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PSYD51H3 (1)
Chapter 5-9

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Department
Psychology
Course
PSYD51H3
Professor
Douglas Frayne
Semester
Fall

Description
PSYCHOLOGY EXAM NOTES CHAPTER 5: SENSATION Sensory Processing - Sensation: the detection of the elementary properties of a stimulus (such as brightness, colour, warmth, and sweetness) - Perception: the detection of the more complex properties of a stimulus, including its location and nature; involves learning - E.g. seeing the colour red is sensation, but seeing a red apple is perception. Seeing a movement is a sensation, but seeing a soccer ball coming toward us and realizing that we will have to move to the left to block it is a perception - Experience is essential to the development of some of the most elementary features of sensory systems Transduction - Sense organs detect stimuli provided by light, sound, odour, taste, or mechanical contact with the environment. Information about these stimuli is transmitted to the brain through neural impulses - action potentials carried by the axons of sensory nerves - The task of the sense organs is to transmit signals to the brain that are coded in such a way as to represent faithfully the events that have occurred in the environment. The task of the brain is to analyze this information and reconstruct what has occurred - Transduction: the conversion of physical stimuli into changes in the activity of receptor cells of sensory organs. Sense organs convert energy from environmental events into neural activity - Receptor cell: a neuron that directly responds to a physical stimulus, such as light, vibrations, or aromatic molecules Location of Sense Organ Environmental Stimuli Energy Transduced Eye Light Radiant energy Ear Sound Mechanical energy Vestibular system Tilt and rotation of head Mechanical energy Tongue Taste Recognition of molecular shape Nose Odour Recognition of molecular shape Skin, Internal organs Touch Mechanical energy Temperature Thermal energy Vibration Mechanical energy Location of Sense Organ Environmental Stimuli Energy Transduced Muscle Pain Chemical reaction Stretch Mechanical energy Sensory Coding - Sensory information must accurately represent the environment - A code is a system of symbols or signals representing information - As long as we know the rules of a code, we can convert a message from one medium to another without losing any information - Two general forms of transmitting information to the brain: anatomical coding and temporal coding Anatomical Coding - The brain learns what is happening through the activity of specific sets of neurons - Sensory organs located in different places in the body send their information to the brain through different nerves - Anatomical coding: a means by which the nervous system represents information; different features are coded by the activity of different neurons - The primary somatosensory cortex contains a neural “map” of the skin. Receptors in the skin in different parts of the body send information to different parts of the primary somatosensory cortex. Similarly, the primary visual cortex maintains a map of the visual field Temporal Coding - Temporal coding: a means by which the nervous system represents information; different features are coded by the pattern of activity of neurons - The simplest form of temporal code is rate. By firing at a faster or slower rate according to the intensity of a stimulus, an axon can communicate qualitative information to the brain - E.g. A light touch to the skin can be encoded by a low rate of firing, and a more forceful touch by a high rate. Thus, the firing of a particular set of neurons (an anatomical code) tells where the body is being touched; the rate at which these neurons fire (a temporal code) tells how intense that touch is Psychophysics - Psychophysics: a branch of psychology that measures the quantitative relation between physical stimuli and perceptual experience. The relation between the physical characteristics of a stimuli and the sensations they produce - Two methods to study perceptual phenomena: the just-noticeable difference and the procedures of signal detection theory The Principle of the Just-Noticeable Difference - Ernst Weber investigated the ability of humans to discriminate between various stimuli - Just-noticeable difference (jnd): the smallest change in the magnitude of a stimulus that a person can detect. Also called the difference threshold - The jnd is directly related to the magnitude of that stimulus - Weber Fractions: the ratio between a just-noticeable difference and the magnitude of a stimulus; reasonably constant over the middle range of most stimulus intensities - Gustav Fechner used Weber’s concept of the just-noticeable difference to measure people’s sensations. Assuming that the jnd was the basic unit of a sensory experience, he measured the absolute magnitude of a sensation in jnds - Fechner’s contribution to psychology was to show that a logarithmic function could be derived from Weber’s principle - S.S. Stevens suggested a power function to relate physical intensity to the magnitude of sensation. In mathematical notation, if S is the psychological magnitude of the sensation, and I is the intensity of the physical stimulus, then the function is: S = KI . - The symbol K stands for a mathematical constant that adjusts for the way physical intensity is measure. The important change is that the intensity (I) is raised to the power b - If b is between 0 and 1 (a fraction) the curve looks like Fechner’s, if b is greater than 1, the curve looks like Stevens’ power function - The power law provides a systematic way to compare different sensory systems Signal Detection Theory - Threshold: the point at which a stimulus, or a change in the value of a stimulus, can just be detected. A line between not perceiving and perceiving - Difference threshold: an alternative name for the just-noticeable difference (jnd). The minimal detectable difference between two stimuli - Absolute threshold: the minimum value of a stimulus that can be detected - Signal detection theory: a mathematical theory of the detection of stimuli, which involves discriminating a signal from the noise in which it is embedded and which takes into account participant’s willingness to report detecting the signal - Every stimulus event requires discrimination between signal (stimulus) and noise (consisting of both background stimuli and random activity of the nervous system) - Response bias, your tendency to say yes or no when you are not sure whether you detected the stimulus - According to the terminology of signal detection, hits are saying “yes” when the stimulus is presented, misses are saying “no” when it is presented, correct negatives are “no” when the stimulus is not presented, and false alarms are saying “yes” when the stimulus is not presented. Hits and correct negatives are correct responses; misses and false alarms are incorrect responses - A person’s response bias can seriously affect an investigator’s estimate of the threshold of detection. A person with a response bias to avoid false alarms will appear to have a higher threshold than will someone who does not want to let a tone go by without saying “yes” - Receiver operating characteristic curve (ROC curve): a graph of hits and false alarms of participants under different motivational conditions; indicates people’s ability to detect a particular stimulus - The signal detection method is the best way to determine a person’s sensitivity to the occurrence of a particular stimulus - Signal detection theory emphasizes that sensory experience involves factors others than the activity of the sensory systems, such as motivation and prior experience Vision Light - Light consists of radiant energy similar to radio waves. Radiant light oscillates as it is transmitted from its source - Wavelength: the distance between adjacent waves of radiant energy; in vision most closely associated with the perceptual dimension of hue - The wavelength of visible light ranges from 380 through 760 nm - Invisible to our eyes: ultraviolet radiation, x-rays, gamma rays, radar, radio waves - The entire range of wavelengths is known as the electromagnetic spectrum; the part our eyes that can detect is referred to as the visible spectrum The Eye and Its Functions - Each eye is housed in a bony socket and can be covered by the eyelid to keep dirt and dust out - The eyelids are edged by eyelashes, which helps keep foreign matter from falling into the open eye - The eyebrows prevent sweat on the forehead from dripping into our eyes - Reflex mechanisms provide additional protection: the sudden approach of an object towards the face or a touch on the surface of the eye causes automatic eyelid closure and withdrawal of the head - Cornea: the transparent tissue covering the front of the eye - Sclera: the tough outer layer of the eye; the “white” of the eye - Iris: the pigment muscle of the eye that controls the size of the pupil. Consists of two bands of muscles that control the amount of light admitted into the eye, and the brain controls these muscles, therefore regulates the size of the pupil, constricting it in bright light and dilating it in dim light - The space behind the cornea is filled with aqueous humour, which means “watery fluid”, a fluid that is produced by the tissues behind the cornea that filters the fluid from the blood. This fluid must circulate and be renewed, if this fluid is produced too quickly or if the passage that returns it to the blood becomes blocked, the pressure within the eye can increases and cause damage to vision - Lens: the transparent organ situated behind the iris of the eye; helps focus an image on the retina - The shape of the cornea is fixed but the lens is flexible; a special set of muscles can alter its shape so that the eye can obtain images of either nearby or distant objects. This change in the shape of the lens to adjust for distance is called accommodation - People whose eyes are too long (front to back) are said to be nearsighted; they need to a concave lens to correct the focus - People whose eyes are too short are said to be farsighted; they need a convex lens - Retina: the tissue at the back inside surface of the eye that contains the photoreceptors and associated neurons. Performs the sensory functions of the eye - Photoreceptors: a receptive cell for vision in the retina; a rod or a cone. Specialized neurons that transduce light into neural activity - The information from the photoreceptors is transmitted to neurons that send axons toward one point at the back of the eye - the optic disc - Optic disc: a circular structure located at the exit point from the retina of the axons of the ganglion cells that form the optic nerve - All axons leave the eye at this point and join the optic nerve which travels to the brain - Johannes Kepler is credited with the suggestion that the retina, not the lens, contain the receptive tissue of the eye - Christopher Scheiner demonstrated that the lens is simply a focusing device - The retina has three principal layers: light passes successively through the ganglion cell layer (front), the bipolar cell layer (middle), and the photoreceptor layer (back) - Photoreceptors respond to light and pass the information on by means of a neurotransmitter to the bipolar cells, the neurons which they form synapses - Bipolar cells transmit this information to the ganglion cells, neurons whose axons travel across the retina through the optic nerves - Visual information path: photoreceptor -> bipolar cells -> ganglion cells -> brain - The human retina contains two general types of photoreceptors: rods and cones - Rod: a photoreceptor that is very sensitive to light but cannot detect changes in hue - Cone: a photoreceptor that is responsible for acute daytime vision and for colour perception - Fovea: a small pit near the centre of the retina containing densely packed cones; responsible for the most acute and detailed vision - Farther away from the fovea, the number of cones decreases and the number of rods increases - A ganglion cell that receives information from so many rods is sensitive to very low light levels - Rods are responsible for our sensitivity to dim light but because many of them from different areas connect to just one ganglion cell, visual information they provide lacks sharpness Transduction of Light by Photoreceptors - A molecule derived from vitamin A is the central ingredient in the transduction of the energy of light into neural activity - Photopigment: a complex molecule found in photoreceptors; when struck by light, it splits and stimulates the membrane of the photoreceptor in which it resides - The photoreceptors of the human eye contain four kinds of photopigment (one for rods, and three of cones) but their basic mechanism is the same - When a photon strikes a photopigment, the photopigment splits into two constituent molecules. This events starts the process of transduction. The splitting of the photopigment causes a series of chemical reactions that stimulate the photoreceptor and causes it to send a message to the bipolar cell with which it forms a synapse. The bipolar cell sends a message to the ganglion cell, which then sends one on to the brain - Rhodopsin: the photopigment contained by rods (pink) - Once the photopigments are split by light, they lose their colour - Franz Boll discovered this when he removed an eye from an animal and pointed it toward a window that opened onto a brightly opened scene. He then examined the retina under dim light and found that the image of the scene was still there. The retina was pink when little light had fallen and pale when the image had been bright - After the light cause the photopigment to split and become bleached, energy from the photoreceptor’s metabolism causes the two molecules to recombine - The number of unbleached molecules of photopigments depend on the relative rate at which they are being split by light and being put back together by the cell’s energy. The brighter the light, the more bleached photopigments are Adaptation to Light and Dark - The detection of light requires that the photons split molecules of rhodopsin or one of the other photopigments - Dark adaptation: the process by which the eye becomes capable of distinguishing dimly illuminated objects after going from a bright area to a dark one Eye Movements - Our eyes are never at rest, even when our gaze is fixed on a particular place called the fixation point - Our eyes make fast, aimless, jittering movements, and they also make slow movements away from the target they are fixed on, which are terminated by quick movements that bring the image of the fixation point back to the fovea - Riggs, Ratliff, Cornsweet devised a way to project stabilized images onto the retina - images that remain in the same location on the retina - The disappearance of stabilized images suggests that elements of the visual system are not responsive to an unchanging stimulus - The photoreceptors or the ganglion cells or both, cease to respond to a constant stimulus. The small, involuntary movements of our eyes keeps the image moving and thus keep the visual system responsive to the details of the scene before us. Without these movements, our vision would become blurry after we fixate our gaze on a single point and our eyes became still - The eyes can also make three types of “purposive” movements: vergence movements, saccadic movements, and pursuit movements - Vergence movements: the co-operative movement of the eyes, which ensures that the image of an object falls on identical portions of both retinas. Assist in depth perception - the perception of distance - Saccadic movements: the rapid movement of the eyes that is used in scanning a visual scene, as opposed to the smooth pursuit movements used to follow a moving object. Enhances the McCollough effect - Pursuit movements: the movement that the eye makes to maintain an image of a moving image upon the fovea Colour Vision - Light of different wavelengths gives rises to sensations of different colours - There are three different types of cones in the human eye each containing a different type of photopigment. Each type of photopigment is most sensitive to light of a particular wavelength. That is, light of a particular wavelength causes a particular photopigment to split. Thus, different types of cones are stimulated by different wavelengths of light. Information from the cones enables us to perceive colours The Dimensions of Colour - Colours can be described in terms of three physical dimensions: wavelength, intensity, and purity; and three perceptual dimensions: hue, brightness, and saturation - Hue: a perceptual dimension of colour, most closely related to the wavelength of a pure light - Brightness: a perceptual dimension of colour, most closely related to the intensity or degree of radiant energy emitted by a visual stimulus - Saturation: a perceptual dimension of colour, most closely related with the purity of a colour. A fully saturated colour consists of light of only one wavelength. Desaturated colours look pastel or washed out - White light is completely desaturated; no single wavelength is dominant - If we begin with light of a single wavelength and then mix in a little amount of pure light, we will have reduced the saturation of that colour Colour Mixing - Vision is a synthetic sensory modality. It synthesis (puts together) rather than analyzes (takes apart) - When two wavelengths are present, we see an intermediate colour rather than the two components - Colour mixing: the perception of two or more lights of different wavelengths seen together as light of an intermediate wavelength - Mixing two beams of light of different wavelengths always yields a brighter colour Colour Coding in the Retina - Thomas Young noted that the human visual system can synthesize any colour from various amounts of almost any set of three colours of different wavelengths - Trichromatic theory: the theory that colour vision is accomplished by three types of photoreceptors, each of which is maximally sensitive to a different wavelength of light. Pure blue, green, and red - Ewald Hering noted that the four primary hues appeared to belong to pairs of opposing colours: red/green and yellow/blue. Hering was wrong! - Two types of ganglion cells encode colour vision: red/green cells and yellow/blue cells. Both types of ganglion cells fire at a steady rate when they are not stimulated. - The brain learns about the presence of red or green light by the increased or decreased rate of firing of axons attached to red/green ganglions cells. Same works for the yellow/blue cells - Opponent process: the representation of colours by the rate of firing of two types of neurons: red/green and yellow/blue - The retina contains red/green and yellow/blue ganglion cells because of the nature of the connections betweens the cones, bipolar cells, and ganglion cells. The brains detects the various colours by comparing the rates of firing of the axons in the optic nerve that signal red or green and yellow or blue. We cannot perceive a reddish green or bluish yellow because: an axon that signals red or green (or yellow or blue) can either increase or decrease its rate of firing. It cannot do both at the same time. A reddish green would have to be signaled by a ganglion cell firing slowly and rapidly at the same, which is obviously impossible Negative Afterimages - Negative Afterimage: the image seen after a portion of the retina is exposed to an intense visual stimulus; a negative afterimage consists of colours complementary to those of the physical stimulus - Complementary colours are those that make white when added together - The most important cause of negative afterimage is the adaptation to the rate of firing of retinal ganglion cells. When ganglion cells are excited or inhibited for a prolonged period of time, they later show a rebound effects, firing faster or slower than normal Defects in Colour Vision - Males are more affected with colour blindness because many of the genes for producing photopigments are located on the X chromosome, and because males have only one X chromosome, a defective gene there will always be expressed - Protanopia: a form of hereditary anomalous colour vision; caused by defective “red” cones in the retina. Their red cones are filled with green photopigment. To a protanope, red looks much darker than green - Deuteranopia: a form of hereditary anomalous colour vision; caused by defective “green” cones in the retina. Green cones are filled with red photopigment - Tritanopia: a form of hereditary anomalous colour vision; caused by a lack of “blue” cones in the retina. Tritanopes sees the world in greens and reds; to them, a clear blue sky is bright green, and yellow looks pink Audition Sound - Sound consists of rhythmical pressure changes in air. As an object vibrates, it causes the air around it to move - When the object is in the phase of vibration it moves towards you, it compresses molecules of air; as it moves away, it pulls the molecules of air apart. As a pressure wave arrives at your ear, it bends your eardrum in. The following wave of negative pressure causes your eardrum to bulge out - Hertz (Hz): the primary measure of the frequency of vibration of sound waves; cycles per second - Sound waves can vary in intensity and frequency, these variations produce corresponding changes in sensations of loudness and pitch - Timbre corresponds to the complexity of the sound vibration The Ear and Its Functions - Pinna: the flesh-covered cartilage attached to the side of the head. It helps funnel sound through the ear canal toward the middle and inner ear - The eardrum is a thin, flexible membrane that vibrates back and forth in response to sound waves and passes these vibrations on to the receptor cells in the inner ear - The eardrum is attached to the first of a set of three middle ear bones called the ossicles - Ossicles: one of the three bones of the middle ear (the hammer, anvil, and stirrup) that transmit acoustical vibrations from the eardrum to the membrane behind the oval window of the cochlea - These three bones acts together, in lever fashion, to transmit the vibrations of the eardrum to the fluid filled structure of the inner ear that contains the receptive organ - Cochlea: a snail-shaped chamber set in bone in the inner ear, where auditory transduction takes place. It is filled with liquid. - A bony chamber attached to the cochlea contains two openings, the oval window and the round window - The last of the three ossicles (the stirrup) presses against a membrane behind an opening in the bone surrounding the cochlea called the oval window - Oval window: a opening in the bone surrounding the cochlea. The stirrup presses against a membrane behind the oval window and transmits sound vibrations into the fluid of within the cochlea - The cochlea is divided into three chambers by two membranes, one of which is the basilar membrane - Basilar membrane: one of two membranes that divide the cochlea of the inner ear into three components; the receptive organ for audition resides here. - As the footplate of the stirrup presses back and forth against the membrane behind the oval window, pressure changes in the fluid above the basilar membrane cause the basilar membrane to vibrate back and forth. Because the basilar membrane varies in width and flexibility, different frequencies of sound cause different parts of the basilar membrane to vibrate - High-frequency sounds cause the end near the oval window to vibrate, medium- frequency sounds cause the middle to vibrate, and low-frequency sounds cause the tip to vibrate - The basilar membrane can vibrate freely only if the fluid in the lower chamber of the cochlea has somewhere to go - Round Window: an opening in the bone surrounding the cochlea. Movements of the membrane behind this opening permit vibrations to be transmitted through the oval window into the cochlea. Provides free space - When the basilar membrane flexes down, the displacement of the fluid causes the membrane behind the round window to bulge out. In turn, when the basilar membrane flexes up, the membrane behind the round window bulges in - Auditory hair cells: the sensory neuron of the auditory system; located on the basilar membrane. Transduce mechanical energy caused by the flexing of the basilar membrane into neural activity - Cilia: a hair-like appendage of a cell; involved in movement or in transducing sensory information. Cilia are found on the receptors in the auditory and vestibular systems - Tectorial membrane: a membrane located above the basilar membrane; serves as a shelf against which the cilia of the auditory hair cells move - When sound vibrations cause the basilar membrane to flex back and forth, the cilia are stretched. This pull on the cilia is translated into neural activity - When a mechanical force is exerted on the cilia of the auditory hair cells, the electrical charge across the membrane is altered - Pressure on the cilia is known to increase calcium flow into the hair cells Detecting and Localizing Sounds in the Environment - Sounds can differ in loudness, pitch, and timbre. They also have sources; they come from particular locations Loudness and Pitch - Axons cannot fire rapidly enough to represent the high frequencies that we can hear - Sounds of different frequencies stimulate different groups of auditory hairs cells located along the basilar membrane - The brain is informed of the pitch of a sound by the activity of different sets of axons from the auditory nerve - When medium-frequency sound waves reach the ear, the middle of the basilar membrane vibrates, and auditory hair cells located in this region are activated. In contrast, high-frequency sounds activates auditory hair cells located at the base of the basilar membrane near the oval window - Two kinds of evidence indicate that pitch is detected in this way: 1. direct observation of the basilar membrane has shown that the region of maximum vibration depends on the frequency of the stimulating tone. 2. experiments have found that damage to specific regions of the basilar membrane causes loss of the ability to perceive specific frequencies - Kiang recorded the electrical activity of single axons in the auditory nerve and found many that responded to particular frequencies. Presumably, these axons were stimulated by hair cells located on different regions of the basilar membrane - Frequencies lower than 200 Hz cause the very tip of the basilar membrane to vibrate in synchrony with the sound waves. Neurons that are stimulated by hair cells located there are able to fire in synchrony with these vibrations, thus firing at the same frequency as the sound - The axons of the cochlear nerve appear to inform the brain of the loudness of a stimulus by altering the rate of firing - More intense vibrations stimulate the auditory cells more intensely. This stimulation causes them to release more neurotransmitter, which results in a higher rate of firing by the axons in the auditory nerve - Pitch is signaled by which neurons fire, and loudness is signaled by their rate of firing - However, the neurons that signal lower frequencies do so with their rate of firing. If they fire more frequently, they signal a higher pitch by the same means - The loudness of low-frequency sounds is signaled by the number of auditory hair cells that are active at a given time. A louder sound excited a larger number of hair cells Timbre - The enormous variety of sounds we can distinguish is due to a characteristic called timbre - The combining, or synthesis, of two or more simple tones, each consisting of a single frequency, can produce a complex tone - Complex sounds that have a regular sequence of waves can be reduced by means of analysis into several simple tones - We can distinguish sounds because of unique sets of simple tones called harmonics - Harmonics: a component of a complex tone; one of a series of tones whose frequency is a multiple of the fundamental frequency. In music theory, also known as an overtone - Fundamental frequency: the lowest, and usually most intense, frequency of a complex sound; most often perceived as the sound’s basic pitch - Timbre: a perceptual dimension of sound, determined by the complexity of the sound. The distinctive combination of harmonics with the fundamental frequency - The fundamental frequency causes one part of the basilar membrane to flex, while each of the harmonics cause another portion to flex - During a complex sound, many different portions of the basilar membrane are flexing simultaneously - Information about the fundamental frequency and each of the harmonics is sent to the brain through the auditory nerve, and the person hears a complex tone having a particular timbre - The task of the auditory system in identifying particular sound sources is one of pattern recognition - The auditory system must recognize that particular patterns of constantly changing activity received from the hair cells on the basilar membrane belong to different sound sources Locating the Source of a Sound - Relative loudness is the most effective means of perceiving the location of high- frequency sounds - Low-frequency sounds can easily make a large solid object vibrate, setting the air on the other in motion and producing a new sound across the barrier. But large, solid objects cannot vibrate rapidly, so they effectively damp out high-frequency sounds - The second method involves detecting differences in the arrival time of the sound pressure waves at each ear drum. This method works best with frequencies below 3000 Hz. A 1000 Hz tone produces pressure waves approximately 0.3m apart. Because the distance between a person’s eardrums is somewhat less than half of that, a source of 1000 Hz sound located to one side of the head will cause one eardrum to be pushed in while the other eardrum is pulled out. If the source of the sound is directly in front of the listener, both eardrums will move in synchrony - When the source of the sounds is located to the side of the head, axons in the right and left auditory nerves will fire at different times - The brain detects this disparity, which causes the sound to be perceived as off to one side - The easiest stimuli to locate are those that produce brief clicks, which cause brief bursts of neural activity - Initial processing occurs in the brain stem in a region known as the superior olive - Stimulation involving different temporal discrepancies activates different regions of the but these areas do not have a simple relationship of sectors within this region to locations of sounds in space - Spatial location in general is processed widely in the auditory cortex. But when the location concerns a particular object, it is processed in an area close to the parietal lobe Age-Related Losses in Hearing - An important capacity in hearing is our ability to use background information to process a sound - Under laboratory conditions, if you are trying to hear a tone against some background noise, your threshold is better if the noise goes to both ears than to one. The difference is called the masking-level difference (MLD) - Other age-related changes concern loss of sensitivity to different bands of frequencies Gustation - We have two senses specialized for detecting chemicals in our environment: taste and smell. Together they are referred to as chemosenses - Chemosenses: one of the two sense modalities (gustation and olfaction) that detent the presence of particular molecules present in the environment - Taste, or gustation, is not the same as flavour (includes its odour, texture, and touch as well as its taste) Receptors and the Sensory Pathway - Papilla: a small bump on the tongue that contains a group of taste buds - Taste bud: a small organ on the tongue that contains a group of gustatory receptor cells - The cells have hair-like projections called microvilli that protrude through the pore of the taste bud into the saliva that coats the tongue and fills the trenches of the papillae - Molecules of chemical dissolved in the saliva stimulate the receptor cells by interacting with the special receptors on the microvilli The Five Qualities of Taste - Five qualities: sourness, sweetness, saltiness, bitterness, and umami - Umami refers to the taste of monosodium glutamate - These five qualities arise when different molecules stimulate different types of receptors - Salty taste is due to sodium chloride - Both bitter and sweet substances seem to consist of large, non-ionizing molecules - Function of bitterness is to avoid ingesting poisons - Sour tastes are produced by acids Olfaction - The sense of smell - The olfactory system sends information to the limbic system, a part of the brain that plays a role in both emotions and memories - Pheromones: chemical signals, usually detected by smell or taste, that regulate reproductive and social behaviours between animals. The second olfactory system, “the accessory olfactory system” Anatomy of the Olfactory System - Olfactory mucosa: the mucous membrane lining the top of the nasal sinuses; contains the cilia of the olfactory receptors - They also have axons that pass through small holes in the bone above the olfactory mucosa and form synapses with neurons in the olfactory bulbs - Olfactory bulbs: stalk-like structure located at the base of the brain that contain neural circuits that perform the first analysis of olfactory information - When a molecule of an odorous substance fits a receptor molecule located on the cilia of a receptor cell, the cell becomes excited. This excitation is passed on to the brain by the axon of the receptor cell. Thus, similar mechanisms may detect the stimuli for taste and olfaction - Olfactory information is sent directly to several regions of the limbic system - to the amygdala and to the limbic cortex of the frontal lobe The Dimensions of Odour - We can use such a relatively small number of receptors to detect so many different odorants because a particular odour binds to more than one receptor. Thus, the brain receives signals from several receptors. Recognizing a particular odour is a matter of recognizing a particular pattern of activity - The brain recognizes particular odours by recognizing different patterns of activation that it receives from the olfactory bulbs The Somatosenses - Bodily sensations; sensitivity to such stimuli as touch, pain, and temperature The Skin Senses - The entire surface of the human body is innervated (supplied with nerve fibres) by the dendrites of neurons that transmit somatosensory information to the brain - Cranial nerves convey information from the face and front portion of the head; spinal nerves convey information from the rest of the body’s surface - All somatosensory information is detected by the dendrites of neurons; the system uses no separate receptor cells. However, some of these dendrites have specialized ending that modify the way they transduce energy into neural activity - Free nerve ending: a dendrite of somatosensory neurons. They infiltrate the middles layers of both smooth and hairy skin and surround the hair follicles in hairy skin - Pacinian corpuscle: a specialized somatosensory nerve ending that detects mechanical stimuli, especially vibrations Touch and Pressure - Touch is defined as the sensation of very light contact of an object with the skin, and pressure as the sensation produced by more forceful contact - Sensations of pressure occur only when the skin is actually moving (being pushed in), which means that the pressure detectors respond only while they are being bent - Two-point discrimination threshold: the minimum distance between two small points that can be detected as separate stimuli when pressed against a particular region of the skin Temperature - So far we know of six thermoreceptors - One of these which is sensitive to ranges of temperatures close to body temperate is found in the anterior hypothalamus, the region of the body that is responsible for measuring and maintaing our body temperature - Some of the thermal receptors respond to particular chemicals as well as to changes in temperatures Pain - Pain is accomplished by the networks of free nerve endings in the skin - There appear to be at least three types of pain receptors (usually referred to as “nociceptors”) - High-threshold mechanoreceptors are free nerve endings that respond to intense pressure, or pinching to the skin - A second type of free nerve ending appears to respond to extremes of heat, to acids, and to the presence of capsaicin, the active ingredients in chili peppers - Another type of nociceptor contains receptors that are sensitive to ATP, a chemical that serves as an energy source in all cells of the body. ATP is also released when the blood supply to a region of the body is disrupted or when a muscle is damaged - Pain is a complex sensation involving not only intense sensory stimulation but also an emotional component. That is, a given sensory input to the brain might be interpreted as pain in one situation and as pleasure in another - The sensation of pain is quite different from the emotional reaction to pain. Opiates such as morphine diminish the sensation of pain by stimulating opioid receptors on neurons in the brain; these neurons block the transmission of pain information to the brain. Tranquilizers depress neural systems that are responsible for the emotional reaction to pain but do not diminish the intensity of the sensation - Prefrontal lobotomy blocks the emotional component of pain by does not affect the primary sensation - Many noxious stimuli stimuli elicit two kinds of pain: an immediate sharp or bright pain followed by a deep, dull, sometimes throbbing pain. Some stimuli elicit only one of these two kinds of pain - Phantom Limb: sensations that appear to originate in a limb that has been amputated - Melzack suggests that the phantom limb sensation is inherent in the organization of the parietal cortex (involved in our awareness of our own bodies) The Internal Senses - Sensory endings located in our internal organs, bones, joints, and muscles convey painful, neutral, and in some cases pleasurable sensory information - Muscles contain special sensory endings. One class of receptors located at the junction between muscles and the tendons that connect them to the bones, provides information about the amount of force the muscle is exerting - Another set of stretch detectors consist of spindle-shaped receptors distributed throughout the muscle - Muscle spindle: a muscle fibre that functions a stretch receptor; arranged parallel to the muscle fibres responsible for contraction of the muscle, it detects the muscle length The Vestibular Senses - The receptive organs of the inner ear that contribute to balance and perception of head movements - Semicircular canal: one of a set of three organs in the inner ear that respond to rotational movements of the head - These canals contain a liquid. Rotation of the head makes the liquid flow, stimulating the receptor cells located in the canals - Vestibular sac: one of a set of two receptor organs in each inner ear that detect changes in the tilt of the head. Contain crystals of calcium carbonate that are embedded in a gelatin-like substance attached to receptive hair cells. In one sac, the receptive tissue is on the wall; in the other, it is on the floor. When the head tilts, the weight of the calcium carbonate crystals shifts, producing different forces on the cilia of the hair cells. These forces change the activity of the hair cells, and the information is transmitted to the brain. However, they must also be coordinated with information from the semicircular canals - The vestibular sacs are very useful in maintaining an upright head position. They also participate in a reflex that enable us to see clearly even when the head is being jarred. When we walk, our eyes are jostled back and forth. The jarring of the head stimulates the vestibular sacs to cause reflex movements of the eyes that partially compensate for the head movements CHAPTER 6: PERCEPTION - Perception: a rapid, automatic, unconscious process by which we recognize what is represented by the information provided by our sense organs Brain Mechanisms of Visual Perception - Visual perception by the brain is often described as a hierarchy of information processing. Circuits of neurons analyze particular aspects of visual information and send the results of their analysis to another circuit, which performs further analysis - The higher levels of the perceptual process interacts with memories: the viewer recognizes familiar objects and learns the appearance of new, unfamiliar ones The Primary Visual Cortex - The surface of the retina is “mapped” on the surface of the primary visual cortex. However, this map on the brain is distorted, with the largest amount of area given to the centre of the visual field, where our vision is most precise - Module: a block of cortical tissue that receives information from the same group of receptor cells - Because each module in the primary visual cortex receives information from a small region of one retina, this means it receives information from a small region of the visual cortex - the scene that is currently projected onto the retina - Hubel and Wiesel found that neural circuits within each module analyzed various characteristics of their own particular part of the visual field - that is, of their receptive field - Receptive field: that portion of the visual field in which the presentation of visual stimuli will produce an alternation in the firing rate of a particular neuron The Visual Association Cortex Two Streams of Visual Analysis - Visual information analyzed by the primary visual cortex is further analyzed in the visual association cortex - Circuits of neurons analyze particular aspects of visual information and send the results of their analysis to the other circuits, which perform further analysis - At each step in the process, successively more complex features are analyzed. Within a matter of milliseconds, the process leads to the perception of scene and objects in it. the higher the levels of the perceptual process also interact with memories. The viewer learns to recognize familiar objects and learns to recognize new, unfamiliar ones - Neurons in the primary visual cortex send axons to the region of the visual association cortex that surrounds the striate cortex - The visual association cortex divides into two pathways: the ventral stream and the dorsal stream. - Ventral stream: the flow of information from the primary visual cortex to the visual association area in the lower temporal lobe; used to form the perception of object’s shape, colour, and orientation (the “what” system) - Dorsal stream: the flow of information from the primary visual cortex to the visual association area in the parietal lobe; used to form the perception of an object’s location in three-dimensional space (the “where” system), also determines if the object is moving The Ventral Stream: Perception of Form - Takes place in inferior temporal lobe, located at the end of the ventral stream. It is there that analyses of form and colour are put together and perceptions of three- dimensional objects emerge - Visual agnosia: the inability of a person who is not blind to recognize the identity of an object visually; caused by damage to the visual association cortex - Prosopagnosia: a form of visual agnosia characterized by difficulty in the recognition of people’s faces; caused by damage to the visual association cortex - Fusiform face area (FFA): a region of the ventral stream of the visual system that contains face-recognition circuits - Extrastriate body area (EBA): a region of the occipital cortex, next to the primary visual cortex, that responds to forms resembling the human body. (photographs, silhouettes, or stick figures) - Parahippocampal place area (PPA): a region of the ventral stream, below the hippocampus, that is activated by visual scenes The Ventral Stream: Perception of Colour - Individual neurons in a region of the ventral stream respond to particular colours, which suggests that this region is involved in combining the information from red/green and yellow/blue signals that originate in retinal ganglion cells - Lesions of a particular region of the human ventral stream can also cause loss of colour vision without disrupting visual acuity - Cerebral achromatopsia: the inability to discriminate among different hues; caused by damage to the visual association cortex The Dorsal Stream: Perception of Spatial Location - The parietal lobe receives visual, auditory, somatosensory, and vestibular information and is involved in spatial and somatosensory perception - Damage to the parietal lobe disrupts performance on a variety of tasks that require (a) perceiving and remembering the location of objects, and (b) controlling the movement of the eyes and the limbs. The end of the dorsal stream is located in the posterior parietal cortex - Neurons in the dorsal system are involved in visual attention and control of eye movements, the visual control of reaching and pointing as well as the visual control of grasping and other hand movements, and the perception of depth - The function of the dorsal stream is captured better by the notion of how rather than where should not imply an absence of the capacity to recognize spatial location The Dorsal Stream: Perception of Movement - The region of the brain that contains neurons that respond differentially to movement is located in the extrastriate cortex, which surrounds the primary visual cortex - Akinetopsia: an inability to see motion Form from Motion - Perception of movement can even help us perceive three-dimensional forms, a phenomenon known as form from motion - Johansson demonstrated how much information we derive from movement - Form from motion involves brain mechanisms different from those involved in the perception of object Visual Perception of Object Figure and Ground - Objects are things that have particular shapes and particular locations in space - Backgrounds are essentially formless and serve mostly to help us judge the location of objects we see in front of them - Figure: a visual stimulus that is perceived as a self-contained object - Ground: a visual stimulus that is perceived as a formless background against which objects are seen - One of the most important aspects of form perception is the existence of a boundary Gestalt Laws of Perceptual Organization - Gestalt psychology: a branch of psychology that asserts that the perception of objects is produced by particular configuration of the elements of stimuli - They argued that the whole is more than the sum of its parts. Because of the characteristics of the visual system of the brain, visual perception cannot be understood simply by analyzing the scene into elements. Instead, what we see depends on the relationships of the elements to one another - Law of proximity: a Gestalt law of organization; elements located closest to each other are perceived as belonging to the same figure - Law of similarity: a Gestalt law of organization; similar elements are perceived as belonging to the same figure - Good continuation: a Gestalt law of organization; given two or more interpretations of elements that form the outline of the figure, the simplest interpretation will be preferred - Law of closure: a Gestalt law of organization; elements missing form the outline of a figure are “filled in” by the visual system - Law of common fate: a Gestalt law of organization; elements that move together give rise to the perception of a particular figure Models of Pattern Perception Templates and Prototypes - Our ability to recognize shapes of objects might be explained by our use of templates - Templates: a hypothetical pattern that resides in the nervous system and is used to perceive objects or shapes by a process of comparison - A more feasible model of pattern perception suggests that patterns of visual stimulation are compared with prototypes rather than templates - Prototypes: a hypothetical idealized pattern that resides in the nervous system and is used to perceive objects or shapes by a process of comparison recognition can occur even when an exact match is not found Distinctive Features - Psychologists suggest that the visual system encodes images of familiar patterns in term of distinctive features - Distinctive features: a physical characteristics of an object that helps distinguish it from other objects - The visual system first identifies the component features of an object and then adds up the features to determine what the object is Bottom-Up and Top-Down Processing: The Role of Context - Context helps us easily recognize objects - Bottom-up processing: a perception based on successive analyses of the details of the stimuli that are present - Top-down processing: a perception based on information provided by the context in which a particular stimulus is encountered Perceptual (“What”) and Action (“Where”) Systems: A Possible Synthesis - The “what” system provides us with information about objects and their meanings and involves pathways that lead to the temporal lobe (the ventral stream) - The “where” system provides us with information necessary for acting on objects with guided movement and involves pathways leading through the parietal lobe (the dorsal stream) - The dorsal stream system provides information necessary for guiding our actions towards objects but does not provide us with the ability to recognize or name them - The dorsal stream responds to the location and orientation of objects and coordinates the actions we take with respects to them - The ventral stream gives us information about what the objects are so that we know, for example, that it will take less less effort to turn a page than it will to turn the cover of a books - Principle of linguistic relativity: the hypothesis that the language a person speaks determines his or her thoughts and perceptions Visual Perception of Space and Motion Depth Perception - Requires that we perceive the distance of objects in the environment from us and from each other - We do this by two kinds of cues: binocular (“two-eye”) and monocular (“one-eye”) - Binocular cues: cues to distance that depend on input from two eyes - Monocular cues: cues to distance the depend on input from only one eye Binocular Cues - An important cue about distance is supplied by convergence - Convergence: the result of vergence eye movements whereby the fixation point for each eye is identical; feedback from these movements provides information about the distance of objects from the viewer - Another important factor in the perception of distance is the information provided by retinal disparity - Retinal disparity: the fact that points on objects located on different distances from the observer will fall on slightly different locations on the two retinas; provides the basis for stereopsis, one of the forms of depth perception - Stereopsis: a form of depth perception based on retinal disparity Monocular Cues - One of the most important sources of information about relative distance of objects is interposition - Interposition: a monocular cue of depth perception; an object that partially blocks another object is perceived as closer - Just as the Gestalt law of good continuation plays a role in form perception, the principle of good form affects or perception of the relative location of objects: We perceive the objective having the simpler border as being closer - Another important monocular cue is provided by our familiarity with the sizes of objects - Linear perspective: a monocular cue of depth perception; the arrangement or drawing of objects on a flat surface such that parallel lines receding from the viewer are seen to converge at a point on the horizon - Texture: a monocular cue of depth perception; the fineness of detail present in the surfaces of objects or in the ground or floor of a scene - Haze: a monocular cue of depth perception; objects that are less distinct in their outline and texture are seen as farther away from the viewer - Shading: a monocular cue of depth perception; determines whether portions of the surface of an object are perceived as concave or convex - Elevation: a monocular cue of depth perception; objects nearer the horizon are seen farther from the viewer - Another important source of distance information depends on our own movements - Head and body movements cause the images from the scene before us change; the closer the object, the more it changes relative to the background. The information contained in this relative movement helps us perceive distance - Motion parallax: a monocular cue of depth perception. As we pass by a scene, objects closer to us pass in front of objects farther away Constancies of Visual Perception - Repeated exposure to a particular set of objects may allow us eventually to classify them accurately despite dramatic differences in the sensory information they produce - Perceptual constancy: a mechanism that maintains a perceptual judgement as the external stimulus changes Perception of Motion - We are capable of seeing what is moving in our environment and can detect the direction in which it is moving Adaptation and Long-Term Modification - One of the most important characteristic of all sensory systems is that they show adaptation and rebound effects - A study by Ball and Sekuler suggests that even the long-term characteristics of the system that detects movement can be modified by experience Interpretation of a Moving Retinal Image - Perception of movement requires coordination between movements of the image on the retina and those of the eyes Combining Information from Vision and Audition - Space and movement, however, often involve sounds - Doppler effect, which an approaching sound, like that of an oncoming train, increases in frequency - Changes in both pitch and loudness are therefore good cues to whether a sound is coming toward you - We have two spatial channels for sound localization: one to each side, with about 30 degrees of overlap on each side of the point directly in front of us - Ventriloquism effect: an apparent shift in location of a sound from its auditory source to its perceived visual location - What leads us, for example, to think that the squeaky voice is coming from the ventriloquist’s dummy rather than from the human beside him? This is issue is sometimes called “the binding problem” - When combining auditory and visual perceptions of space, the brain must connect these two sources of sensory input Perception of Movement in the Absence of Motion - Phi phenomenon: the perception of movement caused by the turning on of two or more lights, one at a time, in sequence; often used on theatre marquees; responsible for the apparent movement of images in movies and television CHAPTER 7: LEARNING AND BEHAVIOUR - Our behaviour is changeable in response to certain experiences - Learning: an adaptive process in which the tendency to perform a particular behaviour is changed by experience - Learning cannot be observed directly; it can only be inferred from changes in behaviour - Experiences alters the structure and chemistry of the brain. These alterations affect how the nervous system responds to subsequent events - Performance: the behavioural change produced by the internal changes brought about by learning - Performance is the evidence that learning has occurred Habituation - Orienting response: any response by which an organism directs appropriate sensory organs (eyes, ears, nose) toward the source of a novel stimulus - Habituation: the simplest form of learning; learning not to respond to an unimportant event that occurs repeatedly - Habituation makes sense from an evolutionary perspective. If a once-novel stimulus occurs again and again without any important result, the stimulus has no significance to the organism - The simplest form of habituation is temporary, and is known as short-term habituation - Animals, particularly those with more complex nervous systems, are capable of long- term habituation - What distinguishes short term from long term habituation? The pattern of experience plays a role. When stimuli are massed into quick repetitions, habituation is rapid but short term; when these stimuli are presented in small groups that are space in time, habituation is slower but long term Classical Conditioning - Classical conditioning involves learning about the conditions that predict that significant event will occur Pavlov’s Serendipitous Discovery - Classical Conditioning: the process by which a response normally elicited by one stimulus (the unconditional stimulus or UCS) comes to be controlled by another stimulus (the conditional stimulus or CS) as well - Classical conditioning provides us with a way to learn cause-and-effect relationships between environmental events - Unconditional stimulus (UCS): in classical conditioning, a stimulus, such as food, that naturally elicits a reflective response, such as salivation - Unconditional response (UCR): in classical conditioning, a response, such as salvation, that is naturally elicited by the UCS - Conditional stimulus (CS): in classical conditioning, a stimulus that, because of its repeated association with the UCS, eventually elicits a conditional response (CR) - Conditional response (CR): in classical conditioning, the response elicited by the CS The Biological Significance of Classical Conditioning - Pavlov’s experiment demonstrated that an innate reflexive behaviour, such as salivation, can be elicited by novel stimuli. Thus, a response that is naturally under the control of appropriate environmental stimuli, such as salivation cause by the presence of food in the mouth, can also come to be controlled by other kinds of stimuli - Classical conditioning accomplishes two functions: 1. the ability to learn to recognize stimuli that predict the occurrence of an important event that allows the learner to make the appropriate response faster and more effectively. 2. through classical conditioning, stimuli that were previously unimportant acquire some of the properties of the important stimuli with which they have been associated and thus become able to modify behaviour. A neutral stimulus becomes desirable when it is associated with a desirable stimulus or becomes undesirable when it is associated with an undesirable one - The stimulus takes on a symbolic value (e.g. a stack of money is more desirable due to things you could buy with money, than a stack of napkins) Basic Principles of Classical Conditioning Acquisition - In classical conditioning, the time during which a CR first appears and increases in frequency - Two factors that can influence the strength of the CR are the intensity of the UCS and the timing of the CS and UCS. This intensity of the UCS can determine how quickly the CR will be acquired: more intense UCSs usually produce more rapid learning - The more intense the UCS, the stronger the CR generally is - The second factor affecting the acquisition of the CR is the timing of the CS and UCS. Classical conditioning occurs fastest when the CS occurs shortly before the UCS and both stimuli end at the same time Extinction and Spontaneous Recovery - In classical conditioning the elimination of a response that occurs when the CS is repeatedly presented without being followed by the UCS - It is important to realize that extinction occurs only when the CS no longer signals the UCS - The participant must learn that the CS no longer predicts the occurrence of the UCS - and that it cannot happen if neither stimulus is presented - Spontaneous recovery: after an interval of time, the reappearance of a response that had previously been extinguished Stimulus Generalization and Discrimination - No two stimuli are exactly alike. Once a response has been conditioned to a CS, similar stimuli will also elicit that response. The more closely the other stimuli resemble the CS, the more likely it will elicit the CR - Generalization: in classical conditioning, CRs elicited by stimuli the resemble the CS used in training - An organism can be taught to distinguished between similar but different stimuli - Discrimination: in classical conditioning, the appearance of a CR when one stimulus is presented (the CS+) but not another (the CS-) - Discrimination training is accomplished by using two different CSs during training. One CS is always followed by the UCS; the other CS is never followed by the UCS - Discrimination involves learning the difference between two or more stimuli. An animal learns that differences among stimuli are important - it learns when to respond to one stimulus and when not to respond to a different stimulus Conditional Emotional Responses - Many stimuli are able to arouse emotional responses, such stimuli like a phrase or a song. Originally these stimuli had no special significance, however, because these stimuli were paired with other stimuli that elicited strong emotional reactions, they acquired emotional or evaluative significance - Classical conditioning may play a role in the development of personal likes and dislikes or in the emotional reaction to other stimuli - Phobias: unreasonable fear of specific objects or situations, such as insects, animals, or enclosed spaces, learned through classical conditioning - Classical conditioning can occur even without direct experience with the conditional and unconditional stimuli What is Learned in Classical Conditioning? - A neutral stimulus becomes a CS only when the following conditions are satisfied: 1. The CS regularly occurs prior to the presentation of the UCS 2. The CS does not regularly occur when the UCS is absent - The key factor in classical conditioning is the reliability of the CS in predicting the presentation of the UCS - Blocking: the prevention of or attenuation in learning that occurs to a neutral CS when it is conditioned in the presence of a previously conditioned stimulus - Classical conditioning would seem to provide two types of information: the what and the when of future events - The first type of information, the what, allows animals to learn that a particular event is about to occur. It has been said that their behaviour is determined by their memory of events - The second type of information, the when, is about the timing of events - Inhibitory conditional response: a response tendency conditioned to a signal that predicts the absence of the UCS; generally not observed directly by assessed through other tests - Excitatory conditional response: a response tendency conditioned to a signal that UCS is about to occur. This is the type of CR exemplified by Pavlov’s salivation response Operant Conditioning - A form of learning in which behaviour is affected by its consequences. Favourable consequences strengthen the behaviour and unfavourable consequences weaken the behaviour - When a particular action has good consequences, the action will tend to be repeated; when a particular action has bad consequences, the action will tend not to be repeated The Law of Effect - Thorndike discovered the operant conditioning - Law of effect: Thorndike’s idea that the consequences of a behaviour determine whether it is likely to be repeated - The law of effect determines which responses will survive and become part of an organism’s behavioural repertoire (similar to natural selection) - Stimulated the beginning of behaviour analysis Skinner and Operant Behaviour - Skinner championed the laboratory study of the law of effect and advocated the application of behaviour analysis and its methods to solving human problems - Operant chamber: an apparatus in which an animal’s behaviour can be easily observed, manipulated, and automatically recorded - Behaviour analysts manipulate environmental events to determine their effects on response rate, the number of responses emitted during a given amount of time. Events that increase response rate are said to strengthen responding; events that decrease response rate weaken responding - Cumulative recorder: a mechanical device connected to an operant chamber for the purpose of recording operant responses as they occur in time - Skinner’s development of the operant chamber and the cumulative recorder represent clear advances over Thorndike’s research methods because participants can (1) emit responses more freely over a greater time period, and (2) be studied for longer periods of time without interference produced by the researcher handling or otherwise interacting with them between trials The Three-Term Contingency - Discriminative stimulus: in operant conditioning, the stimulus that sets the occasion for responding because, in the past, a behaviour has produced certain consequences in the presence of that stimulus - The three-term contingency: the relation among discriminative stimuli, behaviour, and the consequences of that behaviour. A motivated organism emits a specific response in the presence of a discriminative stimulus because, in the past, that response has been reinforced only when the discriminative stimulus is present. The relationship among three items: the preceding event, the response, and the following event - The preceding event - the discriminative stimulus - sets the occasion for responding because, in the past, when that stimulus occurred, the response followed by certain consequences. If the phone rings, we are likely to answer it because we have learned that doing so has particular consequences - The response we make - in this case, picking up the phone and saying “Hello” when it rings - is called an operant behaviour - The following event - the voice on the other end of the line - is the consequence of the operant behaviour - In the presence of discriminative stimulus, a consequence will occur if and only if an operant behaviour occurs - Once an operant behaviour is established, it tends to persist whenever the discriminative stimulus occurs, even if other aspects of the environment changes Reinforcement, Punishment, and Extinction - Behaviour analysts study behaviour - environment interactions by manipulating the relations among components of the three-term contingency - Operant behaviour can be followed by five different kinds of consequences: positive reinforcement, negative reinforcement, punishment, response cost, and extinction Positive Reinforcement - an increase in the frequency of a response that is regularly and reliably followed by an appetitive stimulus - An appetitive stimulus is any stimulus that an organism seeks out - If an appetitive stimulus follows a response and increases the frequency of that response, we call it positive reinforcer - E.g. If you visit a restaurant and you really enjoy the food, you are likely to go there again. Your enjoyment of the food (the appetitive stimulus) reinforces your going to the restaurant and ordering dinner (the response) Negative Reinforcement - an increase in frequency of a response that is regularly and reliably followed by the termination of an aversive stimulus - An aversive stimulus is unpleasant or painful - If an aversive stimulus is terminated as soon as the response occurs and thus increases the frequency of that response, we call it negative reinforcer - E.g. If you walk barefoot on hot pavement, the termination of the painful sensation negatively reinforces your response of sticking your feet into a puddle of cool water - Both positive and negative reinforcement increases the likelihood that a given response will occur again. However the positive reinforcement involves the increase of an appetitive stimulus; and a negative reinforcement involves the termination of an aversive stimulus Punishment - is a decrease in the frequency of a response that is regularly and reliably followed by an aversive stimulus - If an aversive stimulus follows a response and decreases the frequency of that response, we call it a punisher - E.g. Receiving a painful bite would punish the response of sticking your finger into a parrot’s cage - Although punishment is effective in reducing or suppressing undesirable behaviour, it can also produce several negative side effects: - Unrestrained use of physical force may cause serious bodily injury - Punishment often induces fear, hostility, and other undesirable emotions in people receiving punishment. It may result in retaliation against the punisher - Through punishment, organisms learn only which response not to make. Punishment does not teach the organisms desirable responses - Reinforcement and punishment are most effective in maintaining or changing behaviour when a stimulus immediately follows the behaviour Response Cost - is a decreas
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