11Lecture 17Chap. 7 – Visual PerceptionOctober 19, 2010Skip Chapter 8 for now. Start reading Chap. 9 on Color. http://www.yorku.ca/eye/toc-sub.htmhttp://www.michaelbach.de/ot/index.htmlLight and Color web sites: 2Big Moon Illusion2What you remember. Actual33Frankfurter illusionWhile focused on the background, hold your two index fingers horizontally in front of your eyes, not touching. A piece of finger will appear to float in space. 4Simultaneous orientation contrastWhich line leans the most? Simultaneous orientation contrast5Are the lines straight? 5Hering IllusionSimultaneous orientation contrast6Does the square have straight sides?6http://www.michaelbach.de/ot/ang_hering/index.htmlSimultaneous orientation contrast78Are the squares level?Simultaneous orientation contrast9Is the oval a perfect circle? Simultaneous orientation contrast10Poggendorff Illusion10http://www.michaelbach.de/ot/ang_poggendorff/index.htmlAre the lines continuous and straight “behind” the yellow columns?11Poggendorff Illusion11http://www.michaelbach.de/ot/ang_poggendorff/index.html1212Art that mimics 3-d.13Review - AnatomyPhotoreceptors, rhodopsinHorizontal cells,bipolar cells & amacrine cells Ganglion cellsAxonsOptic nerveOptic chiasma (complicated crossover!)Visual cortex of the brain14Review - ConceptsBrightness and lightnessWeber’s lawLateral inhibition, receptive fieldEdge enhancementLightness constancy (illumination varies)Simultaneous lightness contrast Simultaneous size contrast Simultaneous orientation contrast15Clicker question - 1If the left side of your brain is injured, you might lose vision in yourA. left eyeB. right eyeC. left field of viewD. right field of viewE. some loss in left and right field of view16Clicker question - 2A white sheet of paper continues to look white as the light is reduced. A. Simultaneous lightness contrastB. Lateral inhibitionC. Weber’s law D. Lightness constancyE. Edge enhancement17Clicker question - 3The bands of gray look lighter on their right side because of:A.Simultaneous lightness contrastB. Lightness constancy C. Weber’s law D. Lateral inhibitionE. Both A and D 18Clicker question - 4The Hermann grid (at right) illustratesA. Simultaneous lightness contrastB. Lateral inhibitionC. Weber’s law D. Lightness constancyE. Edge enhancement19Clicker question - 5The arrow points to: A. Photoreceptors B. Horizontal cellsC. Bipolar cellsD. Amacrine cellsE. Ganglion cells20Clicker question - 6The arrow points to: A. Photoreceptors B. Horizontal cellsC. Bipolar cellsD. Amacrine cellsE. Ganglion cells21Clicker question - 7The green circles are regions on the retina and the yellow regions are light. The greatest nerve response is created by A. B. 22Time and motionFatigue: prolonged stimulation (staring at a lamp) causes a weaker response and a negative afterimage. Successive lightness contrast: a gray object looks darker after looking at white.Positive afterimage: We see a flash as a bright spot after it has gone away. Overstimulatednerves keep firing. 2223Successive lightness contrastNegative afterimage23Stare at this, stare at the next slide. 2424Positive after image2525Stare at this, stare at the next slide. 2626Negative after image272728Negative after image29Involuntary eye movementEye movement moves the image around so that new areas are stimulated. Without eye movement, images fade. This has been verified by experiments that fix the image on the retina. Eye movement causes wavy lines to appear as though in motion, because the afterimage interferes with the moved image. 29Involuntary eye movement3030Recall that after sitting in a bathtub you no longer feel the water, except where the air and water meet.3131http://www.michaelbach.de/ot/mot_eyeJitter/index.htmlThe only difference between the center and edge is the lack of any feature to “focus” on. Involuntary eye movement32Motion after effect Motion channel, keeps firing after watching a moving object, causing motion aftereffect.http://www.michaelbach.de/ot/mot_adaptSpiral/index.htmlThe following are from Akiyoshi KitaokaDepartment of Psychology, Ritsumeikan University, Kyoto, Japan:http://www.psy.ritsumei.ac.jp/~akitaoka/saishin27e.html32Demo3333Motion illusion (A. Kitaoka)Note that each green circle is rotated slightly from its neighbor.As your eye jumps around, it sees the circles rotation.Involuntary eye movement34Are the ropes tangled?34from Akiyoshi KitaokaInvoluntary eye movement3535from Akiyoshi KitaokaInvoluntary eye movement36Motion illusion (Kitaoka)36Involuntary eye movement3737Motion illusion (Kitaoka)Involuntary eye movement38Motion illusion (Kitaoka)Involuntary eye movement3939Snakes - Akiyoshi KitaokaInvoluntary eye movement4040Dead Snakes -Akiyoshi KitaokaInvoluntary eye movement41Motion effects from Michael Bach’s web page• Silhouette illusion• Motion induced blindnesshttp://www.michaelbach.de/ot/mot_mib/index.html• Motion aftereffect (Waterfall illusion)http://www.michaelbach.de/ot/mot_adapt/index.html• Spiral aftereffect (motion channel activated)http://www.michaelbach.de/ot/mot_adaptSpiral/index.html• Breathing