WEEK 4 & 5 Sensation and Perception PDF

WEEK 4 & 5 – SENSATION AND PERCEPTION SENSORY SYSTEMS Sensation – messages from the senses that make up the raw information that affects many kinds of behaviour and mental processes Perception – the process through which messages from the senses are given meaning. Sense – a system that translates in...

WEEK 4 & 5 – SENSATION AND PERCEPTION SENSORY SYSTEMS Sensation – messages from the senses that make up the raw information that affects many kinds of behaviour and mental processes Perception – the process through which messages from the senses are given meaning. Sense – a system that translates information from outside the nervous system into neural activity Senses respond to energy – eyes: light energy, ears: energy of sound, skin: energy of heat and pressure All of these senses respond to incoming stimulus energy, encode it in the form of nerve cell activity and send this coded information to the brain Transduction – the process of converting incoming energy into neural activity Neural receptors – specialised cells that detect certain forms of energy and transduce them into nerve cell activity. Where transduction occurs. Like neurons, neural receptors respond to incoming energy by firing an action potential that causes the release of neurotransmitters. Sensory adaptation – the process through which responsiveness to an unchanging stimulus decreases over time. Response to constant level of stimulation. For all senses except smell, sensory information entering the brain goes to the thalamus, then relays it to the appropriate sensory area of the cerebral cortex. Absolute threshold – the minimum amount of stimulus energy that can be detected 50 per cent of the time Subliminal stimulation – stimulation that is too weak or brief to be perceived Supraliminal stimulation – stimulation that is strong enough to be consistently perceived Psychophysics – focuses on the relationship between the physical characteristics of environmental stimuli and the psychological experiences those stimuli produce Topographical representations – features near eachother in the world stimulate neurons near eachother in the brain (eg. Two similar sounding noises) Sensitivity – the ability to detect a particular stimulus from a background of competing stimuli Webers law – a law stating that the smallest detectable difference in stimulus energy is a constant fraction of the intensity of the stimulus. This fraction is given the symbol ‘K’, the smaller the K is, the more sensitive a sense is to stimulus differences. Weber's Law says that the ability to notice a change in a stimulus depends on the size of the original stimulus. The bigger or stronger the original stimulus, the larger the change needs to be for a person to detect it. For example, adding a small weight to a heavy object is less noticeable than adding the same weight to a light object Magnitude estimation, Fechners Law - Constant increases in physical energy will produce progressively smaller increases in perceived magnitude. if just noticible differences get progressively larger as stimulus magnitude increases, then the amount of change in the stimulus required to double or triple its perceived intensity must get larger too. Eg. It would take a small increase in volume to make a soft sound seem twice as loud, but imagine how much additional volume it would take to make a rock band seem twice as loud. Sensory systems Aspects Processes Sense – a system that translates Encoding – translating the physical nformation from outside the nervous systemproperties of a stimulus into a pattern of nto neural activity nerve cell activity that specifically identifies Sensations – messages from the senses hose properties hat make up the raw information that affects many kinds of behaviour and mental processes Neural receptors – specialised cells that Transduction – the process of converting detect certain forms of energy and ncoming energy into neural activity ransduce them into nerve cell activity Sensory adaption – the process through which responsiveness to an unchanging stimulus decreases over time Psychophysics – an area of research Signal detection theory – a mathematical ocusing on the relationship between the model of how your personal sensitivity and physical characteristics of environmental response bias combine to determine your stimuli and the psychological experiences decision about whether or not a near hose stimuli produce hreshold stimulus occurred Judging differences – the just noticable difference (Webers Law) is the smallest difference between stimuli that we can detect Magnitude estimation – the perception of stimulus intensity is related to the actual strength (Fechners Law) QUESTIONS Humans are especially dependent on the touch, sight and hearing senses to get information about the world, we depend less on smell and taste Each sense gives us information about the world by responding to a specific kind of energy; for example, for vision, we respond to light HEARING Sound – a repetitive fluctuation in the pressure of a medium, such as air Amplitude - the difference between the peak and the baseline of a waveform, intensity Wavelength - the distance from one peak to the next in a waveform Frequency - the number of complete waveforms/cycles that pass a given point in space every second, described in units called hertz. One cycle per second is one hertz PSYCHOLOGICAL DIMENSIONS OF SOUND Loudness (like amplitude)– a psychological dimensions of sound determined by the amplitude of a sound wave Pitch (like frequency) – how high or low a tone sounds; pitch depends on the frequency of a sound wave. High frequency are sensed as sounds of high pitch Timbre- the quality of sound. The mixture of frequencies and amplitudes that make up the quality of sound. THE EAR - Auditory accessory structures Tympanic membrane (eardrum) – a membrane in the middle ear that generates vibrations that match the sound waves striking it. Cochlea – A fluid-filled spiral structure in the ear in which auditory transduction occurs Basilar membrane- the floor of the fluid filled duct that runs through the cochlea Acoustic nerve (auditory nerve) - the bundle of axons that carries stimuli (messages) from the hair cells of the cochlea to the brain Auditory transduction – sound vibrations reach the fluid-filled cochlea. As the fluid moves with sound, this causes the basilar membrane in the cochlea to vibrate. This movement of the basilar membrane bends the hair cells that connect to the auditory nerve. The bending of hair cells stimulate neurons in the auditory nerve, causing them to fire. The pattern of firing creates a coded message that tells the brain about the amplitude and frequency of incoming sound waves, experienced as loudness and pitch. Types of deafness – conduction & nerve Conduction – bones of the middle ear fuse together, preventing accurate conduction of vibrations Nerve – when the auditory nerve or hair cells are damaged. Treatment – stimulate growth of hair cells and hearing aids AUDITORY PATHWAYS TO THE BRAIN Before sounds can be heard, the information encoded in the firing of the axons that make up the auditory nerve must be sent to the brain. This transmission process begins when the auditory nerve conveys the information to the thalamus. From there, the information is relayed to the primary auditory cortex where complex analysis occurs. Auditory cortex – the area in the brains temporal lobe that is the first to receive information about sounds from the thalamus Frequency appears to be coded in two ways, which are described by place theory and frequency-matching theory Place theory – von Bekesy. Explains how we distinguish between high and low pitch sounds by associating each pitch with a specific location in the cochlea. A theory that hair cells at a particular place on the basilar membrane respond most to a particular frequency of sound. The greatest response by hair cells occurs at the peak of the wave. Location of peak depends on the frequency of the sound that produces them. Higher frequency peak soon after it starts down the basilar membrane, lower frequency produce a wave that peaks further along the basilar membrane. Place theory does not explain coding of very low frequencies as no auditory nerve fibres response to very low characteristic frequencies – leading to frequency matching theory Frequency matching theory (aka. Volley theory) - the firing rate of an auditory nerve matches a sound waves frequency. A process in which certain neurons in the auditory nerve fire each time a sound wave passes. Eg) soundwave that is 25 cycles per second would cause neurons to fire 25 times per second Frequency matching vs. Place theory The lowest sound frequencies are coded by frequency matching, whereby the frequency is matched by the firing rate of auditory nerve fibres. Low to moderate frequencies are coded by both frequency matching and the place on the basilar membrane at which the wave peaks. High frequencies are coded only by the place at which the wave peaks. HEARING SUMMARY Aspect of sensory system Elements Key characteristics Accessory structures Ear- pinna, tympanic Changes in pressure membrane, malleus, incus, produced by the original stapes, oval window, basilar wave are amplified membrane Energy Sound – pressure fluctuationsThe amplitude, frequency and of air produced by vibrations complexity of sound waves determine the loudness, pitch and timbre of sounds Pathways and Acoustic (auditory nerve to Auditory cortex decodes representations halamus to auditory cortex patterns of information from he auditory nerve, creating sensations of loudness, pitch and timbre Transduction mechanism Hair cells of the organ of CortiFrequencies are coded by the ocation of the hair cells receiving the greatest stimulation (place theory) and by the firing rate of neurons frequency matching theory) QUESTIONS Sound energy is converted to nerve cell activity in an inner ear structure called the cochlea Pitch is how high or low a sound sounds and is determined by the frequency of a sound wave VISION Light – electromagnetic radiation that has a wavelenths of approximately 400-750 nanometres Sensations of light depend on two physical dimensions of light waves: intensity and wavelength Light intensity – a physical dimension of light waves that refers to how much energy the light contains; it determines the brightness of light Light wavelength – a physical dimension of light waves that refers to their length, the distance between peaks in light waves, and produces sensations of different colours FOCUSING LIGHT Cornea – the curved, transparent, protective layer through which light rays enter the eye Pupil – an opening in the eye, just behind the cornea, through which light passes Iris – the colourful part of the eye, which constricts or releases to adjust the amount of light entering the eye Lens – the part of the eye behind the pupil that bends light rays, focusing them on the retina Retina – the surface at the back of the eye onto which the lens focuses light rays Ocular accomodation – ability to change the shape of the lens to bend light rays CONVERTING LIGHT INTO IMAGES Photoreceptors – specialised cells in the retina that convert light energy into nerve cell activity. They contain photopigments Photopigments – chemicals in photoreceptors that respond to light and assist in converting light into nerve cell activity Dark adaption – the increasing ability to see in the dark as time in the dark increases Rods – highly light sensitive photoreceptors in the retina that allow vision even in dim light but cannot distinguish colours Cones – phhotoreceptors in the retine that help us distinguish colours. Fovea – a region in the centre of the retina where cones are highly concentrated Visual acuity – visual clarity, which is greatest in the fovea because of its large concentration of cones. FROM RETINA TO BRAIN Light rays pass through several layers of retinal cells before striking rods and cones. Signals generated by the rods and cones go back to the surface of the retina, making connections with bipolar cells and ganglion cells. The ganglion cell axons continue into the brain, forming synapses with the thalamus. Neurons there send axons to connect to the primary visual cortex in the occipital lobe. Optic nerve – a bundle of fibres composed of axons of ganglion cells that carries visual information to the brain. Feature detectors – cells in the cerebral cortex that respond to a specific feature of an object. SEEING COLOUR Psychological dimensions: Hue - the essential ‘colour’ determined by the dominant wavelength of light Colour saturation – the purity of a colour Brightness – the overall intensity of all the wavelengths that make up light TRICHROMATIC THEORY OF COLOUR VISION Trichromatic theory – Helmholtz: a theory of colour vision identifying three types of visual elements, each of which is most sensitive to different wavelengths of light. Theory does not explain aspects of colour vision such as afterimages. Related to rods and cones Short-wavelength cones – respond most to light in the blue range Medium wavelength cones – most sensitive to light in the green range Long wavelength cones – respond best to light in the reddish-yellow range OPPONENT PROCESS THEORY OF COLOUR VISION Opponent process theory – Hering: a theory of colour vision stating that colour sensitive visual elements are grouped into red-green, blue-yellow and black-white elements. Related to ganglion cells Colour blindness – a conditions in which the lack of certain photopigments leaves a person unable to sense certain colours Aspect of sensory system Elements Key characteristics Accessory structures Eye – cornea, pupil, iris, lens Light rats are bent to focus on the etina Colour vision Short, medium and long The combined activity of three cone wavelength cones in the retina; ypes create colour sensations ganglion cells in the retina and cells trichromatic theory); output from n the thalamus and visual cortex ganglion cells signals opponent with colour sensitive colours (opponent process theory) centre-surround visual receptive ields Energy Light – electromagnetic radiation The intensity and wavelength of rom about 400 nanometres to ight waves determine the about 750 nanometres brightness and colour of visual sensations Pathways and representations Optic nerve to optic chiasm to Neighbouring points in the visual ateral geniculate nucleus of world are represented at neighbout halamus to visual cortex points in the lateral geniculate nucleus and visual cortex. Neurons here respond to particular aspects of the visual stimulus – such as colour, movement, distance or form Transduction mechanism Photoreceptors (rods and cones) inRods are more sensitive to light he retina han cones, but cones discriminate among colours. Sensations of colour depend first on the cones, which respond differently to different light wavelengths. nteractions among cells of the etina exaggerate differences in the ight stimuli reaching the  photoreceptors, enhancing the sensation of contrast QUESTIONS The ability to see in very dim light depends on photoreceptors called rods Near-sightedness and far sightedness occur when images are not focused on the eyes retina Colour blindness results when cones in the retina lack one of the three kinds of colour sensitive photopigments CHEMICAL SENSES: SMALL AND TASTE Olfactory perception – the sense of smell Taste perception/gustatory perception – sense of taste Oduor molecules reach olfactory receptors located on the dendrites of specialised neurons that extend into the mucous membrane in the nose Oduor molecules bind to these receptors, causing depolarisation of the dendrites membranes, leading to changes in the firing rates of the neurons. Depolarisation – the change of a neurons electrical charge. When a neuron is stimulated, depolarisation occurs, meaning the inside of the neuron becomes less negative (or positive). This shift in electrical charge can lead to action potential, where the electrical signal travels down the neuron to communicate with other neurons. Olfactory neurons – repeatedly replaced by new ones as each lives for about two months Olfactory receptors – about 1000 different receptors, 2 per cent of genetic code may be devoted to these olfactory receptors Olfactory bulb – a brain structure that receives messages regarding smell Pathways in the olfactory bulb sense the information on for further processing, including the frontal lobe and the amgydala, which is involved in memory and emotional experience Pheromones – chemicals released by one animal and detected by another that shape the second animals behaviour or physiology Vomeronasal system - olfactory system that is senstic to pheromones GUSTATION Papillae – structures on the tongue containing groups of taste receptors, or taste buds Orbitofrontal cortex – where the olfactory and gustatory pathways converge. Aspect of sensory system Elements Key characteristics Energy Smell – volatile chemicals The amount, intensity and Taste – chemicals in solution ocation of the chemicals determine taste and smell sensations Structures of tase and Smell – chemical receptors inOduor and taste molecules smell he mucous membrane of thestimulate chemical receptors nose Taste – taste buds grouped in papillae in the mouth Pathways to the brain Smell – olfactory bulb Axons from the nose bypass Taste – taste buds he thalamus and extend directly to the olfactory bulb QUESTIONS The flavour of food arises from a combination of taste and smell Emotion and memory are linked especially closely to our sense of smell Humans are especially dependent on vision, hearing, and the tactile senses to get information about the world; we depend less on smell and taste. Each sense gives information about the world by responding to a specific kind of energy; for example, for vision we respond to light Sound energy is converted to nerve cell activity in an inner-ear structure called the cochlea. hearing loss due to damage to hair cells or the acoustic nerve is called nerve deafness Pitch is how high or low a sound sounds and is determined by the frequency of a sound wave. The ability to see in very dim light depends on photoreceptors called rods Near-sightedness and far-sightedness occur when images are not focused on the eye's retina Color blindness results when cones in the retina lack one of the three kinds of color-sensitive photopigments The gate control theory offers an explanation as to why we sometimes do not feel pain Professional dancers look at the same spot for as long as possible during repeated spins to avoid the dizziness caused when the sense of balance (or vestibular sense) is overstimulated. Without your sense of taste, you would not be able to swallow food without choking Bottom-up arguments arise for the information contained in the stimuli coming to us from the environment rather than from our interpretations, inferences, and expectations Top-down processes emphasize that our perception is strongly influenced by what we have learned from our experiences Perceptual illusions are where our perceptual experience of a stimulus differs from the actual characteristics of that stimulus The movement we see in movies, videos, and GIFs is due to a perceptual illusion called stroboscopic illusions The grouping principle of closure allows you to identify objects seen through a picket fence SENSING YOUR BODY Cutaneous senses – senses of touch, temperature, pain and kinaesthetic perception A-delta fibres – nerve fibres that carry signals that feel like sharp, prickling sensations C- fibres – create a sensation of dull, continuous aches and burning sensations Gate control theory of pain – a theory suggesting that a functional ‘gate’ in the spinal cord can either let pain impulses travel upwards to the brain or block their progress Analgesia – the absence of pain sensations in the presence of a normally painful stimulus PROPRIOCEPTION: SENSING BODY POSITION Proprioceptive senses - (proprioception) the sensory systems that tell us about the location of our body parts and what each part is doing Sense of equilibrium (vestibular sense) - the proprioceptive sense that provides information about the position of the head (and hence the body) in space and about its movements Vestibular sacs – organs in the inner ear that connect the semicircular canals and the cochlea and contribute to the bodys sense of balance Otoliths – small crystals in the fluid-filled vestibular sacs of the inner ear that, when shifted by gravity, stimulate nerve cells that inform the brain of the position of the head Semicircular canals - tubes in the inner ear whose fluid stimulates nerve cells that tell the brain about those movements Kinaesthetic perception – the proprioceptive sense that tells you where the parts of your body are in respect to one another Proprioceptors – receptors in muscles and joints that provide information to the brain about movement and body positions Sense Energy Conversion of physical Pathways and energy to nerve activity characteristics Touch Mechanical deformation ofSkin receptors Nerve endings respond to he skin changes in weight and ocation of touch Temperature Heat Sensory neurons in the Changes in temperature skin are detected by warm sensing and cool sensing ibres Pain ncreases with intensity of Free nerve endings in or Changes in intensity cause ouch or temperature near the skin surface he release of chemicals detected by receptors in pain nurons Sense of equilibrium Mechanical energy of Neural receptors in the nformation about fluid head movements nner ear moving in the semicircular canals is sent to the brain along the acoustic nerve Kinaesthetic perception Mechanical energy of joint Neural receptors nformation from joints and and muscle movement proprioceptors) in joints muscle fibres is sent to the and muscle fibres spinal cord, thalamus, cerebellum and cortex QUESTIONS The gate control theory offers an explanation as to why we sometimes do not feel pain Without your sense of taste you would not be able to swallow food without choking PERCEPTION Perception – the process through which people tak raw sensations from the environment and interpret them, using knowledge, experience and understanding of the world so that the sensations become meaningful experiences Three approaches to perception Approach Description Computational model An approach to perception that focuses on how computations by the nervous system ranslate raw sensory stimulation into an experience of reality Constructivist approach An approach to perception taken by those who argue that the perceptual system uses ragments of sensory information to construct an image of reality Ecological approach An approach to perception maintaining that humans and other species are so well adapted to their natural enviornment that many aspects of the world are perceived without requiring higher level analysis QUESTIONS Ecological arguments arise for the information contained in the stimuli coming to us from the environment rather than from our interpretations, inferences and experiences Constructivist theories emphasise that our perception is strongly influenced by what we have learnt from our experiences Perceptual illusions are where our perceptual experience of a stimulus differs from the actual characteristics of that stimulus Perceptual organisation - the task of determining what edges and other stimuli go together to form an object BASIC PROCESSES IN PERCEPTUAL ORGANISATION Figure-ground discrimination – the ability to organise a visual scene so that it contains meaningful figures set against a less relevant background Gestalt laws of grouping Proximity – the closer objects are to one another, the more likely we are to perceive them as belonging together Similarity - we tend to perceive similar elements as part of a group Continuity – when sensations appear to create a continuous form, we tend to perceive them as belonging together Closure – we tend to fill in missing contours to form a complete object Texture – when basic features of stimuli have the same texture we tend to group these stimuli together Simplicity – we tend to group features of a stimulus in a way that provides the simplest interpretation of the world Common fate - when objects are moving in the same direction at the same speed, we tend to perceive them as belonging together. Stephen palmer and his three additional grouping principles: Synchrony – when different stimuli occur at the same time, we are likely to perceive them as belonging together Common region – when stimulus elements are located within some boundary, we tend to perceive them as being together Connectedness – when stimulus elements are connected to other elements, we tend to group them together PERCEPTION OF LOCATION AND DISTANCE Depth perception – the ability to perceive distance Interposition - a depth cue whereby closer objects block ones view of things father away Liner perspective – a depth cue whereby objects closer to the point at which two lines appear to converge are perceived as being at a greater distance Gradient of texture – a graduated change in the texture of the visual field, whereby objects with finer, less detailed textures are perceived as more distant Motion parallax – a depth cue whereby a difference in the apparent rate of movement of different objects provides information about the relative distance of those objects. Eg. Looking out window of car, things closer go by quicker Eye convergence - a depth cue involving the rotation of the eyes to project the image of an object on each retina Retinal disparity/binocular disparity – a depth cue based on the difference between two retinal images received by each eye Perception of motion Optical flow: looming – looming is a motion cue involving rapid expansion in the size of an image so that it fills the available space on the retina Stroboscopic illusion – an illusion of motion that is created when we see slightly different images or slightly misplaced lights flashed in rapid succession. When objects appear, disappear and then quickly reappear nearby, perceived as moving smoothly. Like a movie Perceptual constancy – the perception of objects as constant in size, shape, colour and other properties despite changes in their retinal image QUESTIONS The movement we see in movies, videos and dvds is due to a perceptual illusion called stroboscopic illusion People who have lost an eye also lose the depth cue called retinal disparity The grouping principle of closure allows you to identify objects seen through a picket fence Principle Description Example Figure-ground Certain objects or sounds are automatically You see a person discrimination dentified as figures, whereas others become standing against a meaningless background building, not a building with a person shaped hole n it Grouping Properties of stimuli lead us to automatically group People who are hem together. These include proximity, similarity, sitting together or continuity, closure, texture, simplicity, common fate,who are dressed synchony, common region and connectedness similarly are perceived as a group Depth perception – Knowing an objects two dimensional position (left perception of location and right, up and down) and distance enables us to ocat it. The image on the retina and the orientation of the head provide information about the two dimensional position of visual stimuli, auditory ocalisation relies on differences in the information received by the ears. Depth of distance perception uses stimulus cues, such as interposition, relative size, hight in the visual field, gradient of texture, inear perspective, clarity, colour and shadow Perceptual constancy Objects are perceived as constant in size, shape, brightness, colour and other properties, despite changes in their retinal images RECOGNISING THE PERCEPTUAL WORLD Top-down processing – aspects of recognition that are guided by higher level cognitive processes and psychological factors, such as expectations Bottom down processing – aspects of recognition that depend first on the information about the stimulus that comes to the brain from the sensory receptors Schemas - mental represenations (generalisations) of categories of objects, events and people Parallel distributed processing – a theoretical model of object recognition in which various elements of the object are thought to be simultaneously analysed by several widely distributed but connected neural units in the brain Mechanism Description Example Bottom-up processing Raw sensations from the eye You recognise a dog as a dog or ear are analysed into basicbecause its features match eatures, such as form, colouryour perceptual category for or movement; these features a dog are then recombined at higher brain centres, where hey are compared with stored information about objects or sounds Top-down processing Knowledge of the world and On a dark night, what you experience in perceiving see as a small, vague blob allow people to make pulling on the end of a leash nferences about the identity s recognised as a dog of stimuli, even when the because the stimulus occurs quality of raw sensory at a location where you would nformation is low expect a dog to be Parallel distributed Recognition depends on A dog standing behind a processing communication among picket fence will be eature analysis systems recognised as a dog even operating simultaneously and hough each disjointed ‘slice’ enlightened by past of the stimulus may not look experience ike a dog QUESTIONS Your ability to read a battered old sign that has some letters missing is a result of top-down processing When stimulus features match the stimulus we are looking for, ___ takes place Context and prior knowledge can affect perception as they can create differing expectations and processes ATTENTION Attention – the process of directing and focusing psychological resources to enhance perception, performance and mental experience. Attention improves mental processing, takes effort, and is limited Aspects Characteristics Directing attention You can direct your perceptual systems towards different aspects of your external and internal enviornments by overt orienting – pointing sensory systems at a particular stimulus – or by shifting attention without having to move a muscle – called covert orienting gnoring information nattentional blindness is where your attention is voluntarily or involuntarily focused on one part of the environment; you may ignore, or be blind to stimuli occurring in other parts Divided attention Multitasking is the process whereby we divide our attention, which is thought to be limited Attention and automatic Our ability to search for targets rapidly and automatically is processing called parallel processing. Colour recognition is so automatic, t is thought that colour is analysed before the point at which attention is required Attention and the brain Evidence of the extra mental work attention requires is found by using PET and MRI scans QUESTIONS The process of directing and focusing psychological resources to enhance perception, performance and mental experience is called attention A task that requires little to no attention is said to be automatic Attention is a linked set of resources that improves perception