Increased sensitivity to visual illusions of brightness in individuals with schizophrenia

A research group formed by the Cognitive Neurotechnology Unit of the Department of Computer Science and Engineering at Toyohashi University of Technology and the Hoshino Laboratory of the Department of Integrated Health Sciences of the Graduate School of Medicine at Nagoya University discovered that, compared to individuals without schizophrenia, individuals with schizophrenia are more susceptible to perceiving the “glare illusion”, a visual phenomenon in which the central region of an image appears to be brighter than it is, due to a gradient of brightness in the surrounding region. This discovery may provide a clue to understanding how individuals with schizophrenia process visual information. The findings of the study were published in the online version of the journal, Schizophrenia Research: Cognition, on May 19, 2025. https://doi.org/10.1016/j.scog.2025.100366

In our daily lives, the world around us is perceived based on a variety of visual information, such as brightness in the surrounding area and the shape or size of an object. However, physical light and stimuli are not directly perceived; our perceptual experience is constructed by the brain through processes such as inference and interpretation. This phenomenon, in which objects appear to be different from the actual physical stimuli, is called an “illusion”. Individuals vary in their perception of illusions, and studies on how illusions are visually perceived provide clues to understanding the mechanism of perception.

A recent study has shown that individuals with schizophrenia display reactions to illusions that are different from those of individuals without schizophrenia. Schizophrenia is a mental disorder that causes changes in the perception of reality, and it can influence attention, emotions, and social interactions, in addition to causing symptoms, such as hallucinations and delusions. Furthermore, these changes in the information processing of the brain may also affect vision.

The investigators specifically focused on the “glare illusion”, a brightness-illusion phenomenon (Figure 1, left) in which the central region of an image appears to be brighter than it is when there is a brightness gradient in the surrounding region. The central region is perceived as brighter or even glowing, as previously reported.

The investigators conducted an experiment on 30 individuals with schizophrenia and 34 individuals without schizophrenia, to study how they perceive the glare illusion. The participants were asked to compare two images presented on the display of a tablet computer and to judge which image’s central region appeared brighter. Participants viewed images with varying brightness levels. The experiment was conducted in a room in which the participants usually spent time, and the room was configured so that the display was not directly exposed to sunlight. Additionally, the luminance (physical brightness) of the display was strictly adjusted to ensure correct output.

The experiment revealed that individuals with schizophrenia were more susceptible to the glare illusion than individuals without schizophrenia (Figure 1, right). However, there was no association between the increased susceptibility to the glare illusion and the responses to “How easily do you feel your eyes get tired in the evening?”, and other similar questions in a questionnaire. This suggests that the increased susceptibility to the brightness illusion was not simply due to visual fatigue. Also, individual differences in susceptibility to the illusion were greater in individuals with schizophrenia than in individuals without schizophrenia. The investigators postulated that the increased susceptibility to the illusion may be due to the differences in visual processing specific to individuals with schizophrenia. However, the findings of this study warrant further investigation to clarify the underlying mechanisms, as they only shed light on one aspect of visual processing and are not intended for clinical diagnosis or prediction.

Assistant Professor Hideki Tamura of the Department of Computer Science and Engineering at Toyohashi University of Technology, the lead author of this study, states, “Each person has a different susceptibility to illusions; therefore, there is no need to worry whether or not one can clearly perceive an illusion. There are some illusions that I cannot clearly perceive. I am interested in the visual mechanism of how an identical image can be perceived differently, which I will continue to explore in future studies”.

The findings of this study provide the basis for a deeper understanding of the characteristic differences in visual processing observed in individuals with schizophrenia. The investigators endeavor to further clarify the relationship between illusions and brain function, aiming to gain a multifaceted understanding of schizophrenia from the perspective of visual perception.

This study was supported by JSPS KAKENHI (Grants-in-Aid for Scientific Research Number JP22K17987), as well as the Tokai Pathways to Global Excellence (T-GEx), an adopted project of the Strategic Professional Development Program for Young Researchers (Ministry of Education, Culture, Sports, Science and Technology).

Tamura, H., & Hoshino, A. (2025). The glare illusion in individuals with schizophrenia. Schizophrenia Research: Cognition, 41, 100366. https://doi.org/10.1016/j.scog.2025.100366