Inattentional blindness: What captures your attention?
From the February 26, 2009 issue
A nurse pulls a vial of heparin from an automated dispensing cabinet (ADC). She reads the label, prepares the medication, and administers it intravenously to an infant. The infant receives heparin in a concentration of 10,000 units/mL instead of 10 units/mL and dies.
A pharmacist enters a prescription for methotrexate daily into the pharmacy computer. A dose warning appears on the screen. The pharmacist reads the warning, bypasses it, and dispenses the medication as entered. The patient receives an overdose of the medication and dies.
A nurse reaches in the refrigerator for a piggyback antibiotic for her patient. She reads the label, spikes the bag with IV tubing, and administers the medication to her patient. The patient receives a neuromuscular blocking agent instead of the intended antibiotic and dies.
A pharmacy technician labels and delivers an IV infusion to the dialysis unit. The nurse reads the pharmacy label and hangs the bag while preparing her patient for dialysis. The patient receives sterile water for injection instead of 0.9% sodium chloride and dies.
A nurse picks out a prefilled syringe of pain medication for her patient. She reads the label and administers the medication intravenously. The patient receives hydromorphone instead of morphine and experiences a respiratory arrest.
All of these actual errors, and many more in healthcare and other industries, have happened under similar circumstances: the person performing the task fails to see what should have been plainly visible, and later, they cannot explain the lapse.(1) In many cases, people involved in the errors have been labeled as careless and negligent. But these types of accidents are common—even with intelligent, vigilant, and attentive people. The cause is usually rooted in inattentional blindness, a condition all people periodically exhibit.(1)
How do we process information?
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.(2)
In deciding what to focus on, the brain scans about 30-40 pieces of information (e.g., sights, sounds, smells, tactile information) per second, until something captures its attention.(2) Our attention filter selects just a small amount of information to process, and anything leftover gets short shrift. The rest of the information never reaches our consciousness—thus the term inattentional blindness. Unfortunately, the brain is a master at filling in the gaps and compiling an integrated portrait of reality based on just a flickering view.(1)
Accidents happen when attention mistakenly filters away important information and the brain fills in the gaps with what is aptly referred to as a “grand illusion.” (2) Thus, in the examples above, the brains of the individuals involved in the errors filtered out important information on medication labels and computer screens, and filled in the gaps with erroneous information that led them to believe they had the correct medication or had read the warning appropriately.
What captures your attention?
Visual attentiveness, or what captures your attention, is shaped by four factors.
Conspicuity. The degree to which an object or piece of information jumps out to capture your attention falls into two categories: sensory conspicuity and cognitive conspicuity. Sensory conspicuity deals with the physical properties of information. For example, a high degree of contrast with the background is the most important feature in making information conspicuous,(1) and luminance (brightness) contrast is more important than color contrast.(3) Factors such as bright colors, movement, and flicker do not ensure conspicuity;(1) however, pre-attentive properties (the brain automatically processes the information without being aware of it) such as color and shape have been used successfully on visual displays to call attention to specific items or categories.(3)
Cognitive conspicuity deals with the perceived relevance of the information. The “cocktail party” effect(4) is a classic portrayal of this factor. This is the term used for the phenomenon of being in a crowd, listening to a conversation, and still being able to hear your name mentioned across the room.(3) Functioning somewhat like the volume control on a radio, you can turn down the volume of background noise at a cocktail party and turn up the volume as you listen attentively to one conversation at a time. While engaged in conversation, if someone behind you mentions your name, you are automatically attracted to the other conversation because it is meaningful to you. Meaningful visual information can also jump out at you automatically, such as scanning the newspaper and finding your attention drawn to articles that include the first name of your child. Attention to something of particular relevance can also be purposeful. For example, you may scan a luggage carousel for your black suitcase, looking purposefully for the broken wheel or yellow ribbon that distinguishes your suitcase from all the other black suitcases on the carousel.
Mental workload and task interference. Inattentional blindness is more likely to occur if part of your attention is diverted to secondary tasks, like answering the phone while entering prescriptions into the computer, or even thinking about your dinner plans while transcribing an order. We all learn to function amazingly well while multi-tasking, but more complicated tasks require our full attention. However, auditory tasks (listening to the radio) will interfere less with visual tasks (seeing a pedestrian crossing the road) than would a second visual task (focusing on a street sign).(1)
Low workload causes boredom and reduces the mental attention given to tasks, as does carrying out highly practiced tasks, such as drawing medication out of a vial into a syringe. In fact, we spend a large majority of our waking life functioning with the equivalent of an automatic pilot, with occasional conscious checks to ensure tasks are being carried out properly. This makes us particularly prone to inattentional blindness. Reliance on technology has also lessened our ability to notice abnormalities.
Expectation. Expectation has a powerful effect on our ability to pay attention and notice information. If the medication we are looking for comes in a carton with a highly stylized label, we come to expect this presentation every time we look for the medication. If a new medication comes in a similar looking carton, our brain may not pay attention to any information that disconfirms our belief that the new medication is the old one—a well-known phenomenon called confirmation bias to which highly experienced practitioners are most prone.
Our past experiences also teach us what is relevant. Errors occur when new or unusual circumstances happen in highly familiar situations. The nurse who picked up a vial of heparin in the wrong concentration had never experienced removing the wrong medication from an ADC cabinet before this event. The pharmacist who did not notice important information on a computer warning had rarely encountered a clinically significant computer alert. The nurse who picked the wrong pain medication from the narcotics cabinet did not remember making such an error in the past. Each of the practitioners in the examples above had subconsciously learned that there was nothing important to see when carrying out these tasks. Nothing had ever happened, so attention was automatically filtered away from the details to conserve mental processing.
Capacity. The capacity to pay attention is variable from person to person and influenced by age and mental aptitude. From time to time, attention is also variable within an individual due to influences such as distractions, alcohol, drugs, and fatigue.
It is difficult to reduce the risk of inattentional blindness, as it is an involuntary and unnoticed consequence of our adaptive ability to defend against information overload. Error-reduction strategies such as education, training, and rules are of little value. Instead, efforts should center on increasing conspicuity of critical information, and decreasing diversions of attention and secondary tasks when carrying out complex tasks.
References: 1) Green M. “Inattentional blindness” and conspicuity. Visual Expert 2004 (www.visualexpert.com/Resources/inattentionalblindness.html). 2) Angier N. Blind to change, even as it stares us in the face. The New York Times April 1, 2008 (www.nytimes.com/2008/04/01/science/01angi.htm?_r=2&ex=1207713600&en=204&oref=slogin). 3) Federal Aviation Administration (FAA). FAA human factors awareness course. (www.hf.faa.gov/webtraining/Intro/Intro1.htm). 4) Arons B. A review of the cocktail party effect. MIT Media Lab; 1992. (www.media.mit.edu/speech/papers/1992/arons_AVIOSJ92_cocktail_party_effect.pdf).