This observational study aims to characterise individual differences in colour perception and binocular rivalry. Participants will complete computer-based visual perception tasks, including a colour perception task and a binocular rivalry task. The study will first examine whether individuals show measurable differences in these perceptual responses. It will then explore whether these differences are associated with chronotype, sex, sleep-related measures, and subjective fatigue. The findings may help clarify how stable individual characteristics and daily physiological states relate to visual perception.

Colour perception and binocular rivalry both show variability across individuals. However, the extent to which these individual differences are stable and whether they are associated with personal or physiological factors remains unclear. This study will use behavioural visual perception tasks to measure individual differences in colour perception and binocular rivalry. Participants will complete a colour perception task and a binocular rivalry task, along with questionnaire measures related to chronotype, sleep, fatigue, and demographic characteristics including sex.

The primary aim is to determine whether measurable individual differences are present in colour perception and binocular rivalry performance. The secondary aim is to examine whether these differences are associated with chronotype, sex, sleep-related variables, and subjective fatigue. The study is observational and does not involve a clinical intervention, drug, biologic product, or medical device.

Inclusion Criteria:

• Adults aged 18 years or older.
• Normal or corrected-to-normal visual acuity.
• Normal or corrected-to-normal binocular vision.
• Normal colour vision, or no self-reported colour vision deficiency.
• Able to understand the study instructions and provide informed consent.
• Able to complete computer-based visual perception tasks and self-report questionnaires.

Exclusion Criteria:

• Self-reported colour vision deficiency.
• Uncorrected visual impairment or eye conditions that may interfere with visual perception tasks.
• Strabismus, amblyopia, or other binocular vision problems that may interfere with binocular rivalry testing.
• History of neurological disorders, photosensitive epilepsy, or severe sensitivity to flickering visual stimuli.
• Current condition or medication that, in the investigator's judgment, may substantially affect visual perception, attention, or task performance.
• Inability to complete the task procedures or provide valid responses.

Healthy adult volunteers will be recruited from the university community and/or the surrounding community. Participants will complete computer-based colour perception and binocular rivalry tasks, together with self-report measures of chronotype, sleep, fatigue, and demographic characteristics.