_____ source information
(wavelength, intensity, position in space)
(illumination)
_______ information
(reflectance, orientation, shadows, occlusion)
(luminance)
______ information
(optics of the eye, position in space)
1. What is the basic problem that any theory of human perception must address?
2. Describe the assumptions made by the following different perceptual schools of thought:
- Structuralist approach
- Gestalt approach
- Neurophysiological approach
- Constructive approach
- Ecological approach
- Natural Computation approach
3. What do each of these approaches have in common? In what general ways do they differ?
4. What are the pros and cons of each approach?
Visual perception is ____ to do!
“This apparently __________ achievement, which you repeat innumerable times throughout your waking hours, is proving very difficult to understand or to simulate on a computer--much more difficult, in fact, than the understanding and simulation of tasks that most people find quite challenging, such as playing chess or solving problems in logic” (Treisman, 1986, p.114). |
|
“The first great revelation was that the problems [of visual perception] are _________. Of course, these days this fact is a commonplace. But in the 1960s, almost no one realized that machine vision was difficult...The reason for this misperception is that we humans are ourselves so good at vision” (Marr, 1982, p.16). |
The goal of perception:
- to recover meaningful _______________ of the world, on the basis of physical stimulation that originates in the world
What is the basis of this “________ ___________”?
- presumably, a physicist could predict the character of the proximal stimulus when given enough information about:
• the nature of _____,
• the nature of ________, and
• the __________ position in space
The physics of perception:
|
_____ source information (wavelength, intensity, position in space) |
|
|
|
_______ information (reflectance, orientation, shadows, occlusion) |
|
|
|
______ information (optics of the eye, position in space) |
Towards perceptual theories:
- the physical nature of the viewing situation could, in principle, uniquely determine the nature of the object via the laws of ______
- perception, however, cannot be simply described as computing the “________ laws of optics,” because of the problem of underdetermination
A framework for studying perception (Gibson, 1966, 1979):
- ______ stimulus: object or event in the environment
e.g., baking cookies
- _____________ ______: environmental energy (or chemicals) carrying information from the object
e.g., photons reflecting off surface of cookies, molecules released from cookies into the air
- ________ stimulus: information about a distal stimulus that impinges upon receptors
e.g., photons striking receptors on retina, molecules contacting olfactory epithelium in nasal cavity
- __________ ______: mental representation of the distal stimulus
e.g., concept of baking cookies activated--yum!
The basic problem:
- __________________ exists when proximal stimulus information, by itself, cannot lead to a unique distal stimulus interpretation
- however, our perceptual experiences would suggest that such problems are routinely ______
- instead of appearing intrinsically ambiguous, our perceptions appear as if they are unique: a one-to-one mapping between information in the world and our interpretation of it
- how are problems of underdetermination solved?
A perceptual theory can be _______ in terms of the approach it takes in defining a solution to the problem of underdetermination.
Solving problems of underdetermination:
• unsolved problem:
|
|
|
|
proximal stimulus |
|
|
|
- which interpretation is correct?
• solved problem:
|
|
[filter] |
|
|
|
proximal stimulus |
|
||
|
|
- “_____ ______” eliminates all but the correct interpretation
What is the “magic filter”?
- obviously, a basic question to ask is this: What properties are required in order for the “magic filter” to solve various problems of underdetermination?
- different answers to this question define different schools of thought in the study of perception
Central assumptions:
• conscious processes can be analyzed into their basic ________: sensations, images, feelings
• elements are _________ in lawful ways
|
“The primary aim of the experimental psychologist has been to analyze the _________ of mind; to ravel out the elemental processes from the tangle of consciousness, or (if we may change the metaphor) to isolate the constituents in the given conscious formation. His task is a vivisection, but a vivisection which shall yield structural, not functional results. He tries to discover, first of all, what is there and in what quantity, not what it is there for.” (Titchener, 1898, p.449) |
Names and dates:
- Wilhelm Wundt (b.1832-d.1920): opened first psychology lab, University of Leipzig, 1879
- Edward Titchener (b.1867-d.1927): brought psychology to America
Research questions:
• What are the basic ________ of immediate conscious experience in general, and perception in particular?
• What are the preferred ____________ among these elements?
• What are the _____ for forming these associations?
Research example:
Titchener (1901):
- applied systematic _____________ (analysis of one’s own conscious experience) to determine the structure of perceptual phenomena
- designed to overcome contamination by stimulus _____, an observer’s tendency to report what they know an object to be, rather than to report the sensations that lead to such an inference
“Thus the ‘taste’ of lemonade is made up of a sweet taste, an acid taste, a scent (the fragrance of lemon), a sensation of temperature and a pricking (cutaneous) sensation.
“The ‘taste’ of lime-water is made up of a weakly sweet taste, a sensation of nausea (common sensation), a sensation of temperature and a biting (cutaneous) sensation.”
Pros and Cons:
provided a ________ point for the science of psychology
introspection ______: low between-observer reliability, resistant to quantification, many mental processes not available to self-observation
Central assumptions:
• visual perception is not the result of a series of ___________ stimulus/response events
• instead, it is the result of the organization of a set of interacting events, called the environmental _____
e.g., in apparent movement, two independent stimuli induce two neural fields which interact, yielding a unitary percept
• percepts tend towards the most efficient/simplest state, as in the real world
|
“Instead of reacting to local stimuli by local and mutually independent events, the organism responds to the pattern of stimuli to which it is exposed; and this is a unitary process, a functional _____, which gives, in experience, a sensory scene rather than a mosaic of local sensations” (Köhler, 1947). |
Name and dates:
- Max Wertheimer (b.1880-d.1943): founded Gestalt psychology
- along with Wolfgang Köhler (b.1887-d.1967), and Kurt Koffka (b.1886-d.1941)
Research questions:
• What are the principles of ____________ of the environmental field?
• What types of functional ______ are perceived?
• Why are some functional wholes perceived, while other logically possible ones are not?
Research example:
Shepard (1984):
- presented pairs of polygons in rapid succession
- one was a different view of the other, after having gone through a transformation (e.g., translation, size scaling, rotation, and combinations)
e.g., translation
|
e.g., size scaling
|
e.g., rotation
|
- observers perceived a ______ object moving along a minimum path
Pros and cons:
principles of organization offered good ____________ of perceptual and physiological theory
based on demonstrations, more than _________ evidence
notion of environmental field was too _______ defined to be properly or rigorously tested
Central assumption:
• every different pattern of visual stimulation sets up a unique _______ of physiological activity
|
“The assumption has always been that the eye mainly senses light, whose local distribution is transmitted to the brain in a kind of copy by a mosaic of impulses. Suppose we hold otherwise, that the nervous apparatus in the eye is itself devoted to detecting certain ________ of light and their changes, corresponding to particular relations in the visible world.” (Lettvin et al., 1959, p.1942). |
Names and dates:
- Donald Hebb (b.1904-d.1985): proposed neural ________ for learning and memory
- David Hubel (b.1926-d.2013) and Torsten Wiesel (b.1924): determined function of neurons in the visual cortex
Research questions:
• What is the _______ of particular physiological structures?
• To what stimulus ________ in the world do particular physiological structures respond?
• How is the neural _________ for perception organized; how does this organization serve to mediate perception?
Research example:
Lettvin et al. (1959):
- presented a range of specific stimuli to frogs
- recorded responses of individual cells in the frog retina
- found four types of cells that only responded to particular patterns of stimulation:
• sustained contrast detectors (“_____ detectors”)
• moving edge detectors (“____ detectors”)
• net dimming detectors (“shadow/________ detectors”)
• net convexity detectors (“___ detectors”)
Pros and cons:
assumes that perception is mediated by __________; (therefore, it makes sense to learn about such structures)
central assumption is false; it can’t tell the whole story about perception (even a perfect physiological understanding wouldn’t tell you about __________; different vocabularies are required)
Central assumptions:
• perception is really a process of _________, hypothesis testing, and problem solving
• our knowledge of the world is used to help us perceive
|
“Since perception is a matter of reading non-sensed characteristics of objects from available sensory data, it is difficult to hold that our perceptual beliefs--our basic knowledge of objects--is free of theoretical contamination. We not only believe what we see; to some extent, we see what we _______.” (Gregory, 1970, p.15) |
Names and dates:
- Hermann von Helmholtz (b.1821-d.1894): proposed unconscious _________: vision is mediated by thought-like deductions; percepts are actively constructed, such that we perceive the object that is most likely to be the cause of our sensory stimulation
- Irvin Rock (b.1922-d.1995): believed perception is not automatic; it requires extensive computation which can take place quickly and effortlessly, but is complex and sophisticated nonetheless--drawing inferences, being influenced by experience, basing one perception on another
- Richard Gregory (b.1923-d.2010): integrated perception, cognition, and neuroscience
- Julian Hochberg (b.1923): approached perceptual processes as a unified field of science
Research questions:
• To what extent do changes in our _______ or knowledge of the world affect our perception of the world?
• What kinds of information or representations are used to _______ perception?
• How does learning or __________ alter perception?
Research example:
Attneave & Block (1973):
- kept two-dimensional distance between two stimuli constant while the stimuli were set into apparent motion
- manipulated beliefs about how far the objects were apart in _____ by using different backgrounds:
- found that changes in beliefs about distance affected the perceived optimality of apparent motion
Pros and cons:
perception and _________ must meet at some point; it is important to find out how and when this happens (two-stage theory)
not all perception can be concept-driven, or we wouldn’t be able to survive; some perception must be ____-______, and can’t be described from this theory’s vantage point
Central assumptions:
• all the information you need about the visual world is available in the ______ ______
• the visual system simply “_________” to or picks out this information; perception is direct
|
“The theory to be presented suggests that perception is a function of ___________. More exactly, it asserts that there is always some discoverable variable in stimulation--in the flowing array of energy at the sense organs of an animal--which determines the character of the perceptual processes aroused by it” (Gibson, 1959, p.457). |
Names and dates:
- Egon Brunswik (b.1903-d.1955): emphasized that research in perception needs to be ecologically valid (must consider relationship between the perceiver and the world)
- James J. Gibson (b.1904-d.1979): primary theorist behind the ecological approach, and direct perception
Research questions:
• What properties of the world are perceptually _________?
• What is the relationship between a perceptual invariant and the behaviour that it governs or guides?
• What types of information does the visual system pick up from the optical array?
Research example:
Lee & Reddish (1981):
- _____ ____ field is the set of velocities at each location in the visual field
- a mathematical invariant that can be derived from this field is the parameter tau (τ): inverse of the rate of dilation of the visual image of texture elements
- tau can indicate the time to contact a surface
- analyzed videotape evidence to show that tau is quite likely used by _______ to determine time to impact when diving into the sea
- this allows the birds to choose the correct time to streamline their bodies by folding their wings
- results in a safe dive being accomplished
- advantage of tau: don’t need to know the ________ to the object--just use object expansion rate
Pros and cons:
there is a lot to be learned about perception by looking for __________ that can be derived from
visual stimulation
central assumption is wrong: it does not appear that visual stimulation provides all the information that is required for perception to succeed
Central assumptions:
• visual system exploits certain properties that are generally true of the real world to _______ (in some abstract sense) veridical perceptions and overcome underdetermination
• these assumptions are called _______ ___________; they reduce the number of possible distal stimulus interpretations (like a magic filter)
|
“A classic problem of perception...is that biological systems have available through their senses only very limited information about the external world. Yet these systems make strong assertions about the actual state of the world outside themselves. These assertions are of necessity incomplete. Clearly, a replica of an object and its qualities cannot be embodied within the brain. How can an incomplete description, encoded within neural states, be sufficient to direct the survival and successful adaptive behavior of a living system?” (Richards, 1988, p.3) |
|
“There must exist an additional level of _____________ at which the character of the information processing tasks carried out during perception are analysed and understood in a way that is independent of the particular mechanisms and structures that implement them in our heads... Such analysis does not usurp an understanding at the other levels--of neurons or of computer programs--but it is a necessary complement to them, since without it, there can be no real understanding of the function of all those neurons” (Marr, 1982). |
Names and dates:
- Whitman Richards (b.1932-d.2016): coined the term “_______ ___________” in 1988
- David Marr (b.1945-d.1980): developed computational neuroscience
Research questions:
• What information processing problem must be solved for a particular type of perception to be accomplished?
• What general properties of the _____ must be incorporated into a solution of a problem so described?
• What kinds of procedures can exploit these properties in the prescribed manner, and how might these procedures be implemented biologically?
Research example:
Ullman (1979):
- the visual system is quite adept at computing structure from motion
- given a dynamic, two-dimensional pattern, it can assign a ___ interpretation
- however, the proximal stimulus by itself is not sufficient to uniquely determine what the interpretation should be
- if a system assumes that objects are usually rigid (a natural constraint), then three views of four non-coplanar points are sufficient to compute the 3-D structure of the object
- furthermore, the solution is ________, are as human interpretations of the phenomenon!
Pros and cons:
offers a _______ formulation of the problem of perception; is a good compromise between constructive
and physiological theories
researchers who take this approach often focus more on abstract computation than on finding out how (or whether) such computations might actually be done by the _____ ______ system
interpretation 1
interpretation 2
interpretation 3
