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Depth perception
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  • 1. Depth Perception Monocular Cues Binocular Cues Visual Illusions Clinical Relevance
  • 2. Dep Objectivesthp  deals at first with some general theory about visualer depth cues (oculomotor, monocular and binocularc cues) from the psychological point of view.ep  details about some possibilities to convey depthti and shape surface in computer based visualizationon Gauri S. Shrestha, M.Optom 2
  • 3. Dep Introductionthp  we have developed perceptual systems capable ofe representing three dimensional environment withrc sufficient accuracy to guide our behavior.ep  The human visual system is able to reconstructti depth information from flat images throughon combination of a set of many different impulses, cues and patterns  Distance estimations, hints about an objects surface and other visual cues are essential for all of us Gauri S. Shrestha, M.Optom 3
  • 4. Dep General theory of depth cuethp  Oculomotor cues are, as the name suggests, possibilitiese for depth estimation by controlling the eye axes and ther lens focus using the eye muscles.c  Convergence and accommodation are counted among thatep kind of cues which interact with each other in deptht perception.i  The angle of convergence of the two eyes and theiro accommodative states are one source of scalingn information  They must be supplemented by other cues even at close ranges.  Thus they are considered to be minor cues in depth perception. Gauri S. Shrestha, M.Optom 4
  • 5. Dep Monocular vs. Binocular Cuesthp  Monocular Depth Cueser  Cues perceived as strong with one eye as with two eyesc  Binocular Depth Cuesep  Cues that must be viewed with both eyest Greatly enhance depth perceptioni on Gauri S. Shrestha, M.Optom 5
  • 6. Dep Monocular Depth Cuesthp  Pictorial Depth Cuese  Sizerc  Linear Perspectivee  Texturept  Interpositioni  Clarityo  Lighting and Shadown  Motion Parallax  Accommodation  Aerial perspective Gauri S. Shrestha, M.Optom 6
  • 7. Dep Pictorial Depth Cues -Sizethp  Larger objects are interpretede as being closerrc  Relative Size- If objects aree thought to be the same size, thept one that appears smaller isi perceived as being farthero awayn  Familiar Size-Used viewing objects of a known size. Object distance determined based on previous knowledge of its size Gauri S. Shrestha, M.Optom 7
  • 8. Dep Relative sizethperception Gauri S. Shrestha, M.Optom 8
  • 9. Dep Relative heightthp  Points that are situateder closer to the horizonc seem to be moreep distant than points thatti are farther away fromo the horizon.n Gauri S. Shrestha, M.Optom 9
  • 10. Dep Pictorial Depth Cues-th Linear Perspectivep  Related to relative sizeer  Sense of depth is experienced due to ource conception that objects have a constantp shape and sizetion Gauri S. Shrestha, M.Optom 10
  • 11. Dep Pictorial Depth Cues -Texturethp  Smaller, densely packed objects appear far awayer  Larger, loosely packed objects appear closerc  Observer assumes all objects are the same sizeep  Smaller images are perceived as being farther awaytion Gauri S. Shrestha, M.Optom 11
  • 12. Dep Pictorial Depth Cues -texturethperception Gauri S. Shrestha, M.Optom 12
  • 13. Dep Pictorial Depth Cues -Interpositionthp  One object blocks view of anotherer  Blocked object is perceived as being fartherce awayption Gauri S. Shrestha, M.Optom 13
  • 14. Dep Pictorial Depth Cues -Claritythp  Objects that appear clear aree interpreted as being closer thanrc those objects that appear hazye  Fog, smoke, rain and smog act aspt interposing elements that makei obscured objects seem fartheron away Gauri S. Shrestha, M.Optom 14
  • 15. Dep Pictorial Depth Cues -Lightingth and Shadowp  With Light falling on an object, it casts a shadower  The shadow is interpreted as falling behind thece object-creating a sense of depthption Gauri S. Shrestha, M.Optom 15
  • 16. Dep Monocular Depth Cue:th Motion Parallaxp  Kinetic Depth Cueer  Produced by relativec motion of two or moree objectspt  Near Object Fixationi Far objects move witho n head movement  Distant Object Fixation  Near objects move opposite of head movement Gauri S. Shrestha, M.Optom 16
  • 17. De Monocular Depth Cuepth Motion Parallaxp  Whenever we move, the images projected byer objects located at different distances move acrossc our retina with different speed whereby nearbyep objects tend to cross the retinal image plane fasterti than the distant objects.on Gauri S. Shrestha, M.Optom 17
  • 18. Dep Monocular Depth Cueth Accommodationp  Accommodation is necessary to clearly view nearer objectsce  The signal to accommodate contains informationp regarding the distance of viewed objectstion Gauri S. Shrestha, M.Optom 18
  • 19. Dep Aerial perspectivethp  Over very long distances in the naturaler environment the color of surfaces tends to becomec bluer. (aerial perspective)ep  The outlines of far away objects become blurredti and the contrast gets reducedon Gauri S. Shrestha, M.Optom 19
  • 20. Dep Binocular Depth Cuesthp  Binocular cues are the most important category of cuese that potentiates humans to experience a three dimensionalrc world.e  The term binocular cues refers to the fact that both eyespt are required to gain depth information from the projectedi image of the real world.on  They are  Stereopsis  Corresponding retinal points  Retinal Disparity  Convergence Gauri S. Shrestha, M.Optom 20
  • 21. Dep Stereopsisthp  Retinal locations of imagese signal the distance of therc object being seene  Corresponding points-twopt retinal points thati correspond to the sameon direction in space (foveas)  Retinal Disparity-distance between corresponding points and the image location Gauri S. Shrestha, M.Optom 21
  • 22. Dep Stereopsisthp  Retinal Disparityer  Disparity provides information about spatial depthc when the images of an object fall upon different retinale areas in the left and right eyespt  Allows visual system to determine distance of objectio  It is the function of IPD as welln  Depth is perceived when non corresponding point is stimulated Gauri S. Shrestha, M.Optom 22
  • 23. Dep Retinal Disparitythp  Uncrossed Retinal Disparitye Images fall nasal torc fixated objecte  Object is farther thanpt fixated objecti  Crossed Retinal Disparityon  Images fall temporal to fixated object  Object is closer than fixated object  Stereopsis is the perception of depth produced by binocular retinal disparity Shrestha, M.Optom Gauri S. 23
  • 24. Dep Stereopsisthp  More important while viewing near objectser  Within arm’s lengthc  Binocular disparity provides depth perception onlyep if it is not too greatti  Panum’s Fusional Area-area on the retina thato corresponds to binocular fusionn  Physiological diplopia-occurs when images fall on retinal positions that signal grossly different directions Gauri S. Shrestha, M.Optom 24
  • 25. Dep Demonstrationthp  Hold one index finger 15 cm from noseer  Hold other index finger at arms lengthce  Focus on near fingerpt  Notice diplopiaio  Bring far finger closer to youn  Notice diplopia disappears  THIS IS PANUM’S AREA Gauri S. Shrestha, M.Optom 25
  • 26. Dep Another way to look at itthp  Every retinal point has ae corresponding point in the otherr eyece  Horopter-a plot ofp corresponding points for a giventi distanceo  curved plane due to then curvature of the retina  Objects relatively close to the horopter can be fused Objects are within Panum’s fusional area  Provides stereopsis for these objects Gauri S. Shrestha, M.Optom 26
  • 27. Dep Disparity Detectorsthp  Binocular Cortical Neurons are maximallyer responsive to stimuli at a specific distancece  The same stimulus placed at different distances,p elicits a less vigorous responsetion Gauri S. Shrestha, M.Optom 27
  • 28. Dep Convergencethp  We constantly converge and diverge our eyeser  The amount of convergence required to view ace specific object provides information concerningp the distance of that objectti  It is not understood how this information ison incorporated into conscious depth perception Gauri S. Shrestha, M.Optom 28
  • 29. Dep What Are Visual Illusions?thp  Erroneous Perceptionser  Commonly result from pictorial depth cues toce judge the size of unfamiliar objectsption Gauri S. Shrestha, M.Optom 29
  • 30. Dep Size Constancythp  The apparent size ofer an object does notc normally change withep viewing distanceti  Our visual systemon compensates for differences in retinal image size by taking into account the relative distance Gauri S. Shrestha, M.Optom 30
  • 31. Dep Size Illusionthp  Occurs when judgments of distance are erroneouser  Size Constancy failsce  Examples of Visual Illusions:pt  Corridor Illusionio  Moon Illusionn  Müller-Lyer Illusion Gauri S. Shrestha, M.Optom 31
  • 32. Dep Corridor Illusionthp  Illustrationer  Size Constancy fails due to monocular depth cues:ce  Top line looks farther awaypt  Top line seems largerio  Two lines are actually the same sizen Gauri S. Shrestha, M.Optom 32
  • 33. Dep Corridor Illusionthperception Gauri S. Shrestha, M.Optom 33
  • 34. Dep Moon Illusionthp  Moon appears larger ife viewed on the horizonrc  Moon appears smallerep when viewed directlyt overhead in a clear skyio  Why?n  Moon does not appear to be at the same distance  On the horizon, moon appears farther away  Due to background (trees, houses, fields, etc.) Gauri S. Shrestha, M.Optom 34
  • 35. Dep Müller-Lyer Illusionthp  Lines mimic the corner of a roomer  The line that appears to be an outgoing corner isce judged as being farther awaypt  Perceived as being a longer lineio  The line that appears to be an ingoing corner isn judged as being closer  Perceived as being a shorter line Gauri S. Shrestha, M.Optom 35
  • 36. Dep Müller-Lyer Illusionthperception Gauri S. Shrestha, M.Optom 36
  • 37. Dep Clinically Relevant Topicsthp  Stereopsis and Vision Developmenter  Monovision Contact Lensesception Gauri S. Shrestha, M.Optom 37
  • 38. Depth Stereopsis Clinicallyp  Stereopsis Tested Clinicallyer  Patient views flat surface with two identical figuresce separated by a small distancep  Each eye views only one of the objectsti  Polaroid or Red-Green glasseson  Minimum amount of disparity that allows patient to appreciate depth is determined Gauri S. Shrestha, M.Optom 38
  • 39. Dep Stereo-acuitythp  Can be as small as 3 seconds of arcer  A high degree of stereo-acuity depends on ac normal complement of binocular neurons in theep visual cortext  Anisometropia and Strabismus are two disordersio of binocular vision that retard cortical neuronn development Gauri S. Shrestha, M.Optom 39
  • 40. Dep Monovision Contact Lensesthp  One eye for near, One eye for distanceer  Patient alternates between two eyes to viewce objects at various distances clearlypt  Blurred image is suppressedio  Stereopsis is reduced because patient is not usingn both eyes simultaneously  Monocular depth cues are still present Gauri S. Shrestha, M.Optom 40
  • 41. Dep When Will It Matter?thpe  Stereopsis is more important for near workrc  Driving can be difficult for these patientsep  Patients must be advised of ↓ depth perceptionti  Alternatives while driving:on  Glasses to correct near eye while driving  Distance only contact lenses for driving only Gauri S. Shrestha, M.Optom 41
  • 42. Dep Thank youthperception Gauri S. Shrestha, M.Optom 42