Over the past decades, researchers have explored altered rhythmic responses to visual stimulation in people with schizophrenia using steady state visual evoked potentials (SSVEPs). Here we systematically review studies performed between 1954 and 2021, as identified on PubMed. We included studies if they included people with schizophrenia, a control group, reported SSVEPs as their primary outcome, and used quantitative analyses in the frequency domain. We excluded studies that used SSVEPs to primarily quantify cognitive processes (e.g., attention). Fifteen studies met these criteria. These studies reported decreased SSVEPs across a range of frequencies and electrode locations in people living with schizophrenia compared to controls; none reported increases. Null results, however, were common. Given the typically modest number of subjects in these studies, this is consistent with a moderate effect size. It is notable that most studies targeted frequencies that fall within the alpha and beta band, and investigations of frequencies in the gamma band have been rare. We group test frequencies in frequency bands and summarize the results in topographic plots. From the wide range of approaches in these studies, we distill suggested experimental designs and analysis choices for future experiments. This will increase the value of SSVEP studies, improve our understanding of the mechanisms that result in altered rhythmic responses to visual stimulation in schizophrenia, and potentially further the development of diagnostic tools.

Visual cognition is finely tuned to the elements in a scene but also relies on contextual integration to improve visual detection and discrimination. This integration is impaired in patients with schizophrenia. Studying impairments in contextual integration may lead to biomarkers of schizophrenia, tools to monitor disease progression, and, in animal models, insight into the underlying neural deficits. We developed a nonhuman primate model to test the hypothesis that hypofunction of the N -methyl d -aspartate receptor (NMDAR) impairs contextual integration. Two male rhesus macaques ( Macaca mulatta ) were trained to indicate which of two patterns on the screen had the highest contrast. One of these patterns appeared in isolation, and the other was surrounded by a high-contrast pattern. In humans, this high-contrast context is known to lead to an underestimation of contrast. This so-called Chubb illusion is thought to result from surround suppression, a key contextual integration mechanism. To test the involvement of NMDAR in this process, we compared animals’ perceptual bias with and without intramuscular injections of a subanesthetic dose of the NMDAR antagonist ketamine. In the absence of ketamine, the animals reported a Chubb illusion - matching reports in healthy humans. Hence, monkeys - just like humans - perform visual contextual integration. This reaffirms the importance of nonhuman primates to help understand visual cognition. Injection of ketamine significantly reduced the strength of the illusion and thus impaired contextual integration. This supports the hypothesis that NMDAR hypofunction plays a causal role in specific behavioral impairments observed in schizophrenia.

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