In psychology, the terms “owl” and “lark” correspond to two fundamentally different patterns of sleep. Someone who rises early and feels at his or her best during the morning hours is called a “lark”, while those who prefer to get up late and retire to bed way past midnight are referred to as “owls”.
Despite this being the customary approach to human circadian rhythms (the physical, mental and behavioral changes that follow a regular 24-hour cycle), many people over the years have reported not fitting into either of the two categories. For example, there is a substantial number of individuals who, despite having no medical issues, feel lethargic both in the morning and in the evening. Yet others experience the opposite and function at a high level during all hours of the day.
In order to find out whether the “owl”/”lark” dichotomy is accurate, Arcady Putilov and two other researchers of the Siberian Branch of the Russian Academy invited 130 healthy volunteers (76 of which were women) to their sleep lab and kept them awake for just over 24 hours. During this time the volunteers received no coffee, alcohol or other psychoactive substances. Several times during the 24 hour period they were asked to complete a survey about their current level of wakefulness and a questionnaire about their usual sleeping habits.
An analysis of the collected data revealed that there are four distinct groups in total. Consistent with past research, 29 volunteers were classified as “larks” – they experienced high levels of energy during morning hours, but began feeling progressively more tired as the day wore on. 44 of the volunteers exhibited the opposite pattern and therefore landed in the “owl” camp. But instead of stopping right there, the researchers identified two more groups. There was a “high energetic” group of 25 individuals who felt more or less the same level of energy both in the morning and in the evening, and a “lethargic” group of 32 individuals, who reported feeling woozy in both morning and evening.
Authors of the study claim that their results show that there are “four diurnal types, and each of these types can … be differentiated from any of three other types on self-scorings of alertness-sleepiness levels in the course of 24-hours sleep deprivation.”
Original research article: Arcady Putilov, Olga Donskaya, Evgeniy Verevkin., How many diurnal types are there? A search for two further “bird species”. DOI: 10.1016/j.paid.2014.08.003, source link.