Sensation

Sensory receptors in our sense organs respond to information in the world and send this to the brain, a process called sensation. For example, light causes changes in eye cells which relay messages to the nervous system. We call this information stimuli.

You probably know about our five major senses, but were you aware we also have systems that provide information about balance, body position, movement, pain, and temperature?

Our sensory systems:

• Vision
• Hearing (audition)
• Smell (olfaction)
• Taste (gustation)
• Touch (somatosensation)
• Other senses: Balance (vestibular sense), body position (proprioception), body movement (kinesthesia), pain (nociception), and temperature (thermoception)

Perception

Our sensory receptors are constantly collecting information from the environment. However, our interactions with the world are affected by how we perceive that information. Perception is how we interpret sensory information either automatically (bottom-up) or based in knowledge (top-down)^[1]. For example, imagine searching for keys: you focus on a yellow key chain in sensible places. This is top-down processing influenced by knowledge and expectancy.

Now imagine sitting in a crowded restaurant eating lunch and talking with others. Suddenly, there is a loud sound of breaking glass and clang of metal pans hitting the floor. That crashing sound would likely grab our attention – our brain would have no choice but to notice the sound and then interpret it. Because this attentional capture was caused by the sound from the environment: it would be considered a bottom-up process.

Sensation vs perception

One way to think of the difference between sensation and perception is to remember that sensation is a physical process, whereas perception is psychological. For example, imagine walking into a kitchen and smelling the scent of baking cinnamon rolls, the sensation is the smell receptors reacting to the odor of cinnamon and sending information to the brain, but the perception might be “Mmm, this smells like the holiday bread that Grandma used to bake when I was a kid”.

Sensation is physical; perception is psychological. Smelling cinnamon is a sensation; recalling holiday bread is perception.

Although sensation and perception are defined as separate processes, they are almost impossible to separate, since each influences the other. For example, the strength of a sensation changes with sensory adaptation: If you burn a cake, you might stop noticing the smell after a while, but your roommate will smell it right away.

Similarly, attention affects what we sense and perceive. In a noisy environment, we can tune out background noise to focus on a conversation (top-down processing). Attention determines what we notice in our environment.

The Influence of Culture and Experience

Cultural psychologists, like Shinoba Kitayama and Richard Nisbett and their colleagues, have conducted multiple studies on the effects of culture on visual perception.^[1] In general, White people from the USA tend to be more individualistic in their outlook, whereas people from East Asia are more collectivistic and place a greater emphasis on the importance of community. Multiple studies have shown that US participants tend to focus on central elements in a picture or scene—like the globe in Figure 5.3, whereas East Asian participants attend more to context. Therefore, East Asian participants are more likely to notice the background objects as well as the larger objects in the foreground.^[2]

Culture can also affect our susceptibility to visual illusions. Marshall and colleagues found that individuals from industrialized cultures were more prone to experience certain types of visual illusions than individuals from non-industrialized cultures^[3]

These cultural differences in perception are consistent with differences in the types of environment that people experience. For example, people who are used to seeing buildings with straight lines, often referred to as a “carpentered” world^[4] are more susceptible to the
Müller-Lyer illusion (Figure 5.5) than people living in non-industrialized countries. The Zulu people of South Africa, whose villages are made up of round huts arranged in circles, are less susceptible to the illusion.^[5]

The cross-race effect is another example of how visual perception is affected by culture and experience. We are better at recognizing faces of people of our own race than we are at recognizing those from other races.^[6] In one study, Lee and Penrod found that participant race determines the extent of the cross-race effect. They found that, Asian, White, and Latinx participants all showed larger cross-race effects for Black faces compared to faces of other races.^[7] In other words, people who are not Black have more difficulty recognizing Black faces than White, Asian or Latinx faces. Poorer recognition of Black faces has widespread societal implications, ranging from hurtful classroom interactions where Black students are mistaken for other students^[8] to the increased rates of misidentification of Black people by people witnessing crimes and misdemeanors.^[9] However, research by McKone et al. (2019) offers hope for addressing these issues. They found that exposure to faces of different races before the age of 12 years can help mitigate the cross-race effect.^[10] This suggests that by promoting diverse environments from a young age, we can work towards a future where less discrimination occurs.

Other Factors That Affect Perception

Many other factors can influence perception. Have you ever been expecting a really important phone call and you keep thinking that you hear the phone ringing, only to discover that it is not? If so, then you have experienced how motivation can shift our ability to discriminate between a true sensory stimulus and background noise. Signal detection theory explains this – our ability to detect a stimulus depends on its physical properties and also on the psychological state of the observer. This might explain why a mother is awakened by a quiet murmur from her baby but not by other sounds that occur while she is asleep. Signal detection theory has practical applications, such as air traffic controller accuracy. Controllers need to be able to detect planes among many signals that appear on the radar screen and follow those planes as they move through the sky.^[11]

Another influence on perception ispersonality. For example, children described as thrill seekers are more likely to show taste preferences for intense sour flavors than children who are not.^[12] Expectations influence perception, as demonstrated by consumer research on brands and packaging. For example, in a taste test, participants who identified as Coke drinkers preferred Pepsi when it was served from a Coke bottle more than Coke served from a Pepsi bottle, and vice versa for Pepsi drinkers.^[13] An fMRI study showed that participants rated the same wine as tasting better if it had an expensive price tag compared to a cheap one.^[14] Also, popcorn tastes sweeter if served in a red bowl and saltier if served in a blue one.^[15]

On the following pages, we present three more ways to think about perception. First, a story about how psychologist study developing senses in infants. Second, an introduction to the concept of Theory of Mind, which is about taking the perspective of the other. Finally, we describe the concepts of Gestalt as it relates to sensation and perception. It all comes together to illustrate the theme of “Our perceptions and biases filter our world through an imperfect personal lens.”

In the final section, you are encouraged to take what you have learned and apply it to your own experiences.