Leonard S. Mark

Bio: Leonard S. Mark is an academic researcher from Miami University. The author has contributed to research in topics: Poison control & Hypertext. The author has an hindex of 23, co-authored 53 publications receiving 2614 citations. Previous affiliations of Leonard S. Mark include University of Connecticut.

Eyeheight-scaled information about affordances: a study of sitting and stair climbing.

Abstract: Previous work has shown that both the perceived and actual critical (maximum) heights of surfaces that afford "sitting on " and "climbing on" can be expressed as constant proportions of each actor's leg length. The current study provides evidence that these judgments of critical action boundaries are based on an existing source of size and distance information that is already scaled with reference to the actor's eyeheight. In Experiment 1 changes in judgments of "perceived eyeheight" (an index of the intrinsic scalar) as a function of viewing distance were shown to be highly correlated with changes in the maximum height that was perceived to afford sitting on or climbing on. In Experiments 2 and 3 observers wore 10-cm blocks and made judgments about whether the heights of various surfaces afforded sitting or climbing. The use of eyeheight-scaled information as the basis for their estimates predicted the obtained pattern of errors in these judgments. With a modicum of experience wearing the blocks, however, observers were able to retune accurately their critical action boundary to a degree that would not have been predicted from their consistent overestimation of the height of the block on which they were standing. These results have implications for understanding how observers obtain information about their specific action boundary.

What an actor must do in order to perceive the affordance for sitting.

Abstract: Mark (1987) reported that observers, whose sitting capabilities had been altered by having them wear 10-cm blocks, were able to discover their own maximum height of a surface that afforded sitting ...

Postural dynamics and the preferred critical boundary for visually guided reaching.

Abstract: How do people choose an action to satisfy a goal from among the actions that are afforded by the environment? In 3 experiments the action modes used by actors to reach for a block placed at various distances from them were observed. In each experiment, when actors were not restricted in how they could reach for the object, the transition from their reaching using only arm extension to a mode of reaching in which they used the upper torso to lean forward occurred at closer distances than each actor's absolute critical boundary, beyond which the former action was no longer afforded. In Experiments 2 and 3 actors' seated posture was varied so that the effect of postural dynamics on the distance at which actors actually chose to make the transition between action modes, the preferred critical boundary, could be examined. The results are consistent with the proposal that the preferred critical boundary reflects the relative comfort of available modes of reaching.

Recognition-by-Components: A Theory of Human Image Understanding.

Abstract: The perceptual recognition of objects is conceptualized to be a process in which the image of the input is segmented at regions of deep concavity into an arrangement of simple geometric components, such as blocks, cylinders, wedges, and cones. The fundamental assumption of the proposed theory, recognition-by-components (RBC), is that a modest set of generalized-cone components, called geons (N £ 36), can be derived from contrasts of five readily detectable properties of edges in a two-dimensiona l image: curvature, collinearity, symmetry, parallelism, and cotermination. The detection of these properties is generally invariant over viewing position an$ image quality and consequently allows robust object perception when the image is projected from a novel viewpoint or is degraded. RBC thus provides a principled account of the heretofore undecided relation between the classic principles of perceptual organization and pattern recognition: The constraints toward regularization (Pragnanz) characterize not the complete object but the object's components. Representational power derives from an allowance of free combinations of the geons. A Principle of Componential Recovery can account for the major phenomena of object recognition: If an arrangement of two or three geons can be recovered from the input, objects can be quickly recognized even when they are occluded, novel, rotated in depth, or extensively degraded. The results from experiments on the perception of briefly presented pictures by human observers provide empirical support for the theory. Any single object can project an infinity of image configurations to the retina. The orientation of the object to the viewer can vary continuously, each giving rise to a different two-dimensional projection. The object can be occluded by other objects or texture fields, as when viewed behind foliage. The object need not be presented as a full-colored textured image but instead can be a simplified line drawing. Moreover, the object can even be missing some of its parts or be a novel exemplar of its particular category. But it is only with rare exceptions that an image fails to be rapidly and readily classified, either as an instance of a familiar object category or as an instance that cannot be so classified (itself a form of classification).

A morphable model for the synthesis of 3D faces

Abstract: In this paper, a new technique for modeling textured 3D faces is introduced. 3D faces can either be generated automatically from one or more photographs, or modeled directly through an intuitive user interface. Users are assisted in two key problems of computer aided face modeling. First, new face images or new 3D face models can be registered automatically by computing dense one-to-one correspondence to an internal face model. Second, the approach regulates the naturalness of modeled faces avoiding faces with an “unlikely” appearance. Starting from an example set of 3D face models, we derive a morphable face model by transforming the shape and texture of the examples into a vector space representation. New faces and expressions can be modeled by forming linear combinations of the prototypes. Shape and texture constraints derived from the statistics of our example faces are used to guide manual modeling or automated matching algorithms. We show 3D face reconstructions from single images and their applications for photo-realistic image manipulations. We also demonstrate face manipulations according to complex parameters such as gender, fullness of a face or its distinctiveness.

The Perception of the Visual World. By James J. Gibson. U.S.A.: Houghton Mifflin Company, 1950 (George Allen & Unwin, Ltd., London). Price 35s.

Abstract: Let's read! We will often find out this sentence everywhere. When still being a kid, mom used to order us to always read, so did the teacher. Some books are fully read in a week and we need the obligation to support reading. What about now? Do you still love reading? Is reading only for you who have obligation? Absolutely not! We here offer you a new book enPDFd the perception of the visual world to read.

Categorization of Natural Objects

Abstract: ions and general knowledge more extensive than that of individual categories are required in any account of categorization. For example, Pittenger & Shaw (1975, Pittenger et al 1979) argue that higher order knowledge about transformations serves as the perceptual invariant under­ lying certain types of categorization. In the tradition of constructive mem­ ory research (e.g. Bartlett 1932, Bransford & McCarrell 1974), categories are treated as part of very general schemas. Finally, large scale computer models (Collins & Loftus 1975, Schank & Abelson 1977, Winograd 1 972) treat categories and categorization processes as inseparable from world knowledge and the inference processes used in such knowledge. DECOMPOSABILITY OF CATEGORIES INTO ELEMENTS Virtually all accounts of the representation and processing of categories assume that categories are decomposable into more elementary qualities. This is not surprising: as Dreyfus (1979) has pointed out, since the time of Plato one of the major aspects of what has been meant by an explanation has been the decomposition of the thing to be explained into its elements. In psychology, however, arguments against the indiscriminate use of expla­ nation-by-decomposition have been with the field since its inception (see e.g. James 1 890a on the unitary nature of a single complex thought). The issue of decomposability was the focus of the debate in the early part of this century between the structuralists, who saw all experience as built out of primitive meaningless sensations, and the GestaItists, who emphasized irre­ ducible emergent properties of wholes (see Boring 1 950). At present, while decomposition is the unmarked assumption in model building, the possible need for less analytic factors is periodically acknowl­ edged. For example, in the pattern recognition literature, analysis into features and holistic matching to a template are generally presented as the two major types of alternative models (Reed 1 973), although for good reasons templates are usually treated as straw men (see Palmer 1978). CATEGORIZATION OF OBJECTS 105 Various empirical developments have brought the nature and role of decomposition into current debate. First, categorization has been investi­ gated for types of stimuli that do not have obvious elements at a cognitive level. The most notable of these are color (Rosch 1 973b, 1974) and overall configuration (e.g. Attneave 1 957, Posner 1969, Lockhead 1 972-but see also Barresi et a1 1 975, Homa & Vosburgh 1976). It is not surprising that such stimuli do not strike us as obviously decomposible, since they are themselves normally treated as attributes, i.e. the qualities into which more complex objects are decomposed. There has also been considerable dis­ agreement as to whether faces should be considered special holistically perceived objects (Hochberg & Galper 1 967, Yin 1 969, Rock 1973, Brad­ shaw 1 976). A second development which has offered the opportunity to view categories as wholes is the possibility for spatial representation of withinand between-category structures through techniques such as mul­ tidimensional scaling. For example, Hutchinson & Lockhead (1977) have argued that categories can best be conceived as unanalyzed points in metric multidimensional space. A third trend has been use of the concept of a prototype and the facts of gradients of representativeness to suggest holistic processing (e.g. Rosch 1973b, Dreyfus 1 979). The great majority of arguments over decomposition concern specifying the level of abstraction at which a particular kind of decomposition can or cannot be said to occur. While most categorization models include decom­ position, it is never to the point of infinite regress. Some elements are included as the primitives, although usually by default, rather than by explicit labeling as primitives. Because some elements are not decomposed, many accounts of catego­ rization include an explicit holistic component. For example, this can be introduced by means of a (relatively) holistic processing stage (E. E. Smith et al 1 974). Another possibility is that a given level of abstraction may be a basic and (potentially) holistically perceived level, even if other levels require more analytic mechanisms (Rosch et al 1 976a). Perceptual process­ ing of figures (such as a large letter constructed of smaller letters) has been shown to proceed from global to local analysis under some stimulus condi­ tions (Navon 1 977) but to proceed from local to global under others (e.g. Kinchla & Wolf 1979). In the perception models of Palmer (1975) and Winston ( 1975), the decomposition of a visual scene is viewed as a hierar­ chical network of subscenes, and it is claimed that higher-order properties are processed first, followed by lower-order properties. Depending on the circumstances, however, a given aspect of a scene might be either the higheror the lower-order property. The controversy over lexical decompo­ sition in linguistics and artificial intelligence (does "kill" really mean "cause to die") can be seen as largely an issue of which linguistic level to consider a whole and which to consider the elements (Fodor 1970; McCawley 1971,

Heart rate variability, prefrontal neural function, and cognitive performance: the neurovisceral integration perspective on self-regulation, adaptation, and health.

Abstract: In the present paper, we describe a model of neurovisceral integration in which a set of neural structures involved in cognitive, affective, and autonomic regulation are related to heart rate variability (HRV) and cognitive performance. We detail the pathways involved in the neural regulation of the cardiovascular system and provide pharmacological and neuroimaging data in support of the neural structures linking the central nervous system to HRV in humans. We review a number of studies from our group showing that individual differences in HRV are related to performance on tasks associated with executive function and prefrontal cortical activity. These studies include comparisons of executive- and nonexecutive-function tasks in healthy participants, in both threatening and nonthreatening conditions. In addition, we show that manipulating resting HRV levels is associated with changes in performance on executive-function tasks. We also examine the relationship between HRV and cognitive performance in ecologically valid situations using a police shooting simulation and a naval navigation simulation. Finally, we review our studies in anxiety patients, as well as studies examining psychopathy. These findings in total suggest an important relationship among cognitive performance, HRV, and prefrontal neural function that has important implications for both physical and mental health. Future studies are needed to determine exactly which executive functions are associated with individual differences in HRV in a wider range of situations and populations.