Change blindness

Magic and the Brain
Scientific American 299, 72 – 79 (2008)
Susana Martinez-Conde & Stephen L. Macknik
•Magic tricks often work by covert misdirection, drawing the spectator’s attention away from the secret “method” that makes a trick work.
•Neuroscientists are scrutinizing magic tricks to learn how they can be put to work in experimental studies that probe aspects of consciousness not necessarily grounded in current sensory reality.
•Brain imaging shows that some regions are particularly active during certain kinds of magic tricks.

Scientific American 18, 16 – 17 (2008)
Vilayanur S. Ramachandran & Diane Rogers-Ramachandran
We have eyes, yet we do not see.
PRETEND YOU ARE a member of an audience watching several people dribbling and passing a basketball among themselves. Your job is to count the number of times each player makes a pass to another person during a 60-second period.

Change-blindness as a result of ‘mudsplashes’
Nature 398, 34 (4 March 1999)
J. Kevin O’Regan, Ronald A. Rensink & James J. Clark
Change-blindness occurs when large changes are missed under natural viewing conditions because they occur simultaneously with a brief visual disruption, perhaps caused by an eye movement, a flicker, a blink, or a camera cut in a film sequence.
We have found that this can occur even when the disruption does not cover or obscure the changes.
When a few small, high-contrast shapes are briefly spattered over a picture, like mudsplashes on a car windscreen, large changes can be made simultaneously in the scene without being noticed.
This phenomenon is potentially important in driving, surveillance or navigation, as dangerous events occurring in full view can go unnoticed if they coincide with even very small, apparently innocuous, disturbances. It is also important for understanding how the brain represents the world.

Big Fish Stories Getting Littler
by Robert Krulwich
February 05, 2014

Do we share the same reality?


Do we share the same reality?

– In daily life we typically assume so …

– …but perceptions are powerfully influenced by:

  • What we happen to be paying attention to
  • Contextual factors
  • Past experience
  • Expectations
  • Motivations (we often see what we want to see and don’t see what …)
  • And many other factors

I’d like to say to young people who are struggling in their own life is:
grown-ups are doing the best that they can but they don’t have any idea what your experience is really like and to the best of your ability you have to trust your instincts …

You will outlive your whole clan!

The lesson of framing research is told in the story of a sultan who dreamed he had lost all his teeth.
Summoned to interpret the dream, the first interpreter said, “Alas! The lost teeth mean you will see your family members die.”
Enraged, the sultan ordered 50 lashes for this bearer of bad news.
When a second dream interpreter heard the dream, he explained the sultan’s good fortune: “You will outlive your whole clan!
Reassured, the sultan ordered his treasurer to go and fetch 50 pieces of gold for this bearer of good news.
On the way, the bewildered treasurer observed to the second interpreter, “Your interpretation was no different from that of the first interpreter.”
“Ah yes,” the wise interpreter replied, “but remember: What matters is not only what you say, but how you say it.”

Chapter 1. Introducing Social Psychology
Myers, D. G. (2012). Social psychology (11th ed.). New York: McGraw-Hill.


Common sense is usu. right–after the fact


The point is not that common sense is predictably wrong.
Rather, common sense usually is right— after the fact.
We therefore easily deceive ourselves into thinking that we know and knew more than we do and did.
And that is precisely why we need science to help us sift reality from illusion and genuine predictions from easy hindsight.

Chapter 1. Introducing Social Psychology
Myers, D. G. (2012). Social psychology (11th ed.). New York: McGraw-Hill.


Hindsight bias & CPCs

Hindsight bias: an impediment to accurate probability estimation in clinicopathologic conferences.
Med Decis Making. 1988 Oct-Dec;8(4):259-64.
Dawson NV, Arkes HR, Siciliano C, Blinkhorn R, Lakshmanan M, Petrelli M.

Although clinicopathologic conferences (CPCs) have been valued for teaching differential diagnosis, their instructional value may be compromised by hindsight bias.
This bias occurs when those who know the actual diagnosis overestimate the likelihood that they would have been able to predict the correct diagnosis had they been asked to do so beforehand.

Evidence for the presence of the hindsight bias was sought among 160 physicians and trainees attending four CPCs.
Before the correct diagnosis was announced, half of the conference audience estimated the probability that each of five possible diagnoses was correct (foresight subjects).
After the correct diagnosis was announced the remaining (hindsight) subjects estimated the probability they would have assigned to each of the five possible diagnoses had they been making the initial differential diagnosis.
Only 30% of the foresight subjects ranked the correct diagnosis as first, versus 50% of the hindsight subjects (p less than 0.02).

Although less experienced physicians consistently demonstrated the hindsight bias, more experienced physicians succumbed only on easier cases.

Comment in
Hindsight: artifacts and treatment effects. [Med Decis Making. 1989]

Proverbs make any result make sense

we can draw on our stockpile of proverbs to make almost any result seem to make sense.
If a social psychologist reports that separation intensifies romantic attraction, John Q. Public responds, “You get paid for this? Everybody knows that ‘absence makes the heart grow fonder.’”
Should it turn out that separation weakens attraction, John will say, “My grandmother could have told you, ‘Out of sight, out of mind.’”

“Opposites attract.”
“Birds of a feather flock together.”

Chapter 1. Introducing Social Psychology
Myers, D. G. (2012). Social psychology (11th ed.). New York: McGraw-Hill.



One problem with common sense is that we invoke it after we know the facts.
Events are far more “obvious” and predictable in hindsight than beforehand.
Experiments reveal that when people learn the outcome of an experiment, that outcome suddenly seems unsurprising—much less surprising than it is to people who are simply told about the experimental procedure and the possible outcomes (Slovic & Fischhoff, 1977).

Likewise, in everyday life we often do not expect something to happen until it does.
Then we suddenly see clearly the forces that brought the event about and feel unsurprised.
Moreover, we may also misremember our earlier view (Blank & others, 2008; Nestler & others, 2010).
Errors in judging the future’s foreseeability and in remembering our past combine to create hindsight bias (also called the I-knew-it-all-along phenomenon ).

Chapter 1. Introducing Social Psychology
Myers, D. G. (2012). Social psychology (11th ed.). New York: McGraw-Hill.