60,712 research outputs found

    Default perception of high-speed motion

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    When human observers are exposed to even slight motion signals followed by brief visual transients—stimuli containing no detectable coherent motion signals—they perceive large and salient illusory jumps. This novel effect, which we call “high phi”, challenges well-entrenched assumptions about the perception of motion, namely the minimal-motion principle and the breakdown of coherent motion perception with steps above an upper limit. Our experiments with transients such as texture randomization or contrast reversal show that the magnitude of the jump depends on spatial frequency and transient duration, but not on the speed of the inducing motion signals, and the direction of the jump depends on the duration of the inducer. Jump magnitude is robust across jump directions and different types of transient. In addition, when a texture is actually displaced by a large step beyond dmax, a breakdown of coherent motion perception is expected, but in the presence of an inducer observers again perceive coherent displacements at or just above dmax. In sum, across a large variety of stimuli, we find that when incoherent motion noise is preceded by a small bias, instead of perceiving little or no motion, as suggested by the minimal-motion principle, observers perceive jumps whose amplitude closely follows their own dmax limits

    Visual Perception as Patterning: Cavendish against Hobbes on Sensation

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    Many of Margaret Cavendish’s criticisms of Thomas Hobbes in the Philosophical Letters (1664) relate to the disorder and damage that she holds would result if Hobbesian pressure were the cause of visual perception. In this paper, I argue that her “two men” thought experiment in Letter IV is aimed at a different goal: to show the explanatory potency of her account. First, I connect Cavendish’s view of visual perception as “patterning” to the “two men” thought experiment in Letter IV. Second, I provide a potential reply on Hobbes’s behalf that appeals to physiological differences between perceivers’ sense organs, drawing upon Hobbes’s optics in De homine. Third, I argue that such a reply would misunderstand Cavendish’s objective of showing the limited explanatory resources available in understanding visual perception as pressing when compared to her view of visual perception as patterning

    Hume's Perceptual Relationism

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    My topic in this paper will be Hume’s claim that we have no idea of a vacuum. I offer a novel interpretation of Hume’s account of our ideas of extension that makes it clear why those ideas cannot include any ideas of vacuums, and I distinguish my interpretation from prominent readings offered by other Hume scholars. An upshot of Hume’s account, I will argue, is his commitment to a remarkable and distinctly Humean view I call “perceptual relationism.” Perceptual relationism is a fundamental characteristic of Hume’s “universe of the imagination,” and a manifestation of just how “loose and separate” the constituents of that inner universe are. Once we understand perceptual relationism and its entailments, we are in a better position to understand the rest of Hume’s sometimes puzzling remarks on space and the vacuum

    A new empirical challenge for local theories of consciousness

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    Local theories of consciousness state that one is conscious of a feature if it is adequately represented and processed in sensory brain areas, given some background conditions. We challenge the core prediction of local theories based on recently discovered long-lasting postdictive effects demonstrating that features can be represented for hundreds of milliseconds in perceptual areas without being consciously perceived. Unlike previous empirical data aimed against local theories, proponents of local theories cannot explain these effects away by conjecturing that subjects are phenomenally conscious of features that they cannot report. Only a strong and counterintuitive version of this claim can account for long-lasting postdictive effects. Although possible, we argue that adopting this strong version of the “overflow hypothesis” would have the effect of nullifying the weight of the evidence taken to support local theories of consciousness in the first place. We also discuss several alternative explanations that proponents of local theories could offer

    Why the Imago Dei is in the Intellect Alone: A Criticism of a Phenomenology of Sensible Experience for Attaining an Image of God

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    This paper, as a response to Mark K. Spencer’s, “Perceiving the Image of God in the Whole Human Person” in the present volume, argues in defence of Aquinas’s position that the Imago Dei is limited in the human being to the rational, intellective soul alone. While the author agrees with Spencer that the hierarchical relation between body and soul in the human composite must be maintained while avoiding the various permeations of dualism, nevertheless, the Imago Dei cannot be located in the human body or the principle of the body considered within the body/soul composite without betraying a number of fundamental Thomistic metaphysical principles. Essential to these includes Aquinas’s position that an image of God should image not only the Divine Nature, but also the Trinitarian relations between the Divine Persons. Further, the paper also argues that a phenomenology of sense experience could not, on principle, attain to an image of God in the whole human person within a Thomistic framework generally

    Perception and control of rotorcraft flight

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    Three topics which can be applied to rotorcraft flight are examined: (1) the nature of visual information; (2) what visual information is informative about; and (3) the control of visual information. The anchorage of visual perception is defined as the distribution of structure in the surrounding optical array or the distribution of optical structure over the retinal surface. A debate was provoked about whether the referent of visual event perception, and in turn control, is optical motion, kinetics, or dynamics. The interface of control theory and visual perception is also considered. The relationships among these problems is the basis of this article

    Applications of computer-graphics animation for motion-perception research

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    The advantages and limitations of using computer animated stimuli in studying motion perception are presented and discussed. Most current programs of motion perception research could not be pursued without the use of computer graphics animation. Computer generated displays afford latitudes of freedom and control that are almost impossible to attain through conventional methods. There are, however, limitations to this presentational medium. At present, computer generated displays present simplified approximations of the dynamics in natural events. Very little is known about how the differences between natural events and computer simulations influence perceptual processing. In practice, the differences are assumed to be irrelevant to the questions under study, and that findings with computer generated stimuli will generalize to natural events

    Neural Coding of Real and Implied Motion in the Human Brain

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    Perceiving and processing visual motion is crucial for all animals, including humans. Brain regions in the human brain that are responsive to real motion have been extensively studied with different neuroimaging methods. However, the neural codes that are related to real motion have been primarily addressed using highly reductionist and mostly artificial motion stimuli, mostly using so-called random dot kinematograms. Studies using more natural forms of motion that the brain evolved and developed to deal with are comparably rare. Moreover, real, physical motion is not the only type of stimulus that induces motion perception in humans. Implied motion stimuli also induce motion perception although the stimuli do not carry physical motion information. Implied motion stimuli are for example still images containing a snap-shot of an object in motion. Various contextual cues mediate the percept of motion, including the context of the object in its background, and in particular the object composition and its axial position in the image that mediate both, the impression of implied motion as well as its direction. This means that at the neural level, object processing must be used to generate the implied motion percept. The work described in this thesis investigated the neural coding of real and implied motion in the human brain. The investigation was done using functional brain imaging of human adults and data were collected with a 3-Tesla MRI scanner while the participants viewed a variety of distinct visual stimuli. The visual stimuli contained directional real and implied motion and were created specifically for this study. For real motion stimuli, the aim of was to engage a maximal number of directionally selective units, in order to maximize the overlap to the subset of units potentially involved in coding implied motion. Hence, real motion stimuli were created such that the static component frames had natural image statistics (known to activate neurons more effectively) by using Fourier-scrambled natural images, and motion was presented at a wide range of motion velocities. Similarly, implied motion stimuli were derived from photographs of natural scenes. They were created by placing objects such as airplanes, birds, cars, or snapshots of walking humans on a set of contextual background images such as skylines or streets. For both, real motion and implied motion, stimuli for four directions were created: forwards and backwards,and left- and rightwards
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