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PSYB51H3 (306)
Chapter 3

chapter 3

4 Pages

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Matthias Niemeier

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PSYB51 Chapter 3 Spatial Vision From Stars to Stripes Page1Visual Acuity Oh Say Can You SeeLateral section of the brain illustrating early visual areas andThe basic organization of the pirmary visual pathway from eyeball showing the putative where dorsal and what ventral streams to striate cortex in coronal sectionFalls on single conesee nothing grayfield Contrast Visual angle The difference in luminance bw an object and The angle subtended by an object at the retina aka aliasing the bg or bw lighter and darker parts of theTo calculate the visual angle of your resolutionCones in the fovea have a center to center same object acuity separation of about 05 minute of arch 0008 size of cycledistance where orientation is degree Acuity barely seenarc tan The smallest spatial detail that can be resolved AliasingRods and cones in the periphery and packed Mispreception of a grating due to under Sine wave grating together less tightly therefore visual acuity is A grating with a sinusoidal luminance profile sampling much poorer than the foveaLight intensity in such gratings varies smoothly and continuously across each cycle CycleIf the receptors are spaced such that the whitest For a grating a pair consisting of one dark bar and blackest parts of the gratings fall on separate and one bright bar cones we can make out the conesA Visit to the Eye Doctor Herman Snellen constructed a set of block letters for which the letter as a whole was five times as large as the strokes that formed the letter Visual acuitythe distance at which a person can just identify the lettersthe distance at which a person with normal vision can just identify the letters Later this was altered with the position constant at 20ft and size of letters changing Acuity for LowContrast StripesOtto Schade showed people sine wave gratings with different spatial frequencies and had them adjust the contrast of the gratings until they were just detected Spatial frequency Contrast threshold The number of cycles of a grating per unit of The smallest amount of contrast required to visual angle usually specified in degrees detect a pattern yaxis is the reciprocal of the contrast threshold Cycles per degree The number of dark and bright bars per degree Note that a contrast of 100 corresponds to a of visual angle sensitivity value of 1 Contrast sensitivity function CSF A function describing how the sensitivity to contrast defined as the reciprocal of the contrast threshold depends on the spatial frequency size of the stimulusUpsidedown Ushaped function
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