Getting Sensitive - Picking Your Brain (And Body)

Psychology For Dummies - Adam Cash 2013

Getting Sensitive
Picking Your Brain (And Body)

In This Chapter

Image Sensing the world

Image Seeing things a bit more clearly

Image Feeling the heat

Image Constructing your perceptions

Seeing is believing! I have no idea where that phrase came from, but it says something important about people. That is, people have an easier time understanding or comprehending things if they can see them, touch them, hear them, and so on. Why doesn’t everyone believe in ghosts, UFOs, or any number of things that most people have not experienced firsthand? Precisely the point. Most people haven’t experienced these phenomena with their own senses, so they don’t believe in them. How do you know if something is part of the world you live in or not — and whether it’s real?

The subject of psychology is made up of a bunch of different areas of study that all point to the ultimate questions of why and how humans do what they do. This chapter focuses on the why and how of sensing and perceiving the world. They’re as obvious as the nose on your face, but it’s easy to overlook the impact of senses to everyday thoughts, moods, and actions. Psychology as the study of behavior and mental processes includes taking a look at how our senses — the ability to see, hear, taste, touch, feel, and so on — actually work.

Humans aren’t just little brains floating around inside a body with no contact with the outside world. Quite the contrary; most people are typically in full contact with the world around them, taking in information, processing it, and using what they perceive to navigate a wide range of possibilities. So why is understanding materialism important? Because the way people actually maintain contact with the information that’s processed is through the physical materials that create it.

In this chapter, I take a closer look at the ways people sense and perceive the world.

Building Blocks: Our Senses

Physicists and chemists have, for a long time, been pointing out that the world is made up of material stuff: particles, atoms, molecules, and various forms of energy. Basically, the universe is one big ball of energy. Everything consists of a particular configuration of energy. A working definition of sensation is the process by which we receive raw energy/information from the environment. If you want a definition in a suit and tie, then sensation is the process of mentally acquiring information about the world through the reception of its various forms of energy.

Here are the forms of energy that humans most commonly experience:

Image Light (electromagnetic energy)

Image Sound (acoustic energy, or sound waves)

Image Heat (thermal energy)

Image Pressure (mechanical or physical energy)

Image Chemical energy

Some organisms experience the same kinds of energy as humans do, but other forms of life are sensitive to different ranges of the energy forms. Sharks can smell chemical particles (of blood, for example) in far smaller quantities than people can, and dogs can hear much higher frequencies of sounds.

Image For each form of energy that humans sense, a specific organ system or “device” is used to receive it. Aristotle, an ancient Greek philosopher (around 350 BCE, who some say was the last man to know everything there was to know) claimed that humans have five basic senses. Each of the five basic human senses are receptive to a specific form of energy. Psychologists now know that humans have at least 10 different senses, but Aristotle recognized the major ones:

Image Sight receives light energy.

Image Hearing receives sound energy or sound waves.

Image Touch receives mechanical energy.

Image Smell receives airborne chemical energy.

Image Taste receives chemical energy.

The sensing process

When light travels from a light bulb or sound waves travel from a radio speaker, sensing devices, or accessory structures, intercept them. The eyes, ears, skin, nose, and mouth are called accessory structures because they provide access to the environment. After the energy reaches a sensory structure, it has to get inside the brain somehow. Light, sound waves, and heat waves don’t bounce around inside a person’s head — not in mine, at least. So, how do they get inside?

First, keep in mind that the brain uses its own form of energy. In Chapter 3, I describe a specific type of energy in the brain; it’s called electrochemical energy. Electrochemical energy involves the creation of an electrical signal from chemical reactions. Electrochemical processes occur in many areas of nature. For example, some sea creatures such as eels can generate electric charges by using the electrochemical process. In the brain, this energy is how neurons communicate with each other and operate. So, in order for the brain to process the various forms of energy that a person’s sense organs receive, each form of energy has to undergo a transformation process, called transduction, that turns the raw energy into electrochemical, or neural, energy. Transduction is a fairly common process encountered often in today’s digital world as sounds and images are transduced or transformed into digital “bits” or code and transmitted via the Internet and cellular phone networks across the world.

The presence of specific types of cells, receptors, in each of the sensory systems makes transduction possible. Each sensory system has its own type of receptor cell. After the receptor cells transduce, or convert, the environmental energy, a neural signal travels along a sensory nerve, taking the information to the parts of the brain that are involved in processing and analyzing the information.

Does the music you listen to or human voices have only one tone? Does the light you see come in only one color? Of course not! Each of these sensory experiences, or stimuli, is made up of a complex array of wavelengths of light, frequencies of sound, intensities of smells and tastes, and so on. And your sensory systems are on the job to sort it out for you. Through the process of coding and representation, your brain captures the complexity of the environmental stimuli you encounter.

Humans experience the complexity of a stimulus after the brain translates its different features into a specific pattern of neural activity. The theory of specific nerve energies states that each sensory system provides information for only one sense, no matter how nerves are stimulated. In other words, specific parts of the brain always label the stimulation they receive as light or sound.


Some people claim to hear light and see sounds. Other people report that certain sounds have a color. Synesthesia is the name of an ability that certain people have to sense one (or more) forms of energy with a sensory system other than the one typically used for the stimulus. This phenomenon is estimated to affect about one in every 2,000 people. Scientists suspect that this experience is a result of some “wires” or neural connections in the brain being crossed. Simon Baron-Cohen, a world-famous autism researcher and psychologist, hypothesized that synesthesia is possible when extra connections in the brain allow for otherwise separate sensory systems there to interact. Whatever the cause, I think it sounds kind of cool. I’d love to be able to see the music when I dance because I sure can’t feel it!

Psychologists have worked with neurosurgeons to conduct experiments with patients who, for various medical reasons, need a portion of their skulls removed, which exposes their brains. The neurosurgeons took an electrode and zapped specific parts of the exposed brains with a little jolt of electricity. When they applied this shock, a weird thing happened. The people in the experiment said, “I can hear chickens squawking.” If they zapped the part of the brain that processes taste, a person may have said, “I can taste tomato soup. Mmm, that’s good.”

How is this possible? When a particular part of the brain is stimulated, the brain thinks that it’s receiving a specific kind of information from the sense organ it processes, even if it’s not. So, specific sensory systems are wired into specific brain regions, permitting the brain to know the difference between hearing a sound and seeing a light.

Different aspects of a stimulus are coded in the brain depending on which neurons are activated and the pattern of neuron activation. If neurons in the visual system are activated, for example, the brain senses light. If the pattern of neural activation differs, the brain senses different wavelengths or intensities of light so it can distinguish between sunlight and candlelight. The end of the sensory trail leads to a neural representation of the sensation in a specific region of the brain where you finally hear the music or see the colors.


Sight is arguably one of the most important human senses. Although the other senses are also important, being able to see is critical for getting along in the modern world. In this section, I chronicle a little journey — the journey light takes through the eye and into the brain, completing our sensation of light.

The journey begins with electromagnetic radiation, more commonly known as light. Visible light occupies wavelengths between 400 and 750 nanometers. I remember from physics class that light travels in waves. The intensity of light is calculated by measuring the size of the waves, and its frequency is measured by how many peaks of a wave pass a particular point within a specific period of time. Wavelength is important to the topic of how people sense light because different wavelengths make it possible to experience colors.

Here’s the process:

1. Light enters the eye through the cornea.

2. Light passes through the pupil.

3. The lens of the eye focuses the light onto the retina.

4. Light energy is converted into neural energy — an action known as light transduction.

Grasping the process of light transduction requires a closer look at the retina, a part of the eye that’s located on the back lining of the eyeball. The retina contains some special cells called photoreceptors that are responsible for transduction. These cells contain chemicals called photopigments that are broken apart when the photons of light traveling in the light wave make contact with them. This event starts a chemical reaction that tells the cell to fire a signal to the optic nerve. The signal then travels to the visual cortex of the brain, the part of the brain responsible for analyzing visual stimuli. So, light is transformed into neural energy by literally breaking up chemicals in the retina, which triggers a neural signal. These chemicals are stored in two different cells (called photoreceptors) in the retina, rods and cones.

Rods contain a chemical called rhodopsin, which is very light-sensitive. This chemical reacts to very low-intensity light and helps with peripheral vision. That is why we see mostly in black and white when it is dark; it’s also why we can sees stars at night better if we don’t look right at them.

Cones contain chemicals known as the iodopsins, which are closely related to rhodopsin. Each of three types of cone contains a different form of iodopsin. The three types of cone respond to different wavelengths of light and are involved in seeing color.

Seeing colors

Some people are colorblind to particular shades of blues, greens, and reds. This condition means that these people have a hard time sensing the specific wavelengths of light associated with those specific colors. They lack a photo pigment that is sensitive to the wavelengths. Typically, they only have two types of cones, not three. Fortunately, most people get to see the world in all its rainbow-hued glory.

There are two basic theories of color vision, the trichromatic theory and the opponent-process theory.

Image The trichromatic theory is really basic. The idea is that the retina contains three different types of cones (photoreceptors) that each responds to different wavelengths of light, and these provide our experience of different colors.

Short-wavelength cones respond to light around 440 nanometers, or blue light.

Medium-wavelength cones respond to light around 530 nanometers, or green light.

Long-wavelength cones respond to light around 560 nanometers, or greenish-yellow light.

When each cone system is partially activated, combinations of these three basic colors are visible as colors like aquamarine and orange. But the point here is that the human experience of all colors originates from these three basic cone inputs.

Image The opponent-process theory of color vision states that the brain contains different types of neurons that respond differently to different colors. The idea is that these cells fire more — when compared to their baseline, or background, level of firing — when stimulated by one type of light, and they fire less when stimulated by another. So, if you’re looking at red, your specialized red cells increase their firing rate. When you’re looking at green, your red cells chill out with the firing rate and your green cells increase their firing rate. “Cell sets” exist for yellow and blue as well.

This theory explains something called the negative-afterimage effect images in your mind’s eye that are different colors than the actual image you’re seeing. The most popular example uses a US flag that has black instead of white stars, green stripes replacing the red ones, and yellow instead of a blue background. After looking at the image for a while, a person can close her eyes and see the flag in its real colors because the cells being stimulated by black, green, and yellow light are recovering from the stimulation and begin “seeing” white, red, and blue light instead. Try it. Stare at a 1×1-inch yellow square for about 30 seconds and then look at a white sheet of paper. You should see a blue square instead of the white paper.

So which theory is correct? As is the case frequently in psychology, and in science more generally, an either/or question ends up being answered “both!” Psychologists now know that the trichromatic theory describes what happens in the retina of the eye, whereas the opponent-process theory describes what happens in the brain.

Figuring distances

How can you tell how far away something is from you just by looking at it? Well, maybe you can’t, but some people are really good at eyeballing distances. Personally, I need a tape measure, ruler, land-surveyor, and a global positioning satellite to figure distances, but depth and distance are calculated by the body’s visual systems, using two inputs: monocular cues and binocular cues.

Image Monocular cues are simple; you know that some things are bigger than other things. Dogs are bigger than mice. Cars are bigger than dogs. Houses are bigger than cars. Because you know these things from experience, whenever you see a mouse’s image on your retina that’s bigger than an image of a dog in the same scene, you know that the mouse is closer to you than the dog. Similarly, if you see a dog that’s bigger than a car, you figure the dog is closer.

The rule is that things that cast bigger images on our retinas are assumed to be closer. Artists use this rule all the time when they want to depict a three-dimensional scene on a two-dimensional canvas.

Image Binocular cues are interesting and a little weird. Remember the Cyclopes from the Sinbad movies? He only had one eye. According to binocular vision rules, he would have had a hard time figuring out distances because binocular distance cues depend on two eyes providing information to the brain.

Convergence is a binocular cue and refers to information provided by the muscles of the eyes to the brain in order to calculate distances. When your eyes are pointing inward, toward the nose, the brain knows that you’re looking at something close to you. When your eyes are pointing outward, the brain knows that you’re looking at an object farther away.

ImageStereoscopic vision is the other, and more important, type of binocular cue. Try this real quickly. Make a square, a viewing frame, with your hands by connecting your thumbs and index fingers at the tips while keeping the rest of your fingers folded. Then, close one eye and focus on an object around you. Frame the object in the middle of the box. Now, close that eye and open the other. What happened? The object should have moved. This happens because of stereoscopic vision. Each of your eyes gives you a slightly different angle on the same image because they are set apart. Your brain judges distance by using these different angles by calculating the difference between the two images.


Sound travels in waves and is measured by its amplitude or wave size and frequency or number of waves per unit time. Each of these translates into a psychological experience: Amplitude determines loudness (my neighbor’s rock band), and frequency provides pitch or tone (the screeching lead singer of said neighbor’s rock band). The structures of the ear are specifically designed to transduce, or convert, sound-wave energy into neural energy.

A sound first enters the ear as it is funneled in by the pinna. A human’s crumpled-up outer ear is designed as a “sound scoop.” As the wave passes through the ear canal, it eventually reaches the eardrum, or the tympanic membrane. The vibrating eardrum shakes three little bones (malleus, incus, and stapes, Latin words for hammer, anvil, and stirrup), which amplifies the vibration.

After the sound wave reaches the inner ear, the cochlea, auditory transduction occurs. The cochlea contains the hardware for the transduction process. The cochlea is filled with fluid, and its floor is lined with the basilar membrane. Hair cells (they actually look like hairs) are attached to the basilar membrane. The sound waves coming into the inner ear change the pressure of the fluid inside the cochlea and create fluid waves that move the basilar membrane. Movement of the basilar membrane causes the hair cells to bend, which starts the transduction ball rolling. When the hair cells bend, their chemical properties are altered, thus changing their electrical polarity and positioning them to fire and send a neural signal. The sound waves, now turned into neural electrochemical energy, travel to the auditory cortex (the part of the brain responsible for hearing) for perceptual processing.

Touching and feeling pain

The sense of touch includes sensing pressure, temperature, and pain. Specialized cells in the skin sense touch by sending a signal to the spinal cord and then on to the brain. Transduction in touch is a physical or mechanical process; it’s much more straightforward than the chemical transduction in the eye for vision. When heat, cold, or weight stimulates touch receptors in the skin, a neural signal travels to the brain, much the same way that the hair cells of the inner ear operate.

Pain is a special case for the sense of touch because it would be difficult to avoid harm and survive in this world without a sense of pain. Because it hurts when you touch fire, you’re motivated to avoid getting too close to it, which helps you avoid damaging your flesh and possibly dying. Pain is an important signal that something is harming, damaging, or destroying the body.

Two specific nerve fibers located throughout the skin signal pain to the brain: the A-delta fibers and the C fibers. A-delta fibers carry sharp sensations and work rapidly. C fibers communicate chronic and dull pain and burning sensations.

Image Some people seem to have a really high threshold for pain. The gate-control theory of pain states that pain signals must pass through a gate in the spinal cord that “decides” which signals get through to the brain and which ones don’t. If another sense is using the pain pathways at a given time, the pain signal may not reach the brain. For example, rubbing your thigh when your ankle aches seems to help dull the pain in the ankle. That’s because the rubbing signal (pressure) from the thigh is competing with the pain signal from the ankle for access through the gate. Amazing, right? I’m always blown away by the complexity of the human body.

Smelling and tasting

The sense of smell is called olfaction. Sometimes I can smell my neighbor’s barbecue on the weekend. I have that experience because little particles from the cooking food, volatile chemical particles, become airborne and travel over to the smell receptors in my nose. Inside my nose are thousands of olfactory receptors that can sense tens of thousands of different odors.

The molecules from the volatile chemicals cause a chemical change in the receptors in my nose, which sets the transduction process in motion. The chemical energy is then converted into neural energy by the receptor cells, and a signal hits the olfactory bulb in my brain where the signal is processed. The olfactory bulb also connects with the part of my brain that involves emotion. Some researchers think that this physical connection in the brain is why smells can activate emotional memories from time to time.

Perhaps you’ve heard talk about the impact of pheromones, which are scents that animals send out as signals to other animals during mating season. Some companies market pheromone products for humans, especially for men out there who are desperate to find a date. Do humans really produce pheromones? The research jury is still out, but a few recent findings seem to suggest that the answer is yes. The pheromone system depends on a second organ of smell, the vomeronasal organ, or Jacobsen’s organ. This system is prominent in animals as small as moths and as big as elephants.

Gustation refers to the sense of taste. Taste is a chemical sense made possible by chemical receptors on the tongue known as taste buds. All tastes are variations on five themes: sweet, sour, bitter, salty, and umami. Umami has generally been accepted as a fifth taste dimension. The receptors are activated by monosodium glutamate (MSG), often added to processed food Approximately 10,000 taste buds are on every tongue, reacting to the molecules of food and converting chemical energy into neural energy that sends information to the area of the brain involved in analyzing taste information.

Balancing and moving

Smart as he was, Aristotle missed some important sensory systems. Ballerinas and ice skaters can appear to float through space, their movements balanced and defying gravity. These marvelous abilities are possible in part due to the body senses, the sensory processes of the body’s orientation (in space) and movement — oftentimes referred to as the kinesthetic sense. Without the senses of balance and movement, it would not be possible to walk in a straight line or even stand up.

Structures known as the vestibular organ, located in the inner ear, and receptors located throughout the body are involved in balance and the kinesthetic sense. The vestibular organ consists of a set of “canals” that are filled with fluid that contain hair-like receptor cells. As the head moves around, the fluid inside the canals moves or flows, bending the receptor cells and causing these cells to fire, telling the brain that the head is in motion. Movement of the fluid triggers the sensation of movement.

The kinesthetic sense results from the firing of receptors located throughout the body in the skin, muscles, and joints. The firing of these receptors provides sensory information to the brain about the particular body part in motion, pressure, and the orientation of the body parts to each other. When the sense of movement, balance, orientation, body part in motion, and the body parts in relation to each other are all working together in a well-coordinated manner, graceful and fluid movement is possible.

Finishing the Product: Perception

The world is much more complex than a bunch of singular sounds, smells, tastes, and other sensations may indicate. You hear symphonies, not just notes. You see fireworks, not just single photons of light. You indulge your taste buds with flavorful foods, not individual salty, sour, bitter, umami, and sweet tastes. So take a moment to thank your ability of perception for these pleasures. I’ll wait.

Perception is the process of organizing, analyzing, and providing meaning to the various sensations that you’re bombarded with on a daily basis. If sensation provides the raw material, perception is the final product.

Image Here are two popular views of the complex process related to perception:

Image Ecological: This idea states that the environment provides all the information you need to sense the world; very little interpretation or construction is required. For example, when I perceive a tree, it’s not because I’ve constructed a perception of it in my mind. I perceive the tree because the tree has provided me with all the necessary information to perceive it as it is.

Image Constructionist: In this view, the process of perception relies on previous knowledge and information to construct reality from fragments of sensation. You are not just a passive recipient of sensory information. Instead, you are actively constructing what you see, hear, taste, and feel.

Regardless of whether you’re an ecologist or a constructionist, the process of perceiving has some basic tenets. If sensation is the process of detecting specific types of energy in the environment, how do you know what information is worth detecting and what’s just background noise? After all, you can’t possibly respond to every bit of sensory energy you encounter. All the roaring traffic, howling wind, bustling pedestrians, and other stuff would easily overwhelm a person. That’s why the perceptual systems have a built-in mechanism for determining what information should be detectable.

Threshold theory

Image The concept of an absolute threshold refers to the minimum amount of energy in the environment that a sensory system can detect. Each sensory system has an absolute threshold below which energy does not warrant or garner perceptual attention. A stimulus must be higher than your absolute threshold for you to notice it’s there.

Another type of threshold, the difference threshold, is described by Weber’s law, which introduces the just-noticeable difference (JND). The JND is the smallest difference between two stimuli that lets you know they are different. Each sensory system determines a constant fraction of intensity for each form of energy that represents the smallest detectable difference between energy intensities. The idea is that the difference between two stimuli has to exceed the JND in order for it to be detectable; otherwise, an observer will think the two stimuli are the same. For example, the just-noticeable difference for brightness is about 1/60th: I can barely tell the difference in brightness between a 60-watt and a 61-watt bulb, if they made 61-watt bulbs.

Signal-detection theory

Another theory known as signal-detection theory takes a slightly more complicated look at the problem. An overwhelming amount of environmental energy is considered background noise (think traffic sounds when you are in your automobile). When you encounter a stimulus, called the signal (think your car radio), you need to distinguish between the signal (car radio and traffic noise) and the background noise (just the traffic sounds). That’s why you have to turn up the car radio when there is heavy traffic at rush-hour; there’s more noise, so you need to increase the strength of the signal. Signal- detection theory says that your ability to perceive stimuli is based on your individual sensitivity and response criterion. Sensitivity refers to a basic characteristic of each perceptual system: what it is able to distinguish. The response criterion is determined by situational factors, like emotions and motivations. Based on your sensitivity and response criterion, you can either correctly detect a stimulus (hit), fail to detect a signal when one is available (miss), detect a signal when there isn’t one (false alarm), or report no signal when there isn’t one (correct rejection).

To understand response criterion, imagine that your task is to tell whether I turned a light on. Compare two situations: In one, you earn $100 every time you see the light when it occurs (a hit), but you lose $1 every time you say the light was on when it actually wasn’t (a false alarm). In the other situation, you earn $1 for each hit and lose $100 for each false alarm. Would you behave the same way in each situation? I wouldn’t — in the first case I would say “light” every time I even suspected it had come on; in the second case I would not say “light” unless I was really sure.

Individual biases and motivations determine response criterion and affect whether a person makes an accurate detection or not. This means when people think I’m not listening to them, it’s not my fault. I’m not detecting their signal because my response criterion is set too high. See? I’m an innocent victim of my perceptual processes.

Organizing by Principles

The perceptual system is not made up of a bunch of arbitrary rules and random processes. Psychologists and other researchers over the years have discovered principles that guide the way human perceptual systems organize all the information they receive from the sensory systems:

Image Figure-Ground: Information is automatically divided into two categories: either figure or ground, or foreground and background. Figural information is obvious and immediate; ground information is not very meaningful.

Image Grouping: This large category contains principles that people use to determine whether information belongs in a specific group with similar stimuli. These characteristics of the information or stimuli help with the grouping process:

Proximity: Stimuli that are close together in space are perceived to belong together.

Common fate: Stimuli that move in the same direction and at the same rate are grouped together.

Continuity: Stimuli that create a continuous form are grouped together.

Similarity: Similar things are grouped together.

Image Closure: This principle is the tendency to fill in missing information to complete a stimulus. There is a smart-phone game app that demonstrates this nicely in which only a portion of a popular company’s or corporation’s logo is presented and you have to guess the correct the company by completing or “closing” the rest of the logo.

Most psychologists today are in the constructionist camp. (See the Finishing the Product: Perception section earlier in this chapter.) They view perception as a process of building your sense of reality out of fragments of information. People are born with some of the rules for organizing information, but a few other factors can influence the way you perceive things.

Personal experiences have a powerful impact on how you analyze sensory information. The concept of a perceptual set, defined as an expectation of what you will perceive, attempts to capture this. You use cues from context and experience to help you understand what you’re seeing, tasting, feeling, and so forth. For example, if I’m driving down the street and see someone in a police uniform standing next to someone’s car window, I assume that an officer is making a traffic stop. I could actually be seeing a person in a police uniform asking for directions, but my past experience suggests otherwise.

A person’s culture is another powerful influence on how stimuli is perceived. A good example of the impact of cultural influences on perceptions involves figuring out a story line based on a series of pictures. If I have four pictures, each containing a different piece of a puzzle that, when viewed in sequence, can tell a story, I’m likely to imagine a story that’s different from the one my Spanish colleague imagines. For example, say I’m looking at a series of pictures that show these images:

Image A woman is carrying a bag.

Image A woman is crying.

Image A man is approaching a woman.

Image A woman is standing with no bag.

Tricking the eye

The organizing principles of the perceptual systems make perceptual illusions possible. You may see things that aren’t really in front of you or see things moving when they’re motionless. Illusionists, including magicians, use your perceptual organizing rules against you. They have a keen understanding of how the perceptual systems work, and they take advantage of this knowledge to perform their tricks.

What’s going on here? I may see a woman who is upset because she dropped her bag and a man who is coming to help her. Or, I may see a woman crying out of fear because a man is coming to steal her bag. Depending upon my culture or subculture, not to mention my personal experience, I may see two very different stories.