At the end of this section you can:
- Distinguish between sensation and perception.
- Describe the concepts of absolute threshold and difference threshold.
- Discuss the roles that attention, motivation, and sensory adaptation play in perception.
What does it mean to feel something? Sensory receptors are specialized neurons that respond to specific types of stimuli. When sensory information is captured by a sensory receptor, a sensation has been created. For example, light entering the eye causes chemical changes in the cells lining the back of the eye. These cells transmit messages in the form of action potentials (as you learned from studying biopsychology) to the central nervous system. The conversion of energy from a sensory stimulus to an action potential is calledtransmission.transmissionIt represents the first step to perception and is a translation process in which different types of cells respond to stimuli and produce a signal processed by the central nervous system that results in what we experience as sensations. Sensations allow organisms to feel a face and smell smoke as it burns.
Perceptions, on the other hand, require organizing and understanding incoming sensory information. For sensations to be useful, we must first add meaning to those sensations that our perceptions of those sensations create. The sensations allow us to see a red burner, but the perceptions imply the understanding and representation of the characteristic heat. Furthermore, a sensation would be hearing a high-pitched, shrill sound, while a perception would be the classification and understanding of that sound as a fire alarm. In this chapter, sensations and perceptions are treated as separate events, while in reality sensations and perceptions can be viewed as occurring more along a continuum in which the boundaries between the end of a perception and the beginning of a perception are more fluid.
You've probably known since elementary school that we have five senses: sight, hearing (hearing), smell (smell), taste (gustation), and touch (somatosensory). It turns out that this notion of five senses is overly simplistic. We also have sensory systems that provide information about balance (the vestibular sense), body position and movement (proprioception and kinesthesia), pain (nociception), and temperature (thermoception), and each of these sensory systems has different receptors that are tuned to different stimuli to transmit. The visual system absorbs light using rod and cone receptors located at the back of the eyes, sound is translated through tiny hair-like receptors known as cilia in the inner ear, smell and taste work together most of the time to capture the chemicals within to absorb airborne particles. and food via chemically sensitive cilia in the nasal cavity and chemical receptor clusters on the tongue. Touch is particularly interesting because it consists of responses from many different types of receptors in the skin, which send signals to the central nervous system in response to temperature, pressure, vibration, and skin disturbances such as stretching and tearing.
Free nerve endings embedded in the skin that allow humans to perceive the various differences in our immediate surroundings. Adapted from Pinel, 2009.
The sensitivity of a given sensory system to relevant stimuli can be expressed as an absolute threshold.absolute thresholdrefers to the minimum amount of stimulus energy that must be present for the stimulus to be recognized 50% of the time. Another way to think about it is to ask how dim a light can be or how quiet a sound can be and still be noticed half the time. The sensitivity of our sensory receptors can be quite amazing. It has been estimated that the most sensitive sensory cells at the back of the eye can detect a candle flame 30 miles away on a clear night (Okawa & Sampath, 2007). Under quiet conditions, hair cells (the inner ear's receptor cells) can detect the ticking of a clock 20 feet away (Galanter, 1962). In addition, a teaspoon of sugar can be tasted in two gallons of water, and the human olfactory system can detect the scent of a drop of perfume in a six-room apartment.
It is also possible that we receive messages that are presented below the threshold of consciousness: these are called subliminal messages. A stimulus reaches a physiological threshold when it is strong enough to excite sensory receptors and send nerve impulses to the brain: this is an absolute threshold. A message below this threshold is called subliminal: the message is being processed, but we are not aware of it. There has been much speculation over the years about the use of subliminal messages in advertising, rock music, and self-help audio programs to influence consumer behavior. Research in laboratory settings has shown that humans can process and respond to information outside of their consciousness. But that doesn't mean that we obey these messages like zombies; indeed, hidden messages have little impact on behavior outside the laboratory (Art-Wilson & Zajonc, 1980; Rensink, 2004; Nelson, 2008; Radel, Sarrazin, Legrain, & Gobancé, 2009; Loersch, Durso, & Petty, 2013). Studies attempting to persuade viewers to buy more popcorn and reduce smoking behavior have shown little to no success, suggesting that subliminal messages are mostly ineffective in eliciting certain behaviors (Karremans, Stroebe & Claus, 2006). However, neuroimaging studies have shown clear neural activity related to the processing of subliminal stimuli (Koudier & Dehaene, 2007). Additionally, Krosnick, Betz, Jussim, and Lynn (1992) found that participants presented with images of corpses or buckets full of snakes for several milliseconds (subliminal priming) were more likely to rate a neutral image of a woman with a neutral facial expression. as more uncomfortable compared to the participants who were shown more comfortable images (kittens and bridal couples). That proves itAlthough we are unaware of the stimuli presented to us, we process them at the neural level,and also that while subliminal priming is generally not strong enough to compel unwanted purchases, it can affect our perception of things we encounter in the environment after subliminal priming.
Absolute thresholds are generally measured under incredibly controlled conditions in situations that are optimal for sensitivity. Sometimes we are more interested in how much difference in the stimuli it takes to tell a difference between them. This is known as theonly a noticeable difference(JND, briefly mentioned in the above study comparing color perception of Chinese and Dutch participants) or difference threshold. In contrast to the absolute threshold, the difference threshold changes depending on the intensity of the stimulus. For example, imagine you are in a very dark movie theater. If a viewer received a text message on their cell phone that caused their screen to light up, many people would likely notice the change in lighting in the theater. However, if the same thing happened during a basketball game in a well-lit stadium, few people would notice. The phone's brightness does not change, but its ability to detect a change in lighting varies drastically between the two contexts. Ernst Weber proposed this theory of differential threshold change in the 1830s and it is known as Weber's law.
Weber's law: Each of the different senses has its own constant ratios that determine the difference thresholds.
Weber's ideas on difference thresholds influenced concepts in signal recognition theory, which states that our ability to recognize a stimulus depends on sensory factors (like the intensity of the stimulus or the presence of other processed stimuli) as well as our psychological state (you're tired because you stayed awake the night before). Human factors engineers who design aircraft and automobile control panels constantly use signal detection theory to assess situations that pilots or drivers may experience, such as B. Difficulty seeing and interpreting controls on extremely bright days.
„Although perceptions are made up of sensations, not all sensations lead to perceptions..“
Ultimately, while our sensory receptors are constantly gathering information from the environment, it is how we interpret that information that affects how we interact with the world. Perception refers to the ways in which sensory information is consciously organized, interpreted, and experienced. Perception involves bottom-up and top-down processing. Bottom-up processing refers to the fact that perceptions are constructed from sensory information, stimuli from the environment. On the other hand, the way we interpret these sensations is influenced by our available knowledge, experiences and thoughts related to the stimuli we are experiencing. This is called top-down processing.
One way to think about this concept is that sensation is a physical process while perception is psychological. For example, if you walk into a kitchen and smell the aroma of baked cinnamon rolls, thatSensationare the olfactory receptors that detect the smell of cinnamon, but theperceptionIt could be, "Mmm, that smells like the bread Grandma used to bake when the family got together for the holidays." The sensation is a signal from one of our six senses. Perception is the brain's response to these signals. When we see our professor speaking at the front of the room, we sense the visual and auditory cues from him that he is lecturing on our psychology class.
Although our perceptions are made up of sensations, not all sensations lead to perceptions. In fact, we often do not perceive stimuli that remain relatively constant over a long period of time. This is called sensory adaptation. Imagine walking into a classroom with an old analog clock. When you first enter the room you can hear the clock ticking; When you start talking to your classmates or hear your teacher greeting the class, you stop noticing the ticking. The clock is ticking and this information continues to affect the sensory receptors of the hearing aid. The fact that he no longer perceives sounds demonstrates a sensory adaptation and shows that sensation and perception, while closely related, are different. Also, if you go outside to a dark cinema on a bright day, you will find that it is extremely difficult to see at first. After a few minutes, you'll experience something called dark adaptation, which typically takes about 8 minutes for the cones to adjust (visual acuity and color) and about 30 minutes for the cones to adjust on your retina (light, dark, depth, and distance) (pike & Mendelbaum, 1938; Klaver, Wolfs, Vingerling, Hoffman & de Jong, 1998). If you're wondering why it takes so long to adapt to darkness, in order for rods and cones to change sensitivity, they first have to go through a complex chemical change associated with the protein molecules that doesn't happen instantaneously. Now that you've adjusted to the darkness of the theater, survived the marathon by watching the entire Lord of the Rings series, and exit the theater in what appears to be a short ten hours after entering the theater, you can experience the light adjustment process. except it's still light outside. During light adaptation, the pupils constrict to reduce the amount of light entering the retina and photosensitivity is reduced for both rods and cones, typically lasting less than 10 minutes (Ludel, 1978). So why is the process of increasing sensitivity to light to adapt to darkness more complex than decreasing sensitivity to adapt to light? Caruso (2007) has suggested that adaptation to darkness involves a more gradual process, due to humans' evolutionary tendency to slowly adapt to darkness as the sun sets over the horizon.
There is another factor that influences sensation and perception: attention. Attention plays an important role in determining what is felt and what is perceived. Imagine you are at a party filled with music, talk and laughter. You're having an interesting conversation with a friend, blocking out all background noise. If someone interrupted you to ask what song was playing, you probably wouldn't be able to answer that question.
One of the most interesting demonstrations of how important attention is to our perception of the environment comes from a famous study by Daniel Simons and Christopher Chabris (1999). In this study, participants watched a video of people wearing black and white basketballs walking by. Participants were asked to count the number of times the white team passed the ball. During the video, a person in a black gorilla costume walks between the two teams. You'd think someone would notice the gorilla, right? Almost half of the video's viewers didn't notice the gorilla at all, despite being clearly visible for nine seconds. Because participants were so focused on how many times the white team passed the ball, they completely ignored other visual information. Missing something that is fully visible due to inattention is called inadvertent blindness. Recent work has examined inattentive blindness associated with cell phone use. Hyman, Boss, Wise, McKenzie, and Caggiano (2010) classified participants according to whether they walked on a cell phone, listened to an MP3 player, walked without electronic devices, or walked with a partner. The participants were unaware that a clown would be riding a unicycle right in front of them as they walked across the plaza. After the students reached the outside of the square, they were stopped and asked if they saw the clown on a unicycle riding in front of them. It found that cell phone users walked slower, changed direction more often, were less aware of their surroundings, and were also the group most likely to report not noticing the unicycle clown. David Strayer and Frank Drews also studied cell phone use in a series of driving simulators and found that even when participants viewed objects in the driving environment directly, they were less likely to create a lasting memory of those objects when they were present with a cell phone. This pattern was obtained for objects with high and low relevance to their driving safety, indicating insignificant cognitive analysis of objects in the constrained focus-inattentional driving environment during a cellphone call. In addition, in-vehicle conversations did not impair driving as much as cellular phone conversations, as suggested by Strayer and Drews, drivers are better able to synchronize driving processing requirements with in-vehicle conversations than phone conversations. In general, it is clear that directing our attention can sometimes cause serious damage to other information, and it appears that cell phones can have a particularly dramatic impact on information processing while performing other tasks.
In an experiment similar to the previous activity, the researchers tested unintentional blindness by asking participants to watch images move across a computer screen. They were instructed to focus on either black or white objects regardless of the other color. When a red cross flashed across the screen, about a third of the subjects did not notice it (Figure below) (Most, Simons, Scholl & Chabris, 2000).
Fast ein Drittel der Teilnehmer einer Studie bemerkte kein rotes Kreuz auf dem Bildschirm, das vorbeiscrollte, weil ihre Aufmerksamkeit auf die schwarzen oder weißen Zahlen gerichtet war. (Credit: Cory Zanker)
Motivation can also affect perception. Have you ever been waiting for a really important call and while you were in the shower thought you heard the phone ring, only to find out it wasn't? If so, then you've seen how the motivation to recognize a significant stimulus can alter our ability to discriminate between genuine sensory input and background noise. This motivational aspect of conversation expectancy could also be the reason why unintentional blindness related to cellphone use was so strongly identified. The ability to identify a stimulus when it is embedded in a distracting background is referred to assignal detection theory.
Signal detection theory:A theory that explains how various factors affect our ability to detect weak signals in our surroundings.
The signal detection theory also explains why a mother is awakened by a soft murmur from her baby, but not by other sounds that occur while she is sleeping. This also applies to air traffic controller communications, pilot and driver control panels as mentioned above, and even the monitoring of vital patient information while a surgeon is performing an operation. In the case of air traffic controllers, controllers must be able to spot aircraft among the many markers (turn signals) that appear on the radar screen and follow those aircraft as they move across the sky. In fact, the original work of the researcher who developed the signal detection theory focused on improving the sensitivity of air traffic controllers to aircraft light signals (Swets, 1964).
Our perceptions can also be influenced by our beliefs, values, prejudices, expectations and life experiences. As you will see later in this chapter, people who are deprived of the experience of binocular vision at critical stages of development have difficulty perceiving depth (Fawcett, Wang, & Birch, 2005). The shared experiences of people within a given cultural context can have profound effects on perception. For example, Marshall Segall, Donald Campbell, and Melville Herskovits (1963) published the results of a multinational study showing that individuals in the WestThe cultureThey were more likely to experience certain types of visual illusions than people from non-Western cultures, and vice versa. One of these illusions that westerners were most likely to experience was thisMuller LyerDeception (image below): The lines appear to be different lengths, but are actually the same length.
In the Müller-Lyer illusion, lines appear to be of different lengths even though they are identical. (a) Arrows at the end of lines can make the right line appear longer even though the lines are the same length. (b) When applied to a three-dimensional image, the right line may appear longer again, although both black lines are of equal length.
These perceptual differences were consistent with differences in the types of environmental cues that people regularly experience in a given cultural context. For example, people in Western cultures have a perceptual context of straight-line buildings in what Segall's study called a carpenter's world (Segall et al., 1966). Conversely, people from certain non-Western cultures with a non-carpenter vision, such as the Zulus of South Africa, whose villages are made up of round huts arranged in a circle, are less susceptible to this illusion (Segall et al., 1999). It is not just vision that is influenced by cultural factors. In fact, research has shown that the ability to identify an odor and gauge its liking and intensity varies from culture to culture (Ayabe-Kanamura, Saito, Distel, Martínez-Gómez & Hudson, 1998). Regarding cross-cultural color vision, research has found that derived color terms for browns, oranges, and pinks appear to be influenced by cultural differences (Zollinger, 1988).
Children described as thrill-seekers are more likely to show preferences for strongly acidic tastes (Liem, Westerbeek, Wolterink, Kok, & de Graaf, 2004), suggesting that fundamental aspects of personality can influence cognition. In addition, people who are positive about low-fat foods are more likely to rate foods labeled as low-fat higher than people who are less positive about those products (Aaron, Mela, & Evans, 1994).
Sensations occur when sensory receptors perceive sensory stimuli. Perception involves the organization, interpretation, and conscious experience of these sensations. All sensory systems have absolute and difference thresholds, which relate to the minimum amount of stimulus energy and the minimum amount of difference in stimulus energy, respectively, required to be detected about 50% of the time. Sensory adaptation, selective attention, and cue recognition theory can help explain what is and is not perceived. In addition, our perception is influenced by a number of factors including beliefs, values, prejudices, culture and life experiences.
Text from Openstax Psychology by Kathryn Dumper, William Jenkins, Arlene Lacombe, Marilyn Lovett and Marion Perlmutter under license CC BY v4.0. https://openstax.org/details/books/psychology
1.________ refers to the minimum amount of stimulus energy required to be detected 50% of the time.
a. absolute threshold
b. difference threshold
C. only a noticeable difference
2.The decrease in sensitivity to a fixed stimulus is denoted as ________.
b. difference threshold
C. Sensory adaptation
i.e. blindness from inattention
3.________ involves the conversion of sensory stimulus energy into neural impulses.
a. sensory adaptation
b. blindness from inattention
C. Difference Threshold
4.________ occurs when sensory information is consciously organized, interpreted, and experienced.
i.e. sensory adaptation
Critical thinking question:
1.Not everything that is looked at is also perceived. Do you think there could be a case where something could be perceived without being felt?
2.Generate a novel example of how a perceivable difference can change based on stimulus intensity.
Personal application question:
1.Think of a time when you didn't notice something around you because your attention was elsewhere. If someone pointed this out, were you surprised you didn't notice it right away?
Processing from bottom to top
blindness from lack of attention
only a noticeable difference
signal detection theory
Processing from top to bottom
answers to exercises
Critical thinking question:
1. This would be a good time for students to start thinking about ESP claims. Another interesting topic would be the phenomenon of phantom limbs in amputees.
2. There are many possible examples. An example relates to the detection of weight differences. When two people hold standard envelopes and one contains a quarter while the other is empty, it's easy to see the difference in weight between the two. However, when these envelopes are placed in two textbooks of equal weight, it is much more difficult to distinguish which is heavier.
absolute threshold:Minimum amount of stimulus energy that must be present for the stimulus to be detected 50% of the time
Preprocessing:System in which perceptions are constructed from sensory information
Blindness from inattention:not noticing something that is fully visible due to inattention
only one noticeable difference:Difference in stimuli needed to detect a difference between stimuli
Perception:how sensory information is consciously interpreted and experienced
Sensation:What happens when sensory information is captured by a sensory receptor?
sensory adaptation:Not perceiving stimuli that remain relatively constant over long periods of time
Signal Detection Theory:Change in stimulus recognition as a function of current mental state
subliminal message:Message presented below the threshold of consciousness
Top-down processing:The interpretation of sensations is influenced by existing knowledge, experiences and thoughts.
Translation:Energy conversion from sensory stimuli into action potentials