USE R/G GLASSES. Binocular Combina0on of Images. What can happen when images are combined by the two eyes?

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1 Binocular Combina0on of Images 3D D USE R/G GLASSES What can happen when images are combined by the two eyes? Fusion- when images are similar and disparity is small Monocular Suppression / Rivalry- when images are quite different but disparity is small Diplopia- when images are similar but disparity is large Summa0on (superposi0on)- when contrast is low or presenta0on is brief.

2 Rivalry from crossed gra0ngs Rivalry Summa0on Suppression Rivalry: factors controlling dominance and suppression In the struggle for dominance... Winners: High contrast, mo0on, parerns with lots of contour Losers: Low contrast, sta0c, sparse parerns L WWWW WWWW WWWW WWWW

3 Visual Confusion Visual confusion arises when different images combine in the same visual direction, and may include rivalry, suppression, fusion and summation. Dynamics of rivalry Blake web page: hrp://psych-s1.psy.vanderbilt.edu/faculty/blaker/rivalry/br.html Recent Blake followup ar0cle: hrp://

4 Fusion Panum s Fusional Area: For a single point in one eye, there is an area in the other eye where targets will fuse with that point. Fusion Range: radius of PFA A point in the le\ eye An area in the right eye F F 6-10 min min Foveal size of PFA for a single point Fusion range depends on eccentricity 7% From: Mitchell, DE (1966) A review of the concept of Panum s Fusional Areas Am J Optom D.T.D. refers to disparity threshold for diplopia.

5 Fusion: range depends on spa0al frequency Schor, C. M., Wood, I. C. and Ogawa, J. (1984) Binocular sensory fusion is limited by spa0al resolu0on. Vision Res 24: Summa0on- dichop0c plaids I At low contrast, rivalry takes many seconds to kick in. L R Liu, Tyler 7 Schor (1992). Failure of rivalry at low contrast Vision Research 32,

6 Luminance summa0on Fechner s paradox x Le\ Right Stereopsis- overview What is Stereopsis? Kinds of Stereograms History- da Vinci, Wheatstone, Brewster, etc Stimuli used some fundamental data models of stereopsis

7 Stereopsis- n. What is Stereopsis? The perception of depth based on horizontal, relative, retinal disparity. Perception of Depth The perception of depth depends on the combination of several factors: Binocular Retinal Disparity Motion Shading Interposition Size / Perspective Blur

8 Horizontal, not Vertical disparity Calculating disparity

9 How much depth is 3 arc sec? Compared to 6 meters, 3 arc sec = 1 cm Thickness of a finger Compared to.6 meters (arms length) 3 arc sec =.1 millimeters ridges in your fingerprint How Stereograms are made photograph or construct two pictures from different viewpoints present them separately to the two eyes stereoscope anaglyph (red/green glasses) polaroid glasses free fusion phase haploscope VR goggles auto stereograms

10 Anaglyph (red/green) glasses Free Fusion Helmholtz: "It is very important for anyone who intends to make inves0ga0ons in physiological op0cs to learn how to converge the lines of fixa0on of the eyes or to make them parallel at any moment, without having to use any corresponding visual object; he [or she] should prac0ce doing this." (Physiological Op0cs VIII p57, Southall transla0on) E E E E

11 History Galen (AD 200) Alhazen (AD 1000), Leonardo da Vinci (1500), Aguilonius (1600), all wrote about binocular parallax and double vision. Leonardo knew that binocular parallax contributed to depth, and Aguilonius worked out the geometric horopter. But none of these thinkers understood depth from disparity. Wheatstone ( ) invented the mirror and the lenticular stereoscopes in His device allowed him to experiment systematically with image differences and to firmly establish disparity as a basis for depth perception. Brewster ( ) re-invented lenticular stereoscope in 1849, claimed credit, and fought with Wheatstone for years s to 1890 s 3-D photography craze takes over world Wheatstone Stereoscope (1838) mirror haploscope

12 Brewster Stereoscope 1849 Lens / Prism Combination More on Wheatstone The process of discovery: Recognized an anomaly: depth in glint from shiny metal Invented a tool to investigate it: the stereoscope Started a whole new field of study with his observations. Some of Wheatstone s observations: Disparity, with no other cue, yields a percept of depth. Disparity can override perspective and other depth cues. Vergence movements are not required for stereopsis: afterimages with disparity yield stereoscopic depth Fusion and stereo can tolerate large differences in image size.

13 Stereoscopic Stimuli Three classes of stimuli: 1) dots & lines ( local targets) used for most fundamental, early work 2) random dots (visual noise) revealed sophistication of system 3) gratings (narrow band) attempt to unite stereopsis and spatial vision Stereoscopic S0muli in Vision Science Three common kinds of s0muli used for measuring stereopsis: 1) dots & lines ( local targets) First experiments used these, s0ll used for basic stereo tes0ng 2) random dot stereograms Tests global stereopsis. Used in some clinical tests and for making Magic Eye Pictures. 3) sine wave gra0ngs Used for tes0ng stereopsis with fine, medium, and course scale parerns

14 Takes time to appear Experience with looking at the patterns makes the time shorter. Complex Stereogram Some fundamental results Stereoscopic acuity (disparity threshold) can be as low as 3 arc seconds, in some cases. Stereo judgments can be made for disparities as large as 10 degrees, in some cases (upper disparity limit). Stereo gets worse with eccentricity, short duration, low contrast, etc. Stereopsis gets worse away from the horopter Stereo depends on spatial frequency, to a point.

15 Stereoacuity depends on Duration Contrast Stereoacuity depends on Eccentricity Disparity Pedestal

16 Stereoacuity depends on Spatial Frequency Different SF Spatial Frequency Difference Same SF Stereoacuity Stereoacuity is best with high spa0al frequencies and is very bad when each eye sees a different frequency. (Schor et al. 1984)