How Direct Is Visual Perception? Some Reflections on Gibson ’ s “ Ecological Approach

1. How Direct Is Visual Perception? Some Reflections on Gibson’s “Ecological Approach By J. Fodor & Z. W. Pylyshyn Presented by Allen Houng

2. The establishment theory • Information processing view • Perception requires inference (computational processes) • The postulate of representation

3. Gibson’s ecological approach • Perception = the “direct pickup” of “invariant properties” • For any object x, there is some property P s. t. the direct pickup of P is necessary and sufficient for the perception of x. • no process, no representation involved

4. Gibson’s thesis • The postulation of mental processes is not necessary • Visual perception = direct pickup of information in the ambient light

5. Gibson • The theory of information pickup differs radically from the traditional theories of perception. • First, it involves a new notion of perception, not just a new theory of the process. • Second, it involves a new assumption about what there is to be perceived. • Third, it involves a new concept of the information for perception …

6. Fourth, it requires the new assumption of perceptual systems with overlapping functions… • Finally, fifth, optical information pickup entails an activity of the system not heretofore imagined by any visual scientist … Such is the ecological approach to perception. It promises to simplify psychology by making old puzzles disappear.

7. Fodor’s main points • Gibson’s account is empty unless the notions of “direct pickup” and of “invariant” are suitably constrained. • 不是任何property都可以算作invariant, 不是任何psychological process都可以算作pickup. • To properly constrain these two notion, you have to assume that perception is inferentially mediated.

8. Two constraints for visual perception • Only a certain class properties of the ambient light can be picked. • Spatio-temporal bounds on the properties picked up are determined by effective stimuli.

9. Consequences of these two assumptions • From the properties of ambient light to the perception of object needs inference. • Inference is required for the effective stimuli for perception very often underdetermine what is seen

10. The trivialization problem • Without proper constraints, that perception is direct is true but empty. • For Gibson, to perceive that something is P is to pick up the invariant property P which things of that kind have. • Trivial!

11. Gibson actually accepts the first constraint, i.e., what is picked up in visual perception is only certain properties of the ambient light array. • How to get from the ambient light array to perceptual knowledge of properties of the environment?

12. In other words … • How, if not by inference, do you get from what you pick up about the light to what you perceive about the object? • What is pick up = the information contained in the ambient array

13. First gambit • Invariant properties = ecological properties • Only the ecological properties of the environment are directly perceived. • Examples: texture, shape, illumination, reflectance, resistance to deformation… • Being open, being cluttered, containing a hollow, or an enclosure (environmental layout)

14. Affordances • A class of ecological properties • Properties that concern the goals and utilities of an organism • Being edible, being an obstacle, being capable of being used as a weapon, being a shelter, being dangerous, being a potential mate • Dispositional properties, relational properties

15. Non-ecological properties • Not directly perceivable • examples: being made of atom, being 1000 light years away,

16. Ecological properties 可以serve as a constraint for the notion of direct perception嗎? • No • For if all properties that can be perceived are ipso facto ecological, then the claim that perception is the pickup of ecological properties is vacuously true.

17. Second gambit • Only the projectible properties of ecological optics are directly perceived. • The directly perceptible properties are those figure in the laws of “ecological optics.”

18. The projectible ecological properties would be the ones which are connected, in a lawful way, with properties of the ambient light.

19. But which projectible properties are directly perceivable? • Not all projectible properties are directly perceivable. • Classical optics vs. ecological optics • Gibson 主張只有ecological properties 才是directly perceivable • 他以projectible properties 來限制direct pickup, 又以ecological properties 區隔出perceivable properties，Gibson 欠一個如何區分ecological or non-ecological laws 的原則。

20. Another difficulty • Affordances are not projectible. • Affordances are directly perceivable.

21. Third gambit • Only phenomenological properties are directly perceivable • Child learns early to recognize and to name • Commonsensical, observable, meaningful

22. Objections • Rule out some of Gibson’s favorite examples of ecological invariants: the slant of surfaces, the gradients and flows of texture, … • Whereas the projectability criterion leaves the affordances out, the phenomenological criterion lets almost only the affordances in.

23. The perception of p-salient properties of the stimulus is causally depend on the detection of features whose p-accessibility is negligible.

24. Fourth gambit • Directly perceivable = whatever “perceptual ssytems” respond to • The problem is that Gibson provide no criterion for identifying perceptual systems.

25. The problem of misperception • How to explain false perception? • “X directly perceives that y is edible” entails that y is edible. • For Establishment theory, misperception can be explained by wrong inference.

26. The problem of intentionality • Perceptual relations (such as seeing, hearing, tasting) are extentional. • Our cognitive relations (such as believing, expecting, thinking about, seeing as) are intentional. • The main job of mental representation is to explain intentionality. • How Gibson can explain intentionality without mental representation?

27. Recognizing vs. recognizing as • Seeing vs. seeing as • Intentional context vs. extensional context • Does Gibson’s approach deals with extensional psychology only?

28. Psychology must include a theory of intentional relations. • “To do cognitive psychology, you must know not only what the organism perceives, but how it takes what it perceives.” • Without representation, it is difficult to see how Gibson can explain intentionality.

29. To see the Pole Star as the Pole Star • To see the Pole Star What is the difference? • To see George Bush vs. to see George Bush as American President

30. One sees Venus as The Morning star, while the other may see it as The Evening star. • The Morning Star and The Evening Star are coextensive. • With representation at hand, you can explain this fact by saying that the same object can be represented in many different ways.

31. Gibson’s solution: the same object has two distinct properties of being the Morning Star and Being the Evening Star. • Which way we respond to the object depends on which of these properties we happen to pick up.

32. Ambient light array is correlated with the object perceived. • Ambient light array specifies the perceptual object. • Gibson has seeing but do not have seeing as. • Specification is extentional. • Property is intentional. • Specification cannot explain property pickup.