An Overview and Some Applications of Inattentional BlindnessResearch

Todd A. Ward

A research paper for PSY 440 (Perception)
Stephen F. Austin State University

During a flight, an airline pilot and his crew noticed a bulbflashing on the control panel. Immersed in a search for the cause,they failed to notice the rapidly approaching ground. The crashkilled over 100 people. At a hospital, a nurse takes out a vial,looks at the label, fills a syringe, and gives a patient aninjection. Unfortunately, the patient received the wrong dose anddied. Real life accidents such as these all occur under a commoncircumstance: a person is doing something and does not see what isright in front of them. Later, they cannot explain why it happened(Green, 2003).

Most people believe that if our eyes are open, we are seeing.Cognitive scientists once thought the same way. They thought ourvisual perception acted much like a videotape recorder with the mindrecording everything the eyes take in. We now know that this is notthe case. More and more, perception studies are demonstrating howlittle people actually see when they are not paying attention(Carpenter, 2001). The explanation lies in a relatively recentdiscovery in the field of psychology called inattentional blindness.According to Goldstein (2002), inattentional blindness refers to "asituation in which a stimulus that is not attended is not perceived,even though a person is looking directly at it" (p.131). Arien Mackand Irvin Rock coined the term inattentional blindness in the mid1990s. Mack and Rock (1998) found that "a puzzling and surprisingaspect of all the experiments examining the perception of a smallnumber of critical stimuli under conditions of inattention was that,on average, 25% of the observers failed to detect their presence" (p.13). Thus, Mack and Rock (1998) concluded that conscious perceptionis not possible without attention. This statement triggered the riseof something called the paradox of perceptual attention (Noe &O'Regan, 2000).

The idea of the paradox is this: in order to see something withany detail in the environment, observers must first direct theirattention toward an object. However, if something is not yetperceived, how can observers direct their attention towards it? Itwould seem that in order for someone to direct attention to anobject, the person would already have to perceive that object (Noe& O'Regan, 2000). There is, however, a solution to this paradoxand Noe & O'Regan (2000) begin to explain it by saying:

That we only perceive that to which we attend appears to be inconflict with the common sense observation that we perceive a gooddeal more than we notice. Driving is an example of a visually guidedbehavior which we seem to be able to perform, at least sometimes, inthe nearly complete absence of attention. To give another informaland familiar example, many of us have had the experience of noticing,all at once, that a bell has been chiming, and indeed, that it is nowchiming for, say, the third time. Surely the fact that we are able tosay, now, that the bell has chimed three times indicates that we insome sense heard the bell before we first attended to it. (p.2)

According to Noe & O'Regan (2000), one can now say that aperson does actually perceive environmental stimuli outside of theirconscious awareness. Therefore, "to experience detail, one mustdetect it. But to detect it, there is no requirement that oneexperience it" (p.3). The paradox of perceptual attention falls apartonce the distinction is made between conscious or attended stimuliand unconscious or unattended stimuli. This gives rise to thequestion of what characteristics determine which environmentalstimuli are consciously perceived.

Green (2003) suggests conspicuity can affect inattentionalblindness. Two types of factors affect conspicuity: sensoryconspicuity factors and cognitive conspicuity factors. The mostimportant sensory conspicuity factor is contrast. The greater thecontrast of an object to its background, the more conspicuous theobject is to the observer. Objects that are large and move or flickerare more conspicuous as well, like school busses, ambulances andrailroad crossings (Green, 2003). However, Green tells of a time whenBritain had a flurry of accidents involving people running intopolice cars parked on road shoulders. In response to this, theypainted the back ends of the police cars with big red and whitestripes. Surprisingly, the rate of accidents actually increased, sothese factors alone do not guarantee conspicuity.

Cognitive conspicuity is at least equally important in gettingsomeone's attention. Conspicuity greatly increases if a stimulus isrelevant or meaningful to the observer (Green, 2003). An example ofthis is something called the cocktail party phenomenon. Imagine Johnis at a party having a conversation with Bob. John can easilyunderstand what his partner is saying and he may or may not be awareof the background noise created by everyone else at the party. Peopledo not have the ability to attend to their conversation and theconversations of everyone else in the room so attention limits peopleto one conversation at a time. Now, imagine someone else in the roomsays "John" in their own conversation. This will probably get John'sattention because a person's own name is very meaningful and relevantmost people. Furthermore, in a study by Morray (as cited in Mack& Rock, 1998) participants were asked to ignore one of twomessages coming into both ears. Results showed participants did nothear much of the unattended message but approximately one third ofthem reported hearing their own names if it was in the unattendedmessage. According to Mack & Rock (1998), meaningfulness or"signal value" (p. 228) of the stimulus is second only to location incapturing attention. An object directly in front of someone has agreater chance of being noticed than does an object in the periphery.Attention is roughly fixed. This means we cannot attend to everythingin our environment. Consequently, the more attention someone gives toone task, the less attention there is for everything else in theenvironment (Green, 2003).

This limited supply of attention means that the "mental workloadand task interference" (Green, 2003, p. 3) can affect inattentionalblindness. This was illustrated by a study in which observers watcheda video of a group of people in white shirts playing basketballoverlaid with another video of a group wearing black shirts playingbasketball. The observers were instructed to attend to one of theteams and to press a key whenever that particular team made a pass.After 30 seconds of observing this, a video of a woman holding anumbrella walking across the screen was overlaid and she was visibleon the screen amongst the basketball players for approximately fourseconds. The results indicated that only 21% of naïve observersnoticed the woman (Neisser & Dube, 1978, as cited in Most, 2001).In this experiment, most of the observers' attention was devoted towatching the basketball players so it was very difficult to attend toanything else. Green (2003) illustrates the idea behind these resultsin more everyday situations:

Speaking on a cell phone, adjusting a radio, or carrying on aconversation with someone in the back seat can absorb someattentional capacity and lead to inattentional blindness. Any mentalworkload, such as just thinking about what to make for dinner, canalso reduce available attention. In some situations, such as drivingalong an open road on a bright day with no traffic, for example,there may be enough attention available to engage in all behaviors.But if the situation becomes more complicated (dense traffic, poorweather, etc) there may not be enough attention for all tasks such ascell phone use. (p. 3).

Inattentional blindness can also come about from too little mentalload. This can happen to people performing a routine task such asdriving. The arousal level of drivers drop and their minds wander.Also, when the chance of something important happening is low,attention tends to fade (Green, 2003). Therefore, the observers'expectations can have an effect on inattentional blindness aswell.

Other studies show that many times distinctive stimuli do notautomatically capture attention, instead conscious perception of astimulus can depend on whether the observer expected it. A study byHaines (as cited in Rensink, 2000) looked at how Navy pilots used ahead up display (HUD) on an aircraft simulator. Just before landingon the simulated aircraft carrier, a large airplane was put on thedeck of the aircraft carrier at the point of touchdown. Because theywere not expecting it, the pilots often failed to detect the planeeven though it was very salient and meaningful to their situation. Anexplanation of why this happens is found in something known as thecontingent-capture hypothesis (Folk, Remington, & Johnston, 1992,as cited in Most et al., 2001). This theory is centered aroundsomething called an attentional set. When an observer has anattentional set for an object or for certain characteristics ofobjects, only things in the attentional set will capture theirattention when presented in the perceptual field. Consequently,findings by Simons & Chabris (as cited in Most, 2001)showed that observers were more likely to notice an unexpected objectthe more similar the object was to stimuli they were currentlyattending. Similarly, Most (2001) found that similarity ofunexpected items to items already attended to significantly increasedthe probability that the unexpected items would be noticed.

Cognitive science has come a long way in understanding how themind relates to perception. The discovery of attention's central rolein our perception of the environment has led cognitive scientists torethink the once held "video recorder" model of perception. Manyother discoveries since have taken its place. We now know that manythings actually affect our perception of the environment.

One of these things is the conspicuity of an environmentalstimulus. An object can display sensory conspicuity through contrast,size, and speed. Sensory conspicuity factors are physical qualitiesof an object as opposed to cognitive sensory factors, which are moresubjective. The main cognitive sensory factor is relevance. Howrelevant or meaningful an object is to the observer has a tremendouseffect on whether or not the object receives attention. The cocktailparty phenomenon is a great example of how relevance affects ourperception. The mental load a person is experiencing can also alterenvironmental perception. Anything a person consciously does requiresattention whether it is thinking about weekend plans or talking onthe phone. The more things we are attending to, the more likely it iswe will experience inattentional blindness. Expectation is the lastfactor mentioned that affects our perception of the environment. Thiscan be illustrated with the contingent-capture hypothesis. Theprobability that an object will be attended to is contingent upon itbeing in our attentional set. All of these factors combined atvarious levels affect how we perceive objects in our environment.

Future research in the area of inattentional blindness needs tofocus on two areas: (a) everyday things that people habitually do butcould prove fatal under the veil of inattentional blindness such asthe nurse mistakenly giving a patient the wrong medication, and (b)situations in which many people can be potentially harmed or killedbecause of someone succumbing to inattentional blindness i.e. busdrivers, airline pilots, or ship captains. Awareness of inattentionalblindness needs to be raised worldwide because it is something thathappens to everyone everyday and every once and a while, it will getthe best of someone at the wrong time and someone could get killed.The better inattentional blindness is understood, the less likelypeople will be to end up like the unfortunate pilot or nurse.



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Goldstein, E.B. (2002). Sensation and perception 6th edition.Pacific Grove, CA: Wadsworth.

Green, G. (2003). Inattentional blindness and conspicuity.Retrieved November 22, 2003 from

Mack, A., & Rock, I. (1998). Inattentional blindness.Cambridge, MA: MIT Press.

Most, S.B., Simons, D.J., Scholl, B.J., Jimenez, R., Clifford, E.,& Chabris, C.F. (2001). How not to be seen: the contribution ofsimilarity and selective ignoring to sustained inattentionalblindness. Psychological Science, 12, 9-17.

Noe, A., & O'Regan, J.K. (2000). Perception, attention and thegrand illusion. PSYCHE, 6 (15). Retrieved November 21, 2003 from

Rensink, R.A. (2000). When good observers go bad: changeblindness, inattentional blindness and visual experience. PSYCHE, 6(9). Retrieved November 21, 2003 from

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