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The Important Role of Expectations in Perception

6 October, 2015 - 16:30

Our emotions, mind-set, expectations, and the contexts in which our sensations occur all have a profound influence on perception. People who are warned that they are about to taste something bad rate what they do taste more negatively than people who are told that the taste won’t be so bad (Nitschke et al., 2006), 1 and people perceive a child and adult pair as looking more alike when they are told that they are parent and child (Bressan & Dal Martello, 2002). 2 Similarly, participants who see images of the same baby rate it as stronger and bigger when they are told it is a boy as opposed to when they are told it is a girl (Stern & Karraker, 1989), 3 and research participants who learn that a child is from a lower-class background perceive the child’s scores on an intelligence test as lower than people who see the same test taken by a child they are told is from an upper-class background (Darley & Gross, 1983). 4 Plassmann, O’Doherty, Shiv, and Rangel (2008) 5 found that wines were rated more positively and caused greater brain activity in brain areas associated with pleasure when they were said to cost more than when they were said to cost less. And even experts can be fooled: Professional referees tended to assign more penalty cards to soccer teams for videotaped fouls when they were told that the team had a history of aggressive behavior than when they had no such expectation (Jones, Paull, & Erskine, 2002). 6

Our perceptions are also influenced by our desires and motivations. When we are hungry, food- related words tend to grab our attention more than non-food-related words (Mogg, Bradley, Hyare, & Lee, 1998), 7 we perceive objects that we can reach as bigger than those that we cannot reach (Witt & Proffitt, 2005), 8 and people who favor a political candidate’s policies view the candidate’s skin color more positively than do those who oppose the candidate’s policies (Caruso, Mead, & Balcetis, 2009). 9 Even our culture influences perception. Chua, Boland, and Nisbett (2005) 10 showed American and Asian graduate students different images, such as an airplane, an animal, or a train, against complex backgrounds. They found that (consistent with their overall individualistic orientation) the American students tended to focus more on the foreground image, while Asian students (consistent with their interdependent orientation) paid more attention to the image’s context. Furthermore, Asian-American students focused more or less on the context depending on whether their Asian or their American identity had been activated.

Psychology in Everyday Life: How Understanding Sensation and Perception Can Save Lives

Human factors is the field of psychology that uses psychological knowledge, including the principles of sensation and perception, to improve the development of technology. Human factors has worked on a variety of projects, ranging from nuclear reactor control centers and airplane cockpits to cell phones and websites (Proctor & Van Zandt, 2008). 11 For instance, modern televisions and computer monitors were developed on the basis of the trichromatic color theory, using three color elements placed close enough together so that the colors are blended by the eye. Knowledge of the visual system also helped engineers create new kinds of displays, such as those used on notebook computers and music players, and better understand how using cell phones while driving may contribute to automobile accidents (Lee & Strayer, 2004). 12

Human factors also has made substantial contributions to airline safety. About two thirds of accidents on commercial airplane flights are caused by human error (Nickerson, 1998). 13 During takeoff, travel, and landing, the pilot simultaneously communicates with ground control, maneuvers the plane, scans the horizon for other aircraft, and operates controls. The need for a useable interface that works easily and naturally with the pilot’s visual perception is essential.

Psychologist Conrad Kraft (1978) 14 hypothesized that as planes land, with no other distance cues visible, pilots may be subjected to a type of moon illusion, in which the city lights beyond the runway appear much larger on the retina than they really are, deceiving the pilot into landing too early. Kraft’s findings caused airlines to institute new flight safety measures, where copilots must call out the altitude progressively during the descent, which has probably decreased the number of landing accidents.

Figure 4.38 (image missing in original book) presents the design of an airplane instrument panel before and after it was redesigned by human factors psychologists. On the left is the initial design in which the controls were crowded and cluttered, in no logical sequence, each control performing one task. The controls were more or less the same in color, and the gauges were not easy to read. The redesigned digital cockpit (right on Figure 4.38 (image missing in original book)) shows a marked improvement in usability.

More of the controls are color-coded and multifunctional so that there is less clutter on the dashboard. Screens make use of LCD and 3-D graphics. Text sizes are changeable—increasing readability—and many of the functions have become automated, freeing up the pilots concentration for more important activities.

Figure 4.38 (image missing in original book)

One important aspect of the redesign was based on the principles of sensory adaptation. Displays that are easy to see in darker conditions quickly become unreadable when the sun shines directly on them. It takes the pilot a relatively long time to adapt to the suddenly much brighter display. Furthermore, perceptual contrast is important. The display cannot be so bright at night that the pilot is unable to see targets in the sky or on the land. Human factors psychologists used these principles to determine the appropriate stimulus intensity needed on these displays so that pilots would be able to read them accurately and quickly under a wide range of conditions. The psychologists accomplished this by developing an automatic control mechanism that senses the ambient light visible through the front cockpit windows and that detects the light falling on the display surface, and then automatically adjusts the intensity of the display for the pilot (Silverstein, Krantz, Gomer, Yeh, & Monty, 1990; Silverstein & Merrifield, 1985). 15


  • Sensory interaction occurs when different senses work together, for instance, when taste, smell, and touch together produce the flavor of food.
  • Selective attention allows us to focus on some sensory experiences while tuning out others.
  • Sensory adaptation occurs when we become less sensitive to some aspects of our environment, freeing us to focus on more important changes.
  • Perceptual constancy allows us to perceive an object as the same, despite changes in sensation.
  • Cognitive illusions are examples of how our expectations can influence our perceptions.
  • Our emotions, motivations, desires, and even our culture can influence our perceptions.


  1. Consider the role of the security personnel at the APEC meeting who let the Chaser group’s car enter the security area. List some perceptual processes that might have been at play.
  2. Consider some cases where your expectations about what you think you might be going to experience have influenced your perceptions of what you actually experienced.