Summary: People with schizophrenia show reduced contrast sensitivity, meaning they have difficulty distinguishing differences in light intensity between adjacent areas. This perceptual deficit can impair shape, texture and detail recognition and may reflect disruptions in glutamatergic neurotransmission, a neural mechanism implicated in the disorder.
Researchers propose that measuring contrast sensitivity could become a simple, non-invasive biomarker to aid diagnosis and monitor disease progression or treatment response. The review also highlights the possible influence of antipsychotic medication and attentional lapses on visual performance, underscoring the need for further controlled studies to separate these factors.
Key Facts:
- Impaired contrast perception: People with schizophrenia often struggle to detect differences in luminance, which can compromise daily visual tasks such as face recognition, reading and navigation.
- Glutamate link: Reduced glutamate signaling may lower neural activity in brain regions that process contrast, potentially contributing to the observed sensitivity loss.
- Biomarker potential: Contrast sensitivity testing could help identify patients with prominent glutamatergic dysfunction and select candidates for targeted clinical trials.
Source: University of Barcelona
Schizophrenia and basic visual processing
Schizophrenia affects about 1% of the global population and is primarily known for symptoms such as delusions, hallucinations and disordered thought. In addition to these characteristic symptoms, people with schizophrenia commonly exhibit perceptual differences, including abnormalities in color perception and contrast sensitivity. Understanding these visual changes can provide insight into how altered sensory processing contributes to broader cognitive and behavioral symptoms.
Contrast sensitivity is a fundamental visual function: without adequate sensitivity to luminance differences, objects and their features become harder to detect. This can affect everyday activities such as moving through space, recognizing faces and reading. The University of Barcelona team, from the Vision and Control of Action Group and the UB Institute of Neurosciences (UBneuro), reviewed the literature to synthesize evidence on contrast sensitivity in schizophrenia and to explore its neural underpinnings.
Their analysis points to a plausible role for the glutamatergic system. A decrease in glutamate can reduce activity in cortical areas responsible for processing contrast, producing a measurable decline in contrast sensitivity. Although the magnitude of this reduction is not huge, it may nonetheless indicate an underlying glutamatergic impairment in affected individuals.
Because contrast sensitivity can be measured non-invasively and relatively quickly, it could serve as a practical clinical tool. The researchers suggest that identifying individuals with pronounced contrast deficits may help select participants for trials of drugs that target glutamatergic signaling.
Medication, attention and confounding factors
The review found a substantial overall impairment in contrast sensitivity among people with chronic schizophrenia, but it also identified important potential confounders. One notable finding is a relationship between contrast loss and antipsychotic medication dose, suggesting medication effects could partly explain the deficit. Another concern is attention: none of the reviewed studies systematically measured attentional lapses, and people with schizophrenia are known to be more prone to momentary inattention. A higher frequency of lapses during testing could inflate measured deficits in sensory tasks.
The authors emphasize that a poor score on a perceptual task might reflect a specific sensory deficit, a more general cognitive problem such as reduced sustained attention, or a combination of both. Because prior studies rarely included control measures for attention, the contribution of lapses remains uncertain. Similarly, only a small number of studies fully assessed visual acuity and spatial frequency effects, limiting conclusions about how basic optics or spatial processing contribute to the observed impairment.
To clarify whether reduced contrast sensitivity is a direct consequence of schizophrenia and to validate its use as a biomarker, future research should employ experimental designs that separate sensory processing from attentional and medication effects. The team reports they are currently measuring contrast sensitivity in patients with anti-NMDAR encephalitis—another condition with psychotic symptoms—using paradigms that include control tests to monitor attention.
About this research
Author: Rosa Martínez
Source: University of Barcelona
Contact: Rosa Martínez – University of Barcelona
Image: Image credited to Neuroscience News
Original Research: Open access. “A systematic review and meta-analysis on contrast sensitivity in schizophrenia” by Daniel Linares et al., Schizophrenia Bulletin.
Abstract
A systematic review and meta-analysis on contrast sensitivity in schizophrenia
Background and hypothesis
Perceptual alterations in mental disorders can reveal neural and computational anomalies. In schizophrenia, many visual features are affected, and contrast sensitivity is a core measure of visual function. Prior evidence was fragmented and had not been synthesized comprehensively.
Study design
The authors performed a systematic review and meta-analysis of studies that measured contrast sensitivity in people with schizophrenia versus healthy controls. The search identified 46 studies, 43 of which focused on chronic patients.
Study results
The meta-analysis found that chronic schizophrenia patients have reduced contrast sensitivity (g = 0.74; 95% CI, 0.55 to 0.93; P = 8.2 × 10−10). The authors also found evidence that medication may influence this deficit. Crucially, none of the reviewed studies estimated attentional lapses, leaving open the possibility that increased lapses in patients could contribute to the observed differences. Only two studies thoroughly assessed visual acuity, complicating evaluation of spatial frequency effects.
Conclusions
There is a robust deficit in contrast sensitivity among chronic schizophrenia patients, but the roles of attentional lapses and antipsychotic medication are still unclear. The authors recommend future studies that control for attention, medication status and basic visual acuity to determine the mechanisms underlying this sensory impairment and to evaluate the clinical utility of contrast sensitivity as a biomarker.