall be used.) It was found that psychiatric patients with HHPO had elevated scores on a psychological test (Hoffer-Osmond Diagnostic Test or HOD) which, among other things, purports to measure perceptual instability (Hoffer, 1965, 1966a & b; Hoffer, Kelm & Osmond, 1975; Hoffer & Osmond, 1961a & b, 1962, 1963).

The purpose of the present study is an attempt to shed more light on possible brain dysfunctions associated with HHPO, using a laboratory measure of perceptual instability called the visual figural aftereffect or VFA. Figural aftereffect phenomena, of which the VFA is one type, purports to measure two kinds of brain responses: augmenting and reducing (Petrie, 1978; Barnes, 1976; Kelm, 1981). An augmenting response is one in which an individual increases his/her sensory environment (perceives an expansion in the distance between two figures, called inspection- and test-figures, used in the VFA); a reducing brain response attenuates sensory input (phenomenal contraction of the inspection- test-figure distance). Augmenting and reducing have also been measured with a procedure using cerebral evoked potentials which have been found to correlate significantly with the figural aftereffect (Barnes, 1976).

In VFA-HOD studies of both schizophrenic patients and normal individuals, it was found that those with elevated HOD scores showed relatively large augmenting responses (phenomenal expansion of the inspection- test-figure distance) with relatively mild visual stimulation, but as this stimulation was intensified by repeated exposures of the test-figure (called test-time), the brains of these individuals greatly reduced this stimulation, as manifested by a perceived shrinkage of the inspection- test-figure distance (Kelm, 1981, 1989). Thus, high HOD scores (unstable perceptions) were associated with a relatively wide range of augmenting - reducing, which experientially manifests itself in terms of perceptual instability. Schizophrenic and normal individuals with lower HOD scores showed a significantly narrower range of augmenting - reducing, and thus more stable perceptions.

Since schizophrenic patients with HHPO have been found to have higher HOD scores than schizophrenics without HHPO (Hoffer & Osmond, 1962; Hoffer, 1966b), and since high HOD-scorers were found to have VFAs of different magnitudes than those with lower HOD scores (Kelm, 1981, 1989), it can be predicted that HHPO and HHPO-free schizophrenic patients will have different VFA magnitudes. Also, since high HOD- scorers were found to have a wider range of cerebral augmenting - reducing than low scorers, it can be predicted that HHPO schizophrenic patients will show greater perceptual instability than HHPO-free patients. The present study will test these predictions.