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This 13 page Class Notes was uploaded by Ayden McLaughlin IV on Friday October 23, 2015. The Class Notes belongs to PSYC344 at University of Louisville taught by SandraSephton in Fall. Since its upload, it has received 45 views. For similar materials see /class/228367/psyc344-university-of-louisville in Psychlogy at University of Louisville.
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Date Created: 10/23/15
Lecture H Vision 151168 Arab Philosopher bn alHaythem demonstrated that light rays bounce off any object in all directions but we only see those rays that strike the retina perpendicularly You perceive objects by the energy that they transmit After the information reaches your nervous system you encode it You store information in terms of responses by neurons in these ways 0 which neurons respond their amount of response and the timing of their responses The law of speci c nerve energies first proposed by Johannes Peter Miiller in 1835 is that the nature of perception is defined by the pathway over which the sensory information is carried Hence the origin of the sensation is not important Therefore the differences in sensory quality the difference between seeing and hearing between hearing and touch and so on are not caused by differences in the stimuli themselves but by the different nervous structures that these stimuli excite Activity by a particular nerve always conveys the same kind of information to the brain the brain somehow interprets the action potentials from the auditory nerve as sounds those from the olfactory nerve as odors and so forth If someone electrically stimulated the auditory receptors in your ear how would you perceive it 0 Because of the law of specific nerve energies you would perceive it as sound not as shock The strength of a stimulus determines the amount of a receptor cells depolarization or hyperpolarization The amount of the receptors response determines how many action potentials the next set of neurons sends and their timing Coding also depends on relative rates of firing Descartes believed that the brains representation of a stimulus resembled the stimulus If it were possible to flip your entire brain upside down without breaking any of the connections to sense organs or muscles what would happen to your perceptions of what you see hear and so forth 0 Your perception would not change The way visual or auditory information is coded in the brain does not depend on the physical location in the brain Seeing something as 39on top39 or 39to the left39 depends on which neurons are active but does not depend on the physical location of those neurons Light enters the eye through an opening in the center of the iris called the pupil It is focused by the lens adjustable and cornea not adjustable and projected onto the retina the rear surface of the eye which is lined with visual receptors Light from the left side of the world strikes the right half of the retina and vice versa Light from above strikes the bottom half of the retina and light from below strikes the top half The visual system does not duplicate the image It codes it in various kinds of neuronal activity In the vertebrate retina messages go from receptors at the back of the eye to bipolar cells located closer to the center of the eye The bipolar cells send their messages to ganglion cells located still closer to the center of the eye The ganglion cells axons join together and travel back to the brain Additional cells called amacrine cells get information from bipolar cells and send it to other bipolar cells other amacrine cells and other ganglion cells The ganglion cell axons form the optic nerve which exits through the back of the eye The point at which it leaves which is also where the blood vessels enter and leave is the blind spot because it has no receptors Fovea meaning quotpitquot is a tiny area specialized for acute detailed vision 0 Each receptor in the fovea connects to a single bipolar cell which in turn connects to a single ganglion cell which has an axon to the brain 0 The ganglion cells in the fovea of humans and other primates are called midget ganglion cells because each is small and responds to just a single cone The vertebrate retina contains two types of receptors rods and cones o The rods which are abundant in the periphery of the human retina respond to fain light but are not useful in daylight because brain llight bleaches them 20 to 1 ratio to cones o Cones which are abundant in and near the fovea are less active in dim light more useful in bring light and essential for color vision Provide about 90 of the brains iput Becuase of the distribution of rods and cones you have good color vision in the fovea but not the periphery Both rods and cones contain photopigment chemicals that release energy when struck by light 0 photopigments consist of 11cisretinal derivative of vitamin A bound to proteins called opsins which modify the photopigments sensitivity to different wavelengths of light You sometimes find that you can see a faint star on a dark night better if you look slightly to the side of the star instead of straight at it Why 0 When looking slightly to the side the light falls on an area of the retina with more rods and more convergence of input If you found a species with a high ratio of cones to rods in its retina what would you predict about its way of life 0 This species would be highly active during the day and seldom active at night Thomas Young was the first to start deciphering the Rosetta stone He also founded the modern wave theory of light defined energy in its modern form founded the calculation of annuities introduced the coefficient of elasticity discovered much about the anatomy of the eye and made major contributions to many other fields o Recognized that color required a biological explanation He proposed that we perceive color by comparing the responses across a few types of receptors each of which was sensitive to a different range of wavelength 0 This theory is now known as the trichromatic theory of color vision or the YoungHelmholt theory According to this theory we perceive color through the relative rates of response by three kinds of cones each kind maximally sensitive to a different set of wavelengths Three kinds of cones are sufficient to account for human color vision Visual field the part of the world that you see before you can identify the color Negative color afterimage o Ewald Hering proposed the opponentprocess theory stating that we perceive color in terms of opposites That is the brain has a mechanism that perceives color on a continuum from red to green another from yellow to blue and black to white mum responds well to red or yellow responds best to green less to yellow responds best to blue The cerebral cortex is responsible for an afterimage Suppose a bipolar cell receives excitatory input from mediumwavelength cones and inhibitory input from all three kinds of cones When it is highly excited what color would one see When it is inhibited what color perception would result 0 Excitation of this cell should yield a perception of green under normal circumstances Inhibition would produce the opposite sensation red Color constancy the ability to recognize colors despite changes in lighting Retinex theory The retinex theory of color proposed by Edwin Land in the 1980s offered an explanation of our ability to perceive color in ambientcolored environments This effect is known as color constancy and was unexplainable by earlier theories of color vision The term retinex is a combination of the words retina and cortex which are the two areas responsible for the processing of visual information When a television set is off its screen appears gray When you watch a program parts of the screen appear black even though more light is actually showing on the screen than when the set was off What accounts for the black perception o The black experience arises by contrast with the other brighter areas The contrast occurs by comparison within the cerebral cortex as in the retinex theory of color vision Color vision deficiency complete color blindness perception of only black and white is rare o In the most common form of color vision deficiency people have trouble distinguishing red from green because their long and mediumwavelength cones have the same photopigment instead of different ones 0 One gene causing this is the X chromosome Many people can use varying amounts of three colors to match any other color that they see Who would be an exception to this rule and how many colors would they need 0 Redgreen color deficient people would need only two colors Women with four kinds of cones might need four Lecture I Sensation and Perception 165179 189208 The rods and cones of the retina make synapses with horizontal cells and bipolar cells The horizontal cells make inhibitory contact onto bipolar cells which in turn make synapses onto amacrine cells and ganglion cells The axons of the ganglion cells form the optic nerve which leaves the retina and travels along the lower surface of the brain The optic nerves from the tow eyes meet at the optic chiasm where in humans half of the axons from each eye cross to the opposite side of the brain Most ganglion cell axons go to the lateral geniculate nucleus part of the thalamus the term geniculate comes from the late root meaning knee Most of the optic nerve goes to the lateral geniculate which in turn sends axons to other parts of the thalamus and the occipital cortex The cortex returns many axons to the thalamus so the thalamus and cortex constantly feed information back and forth Where does the optic nerve start and where does it end o It starts with the ganglion cells in the retina Most of its axons go to the lateral geniculate nucleus of the thalamus some go to the hypothalamus superior colliculus and elsewhere Lateral inhibition is the retinas way of sharpening contrasts to emphasize the borders of objects Rods and cones have spontaneous levels of activity and light striking them decreases their output They have inhibitory synapses onto the bipolar cells and therefore light decreases their inhibitory output When light strikes a receptor does the receptor excite or inhibit the bipolar cells What effect does it have on horizontal cells What effect does the horizontal cell have on bipolar cells o The receptor excites both the bipolar cells and the horizontal cell The horizontal cell inhibits the same bipolar cell that was excited plus additional bipolar cells in the surround If light strikes only one receptor what is the net effect excitatory or inhibitory on the nearest bipolar cell that is directly connected to that receptor What is the effect on bipolar cells off to the sides What causes the effect o It produces more excitation than inhibition for the nearest bipolar cell For surrounding bipolar cells it produces only inhibition The reason is that the receptor excites a horizontal cell which inhibits all bipolar cells in the area Each cell in the visual system of the brain has a receptive eld which is the part of the visual field that excites or inhibits it The receptive field of a receptor is simply the point in space from which light strikes the cell The receptive field of a ganglion cell can be described as a circular center with an antagonist doughnut shaped surround Primate ganglion cells fall into three categories 1parvocellular neurons 2 magnocellular 3 knoiocellular Parvocellular neurons with small cell bodies and small receptive fields are mostly in or near the fovea 0 Well suited to detect visual details They also respond to color each neuron being excited by some wavelengths and inhibited by others Magnocellular larger cell bodies and receptive fields are distributed evenly throughout the retina 0 Not color sensitive They respond strongly to moving stimuli and large overall patterns but not details Not sensitive to color or details Koniocellular neurons have small cell bodies similar to parvocellular neurons but they occur throughout the retina Have a granular appearance lldustquot o Axons terminate in several locations The existence of so many kinds of ganglion cells implies that the visual system analyzes info in several ways from the start Cells of the lateral geniculate have receptive fields that resemble those of the ganglion cells As we progress from bipolar cells to ganglion cells to later cells in the visual system are receptive fields ordinarily larger smaller or the same size Why 0 They become larger because each cells receptive field is made by inputs converging at an earlier level Most visual information from the lateral geniculate nucleus of the thalamus goes to the primary visual cortex in the occipital cortex also known as area V1 or the striate cortex because of its striped appearance People with damage to area V1 report no conscious vision no visual imagery and no visual images in their dreams 0 Some people with damage to area V1 show a surprising phenomenon called blindsight an ability to respond to visual information that they report not seeing 0 An alternative explanation to blindsight is that tiny islands of healthy tissue remain within an otherwise damaged visual cortex not large enough to provide conscious perception but nevertheless enough for blindsight o In one study experimenters temporarily suppressed the visual cortex of healthy sighted people by transcranial magnetic stimulation If you were in a darkened room and researchers wanted to lread your mind just enough to know whether you were having visual fantasies what could they do 0 Researchers could use fMRI EEG or other recording methods to see whether activity was high in your visual cortex What is an example of an unconscious visually guided behavior o In blindsight someone can point toward an object or move the eyes toward the object despite insisting that he or she sees nothing The primary visual cortex sends info to the secondary visual cortex area V2 which processes the information further and transmits it to additional areas The visual paths in the temporal cortex is the ventral stream or the what pathway because it is specialized for identifying and recognizing objects The visual path in the parietal cortex is the dorsal stream or the quotwherequot or quothowquot pathway because it helps the motor system find and use objects People with damage to the ventral system temporal cortex cannot fully describe what they see They are also impaired in their visual imagination and memory People with damage to the dorsal stream parietal cortex cannot accurately reach out to grasp an object even after describing its size shape and color Suppose someone can describe an object in detail but stumbles and fumbles when trying to walk toward it and pick it up Which is probably damaged the dorsal path or the ventral path 0 The inability to guide movement based on vision implies damage to the dorsal path David Hubel and Torsten Wiesel pioneered the use of microelectrode recordings to study the properties of individual neurons in the cerebral cortex 0 Simple cell has a receptive field with fixed excitatory and inhibitory zones The more light that shines in the inhibitory zone the less the cell responds 0 Complex cells located in areas V1 and V2 do not respond to the exact location of a stimulus A complex cell responds to a pattern of light in a particular orientation anywhere within its large receptive field Responds most strongly to a stimulus moving perpendicular to its axis The best way to classify a cell as simple or complex is to move the stimulus A cell that responds to a stimulus in only one location is a complex cell Endstopped or hypercomplex cells resemble complex cells with one exception An endstopped cell has a strong inhibitory area at one end of its bar shaped receptive field largest Feature receptors neurons whose responses indicate the presence of a particular feature Prolonged exposure to a given visual feature decreases sensitivity to that feature as if one has fatigues the relevant detectors Many cortical neurons respond best to a particular spatial frequency and hardly at all to other frequencies Most visual researchers therefore believe that neurons in area V1 detect spatial frequencies rather than bars or edges Feature detector a neuron that detects the presence of a particular aspect of an object such as a shape or a direction of movement Inferior temporal cortex cerebral cortex on the inferior convexity of the temporal lobe in primates including humans It is crucial for visual object recognition and is considered to be the final stage in the ventral cortical visual system Cells in the inferior temporal neurons presumably contribute to our capacity for shape constancy the ability to recognize an objects shape even as it changes position angle lighting and so forth An inability to recognize objects despite otherwise satisfactory vision is called visual agnosia meaning lack of knowledge It usually results from damage in the temporal cortex Prosopagnosia inability to recognize faces People with prosopagnia can read so visual acuity is not the problem 0 Prosopagnosia occurs after damage to the fusiform gyrus of the inferior temporal complex especially in the right hemisphere According to fMRI scans recognizing a face depends on increased activity in the fusiform gyrus and part of the prefrontal cortex 0 People with damage to the fusiform gyrus have trouble recognizing cars bird species and so forth What does prosopagnosia tell us about separate shape recognition systems in the visual cortex o It implies that the cortical mechanisms for identifying faces are different from the mechanisms for identifying other complex stimuli Two areas that are especially activated by motion are area MT middle temporal cortex also known as area V5 and an adjacent region area MST medial superior temporal cortex Areas Mt and MST receive input mostly from the magnocellular path which detects overall patterns including movement over large areas of the visual field Cells in the dorsal part of area MST respond best to more complex stimuli such as expansion contraction or rotation ofa large visual scene People with damage to area MT become motion blind able to see objects but impaired at seeing whether they are moving or if so which direction and how fast When you wiggle your eyes back and forth why don t you see a blur 0 During your eye movements responsiveness decreases sharply in much of your visual cortex What symptoms occur after damage limited to area MT What may occur if MT is intact but area V1 is damaged 0 Damage in area MT can produce motion blindness farea MT is intact but are V1 is damaged the person may be able to report motion direction despite no conscious identification of the moving object Saccades a fast movement of an eye head or other part of an animal39s body or device It can also be a fast shift in frequency of an emitted signal or other quick change Saccades are quick simultaneous movements of both eyes in the same direction Initiated by eye fields in the frontal and parietal lobes of the brain saccades serve as a mechanism for fixation rapid eye movement and the fast phase of optokinetic nystagmus The outer ear includes the pinna the familiar structure of flesh and cartilage attached to each side of the head helps locate the source of a sound Tympanic membrane eardrum in the middle ear The tympanic membrane vibrates at the same frequency as the sound waves that strike it The TM connects to three tiny bones that transmit the vibrations to the oval window a membrane of the inner ear Hammer Anvil and Stirrup aka by their Latin names Malleus incus and stapes The net effect of the system converts the sound waves into waves of greater pressure on the small oval window This transformation is important because more force is required to move the viscous fluid behind the oval window than to move the eardrum which has air on both sides The inner ear contains a snail shaped structure called the cochlea A cross section through the cochlea shows three long fluid filled tunnels the scala vestibule scala media and scala tympani The stirrup makes the oval window vibrate at the entrance to the scala vestibule thereby setting in motion the fluid in the cochlea o The inner ear consists of the pinna cochlea and auditory meatus Gathers sound energy and focuses it on the eardrum or tympanic membrane Convert sound into neural activity Within the scala media and atop the basilar membrane is the organ of Corti the collective term for all the elements involved in the transduction of sounds The organ of Corti includes three main structures the sensory cells hair cells an elaborate framework of supporting cells and the terminations of the auditory nerve fibers The auditory receptors known as hair cells lie between the basilar membrane of the cochlea on one side and the tectorial membrane of the cochlea on one side and the tectorial membrane one the other Plate theory the basilar membrane resembles the strings of a piano in that each area along the membrane is tuned to a specific frequency Frequency theory the basilar membrane vibrates in synchrony with a sound causing auditory nerve axons to produce action potentials at the same frequency Volley principle information encoding scheme used in human hearing Nerve cells transmit information by generating brief electrical pulses called action potentials Through which mechanism do we perceive lowfrequency sounds up to about 100 Hz 0 At low frequencies the basilar membrane vibrates in synchrony with the sound waves and each responding axon in the auditory nerve sends one action potential per sound wave How do we perceive middlefrequency sounds 100 to 4000 Hz 0 At intermediate frequencies no single axon fires an action potential for each sound wave but different axons fire for different waves and so a volley of axons fires for each wave How do we perceive highfrequency sounds above 4000 0 At high frequencies the sound causes maximum vibration along the basilar membrane What evidence suggests that amusia depends on genetic differences What evidence suggests that absolute pitch depends on special experiences 0 Many relatives ofa person with amusia have the condition also Absolute pitch occurs almost entirely among people who had early musical training and is much more common among people who speak tonal languages which require greater attention to pitch Primary auditory cortex area Al the region of the brain that is responsible for processing of auditory sound information It is located on the temporal lobe and performs the basics of hearing pitch and volume Superior temporal cortex includes areas important for detecting visual motion and the motion of sounds People with damage to the primary auditory cortex hear simple sounds reasonably well unless the damage extends into subcortical brain areas How is the auditory cortex like the visual cortex 0 Both vision and hearing have quotwhatquot and quotwherequot pathways Areas in the superior temporal cortex analyze movement of both visual and auditory stimuli Damage there can cause motion blindness or motion deafness The visual cortex is essential for auditory imagery Both the visual and auditory cortices need normal experience early in life to develop normal sensitivities What is one way in which the auditory and visual cortices differ o Damage to the primary visual cortex leaves someone blind but damage to the primary auditory cortex merely impairs perception of complex sounds without making the person deaf What kinds of sounds most strongly activate the auditory complex 0 Each cell in the primary auditory cortex has a preferred frequency Many or most cells respond best to complex sounds that include harmonics Outside the primary auditory cortex most cells respond to llauditory objectsquot that mean something Two categories of hearing impairment conductive deafness and nerve deafness o Diseases infections or tumorous bone growth can prevent the middle ear from transmitting sound waves properly to the cochlea The result is conductive deafness or middle ear deafness Because people with conductive deafness have a normal cochlea and auditory nerve they hear their own voices which can be conducted through the bones of the skill directly to the cochlea bypassing the middle ear 0 Nerve deafness or innerear deafness results from damage to the cochlea the hair cells or the auditory nerve It can occur in any degree and may be confine to one part of the cochlea In which case someone hears certain frequencies and not others 0 Nerve deafness often produces tinnitus frequent or constant ringing in the ears Which type of hearing loss would be more common among members of rock bands and why Would they be likely to benefit from hearing aids o Nerve deafness is common among rock band members because their frequent exposure to loud noises causes damage to the cells of the ear Hearing aids are usually not helpful in cases of nerve deafness Which method of sound localization is more effective for an animal with a small head Which is more effective for an animal with a large head Why 0 An animal with a small head localizes sounds mainly by differences in loudness because the ears are not far enough apart for differences in onset time to be very large An animal with a large head localizes sounds mainly by differences in onset time because its ears are far apart and well suited to noting differences in phase or onset time Sound localization sound shadow time ofarrival phase difference Sensations from the vestibular organ detect the direction of tilt and the amount of acceleration of the head Calcium carbonate particles called otoliths lie next to the hair cells The vestibular organ consists of the saccule utricle and three semicircular canals o The three semicircular canals oriented in perpendicular planes are filled with a jellylike substance and lines with hair cells Acceleration of the head at any angle causes the jellylike substance in one of these canals to push against the hair cells People with damage to the vestibular system have trouble reading street signs while walking Why 0 The vestibular system enables the brain to shift eye movements to compensate for changes in head position Without feedback about head position a person would not be able to correct the eye movements and the experience would be like watching a jiggling book page Pacinian corpuscle detects sudden displacements or high frequency vibrations on the skin They respond only briefly to steady pressure on the skin The onionlike outer structure provides a mechanical support to the neuron inside it so that a sudden stimulus can bend it but a sustained stimulus cannot Information from touch receptors in the head enters the central nervous system through the cranial nerves Information from receptors below the head enters the spinal cord and passes toward the brain through the 31 spinal nerves including 8 cervical nerves 12 thoracic nerves 5 lumbar nerves 5 sacral nerves and 1 coccygeal nerve Each spinal nerve has a sensory component and a motor component Each spinal nerve innervates or connects to a limited area of the body called a dermatome The axons carrying pain information have little or no myelin and therefore conduct impulses relatively slowly in the range of 2 to 20 meters per second The thicker and faster axons convey sharp pain and the thinner ones convey duller pain Pain axons release two neurotransmitters in the spinal cord Mild pain releases the neurotransmitter glutamate whereas stronger pain releases both glutamate and substance P Someone suffers a cut through the spinal cord on the right side only Will the person lose pain sensation on the left side or the right side Will he or she lose touch sensation on the left side or the right side 0 The person will lose pain sensation on the left side of the body because pain information crosses the spinal cord at once He or she will lose touch sensation on the right side because touch pathways remain on the ipsilateral side until they reach the medulla What would happen to a pain sensation if glutamate receptors in the spinal cord were blocked What if substance P receptors were blocked o Blocking glutamate receptors would eliminate weak to moderate pain however doing so would not be a good strategy for killing pain Glutamate is the most abundant transmitter and blocking it would disrupt practically everything the brain does Blocking substance P receptors make intense pain feel mild Opioid mechanisms systems that respond to opiate drugs and similar chemicals 0 Opiates bind to receptors found mostly in the spinal cord and the periaqueductal gray area of the midbrain Vertebrate muscles fall into three categories 0 Smooth muscles which control the digestive system and other organs 0 Skeletal or striated muscles control movement of the body in relation to the environment 0 Cardiac muscles have properties intermediate between those of smooth and skeletal muscles
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