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Global shape aftereffects have a local substrate: A tilt aftereffect field.
- Journal of Vision,
, 2010
"... Adaptation to prevailing stimuli is a ubiquitous property of the visual system that optimizes its dynamic range. The perceived difference in orientation of successively presented lines of similar orientation is exaggerated and the perceived shape of an object is influenced by previously experienced ..."
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Adaptation to prevailing stimuli is a ubiquitous property of the visual system that optimizes its dynamic range. The perceived difference in orientation of successively presented lines of similar orientation is exaggerated and the perceived shape of an object is influenced by previously experienced shapes. Change in perceived shape is assumed to arise through the adaptation of shape detectors. Here we consider an alternative: adaptation within a substrate of local oriented line detectors resulting in enhanced shape contrast in similar shapes. We show that the perceived shapes of a spatially coincident circle and Cartesian grid can be manipulated independently by adaptation to geometrically transformed copies of themselves. The same transformation was applied to the circle and the grid to create the adaptors; therefore, the specificity of the effects of adaptation demonstrates that the visual system adapts to the shape of objects rather than applying transformations to the reference frame of the visual field. The tilt aftereffect predicts local changes in perceived orientation, and fields of such local effects can often account for the global change in perceived shape of complex objects, including faces.
Statistical Models of Linear and Non–linear Contextual Interactions in Early Visual Processing
"... A central hypothesis about early visual processing is that it represents inputs in a coordinate system matched to the statistics of natural scenes. Simple versions of this lead to Gabor–like receptive fields and divisive gain modulation from local surrounds; these have led to influential neural and ..."
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A central hypothesis about early visual processing is that it represents inputs in a coordinate system matched to the statistics of natural scenes. Simple versions of this lead to Gabor–like receptive fields and divisive gain modulation from local surrounds; these have led to influential neural and psychological models of visual processing. However, these accounts are based on an incomplete view of the visual context surrounding each point. Here, we consider an approximate model of linear and non–linear correlations between the responses of spatially distributed Gaborlike receptive fields, which, when trained on an ensemble of natural scenes, unifies a range of spatial context effects. The full model accounts for neural surround data in primary visual cortex (V1), provides a statistical foundation for perceptual phenomena associated with Li’s (2002) hypothesis that V1 builds a saliency map, and fits data on the tilt illusion. 1
Probabilistic Theories of the Visual Cortex
"... THE VERY EARLY VISUAL SYSTEM This lecture first briefly reviews the structural organization of V1, the properties of simple cells, and divisive normalization. The lecture also illustrated principles such as sparsity, independence, and inverting generative models. A. Review: From Retina and LGN to V1 ..."
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THE VERY EARLY VISUAL SYSTEM This lecture first briefly reviews the structural organization of V1, the properties of simple cells, and divisive normalization. The lecture also illustrated principles such as sparsity, independence, and inverting generative models. A. Review: From Retina and LGN to V1 Light is captured in the retina, transmitted to the LGN, and then to area V1 of the visual cortex. Receptive field properties of neurons in retina and LGN are generally believed to be modelled by symmetric centersurround cells – i.e. the Laplacian of a Gaussian filter, which looks like a Mexican Hat. This may be an over-simplification (e.g., see meister for an alternative viewpoint) but Yang Dan reports that it is possible to reconstruct the input image from the responses of neurons in retina or LGB (which would seem to be impossible if the standard models were badly wrong). There is an expansion (by a factor between 80 and 400) as we move from the LGN to V1. This is not surprising because V1 starts the hard problem of interpreting the image (while the retina and LGN perform the simpler tasks of capturing the image and transmitting it to the cortex – at least this is the
Running head: RECONCILING INTUITIVE PHYSICS AND NEWTONIAN MECHANICS 1 Reconciling Intuitive Physics and Newtonian Mechanics for Colliding Objects
"... People have strong intuitions about the influence objects exert upon one another when they collide. Because people’s judgments appear to deviate from Newtonian mechanics, psychologists have suggested that people depend on a variety of task-specific heuristics. This leaves open the question of how th ..."
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People have strong intuitions about the influence objects exert upon one another when they collide. Because people’s judgments appear to deviate from Newtonian mechanics, psychologists have suggested that people depend on a variety of task-specific heuristics. This leaves open the question of how these heuristics could be chosen, and how to integrate them into a unified model that can explain human judgments across a wide range of physical reasoning tasks. We propose an alternative framework, in which people’s judgments are based on optimal statistical inference over a Newtonian physical model that incorporates sensory noise and intrinsic uncertainty about the physical properties of the objects being viewed. This “noisy Newton ” framework can be applied to a multitude of judgments, with people’s answers determined by the uncertainty they have for physical variables and the constraints of Newtonian mechanics. We investigate a range of effects in mass judgments that have previously been taken as strong evidence for heuristic use and show that they are well explained by the interplay between Newtonian constraints and sensory uncertainty. We also consider an extended model that handles causality judgments, and obtain good quantitative agreement with human judgments across tasks that involve different judgment
coding accuracy
"... Abstract Most neurons in the primary visual cortex initially respond vigorously when a preferred stimulus is presented, but adapt as stimulation continues. The functional consequences of adaptation are unclear. Typically a reduction of firing rate would reduce single neuron accuracy as less spikes a ..."
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Abstract Most neurons in the primary visual cortex initially respond vigorously when a preferred stimulus is presented, but adapt as stimulation continues. The functional consequences of adaptation are unclear. Typically a reduction of firing rate would reduce single neuron accuracy as less spikes are available for decoding, but it has been suggested that on the population level, adaptation increases coding accuracy. This question requires careful analysis as adaptation not only changes the firing rates of neurons, but also the neural variability and correlations between neurons, which affect coding accuracy as well. We calculate the coding accuracy using a computational model that implements two forms of adaptation: spike frequency adaptation and synaptic adaptation in the form of shortterm synaptic plasticity. We find that the net effect of adaptation is subtle and heterogeneous. Depending on adaptation mechanism and test stimulus, adaptation can either increase or decrease coding accuracy. We discuss the neurophysiological and psychophysical implications of the findings and relate it to published experimental data.
U N I V E R S
"... Contextual modulations and the ‘unaware’ read-out: bridging the gap between physiology and psychophysics ..."
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Contextual modulations and the ‘unaware’ read-out: bridging the gap between physiology and psychophysics
doi: 10.3389/fpsyg.2011.00119 Perception of 3D slant out of the box
, 2011
"... Evidence for contextual effects is widespread in visual perception. Although this suggests that contextual effects are the result of a generic property of the visual system, current explanations are limited to the domain in which they occur. In this paper we propose a more general mechanism of globa ..."
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Evidence for contextual effects is widespread in visual perception. Although this suggests that contextual effects are the result of a generic property of the visual system, current explanations are limited to the domain in which they occur. In this paper we propose a more general mechanism of global influences on the perception of slant. We review empirical data and evaluate proposed explanations of contextual biases. By assessing not only a model about three-dimensional slant perception but also evaluating more generic mechanisms of contextual modulation, we show that surround suppression of neural responses explains the major phenomena in the empirical data on contextual biases. Moreover, contextual biases may be part of a mechanism of grouping and segmentation.
Citation:
, 2014
"... What visual illusions tell us about underlying neural mechanisms and observer strategies for tackling the inverse problem of achromatic perception. Front. Hum. Neurosci. 9:205. doi: 10.3389/fnhum.2015.00205 What visual illusions tell us about underlying neural mechanisms and observer strategies for ..."
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What visual illusions tell us about underlying neural mechanisms and observer strategies for tackling the inverse problem of achromatic perception. Front. Hum. Neurosci. 9:205. doi: 10.3389/fnhum.2015.00205 What visual illusions tell us about underlying neural mechanisms and observer strategies for tackling the inverse problem of achromatic perception
