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Binocular depth perception in individuals at clinical high risk for psychosis: no evidence of dysfunction.

OBJECTIVE
In the last decade the interest in the role of the visual system in schizophrenia has grown, with evidence pointing to dysfunction in bottom-up visual processing that leads to early visual processing deficits. A fundamental component of visual perception is binocular depth perception (BDP), that is, depth perception derived by the difference between the images impressed upon the left and right retina. Two studies reported impaired BDP in schizophrenia and suggested a possible developmental deficit of brain structures involved in early visual processing. The aim of this study was to examine BDP in a young population at clinical high risk (CHR) of developing psychosis to determine whether this dysfunction is present in this potentially prepsychotic period.


METHODS
Forty-two CHR participants and 44 healthy controls were assessed using a computerized test of depth perception; a subsample completed a test of stereopsis. The computerized test comprised two trial blocks, with four conditions at increasing level of difficulty, in which participants were asked to discriminate the relative depth of two stimuli simultaneously presented on the screen.


RESULTS
BDP was not impaired in the CHR group, whose performance was similar to that of the control group on both measures. For the CHR group performance in both tests was not correlated to positive symptoms.


CONCLUSIONS
These results indicate that BDP is preserved in individuals at CHR for psychosis, and impaired BDP should not be considered a vulnerability marker for schizophrenia. Nevertheless future studies should verify BDP's potential power in predicting schizophrenia.