In this investigation of monocular perception of egocentric distance, the authors advocate the necessity of a perception-action approach because calibration is intrinsic to definite distance perception. A helmet-mounted camera and display were used to isolate optic flow generated by participants' head movements toward a target, and participants' reaches to place a stylus either in a target hole (Experiments 1, 2, and 4) or aligned under a target surface (Experiment 3) were analyzed. Conclusions are that binocular distance perception is accurate, monocular distance perception yields compression that is not eliminated by feedback, but feedback is used to eliminate underestimation generated by restriction of the size of the visual field.

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Observers are able to judge accurately the weight hfted by another person when only the motions of reflectwe patches attached to the hfter's major hmb jomts and head can be seen (Runeson & Frykholm, 1981) What properttes of these complex kinematic patterns allow judgments of wetght to be made 9 The pattern of vanaUon m veloctty of the hfied object over posmon ~s explored as a source of mformat~on for wetght It ts found to provtde hmtted mformat~on How are variations m kmemaUc patterns scaled to allow judgments of wetght, a ionet~c quanUty9 The posstbd~ty of a source of m formauon for scaling in the Ionematlcs ts mvesUgated Judgments based only on patch-hght chsplays are accurate to a degree that is ,reproved by an extrms~c scahng basts Fmally, the sensttlvaty to scaling of alterna)ave metrics used m judging ts explored Intrlnstc metrics are dtscovered to be less sens~ttve to the absence of an extrlnstc basts for scahng Observers are able to judge with good accuracy the amount of weight be|ng hfted by another person when only the motions of reflectwe patches attached to the htter's major hmb joints and head can be seen (Runeson & Frykholm, 1981). How is th~s possible? Runeson and Frykholm (1981, 1983) suggest that umque patterns of moUon result from mechan|cal constraints on the hfter's acUvlty They have formulated a principle called KSD, or kinematic spec|fication of dynamics, which states that lonemat~c patterns specify to observers varmt~ons in the values of dynamic factors. Further, Runeson and Frykholm (1983) propose that the mformatwe value of lonemaUc properties of These experiments were included m a doctoral dissertation submttted at the Umverstty of Connecticut, Storrs, Connecttcut The research was supported by a Fulbnght-Hays Pre-doctoral Full Grant for Study Abroad and a Umverstty of Conneclacut Pre-doctoral Fellowshtp awarded to the author, as well as a Swedtsh Counol for Research tn the HumamUes and Sooal Soences (HSFR) award to Sverker Runeson The writing was supported in part by a Nattonal Institutes of Health Indwldual Fellowship Award (AM-07412) Research was performed both at the Umverstty of Connecttcut and at the Umvers~ty of Uppsala, Uppsala, SwedenHeartfelt thanks go to Sverker Runeson, whose work and tdeas msptred the present effort I gratefully acknowledge the help and advice of Sverker Runeson, Ball Mace, Bob Shaw, Mtchael Turvey, Carol Fowler, Len Katz, and Dave Mdler, as well as the constructtve cnlaosm provtded by Jtm Cuttmg and two anonymous reviewers Thanks also to Lars-Enk Larsson, Gunnar Agren, and Lars Beckstrom for proxqdmg mvaluable techmcal asststance I also am grateful to the faculty and students at the Department of Psychology m Uppsala and to the staffat the Swedish Fulbnght Commtsmon for malong my tenure at Uppsala an extraordmardy pleasant and ennchmg experience It was a pnxqlege to part~ctpate m the tradmon of research m event perceptton mtuated by Gunnar Johansson and earned on by Sverker Runeson I shall long benefit from the opportumty Correspondence concerning thts ar...

Objects for throwing to a maximum distance were selected by hefting objects varying in size and weight. Preferred weights increased with size reproducing size-weight illusion scaling between weight and volume. In maximum distance throws, preferred objects were thrown the farthest. Throwing was related to hefting as a smart perceptual mechanism. Two strategies for conveying high kinetic energy to projectiles were investigated by studying the kinematics of hefting light, preferred, and heavy objects. Changes in tendon lengths occurring when objects of varying size were grasped corresponded to changes in stiffness at the wrist. Hefting with preferred objects produced an invariant phase between the wrist and elbow. This result corresponded to an optimal relation at peak kinetic energy for the hefting. A paradigm for the study of perceptual properties was compared to size-weight illusion methodology.A task familiar to many from childhood is that of standing on a beach, in a field, or on a cliff and selecting, by hefting, the stone that can be thrown the farthest distance. Like the perfect skipping stone, the optimal throwing stone evokes an ardent glow of confidence in one's ability to discover and use this appealingly simple, yet distinct tool. What is the optimal throwing stone? Assuming a spherical shape and a fairly homogeneous mass distribution, the relevant object properties are size and weight. What is the appropriate configuration of size and weight and how is it determined? Are people truly able to select from objects varying in size and weight those optimal for throwing to a maximum distance? If so, how?The human perception-action system has been described as a system that temporarily assembles smart, special purpose, deterministic machines over relevant physical properties of the organism and the environment to perform specific tasks

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