Why do we find it hard to keep track of days of the week?

Mondays really do make us blue, Fridays are the happiest day of the working week and 'dull' midweek days are easily muddled up  – and it's all due to how the artificial seven-day cycle we live by shapes the way we think, new research has shown.

Psychologists from the universities of Lincoln, York and Hertfordshire created an experiment to test how our mental representations of days of the week are constructed and what effect this has on our perceptions of time.

They asked participants which words they most strongly associated with different days. They found that Monday and Fridays have a higher number of mental representations attached to them than their midweek counterparts – giving them stronger identities than Tuesdays, Wednesdays and Thursdays. Conversely, these non-descript mid-week days carry less meaning, making them more easily confused with each other.

Mondays mainly prompted negative words like 'boring', 'hectic' and 'tired' and Fridays were associated with positive words like 'party', 'freedom' and 'release'.

Almost 40 per cent of study participants confused the current day with the preceding or following day – and most of those mistakes occurred during the middle of the week. The number of mistakes rose to more than half when questioned during a Bank Holiday week, with people often feeling like they were a day behind.

Participants were also quizzed on how quickly they could recall the correct day, with people able to declare it is Monday or Friday correctly twice as fast as they could on a Wednesday. 

Lead researcher Dr David Ellis, from the University of Lincoln's School of Psychology, said: "The seven day weekly cycle is repeated for all of us from birth, and we believe this results in each day of the week acquiring its own character.  

"Indeed, more than a third of participants reported that the current day felt like a different day, and most of those feelings were on Tuesdays, Wednesdays and Thursdays, reflecting the midweek dip in associations attached to different days.

"Our research implies that time cycles can shape cognition even when they are socially constructed. The Bank Holiday effect implies that apparent weekday is not determined solely by the seven-day period of the weekly cycle: transitions between the working week and weekend also play a role."

Dr Rob Jenkins from the Department of Psychology at the University of York, who also worked on the study along with Professor Richard Wiseman from the University of Hertfordshire, added: "One reason behind midweek days evoking fewer associations than other days could be down to how infrequently they occur in natural language, thus providing fewer opportunities for associations to form – for example we have an abundance of pop songs which make use of Mondays and Fridays, while the midweek days are rarely used.

"If links can be made in the future that aspects of behaviour such as risk or tolerance also vary systematically over the week, the implications could be profound, not only for individual behaviour, but also for psychological measurement."

The findings have been published in PLOS ONE today.