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Sensation and Perception Exam 1 review

by: Fiaza Ahmed

Sensation and Perception Exam 1 review EXP 4204

Marketplace > Florida International University > Psychlogy > EXP 4204 > Sensation and Perception Exam 1 review
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Intro to sensation and perception visual system
Sensation and Perception
Timothy Allen
Study Guide
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This 12 page Study Guide was uploaded by Fiaza Ahmed on Monday February 8, 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 284 views. For similar materials see Sensation and Perception in Psychlogy at Florida International University.


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Date Created: 02/08/16
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 Sensation and Perception  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 Vision  Vision is the system that allows us to perceive light  Visible light is an example of electromagnetic energy  Light is made up of particles called photons that behave in a wave-like manner  The shorter the wavelength the higher the energy. The longer the wavelength, the lower the energy  *Red has a wavelength approaching 700 nm (the longest wavelengths we can perceive)  Term photon is used when discussing brightness and intensity. The term wavelength is used when discussing color The Eye  Our eyes are located in the front and slightly spaced which gives us good depth perception  Reflected light enters eye through the pupil and is focused on the retina by the cornea and the lens. The retina contains specialized cells called rods and cones which transduce light energy into an electrochemical signal which is then sent to the brain for processing through the optic nerve. Field of view  Part of the world you can see without eye movements. Approximately 190 degrees horizontally and 140 degrees vertically Cornea  Clear front surface of the eye that allows light in  Major focusing element of the eye  Begins process of refracting light to come into focus on the retina of the eye  Is transparent  Cornea is rigid therefore changes in refraction come from the adjustable lens Sclera: Tough membrane which provides protective covering for the eye Anterior chamber: fluid-filled space between the cornea and the iris Iris: colored part of the eye, muscle that controls the amount of light entering through the pupil Pupil: an opening in the middle of the iris  Light enters through the opening  Pupil expands (dilates) in dim light (iris relaxes control)  Pupil narrows in bright light (iris contracts)  Process not directly under conscious control…known as pupillary reflex  Pupil can range from 2mm to 8mm in diameter Posterior chamber: space between the iris and the lens which is filled with aqueous humor fluid.  The lens  Ciliary muscles: muscles connected to the lens through which accommodation is controlled. Can contract and increase curvature of lens  Zonule fibers: the ciliary muscles work together with these fibers and connects lens to choroid membrane  When looking far, lens relaxes which allows us to look at a distant object  When looking near, lens contracts which allows you to focus  The Retina  The retina is the eye’s photosensitive surface  Goal of other parts of the eye is to focus an image on the retina  The retina is thin and composed of several interconnected layers  The retina is in the location where transduction takes place  Starts the process of transmitting visual information to the brain  The receptors: rods and cones Rods Cones  At the periphery of retina  Clustered at the fovea  Very light sensitive (center)  Specialized for night vision  High visual acuity  120 million in each eye  Responsible for color vision  Only one type  7 million in each eye  Sees only in shades of gray  Three classes of cones (black to white)  Photopigment:  No rods in fovea chromodopsin  Photopigment: rhodopsin  Photopic system  Scotopic system  Transduction of light  Rods and cones are equipped with the ability to convert light into a neural signal by using photopigments.  Photopigments absorb light and release an electric potential  When it absorbs light, it changes shape  Change in shape initiates series of biochemical processes  Nature of photopigment is central to determining how the receptor behaves with regard to light  Absorption of photon by photopigment causes receptor to have more negative voltage inside relative to outside the receptor known as hyperpolarization  Hyperpolarization causes receptor to release less of the neurotransmitter  Light is inhibitory  Light inhibits release of inhibitory neurotransmitter which in turn excites visual system  The Duplex Theory of Vision  There are functionally two distinct ways in which our eyes work  However there is a range of intermediate ambient light intensity within both systems work (mesopic vision) Scotopic system Photopic system  Vision associated with rods  Vision associated with cones  More sensitive to different  More sensitive to longer and shorter wavelengths wavelengths (spectral sensitivity)  Sensitive to about 555 nm  Sensitive to under 500 nm  Difference in sensitivity is  Convergence: is the pooling known as purkinje shift of information happens  One cone usually connects greater for rods than for to one ganglion cell which cones maximizes the ability to  Many rods connect to one pinpoint the source of light retinal ganglion cell in space  Limits spacial confusion  Retinal ganglion cells and receptive fields  Only about 1.1 million ganglion cells  Most ganglion cells receive inputs from many different photoreceptors  Forming of receptive fields (array of photoreceptors from which each retinal ganglion cell receives input)  As you move away from the fovea, ganglion receptive fields get progressively larger which allows greater convergence and greater sensitivity to dim light  Ganglion cells start the process of edge detection  Earliest stage of edge detection occurs in the retinal ganglion cells known as center-surround receptive fields.  Lateral inhibition: goal is to facilitate edge detection  Horseshoe crab  Herman grid 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 Magnocellular Parvocellular konicellular  Layer 1 : receives  Layer 3:  There are 6 (one info from ipsilateral under each of the contralateral eye  Layer 4: magno and  Layer 2: receive contralateral parvocellular layers) info from  Layer 5:  Bistratified ganglion ipsilateral eye ipsilateral cells  Parasol retinal  K cells have more  Layer 6: ganglion cells (M contralateral convergence, lower Cells)  Midget retinal acuity  M cells have large ganglion cells (P receptive field cells) and are sensitive  P cells receive to light but not info from single color cone, contains  Light detection detailed info and motion necessary for detection visual acuity  Sensitive to wavelength and other foveal functions 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”


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