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This 32 page Study Guide was uploaded by Fiaza Ahmed on Saturday April 30, 2016. The Study Guide belongs to EXP 4204 at Florida International University taught by Timothy Allen in Spring 2016. Since its upload, it has received 73 views. For similar materials see Sensation and Perception in Psychlogy at Florida International University.
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Sensation and Perception Dualism: The idea of mind and body “I think, therefore I am” Monism: Mind is a manifest property of the physical matter of the brain Empiricism: Socially facilitated (Experience of the senses, observation, scientific method) Top-down process: using your knowledge (memory, emotional state, beliefs, concepts, expectations) to interpret sensory information Ex: Cedar/orange experiment Bottom-down processes: Building percepts from elemental senses, influence from a neural base The Myth of five senses 7-12 different sensory systems Sensory systems often interact (multisensory processing) One sense can affect the perception of another The basis of perception Sensation: The registration of physical stimuli on sensory receptors. Perception: The process of creating conscious perceptual experience from sensory input. Perception occurs after cognitive processing begins. Transduction: The process of converting a physical stimulus into an electrochemical signal Neural Response: he signal produced by receptor cells that can then be sent to the brain Sensation refers to the process of transduction in which receptors convert physical signals into neural responses and perception refers to the process of taking that signal and processing it into a usable image or experience. Ex: at an orchestra: sensation takes in sounds, perception appreciates music. The beginnings Aristotle conducted conceptual work and observations Gave us our basic list of the five senses The Aristotle illusion Aftereffect: a sensory experience that occurs after prolonged experience of visual motion in one particular direction 19 th century: Johannes Mueller The doctrine of specific nerve energies: the argument that it is the specific neurons activated that determine the particular type of experience What determines hearing, sight, etc. It matters what receptors are activated, not how they are activated Percept is based on what those receptors do Our entire consciousness is based on the activity of our neurons Hemholtz Had a constructivist approach (the idea that perceptions are constructed using information from our senses and our cognitive processes) Held the belief that we must incorporate information from our existing knowledge to completely perceive the world around us. Unconscious interference: perception is not adequately determined by sensory information, so an interference or an educated guess is part of the process this interference is not the result of active problem solving but rather a non conscious cognitive process Hering Opposed Helmholtz Viewed environmental inputs and senses enough to perceive world Weber Weber’s law: a just noticeable difference between two stimuli is related to the magnitude or strength of the stimuli Fechner Father of psychophysics Psychophysics: the study of the relation between physical stimuli and perceptual events Goal was to describe sensation/perception in mathematical terms JND Magnitude estimation th 20 century Gestalt psychology Viewed the world in terms of general patterns and well- organized structures Interested in how edges are perceived Believed perceptual laws and other principles of human behavior were genetically wired German origins You cannot understand perception without organization Law of common fate: we can only interpret sensory info in holistic ways or concepts. Objects with common motion (fate) are grouped together Direct perception (The Gibsonian Approach) Directly opposes concept of unconscious interference World generates rich sources of info that senses need to merely pick up on Ecological realism Information processing approach Info is collected by sensory processes and then flows to a variety of modules that decode info, interpret, and allow organism to act on it. Brain is parallel: many processes can be occurring simultaneously More like Helmholtz’s view Info processing allows for interpretation vs. direct processing which says that sensory info is sufficient enough 21 century Neuroscience Approach Able to measure and manipulate nervous system directly Computational approach Influenced by computer science Marr sought mathematical explanation for perceptual processes Models perception in nonhuman systems Research Methodology: Psychophysical scale: a scale which people rate their psychological experience as a function of the level of a physical stimulus Ex: Scoville scale- measures our detection of the amount of an ingredient called capsaicin in chili peppers The study of human sensory systems starts with psychophysics. The Measures and Methods of Psychophysics Method of limits: stimuli are presented in a graduated scale, and participants must judge the stimuli along a certain property that goes up or down o Ex: A participant may be presented with an increasingly dimmer set of lights. The participant is asked to tell when the lights are no longer visible o Is used to determine absolute and difference thresholds o To determine absolute threshold with method of limits ascending (stimulus gets larger along a physical dimension) and descending (stimulus gets smaller) series is used. o Crossover point o Two point threshold (an absolute threshold) Method of Constant stimuli: A method whereby the threshold is determined by presenting the observer with a set of stimuli, some above threshold and some below it, in a random order o Stimuli is given in a random order o Prevents observer from being able to predict the next stimulus o Reduced errors due to habitation o Time-consuming o Requires many trials Method of Adjustment: method whereby the observer controls the level of stimulus and "adjusts" it to be at the perceptual threshold o Mirrors normal activities; i.e. adjusting volume control o Quickly yields thresholds (advantage) o Great variance from one participant to the next (disadvantage) o Useful for determining PSE Magnitude Estimation: a psychophysical method in which participants judge and assign numerical estimates to the perceived strength of a stimulus “P” = perceived magnitude “c” = scaling constant “I” = stimulus intensity “b” = exponent constant (raised power) o Response compression ( b < 1) sight, hearing, touch etc. o Response expansion ( b > 1) pain o Stevens’ power law Catch Trials o Participant may be willingly or unwillingly misinforming the experimenter about perceptual experience o Catch trials counter this, and limits false reporting o Forced choice method Signal detection theory: the theory that in every sensory detection or discrimination, there is both sensory sensitivity to the stimulus and a criterion used to make a cognitive decision o Sensitivity (the ease or difficulty with which an observer can distinguish signal from noise) o As sensitivity decreases, more false alarms and misses occur. As sensitivity increases, the observer has more hits and correct rejections o d’ (d-prime) o Relationship between sensitivity and criterion o ROC curve simplifies all possible outcomes Visual System: The brain The Optic nerve and chiasm The optic nerve of the left eye and the optic nerve of the right eye meet just a couple centimeters behind the eyes in an area called the optic chiasm The optic nerve from each eye splits in half at the optic chiasm Axons from the right half of the right retina and the ganglion cells from the right half of the left retina combine which forms the optic tract Contralateral representation of visual space occurs: this is opposite side organization in the visual system, the nasal retina projects to the opposite side of the brain Information from each eye goes to both hemispheres (ipsilateral organization) Once optic tract has left chiasm, 90% of axons make their way to LGN of the thalamus 10 % go to other locations The Lateral Geniculate Nucleus LGN is bilateral structure in thalamus that relays information from optic nerve to visual cortex Critical locus for vision Has 6 layers LGN preserves info specific to eye and visual field This is important for us to construct a 3-d image The Superior Colliculus: Main function is the control of rapid eye movements 10% of retinal ganglion cells synapse smooth pursuits: voluntary tracking eye movements Ex: watching a bird fly across the sky Saccades: sudden eye movements used to look at one object from another Is an organ of multisensory integration The Primary Visual Cortex: V1 (Has retinotopic map of the retina) Fovea has larger cortical area than the periphery Also has 6 layers Layer 4 is critical layer that receives input from LGN Receptive fields of V1 cells Simple cells: neurons that respond to stimuli with particular orientations to objects within their receptive fields. Like cells in LGN they have clear excitatory and inhibitory regions Unlike LGN cells they have orientation selectivity rather than center-surround visual fields V1 indicates the orientation of lines in the visual world by having select cells respond to different angles of orientation Complex cells Neurons in V1 that respond optimally to stimuli with particular orientations Unlike simple cells they respond to a variety of stimuli across different locations. Complex cells do not have a peak location sensitivity like simple cells do. Complex cells are found in layers 2, 3, 5, and 6 of V1 but not layer 4. End-stopped neurons: neurons respond to stimuli that end within the cell’s receptive field. Blobs are areas within V1 sensitive to color Interblobs: areas sensitive to the orientation of an object Layer 4B cells V2 After information leaves V1 it travels to other areas in the occipital cortex such as V2 There are 3 distinct regions within V2 which match directly with 3 different types of cells in V1 Blobs connect to thin stripes Layer 4B connects to thick stripes Interblobs connect to interstripes Seems to be involved in representation Functional Pathways in the Visual Cortex: Ventral pathway (P pathway) “what” Dorsal pathway (M pathway “where” Phrenology: Study of the bumps on the head Different areas of the head are thought to correspond to different personality traits Phrenology is now synonymous with pseudoscience… and is often the insult a psychologists in one field hurdles at another field However wrong, phrenology contributed to the idea of localization as opposed to equipotentiality Organization of the brain: Maps – spatial distribution of information from sensory receptors such that adjacent points on the cortex correspond to adjacent areas of the retina Columns – vertical groupings of neurons perpendicular to the cortical surface processing similar sensory information Streams – sequentially-connected structures each contributing specific functions (like an assembly line) Modules – specialized regions of the brain processing specialized functions Distributed Representations – any one perceptual representation requires coding by several neurons in several regions, with a unique combination of activity fMRI: f. M. R. I.= Functional Magnetic Resonance Imaging B.O.L.D. = Blood Oxygen-Level Dependent No tracer needed Blood has ferrous molecules in it (iron) Changes in oxygenation changes signal properties More oxygenation in a given area is thought to correspond to more brain activity Slow (seconds) and large (1 – 2 mm3)—voxels (not pixels) Technique discovered in 1990 P.E.T. = Positron Emission Tomography • Positron emission – radiation from radioactive isotopes (proton to neutron) • Tomography – Mapping via slices • Must inject a radioactive tracer • Image blood flow • Changes in blood flow correspond to changing demands on a given brain region • Note the blood-flow-to-function interpretation is not a direct measure of brain activity • PET is very useful for measuring the spread of drugs, or neurotransmitter pools, etc. with different tracers (it is helpful in asking details about certain molecules) • Technique discovered in 1976… not thought to be dangerous (however it is not ideal to do too many) Visual Streams: “What” pathway “Where” pathway P-cells:(smaller ganglion cells, M-cells : (larger ganglion cells, layers 3-6 of LGN; process color layers 1-2 of LGN; process depth and texture) movement) Ventral (bottom) Dorsal (top) Temporal layer Parietal layer If damaged, people have If damaged, people don’t difficulty identifying faces know where things are in and objects. space Two-choice task: o Temporal lobe lesions: impaired object discrimination but not spatial discrimination o Parietal lobe lesions: impaired spatial discrimination but not object discrimination William Wundt Founded the first laboratory in scientific psychology Father of experimental psychology Structuralism (anti-thesis to Gestalt psychology): Percept is created by the sum of elements called sensations. *However we do have to consider organized perception Object Perception Perceptual Organization: How small parts are organized into wholes Multiple objects in the environment are grouped, to identify those objects in complex scenes. Two important processes in perceptual organization: Grouping: the process by which elements in a figure are brought together in common unit or object Segregation: the process of distinguishing two objects as being distinct or discrete Gestalt Psychology and Perceptual Organization: Gestalt theorists claimed that the brain is holistic with self- organizing tendencies We see greater than individual parts Conscious perception rests upon the building blocks of sensation A. Figure ground organization: The experience viewers have as to which part of an image is in front and which part of an image is in the background of a particular scene We divide the world into two elements: the figure that is the object of regard and the rest, which is ground or background. Things that are more memorable tend to be figure, while those that are not tend to be ground Figure more “thing-like” Figure is in front of the ground – Ground is a uniform material that extends behind the figure (good continuation) The figure has border ownership *Neurons in V1 are affected by figure/ground regions B. Gestalt Laws of Perceptual Grouping: Law of good continuation: the gestalt grouping law stating that edges that are smooth are more likely to be seen as continuous than edges that have abrupt or sharp angles Law of proximity: the gestalt grouping law stating that elements that are close together tend to be perceived as a unified group. Law of similarity: the gestalt grouping law stating that elements that are similar to one another tend to be perceived as a unified group. Law of symmetry: grouping law that states that elements that are symmetrical to each other tend to be perceived as a unified group Law of common fate: elements that are moving together tend to be perceived as a unified group Principle of common region: elements that are within the same region of space appear to be grouped together Principle of Uniform Connectedness: connected regions of visual properties are perceived as a single unit Principle of Synchrony: events that occur at the same time will be perceived as belonging together Perceptual Interpolation: Edge completion: the perception of a physically absent but inferred edge, allowing us to complete the perception of a partially hidden object Illusory contours: perceptual edges that exist because of edge completion but are not actually physically present. These illusory contours display edge completion. Recognition by Components: Bottom-up theory Geons: the basic units of objects, consisting of simple shapes such as cylinders and pyramids Recognition by components: a theory stating that object recognition occurs by representing each object as a combination of basic units (geons) that make up that object; we recognize that object by the relation of its geons Roughly 40 independent geons, and just about any object can be represented by the combination of these geons. Accounts for viewpoint invariance: objects are seen as the same regardless of the vantage point relative to a viewer. Principle of componential recovery: the ability to identify an object if we can identify its geons Limitations of this theory: letter recognition and face recognition *Alternative theory that accounts for viewpoint invariance is the Image description model: Many 2-D images of singular objects are stored in our perceptual memories. Theory accounts for objects that are more abstract Both of these theories tend to be true under certain conditions The Neuroanatomy and Physiology of Object perception: Representation of Shapes in Area V4 After info leaves V1 and heads toward extrastriate cortex along the ventral pathway, one of the important loci is V4 in the occipital lobe. V4 has been linked to color vision and also shapes perception V4 neurons have a preference for edges (complicated analysis) This area is involved in delineating shapes necessary for object recognition. Object Recognition in the Inferotemporal Area Inferotemporal (IT) area: the region in the temporal lobe that receives input from the ventral visual pathway; one of its functions is object identification Neurons in the IT have much larger receptive fields than those in V1 and V4 and seem to be devoted to detecting particular kinds of objects anywhere in the visual field rather than specific features in specific places. IT area seems to specialize in detecting specific objects from chairs to bears to faces rather than edges or contours. The Fusiform Face area and Face Recognition: The FFA: an area in the inferotemporal area of the temporal lobe that specializes in recognizing familiar faces It is located on the ventral surface of the temporal lobe Occipital face area: an area of the brain in the occipital lobe, associated with recognizing faces as distinct from other objects The Grill-Spector experiment Prosopagnosia: Prosopagnosia: face agnosia, resulting in deficit in perceiving faces. Damage to the FFA results in this From the Greek words “face” and “knowledge” Patients with this can recognize faces as faces but have difficulty remembering specific faces Evidence with developmental prosopagnosia supports the view that FFA is an area unique to face recognition Other IT Cortex Areas with Specific Object Recognition Functions The parahippocampal place area (PPA): An area within the IT cortex that appears to have the specific function of scene recognition Recognition of spatial landscapes Topographic agnosia: involves a deficit in recognizing spatial landscapes and is related to damage to the PPA. Another area in the IT cortex with a specific function is the extrastriate body area. This is activated when its cells view bodies or body parts but not faces. It may be that other areas of the IT cortex are also sensitive to particular stimuli. Grandmother Cells and Specific Coding in the IT cortex: Early on scientists debated where in the brain memories are stored Search for the “engram”: specific location of a specific memory Quiroga et al study (2005) able to find cells that were specific to individual people. Color Perception: Wavelengths of Light and Color: Visual spectrum: the band of wavelengths from 400 nm to 700 nm that people with normal vision can detect As frequency increases, wavelength decreases. 400 – 450nm – Violet 450-490nm – Blue 500-575nm – Green 575-590nm - Yellow 590-620nm – Orange 620-700nm – Red Heterochromatic light: white light consisting of many wavelengths Monochromatic light: consisting of one wavelength Spectral reflectance: the ratio of light reflected by an object at wavelength. Every object has particular characteristics that permit it to absorb some wavelengths of light and reflect other wavelengths of light. (Chromatic colors) Surfaces that reflect all light equally can be said to be achromatic, which means, without color. (White: surfaces that reflect the most light, Black: surfaces that absorb the most light and Gray: surfaces that reflect some but not all light) Hue, Saturation, Lightness and Brightness Perception of color refers to the three dimensions of color experience Hue: refers to the color quality of light and corresponds to the color names that we use, such as orange, purple, green, indigo, yellow, cyan, aquamarine, etc. Hue is the quality of color: a value that changes, but it does not make the value larger or smaller. Monochromatic colors (spectral colors): red, green, orange, yellow, and blue Nonspectral colors: combinations of more than one monochromatic colors, purple, brown, silver, gold, etc. Saturation: Refers to the purity of light. The more saturated the stimulus, the stronger the color experience, and the less saturated, the more it appears white or gray or black. Brightness: refers to the amount of light present. The more bright an object is, the easier it is to see and the more noticeable the colors are. Lightness: refers to the amount of light that gets reflected by a surface *Brightness usually applies to colors, whereas lightness usually refers to the white-gray-black continuum. Additive and Subtractive Color Mixing: Most of our sensations and perceptions do not mix the way colors do With a mix of three primary monochromatic colors we can recreate any other monochromatic light. Additive color mixing Subtractive color mixing When lights of different Creation of a new color by wavelengths are mixed the removal of wavelengths Mixing the lights of different from a light with a broad colors spectrum of wavelengths Mixing paints or other Occurs in TV Pointillism colored materials More common in the natural world The Retina and Color: S-Cone M-Cone L-Cone Maximum Maximum Maximum response to response to response to light at 420 nm light at 535 nm light at 565 nm Best at M stands for L stands for long perceiving blue medium Yellow side of Sensitive to Yellow-ish green red lower Sensitive to frequencies higher frequencies *There are many more M and L cones than there are S cones. S cones only make up 5% of the total number of cones *At least two cones are necessary for any color vision to work *M-cones and L-cones are very similar to each other *These cones have slightly different versions of opsin molecules Univariance, or why more than one receptor is necessary to see in color Principle of Univariance: any single cone system is colorblind, in the sense that different combinations of wavelength and intensity can result in the same response from the cone system. Color vision critically depends on the comparative inputs of the different cone systems This principle explains why we cannot see colors under nighttime lighting conditions. Disorders of Color Vision: Monochromat: completely color blind and has one functioning type of photoreceptor o Can match any wavelength in the spectra by adjusting the intensity of any wavelength o Color blind o 1in 100,000 o Poor Visual acuity because only rod vision Dichromat: somewhat color deficient. o Can match any wavelength in the spectra by adjusting any 2 wavelengths of light o Most common forms are sex-linked (X chromosome) Trichromat: Full normal color vision. o Can match any wavelength of light in the spectra by adjusting any 3 wavelengths The Trichromatic Theory of Color Vision Color vision is based on there being three elements in our visual system that respond differently to different wavelengths Occurs at the level of receptors Determined by color matching experiments The Opponent Theory of Color Perception Theory that color perception arises from three opponent mechanisms (red-green, blue-yellow, and black-white) Support for this theory o Non primary colors can look like combinations of two primary colors o In color sorting experiments, people tend to sort colors into four basic groups rather than three o Afterimages o Simultaneous color contrast: when our perception of one color is affected by a color that surrounds it (process is similar to lateral inhibiton) Cone opponent cells: Color sensitive cells that respond best when they are excited by the input from one cone in the center, but inhibited by the input from another cone type in the surround. (in LGN) Color Opponent cells: cells that are specific not to cones but to colors themselves (In V1) Double Opponent cells: cells that have a center, which is excited by one color and inhibited by the other. In the surround the pattern is reversed. Useful for detecting color edges. (In LGN) Depth and Size Perceptio n Monocular Depth Cues Monocular depth cues: information in the retinal image that gives us information about depth and distance but can be inferred from just a single retina Pictorial cues: o Occlusion: when an object partially hides or obstructs the view of a second object. Provides info about relative position, not absolute distance o Relative Height: objects closer to the horizon are seen as more distant. o Relative Size: the more distant the object, the smaller its image will be on the retina. o Familiar size: Comes into play when we judge distance on the basis of our existing knowledge of the sizes of objects. o Linear perspective: the pictorial depth cue that arises from the fact that parallel lines appear to converge as they recede into the distance. This serves as a cue to depth o Texture gradients: monocular depth cue the occurs because textures become finer as they recede in the distance. As the surface gets further away from us, this texture gets finer and appears smoother. o Atmospheric Perspective: pictorial depth cue that arises from the fact that objects in the distance appear blurred and tinged with blue. Our atmosphere scatters light, and it scatters blue light more than other wavelengths. Because not all light is traveling in a straight line to us, more distant objects should appear a bit fuzzy. o Shadows and shading: Enhance the perception of depth in images Motion Cues: o Motion Parallax: monocular depth cue arising from relative velocities of objects moving across the retinae of a moving person. Parallax refers to change in position. o Deletion: gradual occlusion of a moving object as it passes behind another object o Accretion: gradual reappearance of a moving object as it emerges from behind another object. o Optic flow: motion depth cue that refers to the relative motions of objects as the observer moves forward or back in a scene. Binocular Cues to Depth: Stereopsis-the sense of depth that we perceive from the visual system’s processing of the comparison of the two different images from each retina. o Binocular disparity: Arises because our two eyes are in different locations in our head and therefore have slightly different views of the world o Corresponding points on the retinas o Horoptor: The region in space where the two images from an object fall on corresponding locations on the two retinae. Disparate Images o Fall on non-corresponding points of the two eyes o Difference is called angle of disparity o Crossed disparity: images in front of the horoptor move to the temporal regions of the retinas (lateral) o Uncrossed disparity: images behind the horoptor move to the nasal regions of the retinas (medial) Visual Attention: Attention: A set of processes that allow us to select or focus on some stimuli. Selective Attention: Covert Attention Selective Attention: Selective Attention: The process of attention that allow us to focus on one source when many are present. We direct our perceptual resources to one stimulus. o Primates achieve selective attention through foveal fixation o Foveal fixation: directing the center of gaze at the object of interest o Saccades: rapid movements of the eyes that changes fixation from one object of location to another o Smooth Pursuit: eye movement in the eyes move smoothly to follow a moving object o Vergence = eye movements in which the two eyes move in opposite directions (divergence and convergence) Covert attention: attention occurring without fixation (mental attention) Enhance our mental focus on something Pay attention to something not directly on our fixation point Focus on things, at the expense of other things (William James) Divided Attention: process of attending to multiple sources of information Ex: Driving, radio, cell phone Attention and the direction of gaze in space Typically we attend to a particular location in space by directing our gaze to that location If attention shifts, so does our gaze Stimulus onset asynchrony: refers to the difference in time between the occurrence of one stimuli and the occurrence of another. Features of Attention: Stimulus Salience: some objects in the environment attract our attention Attentional capture: The process whereby a salient stimulus causes us to shift attention to that stimulus. Change blindness: The difficulty we experience in detecting differences between two stimuli that are identical except for or more changes to the image. Even when we have engaged our attention and are directing our visual search in a very conscious manner, we may still fail to see the changes in an image. Inattentional blindness: refers to a phenomenon in which people fail to perceive an object or event that is visible but not attended to. This refers to situations in which a well-above threshold event or object is not seen because the person’s attention is direction elsewhere. Visual Search One of the most important tasks in vision Feature search: The search for a target in which the target is specified by a single feature Conjunction Search: The search for a target in which the target is specified by a combination of features. Feature integration Theory: Some features can be processed in parallel and quickly prior to using attentional resources, whereas other visual characteristics require us to use attention and are done serially and therefore less quickly. *Conjunction searches take longer than non-conjunction searches. Attentional Blink and Rapid serial Visual Presentation The Anatomy and Physiology of Attention: The orienting attention network: Allows us to engage in visual search and direct our visual attention to different locations in visual space o Damage to this causes unilateral neglect The Executive Attention Network: A system that focuses on attention as the inhibition of habitual responses and the top- down control of attention; found in the front lobe o Allows us to inhibit auditory stimuli so that we can concentrate on visual stimuli, or it can allow us to inhibit visual stimuli so that we can concentrate on auditory stimuli. o In Models of memory the executive attention network is called central executive. The Neuropsychology of Attention: When there is damage caused to the right posterior parietal lobe, a condition called hemifield neglect or unilateral visual neglect may arise. This condition almost always occurs when the right parietal lobe is affected, leading to a deficit in the left visual world. Hemifield neglect (unilateral visual neglect): a condition in which a person fails to attend stimuli on one side of the visual world (usually left) as a consequence of neurological damage to the posterior parietal lobe. o This is a attentional problem and not a visual one Balint’s syndrome: a rare condition in which function in both the left and right posterior parietal lobes has been compromised o Patients with this have difficulty locating things in space, which results in difficulty of grasping objects. o As a consequence, these patients suffer from simultagnosia, which is a deficit in perceiving more than one object at a time. o Ignore both left and right visual world Synchrony Hypothesis : neurons from different part of the cortex that fire together are processing information about the same object Time scale for the synchrony is milliseconds… not seconds! Attention is thought to increase synchrony between neurons processing the same object Sometimes this is talked about as reducing spike-timing “jitter” Developmental Aspects of Visual Attention: Attention in very young infants is determined by how long they can maintain a gaze at an interesting stimulus o Attention is studied in infants by procedure known as oddball procedure o Infants are better at selective attention than their older family members Bistability: Phenomena in which a static visual image leads to alternating perceptions Blindsight: Blindsight refers to the residual ability to make visual responses when a patient is subjectively blind in certain regions of his or her visual field. The Auditory System Sound as a Stimulus The sound stimulus is the periodic variations in air pressure travelling out from the source of the variations. Water transmits sounds faster than air does Sound Waves: are the waves of pressure changes that occur in the air as a function of the vibration of a source. Alternating high- and low-pressure regions in neighboring regions of air molecules (air pressure changes). Air does not travel, but sound waves permeate through the air. A wave is an oscillation that travels through a medium by transferring one particle or point to another without causing any permanent displacement of the medium. Sound can be measured by the wave’s wavelength and frequency The time between two consecutive high peaks is the cycle of a sound wave Energy of a sound wave weakens across time and space The Physical Stimulus: Sound travels as in a pattern of sine waves. A pure tone is the simplest form of sound that is composed of a uniform sine wave pattern of oscillations (virtually nonexistent in nature) A pure tone can be described by amplitude and frequency. Amplitude: size of pressure change * Frequency and wavelength are inverse to one another. Frequency is the number of cycles per second, and wavelength is the time course on one cycle Frequency and Pitch Frequency: in a sound stimulus, the number of cycles that occur in a second Pitch: The subjective experience of sound that is most closely associated with the frequency of a sound stimulus; related to the experience of whether the sound is high or low, such as the two ends of the keyboard of a piano. Children and young adults hear over a range from about 20 to 20,000 Hz Young adults: we lose much of our hearing in the highest range 40 years: it is unlikely that frequencies above 14,000 Hz are heard. 50 years old, upper limit may be down to 12,000 Hz. Tone Chroma Moving up the piano keys increases the tone height (perceptual term). Notes on chromatic scale: A, A# or Bb, B, C, C# or Db, D, D# or Eb, E, F, F#, G, G# The chromatic scale has 12 divisions between octaves, which is a different frequency with the same tone chroma, like middle C and High C. Different cultures can have a different number of divisions between octaves, resulting in different scales Harmonics: higher frequencies present in a complex sound that are integer multiples of the fundamental frequency. Almost all sounds are complex sounds: which consist of multiple frequencies. These frequencies combine to form a complex waveform. A complex waveform can be broken down into its composite frequencies through a mathematical formula known as Fourier analysis. Fundamental frequency: lowest frequency present in the complex sound and one that determines the perceived pitch of that sound. The fundamental frequency determines the pitch of a sound but the harmonics provide the timbre that differentiates the sounds between different instruments. Timbre: the perceived sound differences between sounds with the same pitch but possessing different higher harmonics. Phase: the position in one cycle of a wave; there are 360 degrees in a single cycle of a wave. Refer to figure 10.10 Anatomy of the Ear: The ear funnels sound waves towards specialized hair cells in the inner ear that transduce the sound from the physical sound energy into a neural impulse which then travels to the auditory regions of the brain The Outer Ear: Pinna: the structure that collects sound and funnels it into the auditory canal. (helps in sound localization) External Auditory canal: the channel that conducts sound from the pinna to the tympanic membrane. About 25 mm long (the length helps to amplify frequencies and helps to protect the tympanic membrane) Tympanic Membrane: Thin elastic sheet that vibrates in response to sounds coming through the external auditory canal; commonly known as the eardrum (damaging this can result in hearing loss) The Middle Ear: Consists of three small bones that transmit sound into the inner ear Ossicles: The small bones in the middle ear. When the tympanic membrane vibrates, it causes motion in these three small bones which then conduct the sounds mechanically. Malleus: The first ossicle in the middle ear; receives vibrations from the tympanic membrane and transmits them to the incus Incus: an ossicle in the middle ear; receives vibrations from malleus and transmits them to the stapes Important functions of the middle ear: The Eustachian tube: a thin tube that connects the middle ear with the pharynx and serves to equalize air pressure on either side of the eardrum o Normally it is closed but it briefly opens when we swallow or yawn (pooping ears phenomenon) o The ossicles also serve a role in attenuating loud sounds. There is a muscle that is attached to the malleus called the tenortympani and a second muscle attached to the stapes called the stapedius. Their job is to tense in the presence of very loud noises, restricting the movements of the ossicles and avoiding damage to the inner ear (acoustic reflex) The Inner Ear: The inner ear contains the parts of the ear that transduce sound into a neural signal. The hair cells situated along the organ of Corti in the cochlea act by taking vibrations and converting them into a neural signal Cochlea: snail-shaped structure of the inner ear that houses the hair cells that transduce sound into a neural signal. The cochlea has three liquid filled chambers o Tympanic canal: one of three chambers in the cochlea; separated from the middle canal by the basilar membrane o Middle canal: separated from the tympanic canal by the basiliar membrane; contains the organ of corti o Vestibular canal: separated from the middle canal by Reissner’s membrane o Round window: A soft tissue substance at the base of the tympanic canal whose function is an “escape” valve for excess pressure from loud sounds that arrive in the cochlea. The Basilar Membrane of the Cochlea Reissner’s membrane: the membrane that separates the vestibular and middle canals Basilar membrane: fibers that separate the tympanic canal from the middle canal; the organ of corti lies on the basilar membrane Organ of corti: a structure on the basilar membrane that houses the hair cells that transduce sound into a neural signal Perilymph: the fluid that fills the tympanic canal and the vestibular canal Characteristic frequency: each location along the basilar membrane responds to this. The Organ of Corti This organ is the structure along the basilar membrane that contains the hair cells that transduce sound into a neural signal Contains dendrites of the auditory nerve that brings the neural signal to the brain Hair cells have hair like filaments called stereocilia Stereocilia bend in response to the movement of basilar membrane There are layers of hair cells that follow basilar membrane 1. Outer hair cells (three times as many inner hair cells) These cells refine and amplify the neural responses of the inner hair cells 2. Inner hair cells (3,500 inner hair cells) these cells are responsible for transducing neural signal Tectorial membrane: A membrane that rests above the hair cells within the organ of Corti George Von Bekesy Won the Nobel Prize in 1928 Place Theory of Hearing: The frequency of a sound is indicated by the place along the Organ of Corti at which the nerve firing is highest. Developed a unique method for dissecting the cochlear in the human cadaver and observe vibrations of the basilar membrane *Temporal code theory is the alternative to place theory Tonotopic map is a the mapping of frequency onto space. Place theory in cochlea confirmed with electrophysiolgical recordings The Cochlea: Fourier analysis is a technique to mathematically break down complex sounds into their constituent parts The cochlear does this mechanically by the vibratory activity and corresponding hair cell activity at different points along its axis The Auditory Brain and Sound Localization Brain Anatomy and the Pathway of Hearing Auditory Nerve Fibers: Inner hair cells in the cochlea form synapses with auditory nerve fibers. Auditory nerve fibers form the eighth cranial nerve, which then makes it way to the brain The auditory tract goes through cochlear nucleus: a structure in the brain stem that receives input from the inner hair cells Attached to the cochlear nucleus is the trapezoid body: a structure in the brain stem that plays a role in determining the direction of sounds From the cochlear nucleus and the trapezoid body, the sound signal goes to the superior olive in the brain stem. It is a structure in the brain stem that receives input from both ears. The next synapse in ascending pathway of auditory information is the inferior colliculus, which then projects information to the medial geniculate nucleus. Auditory nerve fibers from each ear go to each side of the temporal lobe. Auditory Cortex: A large multifaceted area located in the temporal lobe. The areas in the temporal cortex that process auditory stimuli. Auditory core region 1. Primary auditory cortex: the first area in the auditory cortex which receives input from the medial geniculate nucleus. o Cells in this region show tonotopic organization: the organization of neurons within a region in the brain according to the different frequencies to which they respond. 2. Rostal core 3. Rostaltemporal core “What” system: starts in the core region and then moves to more anterior parts of the temporal lobe. o Identifying sounds o Music and language perception “Where” system: begins in the core region of the auditory cortex and then moves to posterior regions of the temporal cortex as well as the parietal lobe. o Responsible for localizing sound in space Localizing Sound In the auditory system, cochlea is organized tonotopically and spatial localization is done by a number of indirect mechanisms. We must be able to localize sound in three dimensional space Azimuth: the left-right or side to side aspect of sound localization Elevation: the up down dimensions of sound localization Distance: refers to how far a sound is from the listener and whether it is in front of or behind the listener. People are best at located sounds in front of their head, compared to the side and back Interaural Time Difference: The time interval between when a sound enters one ear and when it enters the other ear. It takes sound longer to reach one ear versus the other ear in most locations ITD detectors are neurons early in the auditory processing stream that are sensitive to specific ITDs These neurons provide information for topographic maps: mapping auditory space onto brain space Interaural Level Differences The sound level reaching each ear is different, largely because of your head (acoustic shadow: the area on the side of the head opposite from the source of a sound in which the loudness of sound is less because of blocked sound waves.) This information contribute to sound localization along the azimuth ILD is more effective at high frequencies compared to low frequencies Cone of Confusion Region of positions in space in which sounds create the same Interaural time and Interaural level differences Elevation Perception: Our auditory system detects elevation through a series of changes in sound frequency created by the folds in our outer ears. Spectral shape cue: change in a sound’s frequency envelope created by the pinnae. Auditory Scene Analysis: The process of identifying specific sound producing objects from a complex set of sounds from different objects at varying and overlapping frequencies Auditory system uses a number of heuristic rules to determine which frequencies go with other frequencies A. Temporal Segregation: the process whereby sounds that are linked in time are grouped together, whereas sounds that are not correlated with one another are not grouped together. B. Spatial Segregation: The process whereby sounds that are coming from the same location are grouped together, whereas sounds that are coming from different locations are not grouped together C. Spectral Segregation: The process whereby sounds that overlap in harmonic structure are grouped together, whereas sounds that do not overlap in harmonic structure are not grouped together a. Harmonic coherence: when frequencies present in the environment resemble the possible pattern of a fundamental frequency and higher harmonics. Touch and Pain The Skin and its Receptors Epidermis: the outer layer of the skin o Thickest on our palms and the soles of our feet and thinnest on our eyelids o Its function is to keep out pathogens and keep in fluids Dermis: the inner layer of the skin, which also houses touch receptors. Mechanoreceptors: sensory receptors in the skin that transduce physical movement Perceiving Limb Position Proprioception: The sensing of the position of the limbs. Kinesthesis: The sense that enable us to feel the motions and positions of the limbs and body Three different types of sensory receptors in our body that provide us with information about limb movement and position 1. Muscle spindles: muscle cells that have receptors embedded in them that sense information about muscle length and therefore muscle action 2. Joint Receptors: receptors found in each joint that sense info about the angle of the joint 3. Golgi tendon organs: tendons that measure the force of a muscle’s contraction Phantom Limb Syndrome: continued but illusory sensory reception in a missing appendage Thermoreception: Thermoreception: the ability to sense changes in the temperature on the skin Thermoreceptors: the sensory receptors in the skin that signal information about the temperature as measured on the skin Nociception and the Perception of Pain Pain: perception and unpleasant experience of actual or threatened tissue damage Nociceptive pain: pain that develops from tissue damage that causes nociceptors in the skin to fire Neural Pathways: Once in the spinal cord, information is divided into two parallel tracts which head up the spinal column to the brain 1. Dorsal column—medial lemniscal pathway Touch and limb position 2. Spinothalamic pathway: Temperature – pain Somatosensory Cortex Somatosensory Cortex: an area in the parietal lobe of the cerebral cortex devoted to processing the information coming from the skin senses There is a representation of our entire body mapped onto the somatosensory cortex (like retinotopic map) Disproportionate magnification factors for the face and hands (like the fovea) Penfield experiments S2: “What” channel for identifying the nature of the touched object S1: “Where” channel or dorsal system that allows us to control guided movements on the basis of input from the somatosensory system. Taste Basic Taste: The taste system is primarily a system of identifying substances for consumption. If something tastes good we want to eat it, if it tastes bad we don’t want to eat it. More specifically certain motivations are associated with different tastes. Those motivations are modulated by the physiological responses to he concentrations of certain substances in the body (such as blood sugar level), which modulate hunger and satiety. Generally researchers have identified and referred to the five basic tastes o Salty o Sour o Sweet o Bitter o Umami Taste Receptors: Taste receptors are called taste cells Different types of taste cells respond to different chemicals, much like the olfactory system, each with their own unique receptor sites. Tips of tastes cells extend into the taste pore, located in papillae (the bumps and folds all over the tongue) Taste buds are composed of the several taste cells Taste Zones Generally speaking, the tongue has been shown to have different taste zones which are dominated by one of the basic tastes Coding: Specificity coding: The responses of neurons in the taste system help encode only one type of taste, and thus taste identification is determined by these individual neurons. Evidence: o Normal mice do not respond to a substance called PTC, which is terribly bitter to humans o knock-in mice were developed to be given a gene for a single type of bitter receptor that humans have o These knock-in mice now avoided PTC o Alternatively, mice normally avoid a bitter substance called CYX. knock-out mice were developed to lack a bitter receptor. o These knock-out mice now do not avoid CYX o Record from several nerve fibers from the taste system while different substance are presented. • There is amazing segregation of the specificity of responses Distributed coding: The responses of neurons in the taste system help encode several types of taste, and thus taste identification is determined by the pattern of activation in several neurons. o At higher levels of the nervous system (e.g. cortex) this simple segregation is largely lost and neurons seem to respond to several types of stimuli. o This does not imply that information is lost, rather that individual neurons receive o information for several taste types and can represent complex tastes Flavor: Flavor is the combination of taste and olfaction The olfactory mucosa is exposed to molecules of ingested items through the nasal pharynx, the so-called retronasal route. Orbital Frontal Cortex: Orbital frontal cortex is a multimodal region of cortex, meaning it receives inputs from several sensory modalities Flavor can be represented here because taste and olfactory information converge Motivational Cortex: Ed Rolls has hypothesized that a major role of the orbital frontal cortex is to respond to flavors from substances one has not had enough of, or has been deprived of for a sufficient time. Evidence from single-unit recordings in the monkey have provided evidence that this may be the case. The orbital frontal cortex has a unique position for providing information for judgments about substances that should be approached or avoided. That is, pleasantness ratings are provided that take into account not just the flavor, but the satiety and hunger related to that particular flavor. Olfaction: The Nose: Odorants enter the nasal cavity and make their way up to the olfactory epithelium. The turbinates, which are bones covered with epithelial tissue, keep the air circulating up toward the olfactory epithelium. Old Factory Receptor Neurons Olfactory receptors are called olfactory receptor neurons Different types of taste cells respond to different chemicals, much like the taste system, however there are at least 2000 human olfactory different olfactory receptor neurons coded by different genes. Olfactory receptor neurons occupy the olfactory epithelium (10 square centimeters in humans) Axons from olfactory receptor neurons cross the cribriform plate and synapse in glomeruli in the olfactory bulb. The trigeminal nerve carries information from somatosensory receptors in the nose to the thalamus. Olfactory Perception Detection (thresholds) Identifying Odors (olfactory objects) Anosmia is a condition characterized by the inability to identify odors Olfactory illusions are very easy to produce Olfactory abilities decline linearly with age
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