Chronotype Alignment and Time Perception

Participants complete a two-alternative forced-choice duration-comparison task. On each trial, they judge whether a comparison interval is shorter or longer than a standard interval. A psychometric function is fitted to each participant's responses to estimate the point of subjective equality, defined as the comparison duration judged longer than the standard on 50% of trials. Time-perception bias is calculated as signed percentage error: ((point of subjective equality - standard duration) / standard duration) × 100. Positive values indicate a point of subjective equality above the standard duration; negative values indicate a point of subjective equality below the standard duration. The primary comparison is the chronotype-by-session-time interaction, testing whether time-perception bias differs between circadian match and mismatch sessions.

Participants complete a two-alternative forced-choice duration-discrimination task using an adaptive staircase procedure. On each trial, they judge whether a comparison interval is shorter or longer than a standard interval. A psychometric function is fitted to estimate the just-noticeable difference, defined as the smallest duration difference required for reliable discrimination. Temporal precision is calculated as the Weber fraction: just-noticeable difference divided by the standard duration. Lower Weber-fraction values indicate better temporal precision, whereas higher values indicate poorer temporal precision.

Participants rate their subjective passage of time during the laboratory session using a passage-of-time rating scale. The scale ranges from 1 to 7, where 1 indicates that time passed very slowly and 7 indicates that time passed very quickly. Higher scores indicate a faster subjective passage of time, whereas lower scores indicate a slower subjective passage of time.

Subjective sleepiness is assessed using the Karolinska Sleepiness Scale, a 9-point self-report scale ranging from 1 to 9. A score of 1 indicates very alert, and a score of 9 indicates very sleepy or fighting sleep. Higher scores indicate greater subjective sleepiness. The scale is administered before and after the laboratory task battery in each session; the outcome will be analysed as session-level subjective sleepiness, with pre- and post-battery ratings used to characterise changes across the session.

Mood is assessed using the Multidimensional Mood Questionnaire. The questionnaire provides three bipolar mood dimensions: good-bad mood, awake-tired mood, and calm-nervous mood. Each dimension is scored from 4 to 20. Higher scores indicate a more positive mood state: better mood on the good-bad dimension, greater wakefulness on the awake-tired dimension, and greater calmness on the calm-nervous dimension.

Participants complete a unique-hue adjustment task for unique yellow, blue, green, and red. For each unique hue, the selected colour is converted to a hue angle in the Commission Internationale de l'Éclairage Colour Appearance Model 2016 (CIECAM16). Hue angle is measured in degrees (0°-360°), representing the location of the selected colour around the hue circle. The task is completed both with and without blue-blocking glasses. Hue angle is an angular colour-coordinate measure; higher or lower values do not indicate a better or worse outcome but indicate a shift in the perceived unique-hue setting.

Participants view the ambiguous dress image and complete a forced-choice categorisation task. They indicate whether they perceive the image as white/gold or blue/black. The outcome is the categorical response to the image, recorded separately with and without blue-blocking glasses. This measure indexes individual differences in colour-perception interpretation and illuminant assumptions, and whether the perceived category shifts with reduced short-wavelength input or time of day. This is a categorical perceptual outcome; higher or lower values do not indicate a better or worse outcome.

Participants complete a perceptual judgement task before and after exposure to others' responses. Perceptual conformity is measured as the change in the participant's judgement from the initial response to the post-exposure response. Larger absolute change scores indicate greater susceptibility to social influence on perception. Positive or negative scores indicate the direction of change relative to the participant's initial judgement or relative to the displayed social response, depending on the specific perceptual judgement scale used.