Biological Basis of Psychology
Biological Basis of Psychology
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Date Created: 04/25/14
Tuesday April 22 2014 Biopsychology Week 4 Lecture 5 Vision The Visual System what each number represents is higher on the gray scale forming a visual image ie a binary code transforms into a picture analogy for what our eyes pick up and how our brain translates it Light Quanta electromagnetic radiation that comes in very small packets Wavelength each quantum can be described by the distance bt 2 adjacent crests of vibratory activity photons the human visual system responds only to quanta whose wavelengths lie within a very narrow section of the total electromagnetic range The Human Eye Iris the circular donutshaped bands of contractile tissue that gives our eyes its characteristic color pupil the hole formed by the iris that allows light to enter the eye When an environment is brightly lit and sensitivity the ability to detect the presence of objects is not as important then the pupils will constrict in order to enhance acuity the ability to see the details of the object Whereas when an environment that is dimly lit the pupils will dilate in order to increase sensitivity while sacrificing acuity Cornea the transparent outer layer of the eye whose curvature is fixed bends light rays and is primarily responsible for forming the image on the retina Lens the transparent structure behind the pupil that focuses light on the retina Ciliary muscle muscles that control the shape of the lens Tuesday April 22 2014 When an object is really close the muscle tension is adjusted so that the lens becomes more cylindrical in shape and the object comes into sharper focus When an object is distant the muscles flatten the lens to focus on the object This process is called accommodation The Evolution of the Eye Early primitive eyes a couple of neurons sensitive to light coming in through the eye Attracts organisms to the light Eye lips more develop that can focus the light in the retina also develop lens for the eyes that are more specialized adaptations can be seen as stages of the evolution of human eye Looking at different species their eyes are very different and specially adapted for their environment Predators have different eyes than prey predators focused eye sight Prey wide eye range but lose depth perception binocular disparity the slight difference bit the views from the two eyes important for depth perception The Human eye continued retina the receptive surface inside the eye that contains rods amp cones fovea a small depression in the retina that has a dense concentration of cones and maximal visual acuity optic nerve the bundle of ganglion cell axons that extend from the retina to the optic chasm optic disc the region of the retina devoid of receptor cells because the ganglion cell axons and blood vessels exit the eyeball there which leads to a blind spot Re na Receptor Cells the rods and cones most cones in the fovea most rods on outside of the fovea Cones have low sensitivity need a lot of light high in acuity One cone attaches to one ganglion cell Rods have high sensitivity can be stimulated by weak light used for night vision has low acuity Many rods converge on a single ganglion cells Bipolar cells interneurons that pass info from the receptors to the ganglion cells horizontal cells communicates laterally between receptors and bipolar cells Tuesday April 22 2014 amacrine cells communicate laterally bt bipolar and ganglion cells ganglion cells whose axons form the optic nerve communicates info from receptors to the brain Visual Transduction A lot of these processes are the opposite of usual neural transmission in the brain Rod a photoreceptor is a neuron that receives light as input instead of neurotransmitters rhodopsin the photopigment within the outer segment that absorbs light In darkness a rod continuously releases glutamate when it is turned on by weak light it stops releasing glutamate when light is absorbed by rhodopsin in the outer segment it breaks down a G protein and initiates a cascade of chemical events that closes Na channels One photon of light can shut off a million Na from entering This hyper polarizes the cell the size of the hyper polarizing potential determines the magnitude of the reduction in the release of neurotransmitters Turning off a cell to fire a signal Cone in light communicating to 2 different bipolar cells off center and on center bipolar cells The bipolar cells also communicate to two separate ganglion cells an offcenter ganglion cell and an oncenter ganglion cells The glutamate that the turning on a light in the center hyper polarizes the photoreceptor causing them to release less glutamate which depolarizes the oncenter bipolar cell and hyper polarizes the offcenter bipolar cell Glutamate always depolarizes ganglion cells so there is increased firing in the oncenter ganglion cell and decreased firing in the offcenter ganglion cell resulting message the light is on the light is not off turning off a light in the center depolarizes the photoreceptor causing them to release more glutamate causing them to release more glutamate which hyperpolarizes the oncenter bipolar cell and depolarizes the offcenter bipolar cell Glutamate always depolarizes ganglion cells so there is decreased firing in the on center ganglion cell and increased firing in the offcenter ganglion cell Tuesday April 22 2014 Resulting message the light is off and the light is not on 3 major characteristics of the visual system its sensitivity because weak stimuli are amplified to produce physiological effects its integration of the stimulus over time which makes vision relatively slow but increases its sensitivity its adaptation of the visual system to a wide range of light intensities The pupil dilate and constricts depending on the intensity of the light Additionally photoreceptors have different intensity thresholds Visual Pathways Once light is transducer at the retina and sent along the axons of the ganglion cells it departs by the optic nerve and makes the first synapse in the thalamus From there it synapses from another interneuron that takes the info to the back of the head in the visual cortex in the occipital lobe Info from right visual field travels to left hemisphere info from left visual field goes to right hemisphere Not the info from leftright eye but the info from the left and right of the visual field Retinotoppic Organization what is seen is projected in opposite order on the back of the eyeball M amp P channels of the lateral geniculate nucleus Parvocellularlayers layers 36 small cell bodies sensitive to color and fine detail magnocellularlayers layers 1amp2 large cell bodies sensitive to motion Lateral Inhibition A phenomena by which interconnected neurons inhibit their neighbors enhancing the contrast at the edges of a region Enhances differences between shades that allows us to see outlines of objects better Receptive Fields Dvid Hubel amp Torsten Wiesel recording the firings action potentials from single neurons within the visual cortex of a cat They found that the neurons selectively responded to certain kinds of light within a small area of the visual field Tuesday April 22 2014 on centeroffsurround cells concentric receptive fields in which stimuli in the center excites the cell of interest while stimuli in the surround inhibits the cell Thursday April 24 2014 Lecture 5 Continued Receptive Fields Lateral geniculate cell with concentric field are oncenteroffcenter cells response to light in center of cell s field response to light in periphery of cell s field Cortical cell sensitive to orientation This cell responds strongly only when the stimulus is a vertical stripe Cortical cell sensitive to the direction of motion This cell responds strongly only when the stimulus moves downward It responds weakly to upward motion and does not respond at all to sideways motion each neuron responds to a very specific stimulus Visual Cortex is Organized in Columns cortical regions driven by stimuli in four different orientations are each coded in a different color Color Vision Component Theory Trichromatic theory the ability to perceive every color is mediated by three different cone receptors blue green and red The color spectrum may be produced by the combination of the firing of these three cones Opponent Process Theory the color vision depends on systems that produce opposite responses to light of different wavelengths when you see blue it inhibits the yellow receptors same for blackwhite results in color after effects after staring at a color for long time you see the opposite colors when you look away Tuesday April 22 2014 Lecture 6 Visual Perception amp Attention Visual Areas of the Human Cerebral Cortex Primary Visual Cortex the region of cortex where most vial info first arrives Secondary Visual Cortex the region of cortex that receives direct projections from the primary cortex lisual Association Cortex the region of cortex that receives inputs from the secondary visual cortex and from other secondary cortices scotoma damage to the primary visual cortex that can cause blindness in the corresponding area of the visual field ie damage to left primary visual field result in blindness in right field of vision blind sight patient with scotoma could unconsciously points to light above random chance Could be other pathways that bypass the visual cortex and make contact to areas of the brain stem or spared cortical tissue in the damage area Hierarchical Organization of inputs leads to cells or groups of cells that are sensitive to particular object cells fire like crazy when you see a particular someone or something like Jennifer Anniston Dorsal Stream visual info that flows from the primary visual cortex to the parietal visual cortex thought to specialize in visual spatial perception what vs where theory or visually guided behavior action vs perception theory ventral stream visual info that flows from the primary visual cortex to the inferotemporal cortex thought to specialize in visual pattern recognition what vs where theory or conscious visual perception action vs perception theory lisuaIAgnosia the failure to visually recognize objects that is not attributable to a sensory deficit of to verbal or intellectual impairment not a memory failure Damage could be just a certain classification of objects like man made objects Fusiform Face Area FFA a specific region within the ventral stream of the inferior temporal lobe part of the fusiform gyrus that is specialized for the face region Prosopagnosia damage to the FFA can lead to a visual agnosia for faces only trouble with identifying faces They know what a face is but can t recognize who it is Tuesday April 22 2014 Hemispatial neglect neglect syndrome damage to the posterior parietal cortex can lead to a deficit in attention to the opposite or collateral side of space damage to right parietal cortex means that he s not blind to left visual field but has trouble attending to things in the left visual field Everything in left field gets ignored e they only draw half a drawing half a clock Change blindness occurs bc we re not able to take everything at once can only take in certain things at once When one thing is changed within a brief pause in front of somebody they won t notice Need a pause to refresh the visual system Magicians and movie editors rely on this