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PSYC 220

by: Lynde Wangler
Lynde Wangler
GPA 3.836

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About this Document

These are the notes from Friday when we started the visual system.
Meghan Jones
Class Notes
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This 2 page Class Notes was uploaded by Lynde Wangler on Saturday February 13, 2016. The Class Notes belongs to PSYC 220 at University of North Carolina - Chapel Hill taught by Meghan Jones in Spring 2016. Since its upload, it has received 24 views. For similar materials see Biopsychology in Psychlogy at University of North Carolina - Chapel Hill.


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Date Created: 02/13/16
PSYC 220 WEEK 5 Vision  Properties of Perception: perception occurs in the brain, whereas sensation occurs in the sensory organs (nose, ears, eyes, etc.); there are several levels of perception  Law of Specific Nerve Energies: Johannes Muller (1883), posited that each neuron is specific to each type of sensory information o Activity of olfactory nerves is interpreted as smell, photoreceptor activation light, etc. o Perception (rather than sensation) is dependent upon the frequency and patterns of firing  Eye Anatomy: o Cornea – first structure light passes through, immovable structure, does 80% of the focusing o Pupil – light enters eye through this opening o Lens – light is focused (20%), moveable structure that operates by accommodation o Retina – light is projected on the retina which consists of photoreceptors (rods and cones) and various other cells (horizontal, bipolar, amacrine, ganglion)  Retinofugal Pathway: photoreceptors bipolar  ganglion cells; bipolar cells also active amacrine cells which synapse with other bipolar cells; blind spot – occurs where there is an absence of photoreceptors where the optic nerve exits the eye  Types of Cells Within the Retina: Photoreceptors, HBAG (horizontal, bipolar, amacrine, and ganglion); light passes thought all other cells to the photoreceptors in the back of the retina and then information gets filtered forwards through other cells (backwards set up)  Fovea vs. Periphery: o Fovea – small area in the retina composed almost exclusively of cones; low neural convergence = high level of acuity each photoreceptor (cone) converges onto only one bipolar cell o Periphery – composed of rods primarily; high neural convergence = less visual acuity and higher sensitivity to light  Photoreceptors: o Rods – scotopic vision (night vision), lower acuity because of higher neural convergence, higher sensitivity to light, found in periphery and not in the fovea, provides contrast information (outlines of objects), outnumber cones by a lot o Cones – photopic vision (color vision), higher acuity because of lower neural convergence (in the fovea especially), less sensitive to light = mediates day time vision or when a lot of light is available, responsible for 90% of eyes’ input to the brain  Sensitivity vs. Acuity: sensitivity (to light) is the ability to detect objects; acuity is the ability to discern details about objects; pupil constriction = increases acuity; in settings with lower lighting, the pupil will dilate to allow more light to enter (increasing sensitivity to light) but decreasing acuity  Convergence of Input onto Bipolar Cells – bipolar cells can laterally inhibit one another to increase acuity  Electromagnetic Spectrum: visible wavelengths for humans about 400- 700nm; long – red, medium – green/yellow, short – blue, violet  Trichromatic Theory of Color Vision: posits that there are three types of cones (one for short, medium, and long wavelengths) and that nervous system perceives color based on comparing activity of the different receptors (the cones each have different opsins); good explanation at the photoreceptor sensation level  Opponent Process Theory of Color Vision (supported by afterimages) – good at the perception level; red-green, yellow-blue, black-white – we perceive colors in opposites; color coded by response of bipolar cells (more or less firing could mean red or green on that type of cell or blue or yellow for another type of cell); cells that are perpetually stimulated become fatigued so when it stops being stimulated by a certain wavelength of light, perception of the opposite color occurs (after images)  Illusory Square – perception of the square can’t be adequately explained by either theory visual perception depends on more than just activity of neurons in the retina  Retinex Theory: visual cortex compares information from different parts of the retina to determine the brightness and hue of a color for each area in your view visual perception (consciously or not) involves reasoning and inference (BLUE/BLACK or WHITE/GOLD dress example)  Color Deficiency (technically not “color blindness” even though we commonly refer to this characteristic in this way) – occurs when a gene that codes for one of the photopigments in the cone is altered; sex-linked characteristic on the X chromosome so males are more often affected


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