8.1: Sensation and Perception (2023)

learning goals

• Distinguish the processes of sensation and perception.
• Explain the basic principles of sensation and perception.
• Describe the function of each of our senses.
• Describe the anatomy of the sense organs and their projections into the nervous system.
• Apply knowledge of sensation and perception to real-world examples.
• Explain the consequences of multimodal perception.

Introduction

“I was once hiking in Cape Lookout State Park in Tillamook, Oregon. After walking through a colorful and pleasantly scented temperate forest, I arrived at a cliff overlooking the Pacific Ocean. I gripped the edge of the cold metal railing and looked out to sea. Below me, I could see a pack of sea lions swimming in the dark blue water. All around me I smelled the salt of the sea and the smell of wet fallen leaves”.

This description of a single memory underscores the importance of a person's senses in our experience of the world around us.

Before discussing each of our extraordinary senses individually, it is necessary to cover some basic concepts that apply to all of them. It's probably best to start with a very important distinction that can often be confusing: the difference between sensation and perception. Thisphysicallydescribes a process in which our sense organs, for example hearing and taste, react to external stimuliSensation🇧🇷 The sensations appear when you eat pasta, feel the wind on your face or hear a car horn in the distance. Our sense organs are active during perception.streaming, the conversion of one form of energy into another. Physical energy, such as light or a sound wave, is converted into a form of energy that the brain can understand: electrical stimulation. Once our brain receives the electrical signals, we make sense of all these stimuli and begin to appreciate the complex world around us. ThispsychologicalProcess - comprehension of stimuli - is invokedperception🇧🇷 It is during this process that you can do it.identifya gas leak in your house or a song that reminds you of a special night out with friends.

Be it sight, taste or individual senses, there are a number of basic principles that influence the functioning of our sensory organs. The first of these influences is our ability to perceive an external stimulus. Every sense organ, for example our eyes or our tongue, needs minimal stimulation to recognize a stimulus. Thisabsolute thresholdexplains why you can only smell the perfume someone is wearing in a classroom when they are a little closer to you.

We measure absolute limits using a method calledsignal detection🇧🇷 In this technique, a research participant is presented with stimuli of different intensities to determine at what level they can reliably recognize stimuli in a particular sense. For example, during one type of hearing test, a person listens to increasingly loud sounds (starting with silence) to determine the threshold at which he begins to hear (see Additional Resources for a video demonstration of one tap). high frequency sound that can only be heard by teenagers). The correct indication that a sound has been heard is called a hit; failure to do so is called a failure. Also, indicating that a tone was heard when no tone was played is called a false alarm, and correct identification when no tone was played is a correct rejection.

Through these and other studies, we were able to understand how remarkable our senses are. For example, the human eye can see candlelight 30 miles away in the dark. We can also hear the ticking of a clock in a silent environment 6 meters away. If you find this surprising, I encourage you to read more about the extreme sensory abilities of non-human animals; Many animals possess abilities that we would consider superhuman.

A principle similar to the absolute threshold discussed above underlies our ability to distinguish the difference between two stimuli of different intensities. Thisdifferential threshold, oJust Noticeable Difference (JND), for each direction was studied using similar signal detection methods. To illustrate, find a friend and some items of known weight (you'll need items that weigh 1, 2, 10, and 11 pounds, or 1, 2, 5, and 5.5 kg in metric terms). Ask your friend to hold the lightest object (1 pound or 1 kg). Then replace that item with the next heaviest item and ask him to say which one weighs the most. Your friend reliably says the second object at a time. It's very easy to tell the difference when something weighs twice as much as another! However, it is not so simple when the difference is a smaller percentage of the total weight. It will be much more difficult for your friend to confidently tell the difference between 10 and 11 pounds. (or 5 against 5.5 kg) than in 1 and 2 pounds. This phenomenon is calledweber lei, and is the idea that larger stimuli require larger differences to be perceived.

As we enter the world of perception, it becomes clear that our experience affects the way our brain processes things. You've tried foods you like and foods you don't like. There are some bands you like and some you don't. However, when you eat something or listen to a band for the first time, you process these stimuli.Bottom-up processing🇧🇷 Here we build the perception of the individual pieces. Sometimes, however, stimuli we've experienced in the past affect how we process new ones. CalledTop-down processing🇧🇷 The best way to illustrate these two concepts is through our ability to read. Read the following quote aloud:

As you read the triangle text, did you notice anything strange? Did you notice the second "o"? If not, it's probably because you're reading this from a top-down approach. Having a second "he" makes no sense. We know this, our brain knows and doesn't know.supposethere should be a second one, so we tend to ignore it. In other words, your past experiences have changed the way you perceive triangle writing! A beginning reader, someone who uses a bottom-up approach paying attention to each piece, is less likely to make this mistake.

Finally, it should be noted that when we experience a sensory stimulus that does not change, we stop paying attention to it. It's why we don't feel the weight of our clothes, hear the hum of a projector in a conference room, or see every little scratch on our eyeglasses. When a stimulus is constant and unchanging, we experiencesensory adaptation🇧🇷 During this process, we become less sensitive to that stimulus. A good example of this is when we leave the radio on in the car after parking it overnight at home. Listening to the radio on the way home from work, the volume seems reasonable. However, the next morning, when we start the car, we may be surprised by the volume of the radio. We don't remember making so much noise last night. What happened? What happened is that over the course of the previous day we got used to the constant stimulation of the radio volume. This required us to keep increasing the radio volume to counteract the decrease in sensitivity. However, after a few hours without this constant stimulation, the once-reasonable volume levels are too high. We are no longer adapted to this stimulus!

Now that we've introduced some sense basics, let's take a look at each of our fascinating senses, one at a time.

To view

how it works see

Seeing is a delicate matter. When we see a pizza, a feather or a hammer, we actually see light reflected from that object towards our eyes. Light enters the eye through the pupil, a small opening behind the cornea. The pupil regulates the amount of light entering the eye by constricting (shrinking) in bright light and dilating (enlarging) in dim light. After light passes through the pupil, it passes through the lens, which focuses an image onto a thin layer of cells at the back of the eye called the eye.Retina.

Since we have two eyes in different places, the image focused on each retina is from a slightly different angle (binocular disparity), which gives us our perception of 3D space (binocular vision🇧🇷 You might recognize this by holding a pen, stretching your arm in front of your face, and looking at the pen while closing one eye at a time. Note the pen's apparent position in relation to background objects. Depending on which eye is open, the pen appears to jump back and forth! This is how video game makers create 3D perception without special glasses; two slightly different images are displayed one above the other.

In the retina, light is converted, or transformed into electrical signals, by specialized cells called photoreceptors. The retina contains two main types of photoreceptors:At barycones🇧🇷 Rods are primarily responsible for our ability to see in low light, such as at night. Cones, on the other hand, give us the ability to see colors and fine details when the light is strongest. Rods and cones differ in their distribution along the retina; the greatest concentration of cones is in the fovea (the central focal area) and the rods dominate the periphery (see Figure 8.1.2). The difference in distribution may explain why the direct view of a faint star in the sky seems to disappear; Not enough wands to handle the dim light!

The electrical signal is then sent through a layer of cells in the retina and eventually travels down the optic nerve. Once this signal has passed through the thalamus, it goes to theprimary visual cortex, where information about the orientation of light and movement come together (Hubel & Wiesel, 1962). The information is then sent to a variety of different areas of the cortex for more complex processing. Some of these cortical regions are quite specialized, for example, for processing faces (fusiform area of ​​the face) and body parts (extrastriate area of ​​the body). Damage to these areas of cortex can potentially lead to a certain type ofagnosia, causing a person to lose the ability to perceive visual stimuli. A great example of this is found in the writings of the famous neurologist Dr. Played by Oliver Sacks; he triedprosopagnosia, the inability to recognize faces. These specialized regions for visual recognition include theventrally(also called the "what" form). Other areas involved in location and motion processing make up thered back(also called the "Where" path). Together, these pathways process a large amount of information about visual stimuli (Goodale & Milner, 1992). Phenomena often referred to as optical illusions provide misleading information about these "higher" areas of visual processing (see Additional Resources for Amazing Optical Illusions Websites).

color vision

Our cones allow us to see details in normal lighting conditions, as well as colors. We have cones that respondto prefer,not exclusively for red, green and blue (Svaetichin, 1955). Thistrichromatic theoryIt's not new; dates from the beginning of the 19th century (Young, 1802; Von Helmholtz, 1867). However, this theory does not explain the strange effect that occurs when we look at a white wall after looking at an image for about 30 seconds. Try this: stare at the flag image in Figure 8.1.3 for 30 seconds and immediately look at a white piece of paper or a wall. According to the trichromatic theory of color vision, you should see white. Have you experienced this? As you can see, the trichromatic theory does not explain thatafterimageyou just witnessed. Here he isadversary process theoryenter (Hering, 1920). This theory states that our cones send information toretinal ganglion cellswho reactscouplescolors (red-green, blue-yellow, black-white). These specialized cells take information from the cones and calculate the difference between the two colors, a process that explains why we can't see red-green or blue-yellow and why we see afterimages. Color blindness can be due to problems with the cones, or ganglion cells, in the retina that are involved in color vision.

listen (listen)

Some of the world's most famous celebrities and top earners are musicians. Our adoration of musicians may seem silly, considering all they do is vibrate the air a certain way to create something.sound waves, the physical stimulus foraudition.

Human beings can derive a great deal of information from the basic properties of sound waves. ThisAmplitude(or intensity) of a sound wave encodes the volume of a stimulus; Higher amplitude sound waves produce louder noises. Thissubscriptionof a stimulus is encoded in thefrequencya sound wave; higher frequency tones have a higher pitch. We can also assess the qualityTimbre, of a tone due to the complexity of the sound wave. This allows us to differentiate between bright and dull sounds, and between natural and synthetic instruments (Välimäki & Takala, 1996).

In order for us to perceive sound waves from our environment, they must reach our inner ear. Fortunately, we've developed tools that allow you to channel and amplify those waves during that journey. First, the sound waves are directed by you.Ohrmuschel(the outer part of your ear that you can actually see) in your earear canal(the hole you put Q-tips in, although the box advises against it). During their journey, the sound waves finally hit a thin, stretched membrane known as theeardrum(eardrum), which vibrates against the three smallest bones in the body: the malleus (hammer), the incus (anvil), and the stirrup (stirrups), collectively called theear ossicles🇧🇷 Both the eardrum and ossicles amplify sound waves before they enter the fluid.Snail, containing a bony structure similar to a snail shellauditory hairzelsarranged on the basilar membrane (see Figure 8.1.4) according to the frequency to which they respond (referred to as tonotopic organization). Depending on age, humans can normally perceive sounds between 20 Hz and 20 kHz. Inside the cochlea, sound waves are converted into an electrical message.

Since we have an ear on each side of our head, we can localize sounds in 3D space very well (just like having two eyes creates 3D vision). Have you ever dropped something on the floor without seeing where it went? Did you notice that you were able to reasonably locate this object based on the sound it made when it hit the ground? We can reliably localize something depending on which ear receives the sound first. What about the pitch of a note? If both ears receive sound at the same time, how can we localize the sound vertically? Studies in cats (Populin & Yin, 1998) and humans (Middlebrooks & Green, 1991) have indicated differences in sound wave quality depending on vertical position.

After processing by the auditory hair cells, electrical signals are sent through them.Cochlea-Nerv(a division of the vestibulocochlear nerve) to the thalamus and then to theprimary auditory cortexof the temporal lobe. Interestingly, the tonotopic organization of the cochlea is preserved in this area of ​​the cortex (Merzenich, Knight, & Roth, 1975; Romani, Williamson, & Kaufman, 1982). However, the role of the primary auditory cortex in processing the wide range of sound resources is still being explored (Walker, Bizley & Schnupp, 2011).

Toque

Who doesn't love the softness of an old T-shirt or the smoothness of a clean shave? Who likes sand in a swimsuit? Our skin, the largest organ in the body, provides us with all sorts of information, such as whether something is smooth or bumpy, hot or cold, or even painful.somatosensory sin– which includes our ability to sense touch, temperature and pain – converts physical stimuli like soft velvet or boiling water into electrical potentials that the brain can process.

tactile sensation

tactile stimuli– those associated with texture – are transduced by special receptors in the skin calledmechanoreceptors🇧🇷 Like the photoreceptors in the eye and the auditory hair cells in the ear, they allow a type of energy to be converted into a form that the brain can understand.

After the mechanoreceptors convert the tactile stimuli, the information is sent through the thalamus to the thalamus.primary somatosensory cortexfor further processing. This region of cortex is organized into asomatotopic mapwhere the size of the different regions is based on the sensitivity of certain parts of the opposite side of the body (Penfield & Rasmussen, 1950). Simply put, different parts of the skin, such as the lips and fingertips, are more sensitive than others, such as the shoulders or knuckles. This sensitivity can be illustrated with the distorted proportions of the human body in Figure 8.1.5.

Smell and taste: the chemical senses

The two most underrated senses can be grouped into the broad category of senses.chemical senses. Both of themsense of smell(smell) andflavor(taste) require the conversion of chemical stimuli into electrical potentials. I say these senses are underrated because most people would give up any one of them if they were forced to give up a sense. While this may not surprise many readers, consider how much money people spend annually in the perfume industry ($29 billion). Many of us pay a lot more for a favorite food brand because we prefer the taste. Obviously, we humans care about our chemical senses.

want want)

Taste works similarly to smell, only with receptors called taste buds located on the tongue.taste receptor cells🇧🇷 To clear up a common misconception, taste buds are not the bumps on your tongue (papillae) but rather small indentations around these bumps. These receptors also respond to chemicals in the external environment by excluding these chemicals, calledscavengerThey are found in the foods we eat. Binding of these chemicals to taste receptor cells leads to our perception of the five basic tastes: sweet, sour, bitter, salty, and umami (tasty), although some scientists argue that there are more (Stewart et al., 2010). 🇧🇷 Previous researchers thought that these tastes provided the basis for a map-like organization of language; There was even clever logic to the concept that the back of the tongue was bitter so we knew how to spit out poisons and the front of the tongue was sweet so we could identify energy-dense foods. However, we now know that all areas of the tongue with taste receptor cells are capable of responding to any taste (Chandrashekar, Hoon, Ryba, & Zuker, 2006).

When it comes to food, we are not just limited to our taste buds. As we chew, food odors bounce back to areas that contain olfactory receptors. This combination of taste and smell gives us the perception offlavor🇧🇷 If you are in doubt about the interaction between these two senses, I encourage you to think again and consider how the taste of your favorite foods affects you when you have a cold. It's all pretty bland and boring, isn't it?

All together: multimodal perception

Although we've spent most of this module dealing with the senses individually, most of our real-world experience is multimodal, involving combinations of our senses in one perceptual experience. This should be clear after reading the description of the forest walk at the beginning of the module; it was the combination of the senses that made this experience possible. You shouldn't be surprised to learn that, at some point, information from each of our senses will be integrated. Information from one sense has the potential to affect how we perceive information from another, a process believed to beMultimodal Perception.

Interestingly, we actually respond more strongly to multimodal stimuli than to the sum of all individual modalities combined, an effect calledsuperadditive effect of multisensory integration🇧🇷 This might explain why, at a noisy concert, you can still understand what your friends are saying, as long as you get visual cues from watching them speak. If you were having a quiet conversation in a coffee shop, you probably wouldn't need these extra cues. actually thereverse efficiency principlesays you areany lessthey are likely to benefit from additional cues from other modalities if the initial unimodal stimulus is strong enough (Stein & Meredith, 1993).

Since we are capable of processing multimodal sensory stimuli, and the results of these processes are qualitatively different from unimodal stimuli, it is reasonable to assume that the brain is doing something qualitatively different when processing them. Since the mid-1990s, evidence has been accumulating for the neural correlates of multimodal perception. For example, neurons that respond to visual and auditory stimuli have been identified.superior temporal sulcus(Calvert, Hansen, Iversen and Brammer, 2001). In addition, multimodal “what” and “where” pathways have been proposed for auditory and tactile stimuli (Renier et al., 2009). We're not limited to reading about these brain regions and what they do; we can try them out through some interesting examples (see Additional Resources for the McGurk Effect, Double Flash Illusion, and Rubber Hand Illusion).

Conclusion

Our impressive sensory abilities allow us to experience the most pleasurable, the most miserable, and everything in between. Our eyes, ears, nose, tongue and skin provide an interface for the brain to interact with the world around us. While it's easy to cover each sensory modality independently, we are organisms that have evolved the ability to process multiple modalities as a unified experience.

external sources

Audio: Auditory demonstrations from Richard Warren's laboratory at the University of Wisconsin, Milwaukee

www4.uwm.edu/APL/demostraciones.html

Audio: listening to demos. CD published by the Acoustical Society of America (ASA). You can listen to the demos here.

www.feilding.net/sfuad/musi30...1/demos/audio/

Book: Ackermann, D. (1990).A natural history of the senses.🇧🇷 Classic.

http://www.dianeackerman.com/a-natur...diane-ackerman

Book: Sacks, O. (1998). The man who mistook his wife for a hat: and other cases. Simon and Schuster.

http://www.oliversacks.com/books-by-...tomó-esposa-sombrero/

Video: The acquired knowledge and its impact on our three-dimensional interpretation of the world - 3D Street Art

Video: Acquired knowledge and its impact on our three-dimensional interpretation of the world - Anamorphic Illusions

Video: Cybersenses

Video: see the sound, test the color

Video: The Phantom Limb Phenomenon

Web: A regularly updated website covering some of the amazing sensory abilities of non-human animals.

phenomena.nationalgeographic....animal senses/

Web: A special ring audible only to the youngest.

Web: The Incredible Library of Visual Phenomena and Optical Illusions Explained

http://michaelbach.de/ot/index.html

Web: An article on the discoveries of echolocation: the use of sound to locate people and things

http://www.psychologicalscience.org/...et-around.html

Web: An optical illusion demonstrating the counterprocess theory of color vision.

Web: Auges Anatomy

http://www.eyecareamerica.org/eyecare/anatomy/

Web: Animation showing the tonotopic organization of the basilar membrane.

Web: Web of the contest Best Illusion of the Year.

http://ilusionoftheyear.com/

Web: Contrast gain adjustment demo

http://www.michaelbach.de/ot/lum_contrast-adapt/

Web: Demonstration of illusory contours and lateral inhibition. mach tapes

http://michaelbach.de/ot/lum-MachBands/index.html

Web: Demonstration of Illusory Contrast and Lateral Inhibition. Hermann grid

http://michaelbach.de/ot/lum_herGrid/

Web: Demonstrations and illustrations of cochlear mechanics can be found here

http://lab.rockefeller.edu/hudspeth/...calSimulaciones

Web: Double-Flash-Illusion

Web: More information on what and where/how you form

http://www.scholarpedia.org/article/...where_pathways

Web: Great site with a huge collection of optical illusions.

http://www.michaelbach.de/ot/

Web: Video of the McGurk effect

Web: More demonstrations and illustrations of cochlear mechanics

www.neurophys.wisc.edu/animations/

Web: Scientific American Frontiers: Cybersenses

www.pbs.org/saf/1509/

Web: The genetics of taste

http://www.smithsonianmag.com/arts-c...797110/?no-ist

Web: Die Website des Monell Chemical Sense Center

http://www.monell.org/

Web: The Illusion of the Rubber Hand

Web: The Tongue Map: Tasteless Myth Debunked

http://www.livescience.com/7113-tong...-desacreditado.html

discussion questions

1. What physical properties would an organism have to have to be able to localize sound very well in 3D space? Are there organisms currently excellent at sound localization? What features allow you to do this?
2. What problems would there be in visually recognizing an object if a research participant had the corpus callosum cut? What would you have to do to notice these deficits?
3. There are several myths about babies' sensory abilities. How would you design a study to determine what babies' true sensory abilities are?
4. A well-documented phenomenon experienced by millennials is the phantom vibration of a cell phone when no actual text message has been received. How can we use signal detection theory to explain this?

vocabulary

absolute threshold

The smallest amount of stimulation needed for perception by one sense.

agnosia

Loss of ability to perceive stimuli.

anosmia

loss of the ability to smell.

audition

Ability to process auditory stimuli. Also called hearing.

ear canal

Tube that runs from the auricle to the middle ear.

auditory hair cells

Receptors in the cochlea that convert sound into electrical potentials.

binocular disparity

The difference is the images processed by the left and right eye.

binocular vision

Our ability to perceive 3D and depth is due to the difference between the images on each of our retinas.

upstream processing

Based on perceptual experience of individual parts.

chemical senses

Our ability to process smell and taste environmental stimuli.

Snail

Coiled bony structure in the inner ear that contains auditory hair cells.

cones

Color sensitive photoreceptors in the retina. Mainly located in the fovea.

dark adaptation

Adaptation of the eye to low light conditions.

differential threshold

The smallest difference needed to distinguish two stimuli. (See Perceptual Difference Only (JND))

dorsal path

form of visual processing. The "where" path.

flavor

The combination of smell and taste.

flavor

Ability to process taste stimuli. Also called flavor.

Just Noticeable Difference (JND)

The smallest difference needed to distinguish two stimuli. (see differential threshold)

light adjustment

Adaptation of the eye to high light conditions.

mechanoreceptors

Mechanical sensory receptors in the skin that respond to tactile stimulation.

Multimodal Perception

The effects that simultaneous stimulation in more than one sensory modality has on the perception of events and objects in the world.

Nozizeption

Our ability to feel pain.

fragrances

Chemical substances transduced by olfactory receptors.

sense of smell

Ability to process olfactory stimuli. Also called smell.

Riechepithel

Organ that contains olfactory receptors.

opponent process theory

Theory proposing that color vision is affected by cells that respond to color pairs.

ear ossicles

A collection of three small bones in the middle ear that vibrate against the eardrum.

perception

The psychological process of interpreting sensory information.

ghostly

The realization that a link is still missing.

phantom pain in extremities

Pain in a limb that no longer exists.

Ohrmuschel

outermost part of the ear.

primary auditory cortex

Area of ​​the cerebral cortex involved in processing auditory stimuli.

primary somatosensory cortex

Region of the cerebral cortex involved in the processing of somatosensory stimuli.

primary visual cortex

Area of ​​the cerebral cortex involved in processing visual stimuli.

reverse efficiency principle

Recognizing that, in general, for a multimodal stimulus, when the response to each unimodal component (by itself) is weak, the opportunity for multisensory enhancement is great. However, if a single component is sufficient to elicit a strong response, then the effect on the response produced by simultaneous processing of the other components of the stimulus will be relatively small.

Retina

Cellular layer at the back of the eye that contains photoreceptors.

At bar

Retinal photoreceptors sensitive to low light. Located around the fovea.

Sensation

The physical processing of environmental stimuli through the sense organs.

sensory adaptation

Decreased sensitivity of a receptor to a stimulus after constant stimulation.

Shape theory of the sense of smell

Theory that states that different sizes and shapes of fragrance correspond to different odors.

signal detection

Method for examining the ability to correctly recognize sensory stimuli.

somatosensory sin

Ability to sense touch, pain, and temperature.

somatotopic map

Organization of the primary somatosensory cortex, which maintains a representation of the layout of the body.

sound waves

changes in air pressure. The physical stimulus for hearing.

Super additive effect of multi-sensory integration

The discovery that responses to multimodal stimuli are many times greater than the sum of independent responses to each unimodal component when presented separately.

scavenger

Chemical substances transduced by taste receptor cells.

taste receptor cells

Receptors that transmit taste information.

Top-down processing

Experience that affects the perception of stimuli.

transduction

The conversion of one form of energy to another.

trichromatic theory

Theory that proposes color vision affected by three different cones that respond preferentially to red, green, and blue.

eardrum

A thin, taut membrane in the middle ear that vibrates in response to sound. Also called eardrum.

ventrally

form of visual processing. The "what" way.

vestibular system

Parts of the inner ear involved in balance.

weber lei

Indicates that the almost imperceptible difference is proportional to the magnitude of the initial stimulus.

references

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