Chapter 4: Sensation and Perception
Chapter 4: Sensation and Perception Synesthesia: when most of us see letters printed in black. Some people with synesthesia link their perceptions of letters with certain colors and perceive letters as printed in different colors. The perceptual experience of one sense that is evoked by another. Vision is predominant among our senses. Our Senses Encode the Information Our Brains Perceive Sensation is simple stimulation of a sense organ. It is the basic registration of light, sound, pressure, odor, or taste as parts of your body interact with the physical world. After a sensation registers in your central nervous system, perception takes place at the level of your brain: It is the organization, identification, and interpretation of a sensation in order to form a mental representation. Transduction: What takes place when many sensors in the body convert physical signals from the environment into encoded neural signals sent to the central nervous system. Vision: light reflected from surface Audition: vibrations cause changes in air pressure Touch: pressure of a surface against the skin signals its shape, texture and temperature Taste and Smell: molecules dispersed in the air or dissolved in saliva In the mid1800s, the German scientist and philosopher Gustav Fechner developed an approach to measuring sensation and perception called psychophysics: methods that measure the strength of a stimulus and the observer’s sensitivity to that stimulus. The simplest quantitative measurement in psychophysics is the absolute threshold, the minimal intensity needed to just barely detect a stimulus. From the observer perspective As a way of measuring this difference threshold, Fechner proposed the just noticeable difference, or JND, the minimal change in a stimulus that can just barely be detected. The JND is not a fixed quantity; rather, it is roughly proportional to the magnitude of the stimulus. This relationship was first noticed in 1834 by the German physiologist Ernst Weber; now called Weber’s law, it states that the just noticeable difference of a stimulus is a constant proportion despite variations in intensity. Signal detection theory holds that the response to a stimulus depends both on a person’s sensitivity to the stimulus in the presence of noise and on a person’s decision criterion. •
Respond bias: predisposition to act/ no act
Sensory adaptation: the observation that sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions.
At time passes, nerve endings in the skin under your wristwatch send fewer signals to the brain and you become able to feel the watch is called sensory adaption. Vision I: How the Eyes and the Brain Covert Light Waves to Neural Signals Sensing light
Light that reaches the eyes passes first through a clear, smooth outer tissue, called the cornea, and then through the pupil, a hole in the colored part of the eye. This colored part is the iris, a translucent, doughnutshaped muscle that controls the size of the pupil and hence the amount of light that can enter the eye. Immediately behind the iris, muscles inside the eye control the shape of the lens to bend the light again and focus it onto the retina, lightsensitive tissue lining the back of the eyeball. Accommodation: the process by which the eye maintains a clear image on the retina. Eyeball longfocused in front of the retinanearsightedness (myopia) Eyeball shortfocused behind the retinafarsightedness(hyperopia) Photo transduction in the Retina Two types of photoreceptor cells in the retina •
Cones: detect color, operate under normal daylight conditions, and allow us to focus on fine detail
•
Rods: become active under lowlight conditions for night vision. Only gray
Fovea: an area of the retina where vision is the clearest and there are no rods at all. The photoreceptor cells send signals to the oddly shaped bipolar cells; bipolar cells in turn transmit signals to retinal ganglion cells, which organize the signals and send them to the brain.
Perceiving Color Sir Isaac Newton pointed out around 1670 that color is not something “in” light. In fact, color is nothing but our perception of wavelengths. •
Shortest visible wavelengths: purple
•
Longest visible wavelengths: red
Three primary colors of light: red green blue. A genetic disorder in which one of the cone types is missing—and, in some very rare cases, two or all three—causes a color deficiency. Color deficiency is often referred to as color blindness. The Visual Brain: •
Ventral stream: travels across the occipital lobe into the lower levels of the temporal lobes and includes brain areas that represent an object’s shape and identity. Recognition/ identification
•
Dorsal stream: travels up from the occipital lobe to the parietal lobes, connecting with brain areas that identify the location and motion of an object. (Aiming, reaching or tracking with the eyes) visually guide behavior
−
cornea, pupil, retina
−
Cones, rods, retinal ganglion cell
−
Optical nerve, blind spot
−
Reception field
−
Thalamus, occipital lobe V1, ventral and Dorsal steam
Vision II: Recognizing What We Perceive Binding problem: structure in ventral and dorsal visual streams are involved A phenomenon that concerns how features are linked together so that we see unified objects in our visual world rather than freefloating or miscombined features. Illusory conjunction: a perceptual mistake in which features from multiple objects are incorrectly combined. Feature integration theory: The idea that focused attention is not required to detect the individual features that comprise a stimulus but is required to bind those individual features together Anne Treisman The Role of the Parietal Lobe The binding process makes use of feature information processed by structures within the ventral visual stream. But because binding involves linking together features that appear at a particular spatial location, it also depends critically on the parietal lobe in the dorsal stream. Transcranial magnetic stimulation (TMS) is a benign technique that involves placing a powerful pulsed magnet over a person’s scalp, which temporarily alters neuronal activity in the brain. Perceptual Constancy: A perceptual principle stating that even as aspects of sensory signals change, perception remains consistent. Principles of Perceptual Organization Gestalt perceptual grouping rules •
Simplicity: clearly explain
•
Closure: tend to fill in missing elements
•
Continuity: same orientation
•
Similarity: similar in color, lightness, shape or texture
•
Proximity: close together
•
Common fate: single image that move together
Edgar Rubin: Rubin vasereversible figureground relationship Monocular depth cues: Aspects of a scene that yield information about depth when
viewed with only one eye. Size and linear •
Linear perspective: parallel line converge
•
Texture gradient: grow small (far)
•
Interposition: blocking is nearer to blocked object
•
Relative height in the image: closer lower
Binocular disparity: the difference in the retinal images of the two eyes that provides information about depth. Motion perception is subject to sensory adaption. E.g waterfall illusion This perception of movement as a result of alternating signals appearing in rapid succession in different locations is called apparent motion. (flashing light) Change blindness: A phenomenon that occurs when people fail to detect changes to the visual details of a scene. Inattentional blindness: a failure to perceive objects that are not the focus of attention. Audition: More Than Meets the Ear The sense of hearing is all about sound waves—changes in air pressure unfolding over time •
The frequency of the sound wave, or its wavelength depends on how often the peck in air pressure passes the ear or a microphone, measured in cycles per seconds. Pitch: how high or low sound is identify sound
•
The amplitude of a sound wave refers to its height. Amplitude corresponds to loudness, or a sound’s intensity.
•
Differences in the complexity of sound waves correspond to timbre, a listener’s experience of sound quality or resonance
Sensing Sound
The Human Ear
The pinna funnels sound waves into the auditory canal to vibrate the eardrum at a rate that corresponds to the sound’s frequency. In the middle ear, the ossicles pick up the eardrum vibrations, amplify them, and pass them along by vibrating a membrane at the surface of the fluidfilled cochlea in the inner ear. Here fluid carries the wave energy to the auditory receptors that transduce it into electrochemical activity, exciting the neurons that form the auditory nerve, leading to the brain. Cochlea: A fluidfilled tube that is the organ of auditory transduction. Basilar membrane: A structure in the inner ear that undulates when vibrations from the ossicles reach the cochlear fluid. Hair cells: Specialized auditory receptor neurons embedded in the basilar membrane. Sounds are ultimately transduced by movements of the hair cells Area A1: a portion of the temporal lobe that contains the primary auditory cortex The place code, used mainly for high frequencies, is active when the cochlea encodes different frequencies at different locations along the basilar membrane. A temporal code registers low frequencies via the firing rate of action potentials
entering the auditory nerve. −
Pitch: frequency low high/ low a sound is (place code and temporal code) most important
−
Amplitude loudness
−
Timbre sound quality
Temporal lobe The Body Senses: More Than Skin Deep Haptic perception: The active exploration of the environment by touching and grasping objects with our hands. Representation: topographic Four types of receptors located under the skin’s surface enable us to sense pressure, texture, pattern or vibration against the skin. Thermoreceptors, nerve fibers sense cold and warmth
Three important principles: •
The left half of the body is represented in the right half of the brain and vice versa. This is known as contralateral organization.
•
More of the brain is devoted to parts of the skin surface that have greater spatial resolution.
•
The “what” system for touch provides information about the properties of surfaces and objects; the “where” system provides information about a location in external space that is being touched or a location on the body that is being stimulated. “What” and “where” touch pathways involve areas in the lower and upper parts of the parietal lobe
Pain Although pain is arguably the least pleasant of sensations, this aspect of touch is among the most important for survival: Without the ability to feel pain, we might ignore infections, broken bones, or serious burns. Tissue damage is transduced by pain receptors. Fastacting Adelta fibers transmit the initial sharp pain one might feel right away from a sudden injury, and slower C fibers transmit the longerlasting, duller pain that persists after the initial injury. Protecting from over doing itremenber The location and type of pain we experience is indicated by signals sent to the somatosensory cortex. Referred pain occurs when sensory information from internal and external areas converges on the same nerve cells in the spinal cord. E.g. heart attack Gatecontrol theory holds that signals arriving from pain receptors in the body can be stopped, or gated, by interneurons in the spinal cord via feedback from two directions. The fact that a mild surface pain can greatly reduce more agonizing pain in consistent. Body Position, Movement, and Balance Sensations related to position, movement and balance depend on stimulation produced within our bodies. Receptors in the muscles, tendons, and joint signal the position of the body in space. Maintaining balance depends primarily on the vestibular system, the three fluid filled semicircular canals and adjacent organs located next to the cochlea in each inner ear. The Chemical Senses: Adding Flavor The chemical senses of olfaction (smell) and gustation (taste) respond to the molecular structure of substances floating into the nasal cavity or dissolving in saliva. Smell and taste combine to produce the perceptual experience we call flavor. Smell Olfaction is the least understood sense and the only one directly connected to the forebrain, with pathways into the frontal lobe, amygdala, and other forebrain structures. Olfactory receptor neurons (ORNs): Receptor cells that initiate the sense of smell. Olfactory bulb: A brain structure located above the nasal cavity beneath the frontal lobes. Along the roof of the nasal cavity, odorant molecules dissolve in the mucous membrane that forms the olfactory epithelium. Odorants may then bind to olfactory receptor neurons (ORNs) embedded in the epithelium. ORNs respond to a range of odors and, once activated, relay action potentials to their associated glomeruli in the olfactory bulb, located just beneath the frontal lobes. The glomeruli synapse on neurons whose axons form the olfactory nerve, which projects directly into the forebrain.
Pheromones: Biochemical odorants emitted by other members of its species that can affect an animal’s behavior or physiology. Taste The tongue is covered with thousands of small bumps, called papillae, which are easily visible to the naked eye. Within each papilla are hundreds of taste buds, the organ of taste transduction. Five main types of taste receptors: salt, sour, bitter, sweet and umami. Umami: discovered Japanese scientist, evoked by foods containing a high concentration of protein.
Respond bias: predisposition to act/ no act
Sensory adaptation: the observation that sensitivity to prolonged stimulation tends to decline over time as an organism adapts to current conditions.
At time passes, nerve endings in the skin under your wristwatch send fewer signals to the brain and you become able to feel the watch is called sensory adaption. Vision I: How the Eyes and the Brain Covert Light Waves to Neural Signals Sensing light
Light that reaches the eyes passes first through a clear, smooth outer tissue, called the cornea, and then through the pupil, a hole in the colored part of the eye. This colored part is the iris, a translucent, doughnutshaped muscle that controls the size of the pupil and hence the amount of light that can enter the eye. Immediately behind the iris, muscles inside the eye control the shape of the lens to bend the light again and focus it onto the retina, lightsensitive tissue lining the back of the eyeball. Accommodation: the process by which the eye maintains a clear image on the retina. Eyeball longfocused in front of the retinanearsightedness (myopia) Eyeball shortfocused behind the retinafarsightedness(hyperopia) Photo transduction in the Retina Two types of photoreceptor cells in the retina •
Cones: detect color, operate under normal daylight conditions, and allow us to focus on fine detail
•
Rods: become active under lowlight conditions for night vision. Only gray
Fovea: an area of the retina where vision is the clearest and there are no rods at all. The photoreceptor cells send signals to the oddly shaped bipolar cells; bipolar cells in turn transmit signals to retinal ganglion cells, which organize the signals and send them to the brain.
Perceiving Color Sir Isaac Newton pointed out around 1670 that color is not something “in” light. In fact, color is nothing but our perception of wavelengths. •
Shortest visible wavelengths: purple
•
Longest visible wavelengths: red
Three primary colors of light: red green blue. A genetic disorder in which one of the cone types is missing—and, in some very rare cases, two or all three—causes a color deficiency. Color deficiency is often referred to as color blindness. The Visual Brain: •
Ventral stream: travels across the occipital lobe into the lower levels of the temporal lobes and includes brain areas that represent an object’s shape and identity. Recognition/ identification
•
Dorsal stream: travels up from the occipital lobe to the parietal lobes, connecting with brain areas that identify the location and motion of an object. (Aiming, reaching or tracking with the eyes) visually guide behavior
−
cornea, pupil, retina
−
Cones, rods, retinal ganglion cell
−
Optical nerve, blind spot
−
Reception field
−
Thalamus, occipital lobe V1, ventral and Dorsal steam
Vision II: Recognizing What We Perceive Binding problem: structure in ventral and dorsal visual streams are involved A phenomenon that concerns how features are linked together so that we see unified objects in our visual world rather than freefloating or miscombined features. Illusory conjunction: a perceptual mistake in which features from multiple objects are incorrectly combined. Feature integration theory: The idea that focused attention is not required to detect the individual features that comprise a stimulus but is required to bind those individual features together Anne Treisman The Role of the Parietal Lobe The binding process makes use of feature information processed by structures within the ventral visual stream. But because binding involves linking together features that appear at a particular spatial location, it also depends critically on the parietal lobe in the dorsal stream. Transcranial magnetic stimulation (TMS) is a benign technique that involves placing a powerful pulsed magnet over a person’s scalp, which temporarily alters neuronal activity in the brain. Perceptual Constancy: A perceptual principle stating that even as aspects of sensory signals change, perception remains consistent. Principles of Perceptual Organization Gestalt perceptual grouping rules •
Simplicity: clearly explain
•
Closure: tend to fill in missing elements
•
Continuity: same orientation
•
Similarity: similar in color, lightness, shape or texture
•
Proximity: close together
•
Common fate: single image that move together
Edgar Rubin: Rubin vasereversible figureground relationship Monocular depth cues: Aspects of a scene that yield information about depth when
viewed with only one eye. Size and linear •
Linear perspective: parallel line converge
•
Texture gradient: grow small (far)
•
Interposition: blocking is nearer to blocked object
•
Relative height in the image: closer lower
Binocular disparity: the difference in the retinal images of the two eyes that provides information about depth. Motion perception is subject to sensory adaption. E.g waterfall illusion This perception of movement as a result of alternating signals appearing in rapid succession in different locations is called apparent motion. (flashing light) Change blindness: A phenomenon that occurs when people fail to detect changes to the visual details of a scene. Inattentional blindness: a failure to perceive objects that are not the focus of attention. Audition: More Than Meets the Ear The sense of hearing is all about sound waves—changes in air pressure unfolding over time •
The frequency of the sound wave, or its wavelength depends on how often the peck in air pressure passes the ear or a microphone, measured in cycles per seconds. Pitch: how high or low sound is identify sound
•
The amplitude of a sound wave refers to its height. Amplitude corresponds to loudness, or a sound’s intensity.
•
Differences in the complexity of sound waves correspond to timbre, a listener’s experience of sound quality or resonance
Sensing Sound
The Human Ear
The pinna funnels sound waves into the auditory canal to vibrate the eardrum at a rate that corresponds to the sound’s frequency. In the middle ear, the ossicles pick up the eardrum vibrations, amplify them, and pass them along by vibrating a membrane at the surface of the fluidfilled cochlea in the inner ear. Here fluid carries the wave energy to the auditory receptors that transduce it into electrochemical activity, exciting the neurons that form the auditory nerve, leading to the brain. Cochlea: A fluidfilled tube that is the organ of auditory transduction. Basilar membrane: A structure in the inner ear that undulates when vibrations from the ossicles reach the cochlear fluid. Hair cells: Specialized auditory receptor neurons embedded in the basilar membrane. Sounds are ultimately transduced by movements of the hair cells Area A1: a portion of the temporal lobe that contains the primary auditory cortex The place code, used mainly for high frequencies, is active when the cochlea encodes different frequencies at different locations along the basilar membrane. A temporal code registers low frequencies via the firing rate of action potentials
entering the auditory nerve. −
Pitch: frequency low high/ low a sound is (place code and temporal code) most important
−
Amplitude loudness
−
Timbre sound quality
Temporal lobe The Body Senses: More Than Skin Deep Haptic perception: The active exploration of the environment by touching and grasping objects with our hands. Representation: topographic Four types of receptors located under the skin’s surface enable us to sense pressure, texture, pattern or vibration against the skin. Thermoreceptors, nerve fibers sense cold and warmth
Three important principles: •
The left half of the body is represented in the right half of the brain and vice versa. This is known as contralateral organization.
•
More of the brain is devoted to parts of the skin surface that have greater spatial resolution.
•
The “what” system for touch provides information about the properties of surfaces and objects; the “where” system provides information about a location in external space that is being touched or a location on the body that is being stimulated. “What” and “where” touch pathways involve areas in the lower and upper parts of the parietal lobe
Pain Although pain is arguably the least pleasant of sensations, this aspect of touch is among the most important for survival: Without the ability to feel pain, we might ignore infections, broken bones, or serious burns. Tissue damage is transduced by pain receptors. Fastacting Adelta fibers transmit the initial sharp pain one might feel right away from a sudden injury, and slower C fibers transmit the longerlasting, duller pain that persists after the initial injury. Protecting from over doing itremenber The location and type of pain we experience is indicated by signals sent to the somatosensory cortex. Referred pain occurs when sensory information from internal and external areas converges on the same nerve cells in the spinal cord. E.g. heart attack Gatecontrol theory holds that signals arriving from pain receptors in the body can be stopped, or gated, by interneurons in the spinal cord via feedback from two directions. The fact that a mild surface pain can greatly reduce more agonizing pain in consistent. Body Position, Movement, and Balance Sensations related to position, movement and balance depend on stimulation produced within our bodies. Receptors in the muscles, tendons, and joint signal the position of the body in space. Maintaining balance depends primarily on the vestibular system, the three fluid filled semicircular canals and adjacent organs located next to the cochlea in each inner ear. The Chemical Senses: Adding Flavor The chemical senses of olfaction (smell) and gustation (taste) respond to the molecular structure of substances floating into the nasal cavity or dissolving in saliva. Smell and taste combine to produce the perceptual experience we call flavor. Smell Olfaction is the least understood sense and the only one directly connected to the forebrain, with pathways into the frontal lobe, amygdala, and other forebrain structures. Olfactory receptor neurons (ORNs): Receptor cells that initiate the sense of smell. Olfactory bulb: A brain structure located above the nasal cavity beneath the frontal lobes. Along the roof of the nasal cavity, odorant molecules dissolve in the mucous membrane that forms the olfactory epithelium. Odorants may then bind to olfactory receptor neurons (ORNs) embedded in the epithelium. ORNs respond to a range of odors and, once activated, relay action potentials to their associated glomeruli in the olfactory bulb, located just beneath the frontal lobes. The glomeruli synapse on neurons whose axons form the olfactory nerve, which projects directly into the forebrain.
Pheromones: Biochemical odorants emitted by other members of its species that can affect an animal’s behavior or physiology. Taste The tongue is covered with thousands of small bumps, called papillae, which are easily visible to the naked eye. Within each papilla are hundreds of taste buds, the organ of taste transduction. Five main types of taste receptors: salt, sour, bitter, sweet and umami. Umami: discovered Japanese scientist, evoked by foods containing a high concentration of protein.
