University of Arizona Fall 2007 MURI Seminar INDV 101 Sect. 25H University of Arizona Fall 2007 MURI Seminar Massimo Piattelli-Palmarini October 29, 2007 Attribute substitution, perception, and reasoning M. Piattelli-Palmarini

Biological motion More substitutions INDV 101 Sect. 25H M. Piattelli-Palmarini

Biological movement is special INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H http://www.biomotionlab.ca/Demos/BMLwalker.html UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H http://www.ruhr-uni-bochum.de/neuropsy/bild/walker.gif http://www.ruhr-uni-bochum.de/neuropsy/bild/walker.gif UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Biological movement is uniform INDV 101 Sect. 25H 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. UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Illusions and an explanation INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H Trajectory used by Viviani and Stucchi in one of their experiments UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H Curvature Radius of curvature of a function f(t) UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Modularity of biological motion INDV 101 Sect. 25H 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. UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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. UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H A Circle  eccentric ellipsis: visual tracking and manual drawing B Free hand drawing of scribbles (Viviani & Stucchi ibid.) UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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. UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini

Perception, illusions and reasoning INDV 101 Sect. 25H 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 UofA MURI Seminar Perception, illusions and reasoning M. Piattelli-Palmarini