People with schizophrenia have an altered ability to visually perceive contrast

These results could help to decipher dysfunctions in the neural and computational mechanisms of schizophrenia. Furthermore, this perceptual alteration could also be explored as a potential non-invasive biomarker for the diagnosis or monitoring of this disorder. However, the authors stress the need for further studies to confirm this relationship and to clarify the role of other factors such as medication in this visual disturbance.

The article, published in the journal Schizophrenia Bulletin, is signed by researchers Daniel Linares and Cristina de la Malla, together with master's student Aster Joostens, from the Vision and Control of Action Group of the Faculty of Psychology and the UB Institute of Neurosciences (UBneuro).

A key indicator of visual function

The symptoms of schizophrenia are characterized by alterations in thinking and behaviour, such as loss of contact with reality, delusions or hallucinations, but there are also abnormalities in the perception of visual stimuli, such as deficits in the perception of colour or contrast. Understanding these abnormalities may provide clues as to how information processing disturbances contribute to the characteristic symptoms of schizophrenia. "Contrast perception is one of the most fundamental abilities of vision, as without it, we cannot adequately perceive the environment and the objects in it, which can compromise everyday tasks such as moving through space, recognizing faces or reading," explains the research team, part of the Department of Cognition, Development and Educational Psychology.

The neural mechanisms involved in this alteration could be related to the levels of glutamate, a neurotransmitter thought to play a central role in the pathogenesis of the disease. "A decrease in this neurotransmitter can lead to reduced neural activity in the brain areas responsible for processing contrast. Consequently, a decrease in contrast sensitivity, although not of great magnitude, may reflect an underlying impairment in the glutamatergic system of affected individuals," note the experts.

Contrast sensitivity testing could therefore be "a valuable tool for identifying individuals with schizophrenia who show a more pronounced dysfunction in this neurotransmitter pathway. For example, these patients could be ideal candidates for clinical trials evaluating drugs that specifically target glutamatergic signalling," they state.

According to a review of more than 600 studies, these patients would have difficulty in detecting differences in light intensity between adjacent areas, without which they cannot adequately see their surroundings and objects.

Unravelling the impact of medication and care

The results of the study show a large-scale impairment in contrast perception in people with schizophrenia, but also that this dysfunction may be influenced by other factors. "In the study, we have identified a relationship with the dose of antipsychotic medication administered, suggesting that the impairment may be at least partially due to the effects of the medication," they note.

Moreover, it would be crucial to know in more detail what the role of attention, as none of the studies reviewed have considered that patients may perform the test less focused -- although, according to the experts, these people are known to be more prone to attentional lapses. "A deficit in performing a perceptual or cognitive task may derive from a specific impairment in the processes that the task is designed to assess, but it could also reflect a more generalized cognitive impairment, such as attention lapses, which could be estimated by the proportion of errors in easy tests," they explain. The fact that the studies have not taken this factor into account "opens up the possibility that these lapses contribute to the deficit that has been observed," they add. Thus, to determine whether the impairment is directly caused by the illness and to use this indicator as a biomarker of psychosis, the researchers stress the need for further studies with experimental designs that allow the uncoupling of perceptual attention deficits and that include populations with psychotic symptoms, with little or no medication. "In this line, we are currently measuring contrast sensitivity in patients with anti-NMDAR encephalitis, a disease in which there is also psychotic symptomatology, using a paradigm that includes control tests to monitor their attention," they conclude.