Perception: Issues, Problems, & History Pictorial Cues for Depth

1. Perception: Issues, Problems, & History Pictorial Cues for Depth

2. I am an experimental social psychologist who approaches understanding social behavior from a social cognitive perspective (i.e., how we interact with others is determined, in large measure, by what's in our head and how it's organized) . . . -- Allen McConnell, Ph.D. Miami University Note McConnell’s commitment to “primacy of mind” perspective.

3. Here’s the deal:  there appears to be an “in here -- me” and an “out there -- other”   Consider  Buber’s I and Thou versus I and It Remember his argument:  the way we relate to the other depends on which of those two stances we take.             The I-Thou is a singularity, an indivisible unit.  The I-It is a duality.             In I-Thou relations, the participants are not independent of one another – they form a unitary oneness.             In I-It relations, the participants are independent of one another. Most of western psychology, in accord with most of western science, assumes that I-It is the only possible stance; an astounding decision, with enormous implications regarding who and what we are.

4. In view of that decision, we then have to decide how to describe the manner of relating between I and It. The mediator between “Me” and “the Other” has traditionally been characterized as something called perception, which itself depends in part on what the I attends to and how the I attends.  So we need to understand the factors that presumably affect attending.  As we noted in the preceding several days, some of those factors seem to be inside the I – desires, hopes, fears, expectations, interests, curiosity . . . Others seem to be outside, but with the ability to influence or even to compel me to attend –  high contrasts, colors, motion, repeated associations, . . .. There are several difficult problems specifically regarding how the “independent” I perceives the “independent” Other. Several of these problems relate to visual perception alone.

5. Greek theories of visual perception Democritus (c. 425 B.C.) and Epicurus (342-270 B.C.) believed that objects cast off resemblances of themselves, called eidola, rather in the way that snakes cast off their skins. These eidola are captured by the eye. It is the entry of eidola into the eye that allow us to see their shape. The fact that objects can be seen to be mirrored in the cornea of the observer was taken as evidence for the eidola. However this approach leads to unanswered questions - How do eidola pass through one another without interference? How do eidola of large objects shrink to enter the eye? How do eidola from a single object reach many people simultaneously? Plato (c. 427-347 B.C.) believed that visual “fire” emanated from the eye and coalesced with light to form a conduit that allows "motions" of the object to pass to the sensorium. However as Aristotle (384-322 B.C.) points out, it is unreasonable to think that a ray from the eye could reach as far as the stars. These theories have long been rejected in western optical theory, but the idea that perception involves the presence of copy of the object in the eye or brain is represented in many modern perceptual theories. A further issue: if there are objects/images in the mind/sensorium, what determines what the images mean?

6. Modern theories of vision start with Johannes Kepler who in Ad Vitellionem paralipomena (1604) first correctly described the formation of the retinal image in the eye. A few years later Christoph Scheiner (1619) observed the retinal image by scraping away the sclera of the eye of an ox which was placed in a hole in a shutter (reported by Descartes, 1637). However there was a problem - the retinal image was upside down. Why do we not see the world upside down? A number of other problems related to the retinal image as the basis of perception also have been identified:    -- the visual image at the retina is exceedingly tiny compared to the distal object    -- the visual image at the retina is upside down relative to the perceived distal object    -- the visual image at the retina is subject to continuous saccadic movements,             yet the perceived distal object does not appear to be jerking around crazily     -- the visual image at the retina is essentially flat, yet the distal object is 3-D.     --what causes illusions?  Other animals don’t seem to be subject to them, and they are partly but not completely subject to cultural differences.

7. And complicating everything is the fact that we have several sensory modalities in addition to vision.  How does the I integrate information from utterly differing sensory modalities into one perception?  For example, how do I know to look to the left upon hearing a sound emanating from the left?  [M Wertheimer's daughter] Most perceptual psychologists, taking the “primacy of mind” perspective, argue that something about the mind “corrects” the foregoing problems. The Homunculus. . .

8. [Adapted from Wikipedia] The homunculus argument Homunculus arguments are common in the theory of vision. Imagine a person watching a movie. He sees the images as something separate from himself, projected on the screen. How is this done? A simple theory might propose that the light from the screen forms an image on the retinas in the eyes and something in the brain looks at these as if they are the screen. A more sophisticated argument might propose that the images on the retinas are transferred to the visual cortex where it is scanned. .

9. However, neither of the foregoing are full explanations because all that has been done is to place something like an entire person, or homunculus, behind the eye who gazes at the retinas. An “infinite regress” is created: Who tells the homunculus what he is seeing? Another, tinier homunculus inside the first one? And who tells the tinier one . . .? Note: Homunculus arguments are always fallacious. Homunculus argument accounts for a phenomenon in terms of the very phenomenon that it is supposed to explain (Richard Gregory (1987)). However, in psychology and philosophy of mind 'homunculus arguments' are extremely useful for detecting where theories of mind fail or are incomplete

10. Homunculus ideas are very difficult to abandon: Attneave F (1961) In defense of homunculi. In: Sensory Communication. Rosenblith WA, ed., pp. 777-782. New York, NJ: MIT Press and John Wiley. "The Neuronal Correlates of Consciouness". Metzinger, T., ed., pp. 103-110. MIT Press: Camrbidge, MA (2000). The Unconscious Homunculus. Francis Crick... "The Neuronal Correlates of Consciouness" Metzinger, T., ed., pp. 103-110. MIT Press: Camrbidge, MA (2000) The Unconscious Homunculus Francis Crick The Salk Institute and Christof Koch Computation and Neural Systems Program California Institute of Technology

11. As a metaphor for how much of the cortex is related to different parts of the body, a homunculus can be quite vividly effective.

12. Sensory homunculus Motor Homunculus

13. We’ll leave the thorny problem of how perceptual information is “represented” cognitively until we study the knowledge topic. But for now, let’s consider how perceptual psychologists attempt to explain veridical vision, given the “problems” that accrue to the retinal image. That is, since the retinal image is flat (2-d), one of the major concerns of perceptual theorists has been to account for our compelling visual sense of three dimensions in the world around us. Note that this effort is only relevant to the assumption that the retinal image is the basis of visual perception. If we don’t start make that assumption, then these “problems” don’t affect perceptual theory.

14. For theorists who believe that the retinal image is the basis for 3-d vision, the answers lie in the pictorial depth cues, all of which are monocular (they work with just one eye). l. Linear perspective -- apparent convergence of parallel lines in the environment. If you stand between two railroad tracks, they appear to meet near the horizon. Since you know they are parallel, their convergence implies great distance. 2. Relative size. If an artist wishes to depict two objects of the same size at different distances, the artist makes the more distant object smaller. 3. Light and shadow. Most objects in the environment are lighted in ways that create clear patterns of light and shadow. Copying such patterns of light and shadow can give a two dimensional design a three-dimensional appearance. 4. Overlap. (Also known as interposition ) -- an object nearer to the viewer partially blocks another object that is farther away. 5. Texture gradients. Texture of nearer objects will look larger & coarser than of objects farther away. 6. Aerial haze. Smog, fog, dust, and haze add to the apparent distance of an object. Because of aerial perspective, objects seen at great distance tend to be hazy, washed-out in color [“relative brightness”/ vividness], and lacking in detail.

15. Linear perspective, overlap, relative size, texture gradients, shadows, aerial haze

16. Linear perspective, relative size, overlap (interposition), aerial haze, shadows

17. In normal vision, blue wavelengths scatter more with greater distances than do other colors. Thus the sky look blue, and objects in the distance have a bluish quality. Also, since the light is partly scattered, a slight blurring of distant objects occurs. Artists incorporate these two facts into pictures to create a sense of great distances. Note also the brighter colors for near objects, the interpositions, the shadows, the changes in textures for nearer versus farther objects.

18. Victor Vasarely – “Vonal Ksz”

19. Playing depth-tricks with interposition The World's First Impossible Triangle - Reutersvärd - 1934 Reutersvärd's Impossible Staircase Design Although many of us love Escher’s

21. Relative size – Maat is larger, hence closer; smaller objects are farther away Height in the picture – higher objects are farther away Interposition – note Maat’s arms/wings Relative brightness – Maat and the cartouche seem brighter, more vivid, but this is mostly because of their larger size Nevertheless, there’s a curious sense of “flatness” in the picture --No linear perspective --No shading/shadowing --No texture gradients MAAT PROTECTING the CARTOUCHE of NEFERTARI – Original in the Tomb of Nefertari 1250 BC

22. Figure-ground. Introduced as a Gestalt principle by Edgar Rubin, inventor of the famous “vase/face illusion.” Kaiser Porcelain – Vase to commemorate Queen Elizabeth’s Silver Jubilee, 1977

23. A Cup of Water and a Rose on a Silver Plate -- By Francisco de Zurbaran About 1630 Interposition – cup and flower “in front of” ~ “on top of” the saucer Shadowing – shapes of the cup, the saucer, the flower are highlighted & given depth by the shadows. Note the reflections of the cup & the flower in the edge of the saucer –nice effect. Also enhances sense of depth. The color used in the flower and the clearness of the water were interesting additional details that make this simple still life beautiful to me. -- Angela Wagner

24. Paul Klee Picture II, Gnomus. Stage set for Mussorgsky's Pictures at an Exhibition in Friedrich Theater, Dessau. 1928 Klee – Circle in a circle Interposition of circles/lines linear perspective – the two large crossed lines each converges suggesting distance Height in picture – the two large lines’ convergence is at the top of the picture Relative size– smaller circles “farther away” Linear perspective – lines on the right converge, as do the lines depicting where the walls meet floor & ceiling Texture gradient/density – lines on the left grow closer together

25. Vega-Lep By Victor Vasarely I think this is a great example of an illusion of movement and depth, using Linear perspective – lines converge toward the center Texture gradient – dots grow smaller toward the center Shadowing – adds to the sense of bulging sides as well as a bit of haze that implies depth The vibrant colors add to the boldness of the picture, while the circles arranged in square patterns also add to the dimensions of the picture. --Angela Wagner

26. Student’s remarks: This weekend I watched Ed Harris' movie "Pollock," about the life and work of artist Jackson Pollock.  I had seen some of his work before and never really gave it much respect.  Seemed like anyone could drip paint on a canvas.  After watching the movie and thinking about some of the elements discussed in class, I have a greater appreciation for his type of art.  This painting, entitled "Yellow, Grey, and Black" uses organic shape and line along with color to produce a kind of controlled chaos.  The bold yellow combined with interposition create a sense of near foreground, followed by the thick greys overlaying the thick blacks. The smaller, fainter lines seem mostly to recede into the distance.

27. Clearly the pictorial cues for depth exist in the ambient array. They aren’t “in the mind.” In addition, there are major binocular cues for depth perception that work in tandem with the pictorial cues. binocular disparity convergence/divergence etc But the existence of all these cues does not explain how the sensory system knows what they mean. That is, how does the subjective experience of “depth” arise, given that the information is available? This question opens the door to the old “nativist / empiricist” debate: are we born with innate abilities to perceive in depth, or do we learn to do so? And what of modern “constructivist” notions that the mind somehow creates perceptions?

28. Most theorists take the position that the retinal image is the basis for visual perceptions. Seems reasonable. But remember the problems that perceptual theorists have identified regarding perception based on the retinal image:    -- the visual image at the retina is exceedingly tiny compared to the perceived distal object    -- the visual image at the retina is upside down relative to the perceived distal object    -- the visual image at the retina is subject to continuous saccadic movements, yet the perceived distal object does not appear to be jerking around crazily    -- the visual image at the retina is essentially flat, and yet the distal object is three-dimensional.  And there are other questions. -- What causes illusions?  Other animals don’t seem to be subject to them, and they are partly but not completely subject to cultural differences. -- What effects on perception of expectations, beliefs, hopes, fears . . .? -- What effects of prior experience? -- Etc.

29. Next lecture: Theories of depth perception & Gestalt Principles