174 research outputs found
A Quantitative Explanation of Responses to Disparity-Defined Edges in Macaque V2
No full textBredfeldt CE, Read JCA, Cumming BG. A quantitative explanation of responses to disparity-defined edges in macaque V2. J Neurophysiol 101: 701-713, 2009. First published December 10, 2008; doi:10.1152/jn.00729.2007. Previous experiments have shown that V2 neurons respond to complex stimuli such as cyclopean edges (edges defined purely by binocular disparity), angles, and motion borders. It is currently unknown whether these responses are a simple consequence of converging inputs from a prior stage of processing (V1). Alternatively, they may identify edges in a way that is invariant across a range of visual cues defining the edge, in which case they could provide a neuronal substrate for scene segmentation. Here, we examine the ability of a simple feedforward model that combines two V1-like inputs to describe the responses of V2 neurons to cyclopean edges. A linear feedforward model was able to qualitatively reproduce the major patterns of response enhancement for cyclopean edges seen in V2. However, quantitative fitting revealed that this model usually predicts response suppression by some edge configurations and such suppression was rarely seen in the data. This problem was resolved by introducing a squaring nonlinearity at the output of the individual inputs prior to combination. The extended model produced extremely good fits to most of our data. We conclude that the responses of V2 neurons to complex stimuli such as cyclopean edges can be adequately explained by a simple convergence model and do not necessarily represent the development of sophisticated mechanisms that signal scene segmentation, although they probably constitute a step toward this goal
Viewer experience with stereoscopic 3D television in the home
No full textStereoscopic 3D television (S3D TV) is now available in the home. However, little published information is available on viewer use or experience. In this study, 120 people from 29 households were given a new TV (active or passive stereoscopic 3D, or conventional 20) and reported on their television viewing and other screen use on a near-daily basis over 8 weeks. People reported enjoying S3D TV and cinema more than TV and cinema in general, but enjoying S3D video games less than video games in general. S3D TV and video games were both associated with an increased, though still low (similar to 10%) level of adverse effects, such as headache and eyestrain. I speculate that this may be because video games present a particularly strong conflict between vergence and accommodative demand. (C) 2014 The Author. Published by Elsevier B.V
The place of human psychophysics in modern neuroscience
No full textHuman psychophysics is the quantitative measurement of our own perceptions. In essence, it is simply a more sophisticated version of what humans have done since time immemorial: noticed and reflected upon what we can see, hear, and feel. In the 21st century, when hugely powerful techniques are available that enable us to probe the innermost structure and function of nervous systems, is human psychophysics still relevant? I argue that it is, and that in combination with other techniques, it will continue to be a key part of neuroscience for the foreseeable future. I discuss these points in detail using the example of binocular stereopsis, where human psychophysics in combination with physiology and computational vision, has made a substantial contribution.This article is part of a Special Issue entitled: Contributions From Different Model Organisms to Brain Research. (C) 2014 The Author. Published by Elsevier Ltd. on behalf of IBRO. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/3.0/)
Stereo vision requires an explicit encoding of vertical disparity
No full textVertical disparities influence the perception of 3D depth, but little is known about the neuronal mechanisms underlying this. One possibility is that these perceptual effects are mediated by an explicit encoding of two-dimensional disparity. Recently, J. C. A. Read and B. G. Cumming (2006) pointed out that current psychophysical and physiological evidence is consistent with a much more economical one-dimensional encoding. Almost all relevant information about vertical disparity could in theory be extracted from the activity of purely horizontal-disparity sensors. Read and Cumming demonstrated that such a 1D system would experience Ogle\u27s induced effect, a famous illusion produced by vertical disparity. Here, we test whether the brain employs this 1D encoding, using a version of the induced effect stimulus that simulates the viewing geometry at infinity and thus removes the cues which are otherwise available to the 1D model. This condition was compared to the standard induced effect stimulus, presented on a frontoparallel screen at finite viewing distance. We show that the induced effects experienced under the two conditions are indistinguishable. This rules out the 1D model proposed by Read and Cumming and shows that vertical disparity, including sign, must be explicitly encoded across the visual field
Binocular Vision and Stereopsis Across the Animal Kingdom
No full textMost animals have at least some binocular overlap, i.e., a region of space that is viewed by both eyes. This reduces the overall visual field and raises the problem of combining two views of the world, seen from different vantage points, into a coherent whole. However, binocular vision also offers many potential advantages, including increased ability to see around obstacles and increased contrast sensitivity. One particularly interesting use for binocular vision is comparing information from both eyes to derive information about depth. There are many different ways in which this might be done, but in this review, I refer to them all under the general heading of stereopsis. This review examines the different possible uses of binocular vision and stereopsis and compares what is currently known about the neural basis of stereopsis in different taxa. Studying different animals helps us break free of preconceptions stemming from the way that stereopsis operates in human vision and provides new insights into the different possible forms of stereopsis
Stereo vision and strabismus
No full textBinocular stereopsis, or stereo vision, is the ability to derive information about how far away objects are, based solely on the relative positions of the object in the two eyes. It depends on both sensory and motor abilities. In this review, I briefly outline some of the neuronal mechanisms supporting stereo vision, and discuss how these are disrupted in strabismus. I explain, in some detail, current methods of assessing stereo vision and their pros and cons. Finally, I review the evidence supporting the clinical importance of such measurements
Visual Perception: Understanding Visual Cues to Depth
No full textA new study shows that, in vision, object blur can be a more accurate depth cue than stereo disparity
Stereopsis without correspondence
No full textStereopsis has traditionally been considered a complex visual ability, restricted to large-brained animals. The discovery in the 1980s that insects, too, have stereopsis, therefore, challenged theories of stereopsis. How can such simple brains see in three dimensions? A likely answer is that insect stereopsis has evolved to produce simple behaviour, such as orienting towards the closer of two objects or triggering a strike when prey comes within range. Scientific thinking about stereopsis has been unduly anthropomorphic, for example assuming that stereopsis must require binocular fusion or a solution of the stereo correspondence problem. In fact, useful behaviour can be produced with very basic stereoscopic algorithms which make no attempt to achieve fusion or correspondence, or to produce even a coarse map of depth across the visual field. This may explain why some aspects of insect stereopsis seem poorly designed from an engineering point of view: for example, paying no attention to whether interocular contrast or velocities match. Such algorithms demonstrably work well enough in practice for their species, and may prove useful in particular autonomous applications. This article is part of a discussion meeting issue \u27New approaches to 3D vision\u27
Visual Perception: Monovision Can Bias the Apparent Depth of Moving Objects
No full text\ua9 2019 Elsevier Ltd‘Monovision’ — using one eye for near work and one for distance — is a common alternative to reading glasses. New work shows that monovision can cause the distance of moving objects to be misestimated, with potentially serious consequences
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