1 / 19

University of Arizona Fall 2007 MURI Seminar

University of Arizona Fall 2007 MURI Seminar. Massimo Piattelli-Palmarini October 29, 2007 Attribute substitution, perception, and reasoning. Biological motion. More substitutions. Biological movement is special. Everyday experience (biological versus mechanical movement)

morrowr
Download Presentation

University of Arizona Fall 2007 MURI Seminar

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. University of ArizonaFall 2007MURI Seminar Massimo Piattelli-Palmarini October 29, 2007 Attribute substitution, perception, and reasoning

  2. Biological motion More substitutions

  3. Biological movement is special • Everyday experience (biological versus mechanical movement) • Children are (slightly) better than adults in discriminating biological versus non-biological motion • Light points on a black background • Stick figures • Motion capture in animations • Bellugi’s data on sign languages Perception, illusions and reasoning

  4. Perception, illusions and reasoning

  5. http://www.biomotionlab.ca/Demos/BMLwalker.html Perception, illusions and reasoning

  6. http://www.ruhr-uni-bochum.de/neuropsy/bild/walker.gif http://www.ruhr-uni-bochum.de/neuropsy/bild/walker.gif Perception, illusions and reasoning

  7. Biological movement is uniform • The two-thirds power law in motor-perceptual interactions • Tangential velocity and radius of curvature covary in a constrained manner. • The velocity of point stimuli is perceived as uniform if and only if this biological constraint is satisfied. • This is a very robust illusion • Even in the absence of any intention to perform a movement, • certain properties of the motor system implicitly influence perceptual interpretation of the visual stimulus. Perception, illusions and reasoning

  8. Illusions and an explanation • Harmonic motions, whose velocity is highly nonuniform, are accepted by most observers as plausible instances of constant velocity movements. • The process of perceptual selection is constrained or guided by motor schemes, that is, by procedural, implicit knowledge that the central nervous system has with regard to the movements it is capable of producing. • (Paolo Viviani and Pierre Mounoud 1990, Paolo Viviani and Natale Stucchi 1992) • Alvin Liberman and Ignatius Mattingly (1985) for language Perception, illusions and reasoning

  9. Trajectory used by Viviani and Stucchi in one of their experiments Perception, illusions and reasoning

  10. How robust? • Large misjudgments of velocity persist even when the subject is trained with true constant-velocity motion. • Tangential velocity that is in effect constant along the curved trajectory does not appear to be so • It only appears to be so if the two-thirds power law is instantiated Perception, illusions and reasoning

  11. Two-thirds of what? • Let A(t) be the angular velocity • Let C(t) be the curvature • Then, we have, for biological movements • A(t) = K[C(t)]2/3 • More generally: The relation between linear (tangential) velocity V(t) and the radius of curvature R(t) is  is very close to 1/3 for all adults, even closer for children Perception, illusions and reasoning

  12. Curvature • Radius of curvature of a function f(t) Perception, illusions and reasoning

  13. Modularity of biological motion • Akinetopsia is an intriguing condition brought about by damage to the extra-striate area V5/hMT+ that renders humans and monkeys unable to perceive motion (Zihl et al., 1983, 1991) and indicates that there might be a “motion centre”in the brain. Perception, illusions and reasoning

  14. Two-thirds of what? • K (the velocity gain factor) is constant for long segments of the trajectory •  = 0 when the trajectory has no points of inflection • Therefore we have the simpler formula: • A(t) = K[C(t)]2/3 • is very close to 1/3 for all adults, even closer for children Therefore (1-) is very close to 2/3 Perception, illusions and reasoning

  15. Extemporaneous scribbling movements Dots represent flexes Viviani, P., & Stucchi, N. (1992). Biological movements look uniform: evidence of motor-perceptual interactions. Journal of Experimental Psychology: Human perception and Performance, 18(3), 603-623. Perception, illusions and reasoning

  16. A Circle  eccentric ellipsis: visual tracking and manual drawing B Free hand drawing of scribbles (Viviani & Stucchi ibid.) Perception, illusions and reasoning

  17. Drawing and observing • Only the light dot is visible • The subject has to judge the eccentricity of the ellipsis (zero for circles) • Or to draw ellipses and circles • When the observed dot does not follow the 2/3 power law • Judgments are grossly inaccurate (Viviani and de Sperati 2003) • So are drawings or manual tracking impeded by mechanical interference Perception, illusions and reasoning

  18. Notice: • The muscles of the hand and those of the eye have very different masses, tensions, degrees of freedom • Yet they possess strictly common dynamic properties • They obey the two-thirtds power law • As do the muscles of the legs etc. Perception, illusions and reasoning

  19. Lessons • Attribute substitution again • Replace real motion with biological motion whenever possible • IF POSSIBLE • Impervious to learning, again • Top-down and bottom-up processes interfering in subtle ways Perception, illusions and reasoning

More Related