The NMDA neurotransmitter system's role in psychoses is not fully understood, but NMDA antagonists like phencyclidine and ketamine induce psychotic states similar to schizophrenia. Binocular depth inversion, a visual illusion impaired in psychotic states, was tested in 12 healthy male volunteers using stereoscopic pictures of natural and artificial objects. Two subanaesthetic doses of the psychotomimetic S-enantiomer of ketamine were compared with placebo. Despite dose-dependent subjective and objective psychopathology, no significant impairment of binocular depth perception occurred with (S)-ketamine. The findings suggest implications for memory, perception formation, and bottom-up processing in ketamine model psychosis and schizophrenia.
The binocular depth inversion test (BDIT) measures a visual illusion in which implausible objects, such as a hollow face, are perceived as normal and convex. This illusion is common and influenced by familiarity, with cognitive factors overriding binocular disparity cues. The internal mechanism balancing top-down and bottom-up perceptual processes appears disturbed in pro-psychotic states. In this pilot study, patients with anxiety disorders scored significantly higher on the BDIT than matched controls, in a range comparable to pro-psychotic conditions. The findings suggest anxiety patients may have abnormalities in central perceptual processing, top-down processing, and reality testing similar to those seen in pro-psychotic conditions.