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Psychology of Sensation and Perception

by: Glen Hackett

Psychology of Sensation and Perception PSY 4030

Marketplace > Middle Tennessee State University > Psychology (PSYC) > PSY 4030 > Psychology of Sensation and Perception
Glen Hackett
GPA 3.8

Alan Musicant

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Alan Musicant
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This 82 page Class Notes was uploaded by Glen Hackett on Wednesday September 23, 2015. The Class Notes belongs to PSY 4030 at Middle Tennessee State University taught by Alan Musicant in Fall. Since its upload, it has received 10 views. For similar materials see /class/213025/psy-4030-middle-tennessee-state-university in Psychology (PSYC) at Middle Tennessee State University.


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Date Created: 09/23/15
Chapter 1 Introduction to Perception Overview of Questions Why study perception How are perceptions determined by unconscious processes What is the difference between perception and recognition How is perception measured Why Study Perception Future careers Graduate school work in perception Medical applications Devices to assist people with vision and hearing losses Understanding how you perceive the world Language processing Color vision Depth perception Pmcessing Transmissinn Transductjm o Enwranmamai stimuius 9A ttendeo stim u ius o Stimnins 0quot MB recepmrs Figure 11 The perceptual process Thesteps in this process are arranged in a circle to emphasize that the process is dynamic and continually changing See text for description ofeach step In process The Perceptual Process Stimulus All objects in the environment are available to the observer Observer selectively attends to objects Stimulus impinges on receptors resulting in internal representation 1 Environmental stimulus 2 Attended stimulus 3 Stimulus on the receptors a a We Kf Wm 39 Retina a Thervvaods V b Moth on tree 0 image on Ellen s retina Figure 12 a We take the woods as the starting point for our description of the perceptual process Everything in the woods is the environmental stimulus b Ellen focuses on the moth which becomes the attended stimulus c An image of the moth is formed on Ellen39s re i The Perceptual Process continued Electricity Transduction occurs which changes environmental energy to nerve impulses Transmission occurs when signals from the receptors travel to the brain Processing occurs during interactions among neurons in the brain 4Transduction 5Transmission 6 Processing Light ln Electricity out 3 Electricity created 7b One neuron activates another 70 Interactions between neurons Figure 13 a Transduction occurs when the receptors create electrical energy in response to the light b Tranmission occurs as one neuron activates the next one c This electrical energy is processed through networks of neurons S gnaliecelved Signali nl a39ne as new 90 Copy muhls I vansmlssm stimulus I U sgnalir i6 brain ignalsenl idiiierentmaw sintl Percaption I u i i Figure 14 Comparison of signal transmission by cell phone and the nervous system a Cell phone 1 sends an electrical signal that stands for hello The signal that reaches cell phone 2 is the same as the signal sent from cell phone 1 b he nervous system sends electrical signals that stand forthe moth The nervous system processes these electrical signals so the signal responsible for perceiving the moth is different than the original signal sent from Hello I The Perceptual Process Experience and Action Perception occurs as a conscious experience Recognition occurs when an object is placed in a category giving it meaning Action occurs when the perceiver initiates motor activity in response to recognition 7 Perception 8 Recognition 9 Action 2 it i 3 Ellen perceives something b Ellen reallzes It IS a moth 0 Ellen walks toward the moth on the tree Figure 15 3 Ellen has conscious perception of the moth b She recognizes the moth c She takes w action by walking toward the tree to get a better ve E Figure 16 Look at this drawing rst then close your eyes and turn the page so you are looking at the same place on the page directly underthis one Then open and shut your eyes rapidly Adapted Bugelskiamp D Alampay 961 C Figure 19 Did you see a rat or a man Looking at the more ratlike picture in Figure 111 increased the changes that you would see this one as a rat But if you had firs seen the man version Figure 18 you would have been more likely to perceive this gure as a man Adapted Bugelskiamp D Alampay 1961 Figure 111 Man version of the ratman stimulus Adapted Bugelskiamp D Alampay 1961 Two Interacting Aspects of Perception Bottomup processing Processing based on incoming stimuli from the environment Also called databased processing Topdown processing Processing based on the perceiver s previous knowledge cognitive factors Also called knowledgebased processing b Existing knowledge 09 d J Figure 17 Perception is determined by an interaction between bottomup processing which starts with the image of the receptors an topdown processing which brings the observer39s knowledge into play In this example a the image ofthe moth on Ellen39s retina initiates bottomup processing and b her prior nowledge ofmoths contributes to topdown processing Approaches to the Study of Perception Observing perceptual processes at different stages in the system Psychophysical approach PP the stimulusperception relationship Physiological approach PH1 the stimulusphysiology relationship Physiological approach PH2 the physiology and perception relationship These stages are interconnected and communicate with one another Experience and action PhVSJO E ngCB39 lt Stimuli pl OCSSSES PH1 Figure 18 Psychophysical PP and physiological PH approaches to perception The three boxes represent the three major com onents ofthe perceptual process see Figure 11 The three relationships that are usually measured to s udy the perceptual process are the psychophysical PP relations ip between stimuli and perception the physiological PH1 relationship between stimuli and physiological processes and the physiological PH2 relationship between physiological processes and percep ion Stimulus PmWen ff m lbmnt39 Snqu Pmemun Physlnwav myquot asllvllv Figure 110 Experiments that measure the relationships indicated by the arrows in Figure 18 a The psychophysical relationship PP between stimulus and perception Two color d patches are judged to be different b The physiological relationship PH1 between the stimulus andt e ph siologzcal response A light genera es a neural response in the cat39s co ex c The physiological relations ip P 2 between the physiological response and perception A person39s brain activity is monitored as a person indicates what he Is seeIng Psychophysics Overview of Methods of Measurement Qualitative Methods Describing Recognizing Quantitative Methods Detecting Perceiving Magnitude Searching Qualitative Methods of Psychophysical Measurement Description Indicating characteristics of a stimulus First step in studying perception Called phenomenological method Recognition Placing a stimulus in a category by identifying it Categorization of stimuli Used to test patients with brain damage Quantitative Methods Classical Psychophysics Absolute threshold smallest amount of energy needed to detect a stimulus Method of limits Stimuli of different intensities presented in ascending and descending order Observer responds to whether she perceived the stimulus Crossover point is the threshold Y Y Y Y Y Y Y N N N N N N N N Crossover gt985 995 975 995 985 985 985 975 values Threshold Mean of CiassoVers 98 5 Figure 112 The results ofan experiment to determine the threshold usingthe method of limits The dashed lines indicate the crossover point for each sequence of stimuli The threshold the average ofthe crossover values is 985 in this experiment Classical Psychophysics continued Absolute threshold cont Method of adjustment Stimulus intensity is adjusted continuously until observer detects it Repeated trials averaged for threshold Classical Psychophysics continued Absolute threshold cont Method of constant stimuli Five to nine stimuli of different intensities are presented in random order Multiple trials are presented Threshold is the intensity that results in detection in 50 of trials Percentage stimuli detected 0 0 Threshold 1 O 160 170 180 190 200 Light intensity Figure 113 Results ofa hypothetical experiment in which the threshold for seeing a light is measured by the method of constant stimuli The threshold the intensity at which the light is seen on half of its presentations is 180 in this experiment Classical Psychophysics continued Difference Threshold DL smallest difference between two stimuli a person can detect Same methods can be used as for absolute threshold As magnitude of stimulus increases so does DL Weber s Law explains this relationship DL S K mu mourn n Human my Figure 114 The difference threshold DL a The person can detect the difference between a 100gram standard wei ht and a 102 ram weight but cannot detect a smaller difference so the BL is 2 grams With a ZOOgram s andard weigh the comparison weight must be 204 grams before the person can detect the difference so the BL is 4 grams The Weber fraction which is the ratio of DL to the weight ofthe standard Is cons TABLE 11 I Weber Fractions for a Number of Different Sensory Dimensions Electric shock 001 Lifted weight 002 Sound intensity 004 Light intensity 008 Taste salty 008 Table 11 Weber fractions for a number of different sensory dimensions Is There An Absolute Threshold There are differences in response criteria among participants Liberal responder responds yes if there is the slightest possibility of experiencing the stimulus Conservative responder responds yes only if he or she is sure that a stimulus was present Each person has a different response criterion but the sensitivity level for both of them may be the same Signal detection theory is used to take individual s response criteria into account Regina Percent yes responses 1 O Low High Light intensity Figure 117 Data from experiments in which the threshold for seein a light is determined for Julie reen points and Regina red points by means ofthe method of constan stimuli These data indicate tha Julie39s threshold is lowerthan Regina39s But is Julie really more sensitive to the light than Regina or does she just ar 0 be more sensitive because she is a more liberal respon er Quantitative Methods Modern Psychophysics Magnitude estimation scaling Stimuli are above threshold Observer is given a standard stimulus and a value for its intensity Observer compares the standard stimulus to test stimuli by assigning numbers relative to the standard Modern Psychophysics continued Magnitude estimation cont Response compression As intensity increases the perceived magnitude increases more slowly than the intensity Response expansion As intensity increases the perceived magnitude increases more quickly than the intensity 80 l x 70 I 39 I x 3 60 I J N I E 50 x 3 I l a 9 40 I g 4 395 so 7 u I E 20 I I Brlghtness I Line length 10 Eectric shock 7 I l l o 7 0 10 20 SO 40 50 60 7O 80 90100 Stimulus intensity Figure 115 The relationship between perceived magnitude and stimulus intensity for electric shock line length and brightness Adapted from Stevens 1962 Quantitative Methods continued Magnitude estimation cont Relationship between intensity and perceived magnitude is a power function Steven s Power Law P Ksn 1 Brigh39ness 17 Line iength I Elechiu Shook Lug magnitude estimate 39 11 12 13 14 15 16 17 Log stimulus intensity Figure 116 The three functions from Figure 115 plotted on loglog coordinates Taking the logarithm of the magnitude estimates and the logarithm ofthe stlmulus intensity turns the functions Into straight lines Adapted from Stevens Other Measurement Methods Searching for stimuli Visual search observers look for one stimulus in a set of many stimuli Reaction time RT time from presentation of stimulus to observer s response is measured Chapter 2 Introduction to the Physiology of Perception Overview of Questions How are physiological processes involved in perception How can electrical signals in the nervous system represent objects in the environment The Brain History of the Physiological Approach Aristotle 384322 BC heart was seat of mind and soul Galen 130200 AD spirits owed through ventricles of brain Descartes 16305 pineal gland was seat of soul V is 1664 beginning of modern view that the brain is responsible for mental functions The Brain History continued Mueller 1842 doctrine of speci c nerve energies Golgi 1873 developed method of staining speci c neurons Adrian 1920s recordings from single neurons 1950s modern era of brain research began Hpart glm quotSpiritsquot E gt Aristotle 4th century en Galen 2nd century Descartes 1630 Willis 1664 at lb 5 K 6 Golgi slalnad neuron Singleneuron recording Neural networks Golgi 18705 Adrian 1920s quem e 0 ET Figure 21 Some notable ideas and events regarding the physiological workings of the mind Basic Brain Structure The brain has modular organization The sensory modalities have primary receiving areas Vision occipital lobe Audition temporal lobe Tactile senses parietal lobe Frontal lobe coordinates information received from two or more senses Parietal lobe skin senses Frontal be Occupital lobe vision Temporal lobe i l Nil hearing HM Figure 23 The human brain showing the locations ofthe primaryreceiving areas for the senses in the temporal occipital and parietal lobes and the frontal lobe which Is involved with integrating sensory f nctions Neurons Transduction ampTransmission Key components of neurons Cell body Dendrites Axon or nerve ber Receptors specialized neurons that respond to speci c kinds of energy Touch receptor Dmmma Stimulus tram Nerve be Axon my new line m antunrva Figure 24 The neuron on the right consists ofa cell body dendrites and an axon or nerve ber The neuron on the left that receives stimuli from the environment has a receptor in place ofthe cell body 9 a ViSion b Hearing 5 Touch d Smell EH aste Fi ure 25 Receptors for a vision b hearing c touch d smell and e taste Each of these receptors is specialized to transduce a speci Ic type of environmental energy into electricity Arrows indicate the place on the receptor neuron where the stimulus acts to begin the process of transduction Recording Neural Signals Microelectrodes are used to record from single neurons Recording electrode is inside the nerve beL Reference electrode is outside the ber Difference in charge between them is 70 mV This negative charge of the neuron relative to its surroundings is the resting potential Recording Neural Signals continued Electrical signals or action potentials occur when permeability of the membrane changes Na ows into the ber making the neuron more positive K ows out of the ber making the neuron more negative This process travels down the axon in a propagated response mg Clcclruuu axciil sn Dvessuiersensitive iecepwi l4 NBA 5 in Miss Charge inside fiber relative to auisiae mil up m Figure 27 a When a nerve ber is at rest there is a difference in charge of70 mV between the inside and the outside of the ber This difference is measured by the meter on the left the difference in charge measured by the meter is displayed on the right b As the nerve impulse indicated by the gray ban passes the electrode the inside of the ber near the electrode becomes more positive This ositivity is the rising phase of the action potential c As the nerve impulse moves past the electrode the c arge inside the ber becomes more negative This is the falling phase ofthe action potential d Eventually the neuron returns to its resting s a e Basics of Neural Signals Neurons are surrounded by a solution containing ions Ions carry an electrical charge Sodium ions Na positive charge Chlorine ions CI39 negative charge Potassium ions K positive charge Electrical signals are generated when such ions cross the membranes of neurons Membranes have selective permeability K K Figure 28 A nerve ber showing thehigh concentra on of sodium out he ber Other ions such as negatively charged chlorine are not s 0 side the ber and potassium inside h wn Properties of Action Potentials Action potentials show propagated response remain the same size regardless of stimulus intensity increase in rate to increase in stimulus intensity have a refractory period of1 ms upper firing rate is 500 to 800 impulses per second show spontaneous activity that occurs without stimulation a D Time Pressure on Pressure off Figure 210 Response ofa nerve ber to a soft b medium and c sirong stimulation Increasing the stimulus strength increases both the rate and the regularity of nerve ring in this ber Synaptic Transmission of Neural lmpulses Neurotransmitters are released by the presynaptic neuron from vesicles received by the postsynaptic neuron on receptor sites matched like a key to a lock into speci c receptor sites used as triggers for voltage change in the postsynaptic neuron an w 1 a mpr ml vwclmlm lr mm mw f A senmnc mm nmmraim Figure 211 Synagtic transmission from one neuron to another a A signal travelin down the axon ofa neuron reachest e synapse at the end of the axon b The nerve impulse causes e release 0 neurotransmitter molecules from the synaptic vesicles ofthe sending neuron c The neurotransmitters t into receptor sites and cause a voltage change in the receiving neuron VIDEO Synaptic Transmission Types of Neurotransmitters Excitatory transmitters cause depolarization Neuron becomes more positive Increases the likelihood of an action potential Inhibitory transmitters cause hyperpolarization Neuron becomes more negative Decreases the likelihood of an action potential Levci oi depuianzaiinn eded to trigger an action potenhai Charge inside fiber Depolarization Excitatory 7E Levei to trigger an actiun potential Charge inside fiber Hyperpolar Inhlbltory b Figure 212 a Excitatory transmitters cause depolarization an increased positive charge inside the neuron b Inhibitory transmitters cause hyperpolization an increased negative charge inside the axon The charge inside the axon must reach the dashed line to trigger an action poten ia Excilaucn IDWJEl ElRUH lF la L l p VET rmlllllllllllllll E ff aim ll lllllllll esA kvgt m lllllllll fell ill l hlblIlSH stronger Bllmtlut cn Ell LllJ5 m Figure 213 Effect of excitatory E and inhibitory I input on the rin rate of a neuron The amount of excitatory and inhibitory input to the neuron is indicated by the size 0 the arrows at the s na se The responses recorded bythe electrode are indica ed by the records on the right The ring that occurs before the stimulus is resented is s ontaneous activity In a the neuron receives only excitatorytransmitter which causest e neuron to Ire ln b to e the amount of excitatory transmitter decreases while the amount of inh itory transmitter increases As inhibition becomes stronger relative to excitation ring rate decreases until eventually the neuron stops Iring Neu ral Circuits Groups of neurons connected by excitatory and inhibitory synapses A simple circuit has no convergence and only excitatory inputs Input into each receptor has no effect on the output of neighboring circuits Each circuit can only indicate single spot of stimulation 7654321 E o 32 ES 7 Hill Receptors stimulated ehce Right Response ure 214 Le A circuit with no cohverg eptors stimulated Fig rec Neural Circuits continued Convergent circuit with only excitatory connections Input from each receptor summates into the next neuron in the circuit Output from convergent system varies based on input Output of circuit can indicate single input and increases output as length of stimulus increases Figure 21 increasin Firing rate of B Receptors stimulated 5 39 39 39 add 390 Median 39 39 39 quot 39 thereceptors so 9 the size afihe stimulus increases the size of neuron B39s response Neural Circuits continued Convergent circuit with excitatory and inhibitory connections Inputs from receptors summate to determine output of circuit Summation of inputs result in weak response for single inputs and long stimuli maximum ring rate for medium length stimulus 2 3 4 5 0000in W B Inhibitory synapse Firing rate of B Receptors stimulated Figure 2 39 39 39 and i D 39 u me iue 2 6 and 7sends inhibition to neuron B neuron B responds best when just the center 3 5 are stimula ed Receptive Fields Area of receptors that affects ring rate of a given neuron in the circuit Receptive fields are determined by monitoring single cell responses Research example for vision Stimulus is presented to retina and response of cell is measured by an electrode Record signai from optic ne fiber Figure 217 Recording electrical signals from a fiber in the optic nerve of an anesthetized cat Each point on the screen corresponds to a point on the cat39s re ina CenterSu rround Receptive Fields Excitatory and inhibitory effects are found in receptive elds Center and surround areas of receptive fields result in Excitatorycenterinhibitory surround nhibitorycenterexcitatory surround Receptive field b Figure 218 a Response ofa ganglion quot39 39 quot to stimulation quot quot39 quot eld area A on the screen inside the excitatory area ofthe cell39s receptive eld area B and inside the inhibitory area ofthe cell39s receptive eld area C b The receptive eld is shown without the screen CenterSu rround Antagonism Output of centersurround receptive elds changes depending on area stimulated Highest response when only the excitatory area is stimulated Lowest response when only the inhibitory area is stimulated Intermediate responses when both areas are stimulated Figure 219 Response of an excitatorycenterinhibitory surround receptive eld as stimulus size is increased Shading indicates the area stimulated with light The response to the stimulus is indicated below each receptive eld The largest response occurs when the entire excitatory area is illuminated as in b Increasing stimulus size further causes a decrease in ring due to centersurround antagonism Adapted u eland Wiesel Sensory Code Representation of Environment Sensory code representation of perceived objects through neural ring Speci city coding speci c neurons responding to speci c stimuli Leads to the grandmother cell hypothesis Recent research shows cells in the hippocampus that respond to concepts such as Halle Berry Siimulus Neurun 1 Neuron 2 Neulun 3 3 am 2 Mary Figure 221 be coded 4 39 39 39 a E L one specialized neuron to Htppocampus Halle Berry Figure 222 a Location ofthe hippocampus and some ofthe other structures that were studied by Quiroga and coworkers 2005 b Some ofthe stimuli that caused a neuron in the hippocampus to re Sensory Code Representation of Environment continued Problems with speci city coding Too many different stimuli to assign speci c neurons Most neurons respond to a number of different stimuli Distributed coding pattern of ring across many neurons codes speci c objects Large number of stimuli can be coded by a few neurons Slimnlus Neuron Neuron 2 Neuron a 39 Hililiii liil a it Pauhaei int m7qu Figure 223 How faces could be coded by distributed coding Each face causes all the neurons to re but the pattern of ring is different for each face One advantage ofthis method ofcoding is that many faces could be represented by the ring ofthe three neurons Sensory Code Representation of Environment continued How many neurons are needed for an object in distributed coding Sparse coding only a relatively small number of neurons are necessary This theory can be viewed as a midpoint between speci city and distributed coding Mindbody Problem How do physiological processes become transformed into perceptual experience Easy problem of consciousness Neural correlate of consciousness NCC how physiological responses correlate with experience Hard problem of consciousness How do physiological responses cause expenence Sensation and Perception Psych 40305030 Sp 2013 HW1b Ch 2 materials Due Sun 3 Feb 2013 by 1159 PM 1 What are the four lobes of the cerebral cortex and what senses send information as a primary target to the different lobes To what lobe do we find a primary projection for the sense of taste The Occipital Lobe is the primary area for Vision The Temporal Lobe is the primary area related to our hearing The Parietal Lobe is the area that belongs to our skin senses feeling touching temperature pain The Frontal Lobe is the area in the cortex that receives all the senses This lobe is important because it helps our perceptions when we are receiving two or more senses The sense of taste is connected to the parietal lobe Information is sent to the primary gustatory cortex which is located in the ventral parietal lobe 2 Brie y define what an action potential is and what function it serves in the nervous system Explain how it is chemically generated and propagated down an axon 0 An action potential is a fast increase in positive charge in a nerve fiber that goes down the fiber This is part of the process that happens during the firing of a neuron Information is sent down by a neuron to an axon going away from the cell body Neurons communicate with each other by using potential small pulse of electrical activity It s basically the exchange of some positive charged sodium and potassium ions with the negative charged chloride and protein ions This is the resting potential When the charge on the nerve fiber gets to 40 mv its electrical impulse shoots down the nerve fiber creating action potential The function or purpose of action potential why it is important for our nervous system is because it helps receive and analyze information in the brain An important part of action potential is that it is a propagated response When the response is produced it then travels all the way down the axon without getting smaller It is a very important part of action potential because allows the neurons to send out signals for long distances Homework lc Ch 3 Goldstein 8m Psy 4030 7 D01 Spring 2013 Dr Musicant Instructor Due on Sat 9 Feb 2013 1159PM 1 In terms of the visible light spectrum de ne wavelength What is the visible light range for humans Light is explained by its wavelength and frequency The wavelength is the space between two peaks of the wave electromagnetic waves In the electromagnetic spectrums the waves have a big range from short wavelength gamma rays to long wavelength radio waves p44 the colors we see come from the light made up from wavelengths and frequencies We nd the range for humans on the electromagnetic spectrum and it ranges from 400700 nanometers 2 What is transduction in terms of human vision Give a brief description of the process of transduction in human visual receptors Transformation of light to electricity is the process of transduction Transduction is carried out by receptors and the receptors for vision are rods and cones Rods are on the outsides of the retina and can only see black and white Cones can see color and it s in the center of the retina One important part of the rod of transduction is the outer segment the outer segment is important because that s where the light helps create electricity The outer segments have tons of discs and each disc has thousands of visual pigment molecules The most important molecule called the retinal is so important because it s the part of the visual pigment that s sensitive to light Transduction is caused when the retinal receives a photon of light Before the light it absorbed it s beside the opsin When the photon hits the retinal it changes shape into isomerization sticking out from the opsin and this is what triggers the change of light into electricity in the receptors The powerpoint gave certain things that involve the process of transduction Retinal molecule changes shape Opsin molecule separates The retina shows pigment bleaching Retinal and opsin must recombine to respond to light Cone pigment regenerates in siX minutes Rod pigment takes over 30 minutes to regenerate 3 What are the two types of human visual receptors What are they specialized to do in terms of the type of light and the information that the transduction provides What is the distribution of the two human visual receptor types across the human retina Rods They are large and shaped like a cylinder They respond to low levels of light at wavelengths and are only responsible for black and white color These are located on the outside of the retina They have greater convergence than cones Rods are more sensitive to light and dark changes There is around 120 million rods in the retina Cones Look small and tapered Cones are able to see color vision Less sensitive to light and need higher levels oflight to make signals Cones are located in the center of the retina Cones aren t as sensitive to light but they are really sensitive to greens blues and reds There are 5 million cones in the retina The fovea is only on cones o Transduction is carried out by receptors and the receptors for vision are rods and cones 4 One type of receptor has greater sensitivity to light than the second type Which is more sensitive and explain howwhy this greater sensitivity occurs 0 Rods are more sensitive because they need less amount of light to respond Rods are most sensitive to light of 500nm and cones are 560 mn A rod is so sensitive it only needs 1 photon of light to respond Cones can take up to hundreds of photons of light to respond So rod cells take longer to respond to light and like I said above this makes it harder to detect changes because their stimuli are being gathered over longer periods of time making it less accurate than what cones perceive When our vision shifts from cones to rods in the dark we are more sensitive to short wavelength light 5 What is lateral inhibition and how might it have an effect on visual perception 0 Lateral inhibition is inhibition transmitted across the retina Keffer Hartline Henry Wagner and F lyod Ratliff used the horseshoe crab to explain how lateral inhibition effects visual perception They wanted to show how the limulus can affect responses to neurons in a circuit they also chose this animal because of the structure of its eye The crab s eye has hundreds of ommatidia the ommatidia has a lens that is on a receptor The size of the lens and receptor is as small as a pencil point This makes is possible to illuminate and record from the single receptor without illuminating the receptors around it They found out this cause a big response when illuminating the receptor When they added illumination to 3 closest receptors at B receptor A decreased So increasing B would decrease A even more That s how they found that the decrease in firing receptor A is caused by lateral inhibition that s transmitted across the crab s eye by the fibers of lateral plexus All of this transmits signals across the human retina 0 Lateral inhibition can enhance our visual system to react to edges of a surface It happens because neurons react way more strongly to the edge of a stimulus rather than to the middle of a stimulus All sides of the surface coming from the middle of a neuron receive inhibition but the edge neurons only get inhibition from their neighbors on 1 side It makes small hard to see edges seem more clear or sha1per in an image Lateral inhibition is important because it makes the edges more obvious or stand out


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