A research paper for PSY 440 (Perception)
Stephen F. Austin State University
During a flight, an airline pilot and his crew noticed a bulb flashing on the control panel. Immersed in a search for the cause, they failed to notice the rapidly approaching ground. The crash killed over 100 people. At a hospital, a nurse takes out a vial, looks at the label, fills a syringe, and gives a patient an injection. Unfortunately, the patient received the wrong dose and died. Real life accidents such as these all occur under a common circumstance: a person is doing something and does not see what is right 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 our visual perception acted much like a videotape recorder with the mind recording everything the eyes take in. We now know that this is not the case. More and more, perception studies are demonstrating how little people actually see when they are not paying attention (Carpenter, 2001). The explanation lies in a relatively recent discovery in the field of psychology called inattentional blindness. According to Goldstein (2002), inattentional blindness refers to "a situation in which a stimulus that is not attended is not perceived, even though a person is looking directly at it" (p.131). Arien Mack and Irvin Rock coined the term inattentional blindness in the mid 1990s. Mack and Rock (1998) found that "a puzzling and surprising aspect of all the experiments examining the perception of a small number 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 perception is not possible without attention. This statement triggered the rise of something called the paradox of perceptual attention (Noe & O'Regan, 2000).
The idea of the paradox is this: in order to see something with any detail in the environment, observers must first direct their attention toward an object. However, if something is not yet perceived, how can observers direct their attention towards it? It would seem that in order for someone to direct attention to an object, the person would already have to perceive that object (Noe & O'Regan, 2000). There is, however, a solution to this paradox and Noe & O'Regan (2000) begin to explain it by saying:
That we only perceive that to which we attend appears to be in conflict with the common sense observation that we perceive a good deal more than we notice. Driving is an example of a visually guided behavior which we seem to be able to perform, at least sometimes, in the nearly complete absence of attention. To give another informal and 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 now chiming for, say, the third time. Surely the fact that we are able to say, now, that the bell has chimed three times indicates that we in some sense heard the bell before we first attended to it. (p.2)
According to Noe & O'Regan (2000), one can now say that a person does actually perceive environmental stimuli outside of their conscious awareness. Therefore, "to experience detail, one must detect it. But to detect it, there is no requirement that one experience it" (p.3). The paradox of perceptual attention falls apart once the distinction is made between conscious or attended stimuli and unconscious or unattended stimuli. This gives rise to the question of what characteristics determine which environmental stimuli are consciously perceived.
Green (2003) suggests conspicuity can affect inattentional blindness. Two types of factors affect conspicuity: sensory conspicuity factors and cognitive conspicuity factors. The most important sensory conspicuity factor is contrast. The greater the contrast of an object to its background, the more conspicuous the object is to the observer. Objects that are large and move or flicker are more conspicuous as well, like school busses, ambulances and railroad crossings (Green, 2003). However, Green tells of a time when Britain had a flurry of accidents involving people running into police cars parked on road shoulders. In response to this, they painted the back ends of the police cars with big red and white stripes. Surprisingly, the rate of accidents actually increased, so these factors alone do not guarantee conspicuity.
Cognitive conspicuity is at least equally important in getting someone's attention. Conspicuity greatly increases if a stimulus is relevant or meaningful to the observer (Green, 2003). An example of this is something called the cocktail party phenomenon. Imagine John is at a party having a conversation with Bob. John can easily understand what his partner is saying and he may or may not be aware of the background noise created by everyone else at the party. People do not have the ability to attend to their conversation and the conversations of everyone else in the room so attention limits people to one conversation at a time. Now, imagine someone else in the room says "John" in their own conversation. This will probably get John's attention because a person's own name is very meaningful and relevant most people. Furthermore, in a study by Morray (as cited in Mack & Rock, 1998) participants were asked to ignore one of two messages coming into both ears. Results showed participants did not hear much of the unattended message but approximately one third of them reported hearing their own names if it was in the unattended message. According to Mack & Rock (1998), meaningfulness or "signal value" (p. 228) of the stimulus is second only to location in capturing attention. An object directly in front of someone has a greater chance of being noticed than does an object in the periphery. Attention is roughly fixed. This means we cannot attend to everything in our environment. Consequently, the more attention someone gives to one task, the less attention there is for everything else in the environment (Green, 2003).
This limited supply of attention means that the "mental workload and task interference" (Green, 2003, p. 3) can affect inattentional blindness. This was illustrated by a study in which observers watched a video of a group of people in white shirts playing basketball overlaid with another video of a group wearing black shirts playing basketball. The observers were instructed to attend to one of the teams and to press a key whenever that particular team made a pass. After 30 seconds of observing this, a video of a woman holding an umbrella walking across the screen was overlaid and she was visible on the screen amongst the basketball players for approximately four seconds. The results indicated that only 21% of naïve observers noticed the woman (Neisser & Dube, 1978, as cited in Most, 2001). In this experiment, most of the observers' attention was devoted to watching the basketball players so it was very difficult to attend to anything else. Green (2003) illustrates the idea behind these results in more everyday situations:
Speaking on a cell phone, adjusting a radio, or carrying on a conversation with someone in the back seat can absorb some attentional capacity and lead to inattentional blindness. Any mental workload, such as just thinking about what to make for dinner, can also reduce available attention. In some situations, such as driving along 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, poor weather, etc) there may not be enough attention for all tasks such as cell phone use. (p. 3).
Inattentional blindness can also come about from too little mental load. This can happen to people performing a routine task such as driving. 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 as well.
Other studies show that many times distinctive stimuli do not automatically capture attention, instead conscious perception of a stimulus can depend on whether the observer expected it. A study by Haines (as cited in Rensink, 2000) looked at how Navy pilots used a head up display (HUD) on an aircraft simulator. Just before landing on the simulated aircraft carrier, a large airplane was put on the deck of the aircraft carrier at the point of touchdown. Because they were not expecting it, the pilots often failed to detect the plane even though it was very salient and meaningful to their situation. An explanation of why this happens is found in something known as the contingent-capture hypothesis (Folk, Remington, & Johnston, 1992, as cited in Most et al., 2001). This theory is centered around something called an attentional set. When an observer has an attentional set for an object or for certain characteristics of objects, only things in the attentional set will capture their attention when presented in the perceptual field. Consequently, findings by Simons & Chabris (as cited in Most et.al, 2001) showed that observers were more likely to notice an unexpected object the more similar the object was to stimuli they were currently attending. Similarly, Most et.al (2001) found that similarity of unexpected items to items already attended to significantly increased the probability that the unexpected items would be noticed.
Cognitive science has come a long way in understanding how the mind relates to perception. The discovery of attention's central role in our perception of the environment has led cognitive scientists to rethink the once held "video recorder" model of perception. Many other discoveries since have taken its place. We now know that many things actually affect our perception of the environment.
One of these things is the conspicuity of an environmental stimulus. An object can display sensory conspicuity through contrast, size, and speed. Sensory conspicuity factors are physical qualities of an object as opposed to cognitive sensory factors, which are more subjective. The main cognitive sensory factor is relevance. How relevant or meaningful an object is to the observer has a tremendous effect on whether or not the object receives attention. The cocktail party phenomenon is a great example of how relevance affects our perception. The mental load a person is experiencing can also alter environmental perception. Anything a person consciously does requires attention whether it is thinking about weekend plans or talking on the phone. The more things we are attending to, the more likely it is we will experience inattentional blindness. Expectation is the last factor mentioned that affects our perception of the environment. This can be illustrated with the contingent-capture hypothesis. The probability that an object will be attended to is contingent upon it being in our attentional set. All of these factors combined at various levels affect how we perceive objects in our environment.
Future research in the area of inattentional blindness needs to focus on two areas: (a) everyday things that people habitually do but could prove fatal under the veil of inattentional blindness such as the nurse mistakenly giving a patient the wrong medication, and (b) situations in which many people can be potentially harmed or killed because of someone succumbing to inattentional blindness i.e. bus drivers, airline pilots, or ship captains. Awareness of inattentional blindness needs to be raised worldwide because it is something that happens to everyone everyday and every once and a while, it will get the best of someone at the wrong time and someone could get killed. The better inattentional blindness is understood, the less likely people will be to end up like the unfortunate pilot or nurse.
References
Carpenter, S. (2001). Sights unseen. Monitor on Psychology, 32.
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 http://www.visualexpert.com/Resources/inattentionalblindness.html.
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 of similarity and selective ignoring to sustained inattentional blindness. Psychological Science, 12, 9-17.
Noe, A., & O'Regan, J.K. (2000). Perception, attention and the grand illusion. PSYCHE, 6 (15). Retrieved November 21, 2003 from http://psyche.cs.monash.edu..au/v6/psyche-6-15-noe.html.
Rensink, R.A. (2000). When good observers go bad: change blindness, inattentional blindness and visual experience. PSYCHE, 6 (9). Retrieved November 21, 2003 from http://psyche.cs.monash.edu..au/v6/psyche-6-09-rensink.html.