Gorillas in our midst

Imagine you’re a psychology researcher at Harvard. You’ve recruited 200 students to watch a 75-second video. It shows 6 people passing a basketball. You ask the students to count the number of passes. At the 45-second mark, a woman in a full-body gorilla suit walks across the scene for 5 seconds.

How many students do you think will notice the gorilla?

The answer is 50%. Half won’t notice at all.

Experiments like this reveal the brain’s limitations. Other examples:

  • Working memory can hold a maximum of 3 items before performance plunges

  • Attention can only be sustained for 20–30 minutes

  • Talking with a passenger decreases driving performance by 10–20%

Despite its limited performance, the brain is an energy hog. It is 2% of body weight, but consumes 20% of blood sugar. And it tires easily. For example, a study of judges found they approved 65% of parole requests right after eating a snack or lunch. But approvals declined to zero after a few hours.

A designer knows he has achieved perfection not when there is nothing left to add, but when there is nothing left to take away.

-Antoine de Saint Exupéry

Less is more

Reduce cognitive load. Simplify for others:

  • Ask one question at a time

  • Only offer 2–3 choices

  • Send short texts and e-mails

And simplify for yourself:

  • Follow a daily routine

  • Don’t multi-task

  • Declutter possessions, keep only what you love

Many wealthy people are little more than the janitors of their possessions.

-Frank Lloyd Wright

The best way to choose what to keep and what to throw away is to take each item in one’s hand and ask: “Does this spark joy?” If it does, keep it. If not, dispose of it. This is not only the simplest but also the most accurate yardstick by which to judge.

-Marie Kondo


Simons DJ, Chabris CF. (1999). Gorillas in our midst: sustained inattentional blindness for dynamic events. Perception. 28(9): 1059–1074.

  • 192 participants watched 75-second videos of 6 people passing a basketball and were told to count number of passes

  • At the 45-second mark, a woman wearing a gorilla costume, or holding an open umbrella, walked across the scene for 5 seconds

  • 46% of participants failed to notice the unexpected events

Zhang W, Luck SJ. (2008). Discrete fixed-resolution representations in visual working memory. Nature. 453(7192): 233–235.

  • A study with 8 participants found they could store up to 3 images in short-term memory before performance declined

Gobet F, Clarkson G. (2004). Chunks in expert memory: evidence for the magical number four…or is it two? Memory. 12(6): 732–747.

  • A study of 12 novice, intermediate, and expert chess players found that all groups placed 1.5–1.9 chunks when recalling random board positions

  • This suggested short-term memory has a maximum capacity of less than 3 chunks

See JE et al. (1995). Meta-analysis of the sensitivity decrement in vigilance. Psychol Bull. 117(2): 230–249.

  • A review of studies found that decline in vigilance was typically complete 20–35 minutes into an experimental session, and at least half of the final loss occurred during the initial 15 minutes

  • Vigilance decreased faster when looking or listening for an infrequent signal

  • A meta-analysis of 42 studies with 2,938 participants found that vigilance decreased with time (effect size = 0.68)

Caird JK et al. (2018). Does talking on a cell phone, with a passenger, or dialing affect driving performance? An updated systematic review and meta-analysis of experimental studies. Hum Factors. 60(1): 101–133.

  • A meta-analysis of 93 studies with 4,382 participants found that driving reaction time was impaired similarly for handsfree vs. handheld vs. passenger conversations (effect size = 0.21–0.27)

  • Detection reaction time was also impaired similarly for all conditions (effect size = 0.45–0.61)

Danziger S, Levav J, Avnaim-Pesso L. (2011). Extraneous factors in judicial decisions. Proc Natl Acad Sci USA. 108(17): 6889–6892.

  • A 10-month study of 8 Jewish-Israeli judges and 1,112 parole rulings found that favorable rulings dropped gradually from 65% to nearly zero during each deliberative session, and returned abruptly to 65% after a snack break or lunch

Orquin JL, Kurzban R. (2016). A meta-analysis of blood glucose effects on human decision making. Psychol Bull. 142(5): 546–567.

  • A meta-analysis of 36 studies found that low blood glucose increased willingness to work on food-related tasks (effect size = 0.48), but decreased willingness to work on any other task (effect size = 0.33); increased tendency to make intuitive rather than deliberate decisions on tasks that were not food-related (effect size = 0.31); and increased willingness to spend money on food (effect size = 0.16), but lowered willingness to spend money on anything else (effect size = 0.22)

Wardle-Pinkston S, Slavish DC, Taylor DJ. (2019). Insomnia and cognitive performance: A systematic review and meta-analysis. Sleep Med Rev. 48: 101205.

  • A meta-analysis of 48 studies with 4,539 participants found that insomnia impaired problem solving (effect size = 0.39), complex attention (effect size = 0.36), working memory (effect size = 0.30), and alertness (effect size = 0.14)

Mergenthaler P et al. (2013). Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends Neurosci. 36(10): 587–597.

  • The human brain accounts for 2% of body weight, but consumes 20% of glucose-derived energy

  • This corresponds to 5.6 mg of glucose per 100 g of brain tissue per minute

Xie H et al. (2017). The more total cognitive load is reduced by cues, the better retention and transfer of multimedia learning: A meta-analysis and two meta-regression analyses. PLoS One. 12(8): e0183884.

  • A meta-analysis of 32 multimedia learning studies with 3,597 participants found that cueing to reduce cognitive load improved application of learning (effect size = 0.34) and retention (effect size = 0.27)

Chernev A, Böckenholt U, Goodman J. (2015). Choice overload: A conceptual review and meta‐analysis. Journal Consumer Psychology. 25(2): 333–358.

  • A meta-analysis of 53 studies with 7,202 participants found that choice overload was associated with goal of buying a specific option (effect size = 0.56), choice set complexity (effect size = 0.55), decision task difficulty (effect size = 0.37), and preference uncertainty (effect size = 0.32)

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