biospsych week 5
biospsych week 5 PSY 3
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This 10 page Class Notes was uploaded by Anahit Ghaltaghchyan on Sunday July 24, 2016. The Class Notes belongs to PSY 3 at University of California Santa Barbara taught by Staff in Summer 2016. Since its upload, it has received 7 views. For similar materials see Psych 3-Biopsychology in Psychlogy at University of California Santa Barbara.
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Date Created: 07/24/16
▯ Humans see wavelengths between 380-760 nanometers ▯ Wavelength determines perception of color ▯ Intensity (amplitude) determines perception of brightness ▯ ▯ Red has higher wavelength than violet ▯ ▯ Vision ▯ Light enters the eye through the pupil, travels through the lens then hits the retina ▯ Lens- focuses light on the retina Ciliary muscles alter the shape of the lens as needed Accommodation: the process of adjusting the lense to bring images into focus ▯ ▯ Eye position and binocular disparity: perceiving depth Convergence: physical adjustment of the eyes to near or far objects Binocular disparity- the different between the image on the two retinas. Measures how close an object is to you based on the angle your eyes shift to see the object. Both are greater when objects are close- together, they provide the brain with the 3d image and distance information Eye movement We continually scan the world with small and quick eye movements: saccades. About 3 times per second These bits of info are the integrated Stabilize retina image (no movement of image on the retina) see nothing The visual system responds to changes o This is a general characteristic of the way the brain and NS work in many cases. Our neurons are responding to change in movements ▯ The retina: from photons to neurons The retina is, in a sense, inside out o Light passes through several cell layers before reaching its receptors Vertical pathways .. receptors bipolar cells retinal ganglion cels optic nerve Lateral communication- adjacent receptors and ganglion cells can communicate with each other o Horizontal cells o Amacrine cells ▯ Fovea and blind spot Blind spot- no receptors where information exits the eye (beginning of the optic nerve) o The visual system uses info from cells around the blind spot for completing, filling in the blind spot Fovea: highest acuity area of retina located at its center o Thinning of the ganglion cell layer reduces distortion due to cells between the pupil and the retina. Light has to go through less thickness to get through o ▯ Light receptors in the retina: cone and rod vision Duplexity theory of vision: cones and rod mediate different kinds of vision o Cones- photopic (daytime) vision High acuity with color Low sensitivity (needs ample light to function well). o Rods- scotopic (nighttime vision) Low acuity, no color High sensitivity (rods can detect a single photon) ▯ Sensitivity and acuity of rods vs cones ▯ more convergence of Rods than for cones o cones project a single RG cell requires more intense light input to make RG cell fire good acuity (no certainty of where the light hit on the retina) o rod connected RG cells receive input from many rods, allowing for easy activation this comes to a cost of acuity, hard to tell exactly where the light came from don’t need intense light source since there are so many rods all pitching in to the “saw something white/black” message. Not very HD ▯ ▯ Distribution of rods and cones in the retina Photopic vision is best in the fovea because of how the cones are grouped to their highest capacity in that area, while rods are soread out to the sides ▯ ▯ Visual transduction: The conversion of light to neural signals Transduction: conversation of one form of energy to another Visual transduction: conversion of light (photons) to neural signals by visual receptors Pigment: a substance that absorbs light Rhodopsin: the pigment found in rods Rhodopsin is the pigment found in rods A G protein linked receptor that responds to light rather than neurotransmitters In the dark o Sodium ion channels remain partially open, releasing glutamate (depolarizes) When light strikes o Sodium ion channels close o Rods hyperpolarize, inhibiting glutamate release Rods work through inhibition o Another common principle in the brain Rhodopsin- inhibition in activity ▯ ▯ From the retina to primary visual cortex The retinal geniculate striate pathway includes the acons from 90 percent of the retinal ganglion cells The temporal hemi retina of each eye connects to the ipsilateral (same side) latera geniculate nuclease LGN The nasal hemi retina of each eye connects to the contralateral (opposite side) LGN o Nerves cross hemispheres at the optic chiasm o Optic tract leads to LGN The left hemisphere LGN receives input from only right vision field o RVF..) LG o LVF RH The right hemisphere LGN receives input from only the left visual field Retinotopic organization Information received at adjacent portion of the retina remain adjacent in the LGN and striate/visual cortex More cortex is devoted to areas of high acuity like the disproportionate representation of sensitive body parts in the somatosensory cortex o About 25% of primary visual cortex is dedicated to input from the fovea ▯ Layers in the LGN. The M and P channels ▯ Magnocellular layers (M Layers) o Big cell bodies, bottom two layers of LGN o Particularlt responsive to movement o Input primarily from rods Parvocellular layers ( P layers) o Small cell bodies, top four layers of LGN o Color, detail, and still or slow objects o Input primarily from cones The channels project to slightly different areas in lower layers IV in striate cortex. M neurons are just above the P neurons. They project the different parts of visual cortex behind V1 (primarily visual cortex) Color vision : component and opponent processing Component theory (trichromatic theory) o Proposed by young, refined by Helmholtz o 3 types of receptors, each with a different spectral sensitivity o opponent process theory proposed by hering o 2 different classes of cells encoding color, and another class encoding brightness o each encodes two complementary color perception o this theory accounts for color afterimages and colors that cannot appear together (reddish green or bluish yellow) o both theories are correct- coding of color by cones seems to operate on a purely component basis ▯ seeing edges contrast enhancement o mach bands o nonexistent stripes the visual system creates for contrast enhancements o makes edges visual to see o a consequence of lateral inhibition the more a receptor fires, the more it inhibits the receptors around it we see a bigger contrast than there is one in real life inhibits neighboring receptor ▯ receptive fields of visual neurons the area of the visual field within which it is possible for a visual stimulus to influence the firing of a given neuron Hubel and Wisesel looked at receptive fields in the retinal ganglion, LGN and lower later IV of striate cortex of a cat ▯ Similarities seen as Retinal ganglion and LGN Receptive fields of foveal areas are smaller than those in periphery Neurons receptive fields are circular in shape Neurons are monocular ( eye specific) Many neurons at each level had receptive fields with excitatory and inhibitory area Many cells have receptive fields with a center surround organization- excitatory and inhibitory regions separated by a circular boundary Some cells are center and some are off center(light in the middle less activated) ▯ Receptive fields: simple and complex cortical cells In lower layer of IV of the striate cortex, neurons with circular receptive fields (as in retinal ganglion cells and LGN) are rare Most neurons in V1 are either o Simple- receptive fields are rectangular with on and off regions or o Complex also rectangular with larger receptive fields and respond best to a particular stimulus anywhere in their receptive fields. More specific stimuli o Simple (rectangular, on and off regions like cells in layer IV, oriented and location sensitive, all are monocular) Complex (rectangular, larger receptive fields, do not have static on and off regions,(will respond to a line of appropriate orientation no matter which part of the receptive field it follows) not location sensitive, motion sensitive, many are binocular) ▯ Columnar organization of primary visual cortex ▯ Cells with simpler receptive fields send into on to the cells with more complex receptive fields Functional vertical collumns exist such that all cells in a column have the same receptive field and ocular ominance Ocular dominance colums are you move horizontally the dominansce of the columns changes o Some columns are left eye specific and some are right eye specific Flow of visual info o Thalamic relax neurons LGN o V1 Visual primary cortex (striate) o Secondary visual cortex (prestriate) o Visual association cortex o Flows through hierarchy o Become larger o Respond to more complex and specific stimuli o ▯ Dorsal and ventral streams Dorsal- pathway from V1 to dorsal pre striate cortex to posterior parietal cortex o The where pathway o Pathway for the control of behavior o Ventral – pathway from primary visual cortex to ventral pre striate cortex to inferotemporal cortex o The what pathway o Pathway for the conscious perception of objects o ▯ Prosopagnosia Inability to recognize faces Damage to ventral stream ▯ ▯ Akinetopsia Dorsal stream Hard time seeing movement See the world as a series of snapshots ▯