A sense is a system that translates information from outside the nervous system into neural activity, which provides the brain with information about the environment. (see introductory section) Examples: Vision, hearing, olfaction, touch, and taste
Sensations are messages from the senses that provide a link between the self and the world outside the brain. (see introductory section) Example: Feeling a touch on your mouth is a sensation. Knowing that you have been kissed--instead of, say, scratched--and by whom is a perception. REMEMBER:Sensation is the message that is sent to the brain about an object's characteristics. Perception is the brain's interpretation of what is sensed. For example, your senses may tell your brain that there is a bright light filling the top half of your visual system and that the light energy has many different wavelengths. Your brain interprets these messages and perceives a sunset.
Accessory structures modify sensory stimuli prior to transduction. (see Sensory Systems) Example: The lens in the eye bends light before it is picked up by photoreceptors in the retina and transduced into neural activity.
Transduction is the process whereby receptors translate stimulus energy into neural energy that the brain can interpret. (see Sensory Systems) Example: Photoreceptors in the eye pick up information about light and change it into neural energy, which tells the brain about what is in the visual field.
Sensory receptors are specialized cells that detect certain types of energy (such as light or sound) and convert it into neural energy through transduction. (see Sensory Systems) REMEMBER: Just as a receptionist receives people, the receptors in the sensory systems receive information about the world.
Adaptation occurs when a constant stimulus is applied to the body. Initially, the receptors in the skin fire rapidly, but their activity decreases over time. (see Sensory Systems) Example: Try to feel your underwear. You probably had to concentrate to feel it against your skin, if you felt it at all. The reason is that the skin receptors in contact with your underwear may have fired rapidly when you got dressed this morning, but now have decreased their activity.
Coding is the conversion of an item's physical features into a specific pattern of neural activity, which represents those features in the brain. See Key Terms 9 and 10 for examples of different types of coding. (see The Problem of Coding) Example: Someone has just touched your cheek. How do the neurons communicate to the brain that your face has been caressed and not slapped? Coding must convey the intensity of the stimulus to your brain so that it can interpret the touch as a caress or a slap. REMEMBER: Your brain interprets messages or sensations as if they were a type of Morse code.
Specific nerve energies is a doctrine stating that each sensory nerve has a specific sensation associated with it, and that these specific sensations will occur no matter how the nerve is stimulated. (see The Problem of Coding) Example: Putting pressure on your eyeballs, thereby stimulating sensory nerves with touch, generates the sensation of light. This happens because the receptors in the eye will always transmit a message about light, no matter what type of stimulus is experienced.
Temporal codes are based on the timing of neural activity. The speed with which neurons fire becomes a code. (see The Problem of Coding) Example: In the example given for Key Term 7, your brain was looking for information about the intensity of a touch on your cheek. The rate at which the neurons fire is a code that tells the brain about the intensity of the touch. The faster the neurons fire, the harder you have been hit.
Spatial codes are based on the location of neural activity. Two messages that are sent in neurons that are next to each other tell the brain that both stimuli occurred very close to each other. (see The Problem of Coding) Example: You know that you were touched on your toe and your ankle, not your toe and your ear, because of spatial codes. The neurons from your toe and your ankle are located very close to each other whereas the neurons from your ear are not next to your toe.
Sound is a repetitive change in the pressure of a medium like air. This activity can be represented in wave form. (see Hearing) Example: When an object (such as a violin string) vibrates, molecules in the air move, causing temporary changes in air pressure that stimulate the ear.
Amplitude is the difference in air pressure between the top of the wave and the baseline of the wave. Loudness is determined by the amplitude of a sound wave. (see Hearing) REMEMBER: When you amplify something, you make it greater. The greater the amplitude of the sound wave, the greater the loudness of the sound.
Wavelength is the distance from one peak to the next in the wave. Wavelength is related to frequency; the longer the wavelength, the lower the frequency or pitch of the sound. (p. Hearing) REMEMBER:Long Wavelength and Low Pitch: they both begin with L.
Frequency is the number of complete waves that pass a given point in space in one second. As the wave's frequency increases, so does the sound's pitch. Frequency is described in a unit called hertz. (see Hearing) REMEMBER:Frequency means "how often." The frequency of a sound wave tells you how often a complete wave or cycle passes a given point in one second.
The loudness of a sound is determined by the amplitude of sound waves and is measured in decibels. (see Psychological Dimensions of Sound) Example: People using a sound system in an auditorium control the loudness of the sound coming from the speakers by adjusting the amplitude of the sound waves with their equipment.
Pitch--how high or low a sound is perceived to be--is determined by the frequency of sound waves. (see Psychological Dimensions of Sound) Example: Spanky sang a note of the wrong pitch, so his friend told him to sing a slightly higher note. When the frequency of the sound waves coming from Spanky's mouth increased, his friend sensed a higher note.
Timbre is the quality of a sound that distinguishes it from other sounds. The mixture of frequencies and complex wave forms that make up a sound determine timbre. (see Psychological Dimensions of Sound) Example: The next time you listen to music, try to identify the instruments that you hear. The sound of each instrument has a unique timbre. A note played on the piano has a much different sound than the same note played on the cello.
The tympanic membrane, located at the bottom of the ear canal, vibrates when struck by sound waves. (see Auditory Accessory Structures) REMEMBER: The tympanic membrane is stretched tightly across the end of the ear canal, just like the skin stretched tightly across the head of a drum. The tympanic membrane is also called the eardrum.
The cochlea is a spiral structure in the inner ear where transduction occurs. (see Auditory Transduction) REMEMBER: The cochlea is like a coiled hose; it contains fluid that moves when sound waves come in.
The basilar membrane is inside the cochlea. When vibrations come through the oval window and into the cochlea, the basilar membrane moves. As this membrane moves, it moves the hair cells that touch it. The hair cells, in turn, stimulate neural activity in the auditory nerve. (see Auditory Transduction) REMEMBER: The basilar membrane, which runs along the base of the cochlea, moves the hair cells to create a neural signal. Imagine placing your thumb over the bristles on a toothbrush. The bristles bend when you press on them, much like the hair cells are moved when the basilar membrane reacts to the sound wave going through the fluid. Your thumb represents the pressure from the basilar membrane, and each bristle represents a hair cell that will now translate the pressure into neural activity.
The auditory nerve is a bundle of axons that run from the inner ear to the brain. (see Auditory Transduction) REMEMBER: The auditory nerve receives signals from the hair cells and carries them to the thalamus. From the thalamus, the signals are relayed to the primary auditory cortex in the temporal lobe of the brain.
Place theory helps explain the coding of auditory stimuli. It states that a particular place on the basilar membrane responds most to a particular frequency of sound, determining the pitch of a sound. (see Coding Intensity and Frequency) REMEMBER: In your mind, create an image of the basilar membrane all curled up inside the cochlea. Along the length of the membrane, mentally write the names of musical notes. Each place on the membrane is associated with one note or pitch.
Frequency matching (also called the volley theory) helps explain the coding of auditory stimuli. It states that the firing rate of a neuron (how many times a neuron fires per second) matches the frequency of a sound wave (how many cycles or complete waves occur in a second). (see Coding Intensity and Frequency) REMEMBER: The frequency of the neuron's firing matches the frequency of the sound wave.
Primary auditory cortex is the area of the cortex within the temporal lobe that receives auditory input directly from the thalamus. (see Auditory Pathways and Representations)
Visible light is electromagnetic radiation that has a wavelength of 400 to 750 nanometers. (see Light)
Light intensity is a physical dimension of light waves that refers to how much energy the light contains; it determines the brightness of light. (see Light) REMEMBER: Just as a higher-amplitude sound wave is experienced as a louder sound, a higher light intensity is experienced as a brighter light.
Light wavelength is the main determinant of what color you perceive. (see Light) Example: A light wavelength of about 500 nanometers is perceived as green.
The cornea is the curved, transparent, protective layer on the outside of the eye. (see Focusing Light) REMEMBER: Like a plastic wrap covers a bowl, your cornea covers the opening to your eye, yet it allows light to pass through.
The pupil is an opening, located behind the cornea, that looks like a black spot in the middle of your eye. Light passes through it to get to the retina at the back of the eye. (see Focusing Light)
The lens bends light rays, thereby helping to focus them on the retina at the back of the eye. (see Focusing Light)
Transduction takes place in the retina, a network of several different types of cells. (see Focusing Light) REMEMBER: Transduction is the process of converting incoming energy (wavelengths of light) into neural activity.
The iris is the colored part of the eye that controls the amount of light that passes into the eye by dilating or constricting the pupil. (see Focusing Light)
Accommodation is the process whereby the muscles holding the lens in place either tighten or loosen to change the curvature of the lens, thereby focusing the visual image. The degree to which the muscles pull the lens is related to the distance of the object being viewed. (see Focusing Light) REMEMBER: Think of the muscles (when they change the curvature of the lens) as helping the eyes to accommodate to the distance of the object they are looking at.
The photoreceptors in the retina code light energy into neural energy. The photoreceptors of the eye are called rods and cones: rods code light and cones code color. (see Photoreceptors) REMEMBER:Photo means "light," and receptors "receive." Photoreceptors receive light from the visual environment.
Photopigments are chemicals inside the photoreceptors. When light strikes a photoreceptor, these chemicals break apart and cause changes in the photoreceptor's membrane potential. Photopigments are necessary to the transduction process. (see Photoreceptors)
Dark adaptation is the adjustment made by our eyes when the amount of light in our environment decreases. In the dark, photoreceptors synthesize more photopigments, and people can begin to see more and more clearly. The cones adapt to dark more quickly than the rods do (complete adaptation occurs in about forty-five minutes) and allow us to see with greater acuity in dim light. (see Photoreceptors) Example: When Rakesh first sat in the darkened auditorium to watch the school play, he could not read the title on the program. After about a half hour he had no trouble seeing the title.
Rods are photoreceptors that are located in the retina. They are very sensitive to light but cannot distinguish color. (see Photoreceptors) Example: The program for Rakesh's school play had pages of different colors, but while in the dark Rakesh couldn't tell the difference.
Cones are photoreceptors located in the retina that can detect color. It is because cones are less sensitive to light that we have difficulty seeing color in the dark. (see Photoreceptors) REMEMBER: Cones are photoreceptors that can detect color. The C in cones reminds us of color. REMEMBER: Cones, as compared to rods, are less sensitive to light. Thus they need more light to be stimulated. When you are in the dark, the lack of light decreases cone stimulation, which, in turn, decreases your ability to see color.
The fovea is located in the center of the retina. A very high concentration of cones in the fovea makes spatial discrimination or acuity (visual accuracy) greatest in the fovea. (see Photoreceptors) REMEMBER: Use the following sentence to help you remember the definition of fovea: FOcusing Very Easy in this Area.
Acuity is a term that refers to the quality of vision--specifically, to the eye's ability to make spatial discriminations. (see Photoreceptors) Example: When you take a vision test, your acuity is being assessed.
Lateral inhibition occurs when the greater activity in one cell suppresses the activity in neighboring cells. Lateral inhibition exaggerates the sense of contrast that occurs when light hits the photoreceptors. (see Interactions in the Retina) Example: The photoreceptor that receives the greatest amount of light stimulates both a bipolar cell (A) and an interneuron. The interneuron inhibits the bipolar cells that are next to bipolar cell A, thereby sharpening the contrast between the message from the photoreceptor that receives the greatest amount of light and the surrounding inhibited photoreceptors. REMEMBER:Lateral means "next to."
A ganglion's receptive field is that part of the retina and the corresponding part of the visual world to which the cell responds. (see Ganglion Cells and Their Receptive Fields)
Ganglion cells are the cells in the retina whose axons extend out of the retina; their function is to generate action potentials that will reach the brain. (see Ganglion Cells and Their Receptive Fields) REMEMBER: Rods and cones transduce light and send the information to bipolar cells and interneurons, which send their information to ganglion cells, which send their information to the brain. REMEMBER: A gang of ganglion cell axons reach from the retina to the brain.
The axons of all the ganglion cells come together at one point in the back of the retina to make up the optic nerve. There are no photoreceptor cells at the point where this nerve leaves the eye, creating a blind spot. (see Visual Pathways)
A blind spot is located at the exit point of the optic nerve from the retina. It is termed "blind" because it has no photoreceptors and is therefore insensitive to light. (see Visual Pathways)
The optic chiasm is a structure in which fibers of the optic nerve coming from the inside half of both retinas cross over to the opposite side of the brain to provide the brain with complete visual representation. (see Visual Pathways) REMEMBER:Chiasm means "cross."
The lateral geniculate nucleus (LGN) is a region of the thalamus in which ganglion cells in the retina end and form synapses. The neurons are organized into layers that respond to particular aspects of visual stimuli. (see Visual Pathways) Example: When Jenny looks at a red cube, one layer of cells in the LGN may code which area of the visual field is red and what the background colors are. Another layer of cells may be firing in response to the horizontal and vertical orientations of the lines in the cube.
The primary visual cortex is in the occipital lobe and receives visual input directly from the thalamus. Within it is the same topographical representation of the visual field as that found in the retina. (see Visual Pathways)
Feature detector is another name for cells in the visual cortex. Visual cortical cells respond best to particular types of features. (see Visual Representations) REMEMBER: Cortical cells detect features, so they are called feature detectors.
Hue, the essential "color" of an object, is determined by the dominant wavelength of light. (see Wavelengths and Color Sensations) Example: Red and green are two different hues with two different wavelengths. (See also Key Term 51.) REMEMBER: Black, white, and gray are not considered colors because they do not have their own dominant wavelengths.
Saturation is the purity of a color. If many waves of the same length are present, the color is more pure or saturated. (see Wavelengths and Color System) Example: The next time you go to a fast-food restaurant, compare the pictures of food on the wall with the actual food you buy. The colors or hues are the same. However, the pictures appear to be more vibrant. The reason is that the pictures are saturated with wavelengths of similar lengths, whereas the food reflects a broad variety of wavelengths.
The brightness of colors corresponds to the overall intensity of the wavelengths making up light. (see Wavelengths and Color Sensations)
The trichromatic theory states that because any color can be made by combining red, green, and blue light, there must be three types of visual elements, each of which is most sensitive to one of these three colors. Indeed, there are three types of cones that are most sensitive to red, green, and blue wavelengths. (see The Trichromatic Theory of Color Vision) REMEMBER:Tri means "three" and chromo means "color." The trichromatic theory is concerned with the sensation of three colors.
The opponent-process theory states that visual elements sensitive to color are grouped into three pairs, and that each pair member opposes or inhibits the other. The pairs are red-green, blue-yellow, and black-white. Each element signals one color or the other, but not both. The ganglion cells in the retina have color-coded center-surround receptive fields. (see The Opponent Process Theory of Color Vision) Example: One ganglion cell may have a red-green center-surround receptive field. If red light causes the center to be stimulated, the surround is inhibited. If green light causes the surround to be stimulated, the center is inhibited. If both the center and the surround are stimulated, we see gray because the opponent colors cancel each other out. REMEMBER: The color in the center and the color in the surround of a ganglion cell receptive field are opponents; they are competing.
Synesthesia is a blending of sensory experiences. (see The Interaction of Vision and Hearing: Synesthesia) Example: Someone might "taste" the color green as being tart.
Olfaction is our sense of smell. Receptors in the upper part of the nose detect chemicals in the air. (see Olfaction) REMEMBER:Olere means "to smell" and facere means "to make." Olfaction literally means "to make a smell." You can use the following story to help you remember this word. The grandfather of one of the authors worked in a paper mill that was very old and produced an incredibly awful smell. Just remember that the OL' FACTory smells.
The olfactory bulb is a structure in the brain that receives information from nerves in the nose. Neural connections from the olfactory bulb travel to many parts of the brain, especially the amygdala. (see Olfaction) Example: The axons that synapse in Tyrone's olfactory bulb signaled that a flowery odor was being experienced. The information went on to Tyrone's amygdala, where memories of a friend who wore the same flower-scented perfume were activated.
Pheromones are chemicals that animals release into the air. Other animals may experience behavioral and physiological changes as a result of smelling the pheromones. However, there is no evidence that people give off or can smell pheromones. (see Olfaction) Example: Female pigs immediately assume a mating stance after smelling a pheromone called "androsterone" in a boar's saliva.
The vomeronasal organ is a specialized portion of the olfactory system that detects pheromones. (see Olfaction)
Papillae are groups of taste buds. Each taste bud responds to all four categories: sweet, sour, bitter, and salty. However, each responds best to only one or two of them. (see Gustation) Example: The combination of signals from Maggie's papillae results in a salty and sweet taste, which Maggie perceives as caramel corn.
Gustation refers to our sense of taste. Receptors in the taste buds pick up chemical information from substances inside the mouth. (see Gustation) REMEMBER: The first letters of the words in the following sentence spell gustation: Gus's Uncle Sam Tasted All The Indian's ONions.
The somatic senses, also known as the somatosensory systems, are distributed throughout the body instead of residing in a single structure. The senses include touch, temperature, pain, and kinesthesia. (see Somatic Senses and the Vestibular Sense) REMEMBER:Soma means "body." The somatosensory system senses what happens to the body in terms of touch, temperature, pain, and kinesthesia.
The gate control theory states that the nervous system has two methods of preventing pain information from reaching the brain. Other sensory information from the skin may take over the pathways the pain impulses would use to travel up the spinal cord to the brain. Alternatively, the brain can send signals down the spinal cord and prevent pain signals from ascending the spinal cord and entering the brain. (see Pain) REMEMBER: The nervous system can use the spinal cord as a gate that will allow only so much information to go through it in either direction. To better understand this concept, think of what happens when a movie lets out. There are so many people coming out the doors that nobody can get into the theater for a few minutes. Similarly, to prevent pain information from reaching its destination, the brain sends information down the spinal cord that blocks the pain signals from ascending the spinal cord.
Analgesia is the absence of pain sensation in the presence of painful stimuli. (see Pain) Example: Aspirin is an analgesic drug. Our bodies make chemicals, called natural analgesics, that can reduce pain sensation. Endorphins are natural analgesics. Serotonin, a neurotransmitter, also plays a role in blocking pain sensation.
The proprioceptive sensory system provides us with the ability to know where we are in space and what each of our body parts is doing relative to all other body parts. Kinesthesia, which is part of the somatosensory system, and the vestibular system provide proprioceptive information to the brain. (see Proprioception)
The vestibular sense tells the brain about the position of the body in space and its general movements. The vestibular sacs and the semicircular canals in the inner ear provide vestibular information. (see Vestibular Sense) Example: Doing something as simple as a handstand requires vestibular information. If your vestibular senses were not working, you would not know if you were upside-down or right-side-up.
Vestibular sacs are part of the inner ear. They are filled with fluid and contain small crystals called otoliths, which rest on hair endings. When you move your head, the otoliths shift and activate neurons that travel with the auditory nerve, signaling the brain about the amount and direction of head movement. (see Vestibular Sense)
Otoliths, also called ear stones, are located inside the vestibular sacs in the inner ear and function as part of the vestibular system. When you move your head, the otoliths shift and activate neurons that travel with the auditory nerve, signaling the brain about the amount and direction of head movement. (see Vestibular Sense)
Semicircular canals are fluid-filled, arc-shaped tubes located inside the inner ear that function as part of the vestibular system. When you move your head, the fluid also moves, activating neurons traveling with the auditory nerve and, in turn, signaling the brain about the amount and direction of the head movement. (see Vestibular Sense)
Kinesthesia is the sense that tells you where your body parts are in relation to one another. (see Kinesthesia) Example: You must know where your head is in relation to your hands to be able to touch the tip of your finger to your nose while your eyes are shut.
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