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pattern_vision_posted - Pattern Vision P329 Pattern Vision...

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1 P329 Pattern Vision Pattern Vision
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2 P329 Pattern Vision Sine Wave Gratings Sinusoidal variation in intensity over space. x Intensity Position in Space
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3 P329 Pattern Vision + + Summing Gratings Summed Image Add the corresponding points in the two images together to form one summed image. Location (200,25) Location (1,1)
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4 P329 Pattern Vision Who is this? Current Grating Sum of Gratings
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5 P329 Pattern Vision 1. Introduction to Fourier analysis 2. Physiological evidence that the visual system does something like Fourier analysis 3. Behavioral evidence that the visual system does something like Fourier analysis and the multiple channel model 4. Visual phenomena that can be explained by the CSF and the model 5. Why Fourier analysis? 6. Shortcomings of the approach Pattern Vision: Outline
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6 P329 Pattern Vision What is a visual pattern ?
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7 P329 Pattern Vision These are all patterns. Pattern: Anything that varies in intensity and/or color over space and/or time.
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8 P329 Pattern Vision 1. Introduction to Fourier Analysis Jean Baptiste Fourier (1768-1830)
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9 P329 Pattern Vision Sine wave gratings can vary in four ways. i. Frequency ii. Contrast / Amplitude iii. Position / Phase iv. Orientation
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10 P329 Pattern Vision i. Spatial frequency: the number of cycles within a given region of space. Region of Space Region of Space Frequency = 3 Frequency = 8
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11 P329 Pattern Vision Cycles Per Degree of Visual Angle 1 cycle per degree of visual angle frequency on the retina is the same Region of Space
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12 P329 Pattern Vision 1 cycle per degree of visual angle 2 cycles per degree of visual angle x meters Cycles Per Degree and Viewing Distance Cycles per degree (c/deg) is proportional to viewing distance.
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13 P329 Pattern Vision Cycles per Image 1 cycle per degree of visual angle 4 cycles per image
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14 P329 Pattern Vision ii. Contrast/Amplitude: the difference between the highest and lowest intensities in the gratings. high contrast low contrast (contrast ranges between 0-1) Contrast = Intensity max - Intensity min Intensity max + Intensity min
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15 P329 Pattern Vision iii. Position/Phase: the relative position of 2 or more sinusoids. in phase out of phase
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16 P329 Pattern Vision iv. Orientation: gratings can also vary in orientation. Orientation is measured in degrees (0-360).
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17 P329 Pattern Vision Any image can be made by just adding the right combination of gratings varying frequency , contrast , phase , and orientation . Every unique image has a unique combination of sinusoidal components. This unique set is called the image’s Fourier Transform . Fourier’s Theorem
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18 P329 Pattern Vision Demonstration: A Square Wave
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19 P329 Pattern Vision Fourier Transform: A Spatial Frequency Map 1 2 3 4 5 6 7 8 10 2 3 Frequency (cycles per image) Amplitude A square wave has contrast at frequencies that are odd multiples of the lowest frequency.
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20 P329 Pattern Vision Current Grating Sum of Gratings Intensity Profile
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21 P329 Pattern Vision Low Medium High Gross Structure Details/Edges removing high frequencies blurs an image.
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22 P329 Pattern Vision So Far… 1. Introduction to Fourier analysis 2. Physiological evidence that the
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pattern_vision_posted - Pattern Vision P329 Pattern Vision...

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