Perceptual Knowledge: Lecture #2 Space Objects

Transcription

1 Foundations Of Mind Perceptual Knowledge: Lecture #2 Space Objects Slide# 1 Space Perception is Hard We perceive a stable, continuous, 3D spatial layout Perception seems immediate, effortless & nearly error-free The mechanisms of perception are complex and puzzling All senses operate on contact (e.g. surface touches skin, molecules interact with tastebuds) But, Perception brings us knowledge of things at a distance How? Slide# 2 space perception in other modalities: (1) audition Vision: first steps Hussain ibn Abdullah ibn Hassan ibn Ali ibn Sina Latinized: Avicenna ( CE) (av i sen ə) overturned the common idea that somehow the eye emitted rays that bounced off an object being viewed (2) touch (note: modern invented image, 1976) Slide# 3 Slide# 4

2 Descartes (La Dioptrique, 1637) (Traité de l Homme, 1664) René Descartes ( ) (1) depth Some problems of visual space perception: (2) size Slide# 5 Slide# 6 (3) position and motion Visual space perception: depth cues Object motion Interposition Observer motion Linear perspective Slide# 7 Slide# 8

3 Accommodation 2 Depth Cues Discussed by Descartes and Berkeley Question What makes us able to interpret these cues so as to gain knowledge of the surrounding spatial layout? NEAR in focus FAR in focus Two different answers 1. We are endowed with special-purpose cognitive systems for interpreting these cues in the right ways: core knowledge of space nativism Convergence Slide# 9 2. We are endowed with a general-purpose capacity to learn about our surroundings, and this learning leads us to construct appropriate interpretations of spatial cues. no core knowledge of space empiricism Slide# 10 Two Theories of Space Perception Nativism (Descartes): The human mind and brain are built to infer space automatically. Perceptual processes are like reasoning processes: geometric inferences Perception of depth involves internal innate unconscious computations Empiricism (Berkeley): The human mind and brain are built to sense only impinging stimuli (light, muscular effort). We learn through experience to interpret these stimuli in terms of depth, by association with touch: no reasoning involved. Perception of depth involves rote learning, associative pairing Two Theories of Space Perception The prejudice shared by Rationalism and Empiricism is that man does not know things directly but grasps only their impressions (sense data). Both Rationalism and Empiricism needed a new method; the former adopted mathematical deduction, the latter scientific induction. of convergence & accommodation with the sense of touchslide# 11 Slide# 12

4 Descartes Theory of Vision A Nativist Theory of Space Perception René Descartes (The Optics, 1637) philosopher, mathematician, scientist Analogy: the blind man demo Slide# 13 Descartes theory is: mechanistic (light, refraction, nerves, signals to brain) computational (geometric inferences) rationalist and nativist ( natural geometry ) Slide# 14 Berkeley s critique and alternative theory (1709) I appeal to any one s experience, whether, upon sight of an object, he compute its distance by the bigness of the angle made by the meeting of the two optic axes? In vain shall all the mathematicians in the world tell me, that I perceive certain lines and angles which introduce into my mind the various ideas of distance; so long as I myself am conscious of no such thing. Method: introspection Primitives: sensations (e.g., muscular effort) Interpretive process: learning to associate vision & touch Less effort More effort Accommodation Berkeley s effort NEAR in focus: more effortful FAR in focus: less effortful Berkeley s theory is: empiricist associationist Slide# 15 Convergence Slide# 16

5 Hermann von Helmholtz (1850s) on the origins of space perception: Q: Do we perceive depth by innately structured computational mechanisms or by associative learning? A: To answer, must study space perception in infants and children. But we cannot do this! Next best thing: screw around with adult perception Slide# 17 Helmholtz on the origins of space perception: Helmholtz s next-best strategy: Study the modifiability of space perception in adults. --alter the spatial relationship between the perceiver and the layout so that visual space perception is systematically in error. --observe whether the perceiver adapts to the altered relationship & corrects the error. If adaptation occurs: adults are able to learn to perceive space correctly. most reasonable to suppose babies learn too. If no adaptation occurs: the mechanisms of space perception are fixed in adults. most reasonable to suppose they are fixed in infants. Slide# 18 Helmholtz s studies of adaptation to visual rearrangements: Perceptual change or conscious decision? aftereffects (1) Natural observation: walking in the forest with new glasses (2) Experimentation: prism adaptation Pointing with prism Pointing without prism Pointing with prism Before adaptation After adaptation Before adaptation After adaptation Before adaptation After adaptation Perceptual change or conscious decision? Slide# 19 Conclusions: space perception is modifiable in adults on grounds of plausibility, probably learned in children. Slide# 20

6 More on prism adaptation: Harris (1960s) (1) Where does the perceptual change occur: in vision or in touch? (if vision learned by association with touch, as Berkeley claims, then vision should change in adaptation experiments). Prism adaptation: conclusions (1) mechanisms of space perception are modifiable, but touch is more modifiable than vision. Adaptive Shift In Degrees Visual Targets Auditory Targets Straight Ahead (2) how does the perceptual change occur? By associative pairing or active motion? (if Berkeley s associative theory is correct, then (2) modifications depend on active, self-produced motion. If studies of prism adaptation in adults sheds light on visual space perception in infants, then initially Helmholtz s studies show some support for Berkeley, but the further studies of Harris show that the phenomenon more accurately offers some support for Descartes nativist theory and no support for Berkeley --touch doesn t teach vision --learning is not by passive association associative pairing should suffice) Slide# 21 Slide# 22 Helmholtz said: We can t study babies directly Tomorrow Spelke et al. Say: Oh yes we can Slide# 23