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PSY 355 Psychology & Media in the Digital Age

This page was last modified on Feb 27, 2023
Today's and next Monday's classes will look at the Impact of Techno-Digital Media on Human Cognition & Mental Activity

Class 13• The Neuropsychology of Media • I • The Impact of Light

A. Circadian Rhythm
  • SCNThe human sleep-wake cycle is circadian (ca. 24 hours long) and controlled principally by light.
  • The "biological clock" which regulates this cycle is found in the suprachiasmatic nucleus (SCN), a collection of about 20,000 neurons located right above the optic chiasm in the hypothalamus.
  • The SCN receives signals directly from a special group of "intrinsically photosensitive retinal ganglion cells (ipRGCs) which contain a blue light sensitive photopigment called melanopsin. They fire when struck by light of ca. 464-484 nm wavelength (i.e., "blue" light).
Visible light

  • In the normal pattern of human sleep, the rise in the hormone melatonin is associated with increased levels of sleepiness and follows a distinctive pattern as the level of light striking the retina decreases after sunset.
24-hour melatonin cycle
  • If these melanopsin ipRGCs signal the SCN, it causes the brain to stop the production of melatonin which is necessary for sound sleep. Thus, light and, particularly blue light, has the effect of turning off melatonin in the brain. Note, too, that melatonin has also been found to be a potent antioxi (dant and inhibits cancer. 

B. Sleep in Modern Post-Industrial Societies

  • Recall that "techno-digital culture" originated in the 19th century with the advent of steam engines, electricity, modern forms of lighting and transportation, etc.
  • A large proportion of the world's population now live in what is termed "modern post-industrial societies." Using high levels of electrical and other energy sources, post-industrial societies have moved past an emphasis on heavy manufacturing and are "characterized by the provision of services rather than goods; professional and technical work rather than blue-collar, manual work; theoretical knowledge rather than practical know-how; the creation and monitoring of new technologies; and new intellectual technologies to handle such assessment and control” (IGI-Global [https://www.igi-global.com/dictionary/leapfrogging-sector/23078]). 
  • Sleep in the world of post-industrial society is monophasic, that is, individuals go to sleep for one extended period of sleep each day, generally between 6 and 8 hours in total (Samson, 2021)
  • In human monophasic sleep, the sleeper alternates between periods of NREM (non-REM) and REM (rapid eye movement) sleep with NREM periods longer in the first half of the overall sleep cycle and REM periods longer in the second half of the sleep cycle.
  • Sufficient sleep in humans is necessary for a variety of important physical and cognitive issues: immune function, efficient metabolism, cell maintenance and repair, memory consolidation, creativity & innovation, and emotional regulation (Samson, 2021).
  • Chronic sleep deprivation and/or disruption in circadian rhythms "increases the risks for obesity, hypertension, heart disease, and immune system dysfunction, which may increase the risks for infection, inflammation, and several cancers" (Samson, 2021, p. 265)

C. Before the 19th Century and the Industrial Revolution in Europe: A World of Extended Darkness

The evolution of humans and light

1. Nighttime before the Industrial Revolution in Europe

traveller attacked at night    Historical homicide rates in Europe

2. "Segmented" or "Biphasic  or Divided Sleep" in Pre-Industrial Societies {W} (Ekirch, 2001, 2005, 2015, 2016)

Nighttime in Summer &
  • Examining the day-night map above for Syracuse, note how in the winter (Dec. 21) there are a total of 15 hours between sunset & sunrise.
Roger Ekrich, an historian at Virginia Tech, has argued that Pre-Industrial Europe experienced "segmented (or biphasic) sleep" patterns
      • "First Sleep": from about an hour or two after sunset until ca. midnight (about 4-5 hours)
      • Quiet Wakefulness ("First Waking"): about an hour or two
        • Period to complete unfinished housework. Contemplation & prayer. Sex. Conversation by spouses.
        • Sometimes students studied. Others read by whatever light was available.
      • "Second Sleep": from about 1-2 am until the beginnings of dawn (about 4-5 hours)
  • This pattern was clearer for poorer people, that is, those who had no or few sources of light.
  • Ekirch's thesis has been contested by Yetish et al (2015) who found little evidence of segmented sleep in three contemporary societies in the Southern Hemisphere relatively near the Equator (2 in Africa, 1 in South America) which function without industrial factors such as electricity. 
Ekirch (2016) counters that there is clear evidence that bi-phasic sleep has been found "well beyond the bounds of Europe and North America in other cultures and continents, including the Middle East, Africa, South Asia, Southeast Asia, Australia, and Latin America, thereby heightening the likelihood that throughout the pre-industrial world this form of sleep was not at all uncommon, including in equatorial cultures" (2016, p. 715; see also Ekrich, 2015)
  • Other researchers have found alterations in the monophasic (8 continuous hours of sleep) of post-industrial societies among people living in small-scale subsistence societies [4S = those in which the product of adult work is primarily not money but food]. (Samson et al, 2017a, b; Samson, 2022).
Flexible sleep-wake patterns
C. Changes brought by the Industrial Revolution & Techno-Digital Culture
  • Indoor Lighting (Pauley, 2004)
1885 300,000 lamps/year
1914 88.5 million lamps/year
1945 > 795 million lamps/year
The average illumination level in modern offices is 300-500 lux (lx). The average level in a private home is 150-180 lx. (The light of a full moon is 0.1-0.3 lx.).
Research shows that melatonin is suppressed at 0.1 lx of blue light but can generally experience 100 lx of red light without much response. Sources of blue light include high intensity discharge (HID) and fluorescent lighting.
Lighting types
  • Shiftwork {W}

Crossing the Atlantic 1800-2000 Hours

  • Entertainment & Communication Media & Light
  • Computer & tablet self-illuminating screens emit light. A brightly lit screen projects about 80 lx but a dimly lit screen only about 1 lx.
  • Research on whether such screens inhibit melatonin by viewers has been ambivalent.
    • One research study found no effect on adolescents using tablets for 1 hour before sleep (Heath et al. 2014).
    • Similarly, another study failed to find suppression of melatonin in the evening by watching a 70-inch television (Figueiro et al. 2013).
    • On the other hand, the same research team did find a trend toward melatonin suppression when viewers were exposed to a 30 lx light level on computer screens (Figueiro et al., 2011) and a significant effect after 2 hours of exposure to an Apple iPad (40 lx; Wood et al., 2013)

    • A recent summary of the research literature (Wong & Bahkmani, 2022) noted that there are differing effects of blue light from digital screens depending on the time of day/point within an individual's circadian rhythm
Blue Light Effects on Melatonin
    • LED
      Exposure to light-emitting diodes (LED) backlit computer screens (vs. non-LED computer screens) for 5 hours in the evening has been found to cause not only significant reduction of melatonin production but also increased levels of feeling sleepy. There is more than a 2 times greater level of short-wave "blue" light emitted by the LED computer screen (see figure on right). However, compared to non-LED screens, the LED screens also led to higher levels of cognitive performance (including sustained attention & better declarative memory; Cajochen et al., 2011).
    • The research by Shimura et al. (2018) previously cited argues strongly for the negative impact of exposure to electronic screen displays at night upon sleep and other sleep-related outcomes for adolescents: "Using of electronic displays, especially use in bed, strongly affected all sleep-related variables, including sleep disturbance, daytime sleepiness, and chronotype, as evidenced by the high odds ratios by logistic regression analyses. Electronic
      display use at might affect daytime sleepiness indirectly through circadian rhythm dysfunction and consequent sleep disturbance" (p. 18).

    • Randjelović et al. (2023) studied the impact of reducing evening exposure to smartphone screens among 20-22 year old medical students. This research found that " a reduction of blue light emission from LED backlight screens of mobile phones during the night leads to improved subjective quality of sleep in students, as well as improvement in daytime functioning and going to sleep" [Abstract]. 


Cajochen, C., Frey, S., Anders, D., et al. (2011). Evening exposure to a light-emitting diodes (LED)-backlit computer screen affects circadian physiology and cognitive performance. Journal of Applied Physiology, 110, 1432-1438. https://doi.org/10.1152/japplphysiol.00165.2011

Dimitriou, D., Knight, F. L.C., & Milton. (2015). The role of environmental factors on sleep patterns and school performance in adolescents. Frontiers in Psychology, 6, 1717.

Eisner, M. (2003). Long-term historical trends in violent crime. Crime and Justice, 30, 83-142. https://doi.org/10.1086/652229

Ekirch, A. R. (2001). Sleep we have lost: Pre-industrial slumber in British isles. American Historical Review, 106(2), 343-386.

Ekirch, A. R. (2005). At day's close: Night in times past. New York, NY: W. W. Norton.

Ekirch, A. R. (2015). The modernization of Western sleep: or, does insomnia have a history? Past & Present, 226, 149-192.

Ekirch A. R. (2016). Segmented sleep in preindustrial societies. Sleep, 39(3), 715-716. https://dx.doi.org/10.5665/sleep.5558

Figueiro, M. G., Wood, B., Plitnick, B., & Rea, M. S. (2011). The impact of light from computer monitors on melatonin levels in college students. Neuroendocrinology Letters, 32(2), 158-163.

Figueiro, M. G., Wood, B., Plitnick, B., & Rea, M. S. (2013). The impact of watching television on evening melatonin levels. Journal of the Society for Information Display, 21(10), 417-421.

Foster, R. G., Peirson, S. N., Wulff, K., Winnebeck, Vetter, C., & Roenneberg, T. (2013). Sleep and circadian rhythm disruption in social jetlag and mental illness. Progress in Molecular Biology and Translational Science, 119, 325-346. https://doi.org/10.1016/B978-0-12-396971-2.00011-7

Heath, M., Sutherland, C., Bartel, K., Gradisar, M., Williamson, P., Lovato, N., & Micic, G. (2014, January 7). Does one hour of bright or short-wavelength filtered tablet screenlight have a meaningful effect on adolescents' pre-bedtime alertness, sleep, and daytime functioning? Chronobiology International.

Pauley, S. (2004). Lighting for the human circadian clock: Recent research indicates that lighting has become a public health issue. Medical Hypotheses, 64, 588-596.

Randjelović, P., Stojanović, N., Ilić, I., & Vučković, D. (2023, Feb.). The effect of reducing blue light from smartphone screen on subjective quality of sleep among students. Chronobiology International, 1-8. https://doi.org/10.1080/07420528.2023.2173606

Refford, B. (2009). [Review of the book At day's close: Night in times past by A. Roger Ekirch]. The Journal of British Studies, 48(3), 780-781.

Roenneberg, T., Allebrandt, K. V., Merrow, M., & Vetter, C. (2012). Social jetlag and obesity. Current Biology, 22, 939-942. https://doi.org/10.1016/j.cub.2012.03.038

Samson, D. R., Crittenden, A. N., Mabulla, I. A., Mabulla, A. Z. P., & Nunn, C. L. (2017a). Hadza sleep biology: Evidence for flexible sleep-wake patterns in hunter-gatherers. American Journal of Physical Anthropology, 162, 573-582.

Samson, D. R., Manus, M. B., Krystal, A. D., Fakir, E., Yu, J. J., & Nunn, C. L. (2017b). Segmented sleep in a nonelectric, small-scale agricultural society in Madagascar. American Journal of Human Biology.

Samson, D. R. (2021) The human sleep paradox: The unexpected sleeping habits of Homo sapiens. Annual Review of Anthropology, 50, 259-274. https://doi.org/10.1146/annurev-anthro-010220-075523

Shimura, A., Hideo, S., Takaesu, Y., Nomura, R., Komada, Y., & Inoue, T. (2018). Comprehensive assessment of the impact of life habits on sleep disturbance, chronotype, and daytime sleepiness among high-school students. Sleep Medicine.

Wahl, S., Engelhardt, M., Schaupp, P., Lappe, C., & Ivanov, I. V. (2019). The inner clock - Blue light sets the human rhythm. Journal of Biophotonics, 12, e201900102. https://doi.org/10.1002/jbio.201900102

Waterhouse, J., Edwards, B, Nevill, A, et al. (2002). Identifying some determinants of "jet lag" and its symptoms: A study of athletes and other travellers. British Journal of Sports Medicine, 36, 54-60.

Wong, N. A., & Bahmani, H. (2022). A review of the current state of research on artificial blue light safety as it applies to digital devices. Heliyon, 8, e10282. https://doi.org/10.1016/j.heliyon.2022.e10282

Wood, B., Rea, M. S., Plitnick, B., & Figueiro, M. G. (2013). Light level and duration of exposure determine the impact of self-luminous tablets on melatonin suppression. Applied Ergonomics, 44, 237-240.

Yetish, G., Kaplan, H., Gurven, M., et al. (2015). Natural sleep and its seasonal variations in three pre-industrial societies. Current Biology, 25, 2862-2868.

This page was first posted on 2/24/14