People differ in chronotype - whether they function best in the morning ("larks") or the evening ("owls"). This study asks whether the match or mismatch between a person's chronotype and the time of day at which they are tested changes how they perceive time. Healthy morning-type and evening-type adults at three sites (Aarhus, Denmark; Changzhou, China; and Hong Kong) complete the same battery of perception and cognition tasks twice - once in the early morning (about 08:00) and once late in the evening (about 22:00), in counterbalanced order. The primary outcome is the accuracy (signed bias) of time-perception judgements; the key comparison is the interaction between chronotype and time of day (the "synchrony effect"). Secondary measures include timing precision, the subjective passage of time, sleepiness, mood, colour perception (with and without blue-blocking glasses) and perceptual decision-making. By testing the same protocol across three cultures and latitudes, the study examines whether circadian match/mismatch effects on temporal cognition generalise across populations.
Background and rationale: Time perception is shaped by attention and physiological arousal, both of which follow a circadian rhythm that differs systematically between morning-type and evening-type individuals. The "synchrony effect" holds that performance is optimal when testing occurs at a person's circadian-preferred time. Whether this match/mismatch alters the perceived speed and precision of an internal clock, and whether any such effect generalises across cultures and latitudes, is not well established. Design: a 2 (chronotype: morning-type vs evening-type; between-subjects) x 2 (session time: morning about 08:00 vs evening about 22:00; within-subjects, counterbalanced) mixed design, replicated at three sites. "Match" = tested at the circadian-preferred time; "mismatch" = tested at the non-preferred time. Site is included as an additional factor for generalisability. Procedure: volunteers are screened online (Morningness-Eveningness Questionnaire to classify chronotype, with intermediate types excluded; Munich ChronoType Questionnaire; Pittsburgh Sleep Quality Index; demographics; colour-vision and health checks) and keep a 7-day sleep diary. Eligible participants attend two laboratory sessions and complete an identical battery each time: time-perception tasks (interval production/estimation, duration discrimination, passage-of-time judgement), state measures (sleepiness, mood, arousal), colour tasks (unique-hue settings with and without blue-blocking glasses; an ambiguous-colour image), a perceptual conformity task, and a vigilance task. Primary hypothesis: a chronotype-by-time-of-day interaction on time-perception bias. Analysis uses linear mixed-effects models (participant as a random effect; chronotype, session time, their interaction, and site as fixed effects), with false-discovery-rate correction across secondary outcomes. Session order is counterbalanced to separate time-of-day from practice and order effects.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
BASIC_SCIENCE
Masking
NONE
Enrollment
240
Full perception and cognition battery administered shortly after habitual wake (about 08:00): time-perception tasks (interval production/estimation, duration discrimination, passage-of-time judgement), state measures (sleepiness, mood, arousal), colour tasks, a perceptual conformity task, and a vigilance task.
The identical battery administered late in the evening (about 22:00), enabling within-participant comparison of the same measures at the two times of day.
Child Development Centre
Hong Kong, Hong Kong
RECRUITINGTime-perception bias measured by the two-alternative forced-choice duration-comparison point of subjective equality
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Temporal precision measured by the two-alternative forced-choice duration-discrimination Weber fraction
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Subjective passage of time measured by a passage-of-time rating scale
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Subjective sleepiness measured by the Karolinska Sleepiness Scale
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Mood measured by the Multidimensional Mood Questionnaire
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Unique-hue settings measured as hue angle in the Commission Internationale de l'Éclairage Colour Appearance Model 2016 (CIECAM16)
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Ambiguous-colour image perception measured by forced-choice categorisation of the dress image
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
Perceptual conformity measured by change in perceptual judgement after social-response exposure
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.
Time frame: Each of two laboratory sessions, morning about 08:00 and evening about 22:00, completed within about 2 weeks.
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