Monday, July 23, 2012

inattentional blindness

Inattentional blindness is an inability to perceive something that is within one's direct perceptual field because one is attending to something else. The term was coined by psychologists Arien Mack and Irvin Rock, who identified the phenomenon while studying the relationship of attention to perception. They were able to show that, under a number of different conditions, if subjects were not attending to a visual stimulus but were attending to something else in the visual field, a significant percentage of the subjects were "blind" to something that was right before their eyes.
Because this inability to perceive, this sighted blindness, seemed to be caused by the fact that subjects were not attending to the stimulus but instead were attending to something else ... we labeled this phenomenon inattentional blindness (IB).*
Mack and Rock go on to argue that, in their view, "there is no conscious perception without attention." We might add that visual perception does not work like a video or any other kind of recorder. Objects or movements may occur in the visual field that are not attended to and may not be consciously or unconsciously perceived. Things can change in the visual field without our being aware of the changes. Perception, like memory, is a constructive process, and it seems that the brain builds its representations from a few salient details, often determined by our purposes or desires. Thus, two people may witness the same events but see and remember quite different things, even if both are good observers paying close attention to what is going on.

Neisser, Simons, and Chabris have replicated and extended the work of Mack and Rock with experiments that have subjects attending to a specific task while watching a film, such as counting how many times a basketball is passed from one team member to another, while someone walks through the scene carrying an umbrella or wearing a gorilla suit. A surprisingly large percentage of subjects do not perceive something as obvious as a person in a gorilla suit moving through the scene they are observing, if they are attending to something else in their visual field. (Several examples of these experiments can be viewed on the Simons Lab page of the University of Illinois.)

The possibility of inattentional blindness should always be considered when dealing with conflicting eyewitness testimony where one of the parties claims that he did not see something that the other party saw and that might seem like something that anybody who was looking should have seen. The party who says he did not see what might seem too salient to miss may have been paying attention to something else at the time. Of course, one could be lying about not seeing something that one saw, but even the most honest person in the world might not see something that you think anybody should have seen.

Inattentional blindness may explain, for example, how a pilot with an interest in crop circles could fly right over one without even noticing it. The pilot had flown to see a recently discovered crop circle near Stonehenge. After visiting the site, he flew back to the airport to refuel before setting off on a trip that took him back over the site he had just visited. On the return flight he noticed another crop circle near the one he had visited earlier in the day and swears that the new circle was not there just forty-five minutes earlier. The new circle is very elaborate and could not have been produced by human hoaxers in such a short time. He concludes that some mysterious force must have been at work. Perhaps, but it seems more likely that the pilot experienced inattentional blindness when he was flying to the airport. He was focused on other tasks when he flew over the site and didn’t notice what was right beneath him all the time. (See "Crop Circles - Quest for Truth.")

Research by Chabris and Simons indicates that inattentional blindness is a "necessary, if unfortunate, by-product of the normal operation of attention and perception" (The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us. 2010, p. 38). They point out that even radiologists, who are highly trained experts at detecting visual signs of medical problems, "can still miss subtle problems when they 'read' medical images." This may explain why my dentist didn't see a crack in one of my teeth on an x-ray until I started to complain about the pain in a particular area. To eliminate inattentional blindness, we'd have to eliminate focused attention. That would not be a good idea. Even worse would be the condition of being able to attend to everything in our sensory field at once. It would drive us mad.

Research also shows that training people to improve their attention abilities may do nothing to help them detect unexpected objects. "If an object is truly unexpected, people are unlikely to notice it no matter how good (or bad) they are at focusing attention" (Chabris and Simons: p. 32). Remember this the next time you're at the airport watching the transportation security screener do his or her job. It should not be surprising to find that these folks miss a lot of contraband, some of which has been planted by their bosses to test them.

It should go without saying--but I'll say it anyway--that magicians take advantage of inattentional blindness when doing sleight of hand tricks. The process of misdirection involves getting you to pay attention to one thing while the magician does something right before your eyes that you don't see or pay attention to.


  1. Inattentional blindness, also known as perceptual blindness, is failure to notice an unexpected stimulus that is in one's eyesight when other attention demanding tasks are being performed. Inattentional blindness is categorized as an attentional error and is not associated with any vision deficits

  2. Inattentional blindness is the failure to notice a fully-visible, but unexpected object because attention was engaged on another task, event, or object.
    This phenomenon is related to but distinct from other failures of visual awareness such as change blindness, repetition blindness, visual masking, and the attentional blink. In most cases, studies of inattentional blindness involve a single critical trial in which an object appears unexpectedly while observers are performing their task. At the end of the trial, observers are asked a series of questions to determine whether or not they saw the unexpected object.

  3. Most mental processing occurs outside of conscious awareness. The amount of information that can be taken in by our senses is limitless. But the brain has very limited resources when it comes to attentiveness. Our senses receive much more information than can possibly be processed at one time. To combat information overload, the brain allows large amounts of information through almost entirely unassimilated, peeling off just a few pieces of selected information for a closer look