4.1: We experience our world through sensations (2023)

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    learning goals

    1. Review and summarize the capabilities and limitations of human sensitivity.
    2. Explain the difference between sensation and perception and describe how psychologists measure sensory and difference thresholds.

    Sensory Thresholds: What Can We Experience?

    Humans possess powerful sensory abilities that allow us to perceive the kaleidoscope of images, sounds, smells, and tastes that surround us. Our eyes pick up light energy and our ears pick up sound waves. Our skin feels touch, pressure, heat and cold. Our tongues respond to molecules in the food we eat, and our noses pick up smells in the air. The human perceptual system is designed for accuracy, and humans are extremely good at using the wide variety of information available to them (Stoffregen & Bardy, 2001).

    Our senses are remarkable in many ways. The human eye can see the equivalent of a single candle flame burning 30 miles away and can distinguish between over 300,000 different colors. The human ear can perceive sounds from 20idiots(vibrations per second) and up to 20,000 Hertz, and you can hear a clock ticking from 20 feet away in a quiet room. We can taste a teaspoon of sugar dissolved in 2 liters of water and we can smell a drop of perfume diffused in a three-room apartment. We can feel a bee's wing hanging down on our cheek from 1 cm (Galanter, 1962).

    Figure \(\PageIndex{2}\)

    4.1: We experience our world through sensations (2)

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    The dog's highly sensitive sense of smell is useful in searching for missing persons, explosives, food and drugs.

    While we feel many things, there is more we don't feel. Dogs, bats, whales, and some rodents have much better hearing than we do, and many animals have a much richer sense of smell. Birds can see ultraviolet light that we cannot see (Figure \(\PageIndex{3}\)) and they can also feel the gravitational pull of the Earth's magnetic field. Cats have an extremely sensitive and sophisticated sense of touch and can use their whiskers to find their way around in complete darkness. That different organisms feel differently is part of their evolutionary adaptation. Each species is adapted to feeling the things that matter most to them while happily ignoring the things that don't.

    4.1: We experience our world through sensations (3)

    Since birds can see ultraviolet light but humans cannot, what looks to us like a simple black bird looks very different than a bird.

    Source: Adapted from Fatal Light Awareness Program. (2008).Retail investigation- public domain.

    sense of measurement

    psychophysics isthe branch of psychology that studies the effects of physical stimuli on sensory perceptions and mental states. The field of psychophysics was founded by the German psychologist Gustav Fechner (1801-1887), who was the first to study the relationship between the strength of a stimulus and a person's ability to perceive it.

    The measurement techniques developed by Fechner and his colleagues should help, among other things, to determine the limits of human sensitivity. An important criterion is the ability to recognize very weak stimuli. The absolute threshold of a sensation is defined asthe intensity of a stimulus that allows an organism to just recognize it.

    In a typical psychophysical experiment, a subject is presented with a series of trials where sometimes a signal is presented and sometimes not, or where two identical or different stimuli are presented. For example, imagine you are asked to take a hearing test. In each experiment, your task is to say "yes" if you heard a sound, or "no" if you didn't hear it. Signals are intentionally made very weak, making accurate assessment difficult.

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    The problem for you is that very weak signals create uncertainty. Because our ears are constantly sending background information to the brain, sometimes you will think you heard a sound when there wasn't one, and sometimes you won't be able to recognize a sound that is there. Your job is to determine whether the neural activity you are experiencing is due solely to background noise or is the result of a signal within the noise.

    The answers you give in the listening test can be analyzed withsignal detection analysis. The signal detection analysis isa technique used to determine the observer's ability to separate real signals from background noise(Macmillan and Creelman, 2005; Wickens, 2002). As you can see in figure \(\PageIndex{4}\), each judgment leads to four possible outcomes: Abeatarises when you, the listener, correctly say “yes” to a noise. FORfalse alarmOccurs when you don't respond with "Yes" to any signal. In the other two cases, answer "no" or alose(Say “no” when there is a signal) or acorrect rejection(Saying no when in fact there was no signal).

    4.1: We experience our world through sensations (4)

    Our ability to accurately recognize stimuli is measured through signal recognition analysis. Two of the possible choices (correct hits and rejects) are correct; the other two (errors and false alarms) are errors.

    Analysis of data from a psychophysical experiment produces two measures. A measure known assensitivity, refers to the true ability of the individual to recognize the presence or absence of signs. People with better hearing have a higher sensitivity than people with poor hearing. The other measureresponse bias, refers to a behavioral tendency to answer "yes" to attempts that is independent of sensitivity.

    For example, imagine that instead of taking a hearing test, you are a soldier on duty and your job is to detect the very faint sound of a branch snapping, indicating the presence of an enemy nearby. You can see that in this case, raising a false alarm alerting other soldiers to the noise might not be as costly as failing to report the noise, which can be deadly. So you can assume a very mild answer bias where you send a red flag every time you are unsure. In this case, your responses may not be very accurate (your sensitivity may be low because you generate a lot of false positives), and yet extreme response bias can save lives.

    Another application of signal detection is when medical technicians examine body images to detect the presence of cancerous tumors. Again, an error (where the technician incorrectly determines that no tumor is present) can be very costly, but false positives (where patients without tumors are referred for further testing) also have costs. The final decisions technicians make are based on signal quality (image clarity), their experience and training (ability to identify specific tumor shapes and textures), and their best estimates of the relative cost of errors compared to false positives.

    Although we have so far focused on the absolute threshold, a second important criterion concerns the ability to assess differences between stimuli. The difference threshold (or simply perceivable difference [JND]) refers tothe change in a stimulus that is hardly perceptible to the organism.The German physiologist Ernst Weber (1795-1878) made an important discovery about the JND, namely that the ability to recognize difference depends not so much on the size of the difference, but on the size of the difference relative to the absolute size of the stimulus .Weber claims that theThe only perceptible difference in a stimulus is a constant proportion of the original stimulus intensity.. For example, if you want to have a cup of coffee with very little sugar (e.g. 1 colher de chá), adding another colher de chá de açúcar makes a big difference in taste. But if you were to add that same teaspoon to a cup of coffee that already has 5 teaspoons of sugar, then you probably wouldn't notice that much of a difference (according to Weber's law, you would even have to add 5 more teaspoons to see the same difference in sugar or to make taste).

    An interesting application of Weber's law is our daily purchasing behavior. Our tendency to perceive cost differences between products depends not only on the amount of money we spend or save, but also on the amount of money saved relative to the purchase price. I dare say that if you were to buy a soda pop or candy bar at a supermarket and the items range in price from $1 to $1, you would think that the $3 item costs "a lot more" than the $1 item $3 would lie that you are comparing two music systems, one that costs $397 and one that costs $399. You would probably think that the cost of the two systems was "more or less the same" even though buying the cheapest system saved $2.

    Research focus: influence without conscience

    If you study the figure \(\PageIndex{5}\) you will see that the absolute threshold is the point at which we become aware of a weak stimulus. From this point we say that the stimulus isconsciouslybecause we can accurately report its existence (or non-existence) more than 50% of the time. But can subliminal stimuli (Events occurring below the absolute threshold that we are not aware of) influence our behavior?

    4.1: We experience our world through sensations (5)

    When the intensity of a stimulus increases, we are more likely to perceive it. Stimuli below the absolute threshold can at least still influence us, even if we cannot consciously perceive them.

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    A variety of research programs have found that subliminal cues can affect our judgment and behavior, at least in the short term (Dijksterhuis, 2010). But whether presenting subliminal stimuli can affect the products we buy is a more controversial topic in psychology. In a relevant experiment, Karremans, Stroebe, and Claus (2006) had Dutch university students observe a series of computer tests in which a series of letters likeBBBBBBBBBÖBBBbBBBBBBThey appeared on the screen. To ensure they were paying attention to the screen, students were asked to see if the strings contained a smallB. However, immediately before each of the letter sequences, the researchers presented the name of a drink popular in the Netherlands (Lipton Ice) or a control sequence containing the same letters as Lipton Ice (NpeicTol). These words were presented so quickly (just a fiftieth of a second) that the participants could not see them.

    Students were then asked to indicate their intention to drink Lipton Ice by answering questions such as "If you were sitting on a patio right now, how likely are you to order Lipton Ice?" and also how thirsty they were were passage of time. The researchers found that students who were exposed to the words "Lipton Ice" (and particularly those who reported being already thirsty) were significantly more likely to say they would drink Lipton Ice than those who were exposed to the words were. control words.

    If effective, techniques like this (we could call the technique "subliminal advertising" because it advertises a product outside of the conscious mind) would have some important benefits for advertisers, as they would allow them to promote their products without the consumers to interrupt directly. activity and without the consumer noticing that he is being persuaded. Humans cannot disagree or try to avoid being influenced by messages received outside of consciousness. Fearing that people might be influenced without their knowledge, subliminal advertising has been banned by law in many countries, including Australia, the United Kingdom and the United States.

    Although some research has shown it to work, the effectiveness of subliminal advertising is still uncertain. Charles Trappey (1996) conducted a meta-analysis combining 23 large research studies examining the impact of subliminal advertising on consumer choices. The results of their meta-analysis showed that subliminal advertising had a negligible impact on consumer choices. And Saegert (1987, p. 107) concluded that "marketing should stop deciding subliminal advertising when in doubt", arguing that the influences of subliminal stimuli are often so weak that they are often overshadowed by actual uptake become. . .

    Overall, the evidence for the effectiveness of subliminal advertising is weak, and its impact may be limited to just a few people and under just a few conditions. You probably don't have to worry too much about being subliminal persuaded in your everyday life, even if subliminal advertising is allowed in your country. But while subliminal advertising alone is not as effective, there are many other indirect advertising techniques that are used and work. For example, many ads for cars and alcoholic beverages are subtly sexualized and encourage the consumer to indirectly (though not subliminally) associate these products with sexuality. And then there are the increasingly common techniques of "product placement," where images of brands (cars, soft drinks, electronics, etc.) are placed on websites and in popular TV shows and movies. Harris, Bargh, and Brownell (2009) found that exposure to television food advertisements significantly increased snacking behavior in both children and adults, again suggesting that the effects of perceived imagery, even when above the absolute threshold, can be very subtle.

    Another example of processing occurring outside of our consciousness is seen when certain areas of the visual cortex become damaged, leading to blindness.a state in which people are unable to consciously report visual stimuli, but are still able to accurately respond to questions about what they see.When blindsighted individuals are asked directly about the occurrence of stimuli, or to determine whether those stimuli are present, they can do no better than probability levels. They report that they cannot see anything. For more indirect questions, however, they are able to give correct answers. For example, blind people can correctly determine the location and direction of movement of an object, as well as recognize simple geometric shapes and patterns (Weiskrantz, 1997). It appears that although conscious reporting of visual experiences is not possible, there is still an underlying, parallel process at work that enables humans to perceive certain aspects of stimuli.

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    main topics

    • Sensation is the process of taking in information from the environment through our sense organs. Perception is the process of interpreting and organizing incoming information so that we can understand it and respond accordingly.
    • Transduction is the conversion of stimuli sensed by receptor cells into electrical impulses that are sent to the brain.
    • Although our experiences of the world are rich and complex, humans, like all species, have their own customized sensory strengths and limitations.
    • Sensation and perception work together in a flowing and continuous process.
    • Our judgments in detection tasks are influenced just as much by the absolute threshold of the signal as by our current motivations and experiences. Signal detection analysis is used to distinguish sensitivity from response trends.
    • The difference threshold, or simply perceptible difference, is the ability to detect the slightest change in a stimulus about 50% of the time. According to Weber's law, the barely perceptible difference increases in proportion to the overall intensity of the stimulus.
    • Research has found that stimuli can affect behavior even when presented below the absolute threshold (i.e., subliminal). However, the effectiveness of subliminal advertising has not been shown to be of any great magnitude.

    exercises and critical thinking

    1. In wars, unintentional shots are often fired by soldiers themselves (friendly fire). Based on what you've learned about sensation, perception, and psychophysics, why do you think soldiers could mistakenly shoot their own soldiers?
    2. If we take two letters, one that weighs 1 ounce and one that weighs 2 ounces, we can see the difference. But if we take two packages, one that weighs 3 pounds and 1 ounce and the other that weighs 3 pounds and 2 ounces, we cannot tell the difference. Why?
    3. Take a moment and lie down quietly in your room. Note the variety and levels of what you can see, hear and feel. Does this experience help you understand the idea of ​​the absolute threshold?


    Dijksterhuis, A. (2010). Automatically and inconsciente. E.T. Fiske, D.T. Gilbert and G. Lindzey (Eds.),Textbook of Social Psychology(5th ed., vol. 1, pp. 228-267). Hoboken, NJ: John Wiley & Sons.

    Galanter, E. (1962).Contemporary Psychophysics. To R Brown, E Galanter, E H Hess and G Mandler (Eds.),New directions in psychology.. . . . New York, NY: Holt, Rinehart, and Winston.

    Harris, J.L., Bargh, JA, & Brownell, K.D. (2009). Priming effects of food advertising on television on eating behavior.Health Psychology, 28(4), 404–413.

    Karremans, J.C., Stroebe, W. & Claus, J. (2006). Beyond Vicary's Fantasies: The Impact of Subliminal Reproduction and Brand Choice.Journal of Experimental Social Psychology, 42(6), 792–798.

    Macmillan, N.A. and Creelman, C.D. (2005).Theory of Recognition: A User's Guide(2ª Aufl.). Mahwah, Nova Jersey: Lawrence Erlbaum Associates; Wickens, TD (2002).Elementary theory of signal detection.. . . . Nova York, NY: Oxford University Press.

    Saegert, J. (1987). Why marketing should stop giving subliminal advertising the benefit of the doubt.Psychology and Marketing, 4(2), 107–120.

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    Cloth Rain, T.A. & Bardy, B.G. (2001). About specification and directions.Behavioral and Brain Sciences, 24th(2), 195–261.

    Trappey, C. (1996). A meta-analysis of consumer choices and subliminal advertising.Psychology and Marketing, 13, 517–530.

    Weiskrantz, L. (1997).Lost and found consciousness: a neuropsychological investigation.Nova York, NY: Oxford University Press.


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