China
Africa
Explore chapters and articles related to this topic
Psychology and Human Development EMIs
Published in Michael Reilly, Bangaru Raju, Extended Matching Items for the MRCPsych Part 1, 2018
Binocular vision.Colour constancy.Convergence.Figure ground differentiation.Law of closure.Law of proximity.Law of similarity.Linear perspective.Location constancy.Motion parallax.Size constancy.Shape constancy.
Interaction in Augmented Reality Image-Guided Surgery
Published in Terry M. Peters, Cristian A. Linte, Ziv Yaniv, Jacqueline Williams, Mixed and Augmented Reality in Medicine, 2018
Simon Drouin, D. L. Collins, M. Kersten-Oertel
One of the typical approaches to help the visual system solve the occlusion in an AR scene is the virtual window (or Magic Lens) (Bier et al. 1993). Bichlmeier et al. (2007a) cut a virtual window out of the real image by intersecting a 3D model of the patient’s skin surface with a user-defined cuboid. The motion of the HMD generates motion parallax and texture accretion/deletion cues to improve perceived relative depth between the surface and the surgical target. The approach was refined in Bichlmeier et al. (2007b) (Figure 7.4b), where the virtual window position is modified according to line of sight of the HMD, and the opacity of the real image inside the window is modulated by the angle between the skin surface and viewing direction as well as the curvature of the skin surface and distance to the center of the window. Mendez et al. (2006) propose controlling the pose of a virtual 3D surface using an optical tracker tool. The intersection of the 3D surface with the presegmented organ surfaces is used to create a window where internal organ structures, such as blood vessels, are revealed (c.f., Figure 7.4a). Kalkofen et al. (2009) allow users to manipulate the position of a circular virtual lens, where the virtual window is not simply an area where the real image is semitransparent but instead allows for the application of programmable compositing schemes for the different elements in the scene. Different compositing inside the region covered by the virtual window reveals structures of interest while maintaining contextual information. Gras et al. (2015) (Figure 7.4c) proposed to use a tracked surgical dissector equipped with a force-torque sensor to interact with the AR view. Its location and the measurement of the force applied to the tissues are used to modulate the size of a virtual window, and the pq space method of Lerotic et al. (2007) is used to produce realistic occlusion patterns inside the virtual window. Furthermore, Gras and colleagues used force feedback information to distort a virtual model of the organs below the surface, providing a motion cue that improves depth perception even more.
Vision
Published in Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol, Handbook of Aviation and Space Medicine, 2019
Nicholas Green, Steven Gaydos, Hutchison Ewan, Edward Nicol
A number of visual cues used simultaneously and unconsciously to give depth perception: Monocular cues: Relative size.Perspective: parallel lines to a point on horizon.Overlapping of objects.Position in visual field: object moving into distance appears to be closing in on horizon.Aerial perspective: distant objects have more of a blue tinge than near objects, from Rayleigh scattering of atmospheric light.Parallax: disparate movement of objects on head movement.Motion parallax: as observer moves, nearer objects appear to move faster.Binocular cues: Proprioceptive feedback from convergence and accommodation.Stereopsis: ability to perceive depth and three-dimensional structure by neurological processing and interpretation of disparity between images at each eye. Coarse stereopsis used to judge stereoscopic motion in periphery; important, for example, when descending to land in an aircraft.Fine stereopsis based on static differences; important for fine motor tasks such as threading a needle; form that is measured during aircrew selection.Upper limit that stereopsis is effective is estimated as being only up to about 30 metres, only really relevant when taxing fixed wing aircraft or low-level/speed rotary flying.Individuals with poor stereopsis often have other ocular problems (e.g. reduced vision in one eye).Stereopsis ability important for use of biocular/binocular helmet mounted displays.
Comparison of surgical outcomes between 3-dimensional and 2-dimensional laparoscopy of ovarian cyst (LOOC): a randomised controlled trial
Published in Journal of Obstetrics and Gynaecology, 2022
Young Gi Han, Kyung Min Lim, Taejong Song
A laparoscopy is founded as a treatment of choice for benign ovarian cysts (Lui and Cheung 2018). The advantages of laparoscopic surgery over conventional open surgery are less pain, shorter recovery time, shorter hospital stay, and consequently faster return to normal activity, as well as better cosmetic effects. However, laparoscopic surgery is more demanding compared with open surgery because operators should project a three-dimensional (3D) field through a two-dimensional (2D) monitor. This results in loss of depth perception (Sorensen et al. 2016) and consequently more cognitive workload of operators. In the traditional 2D laparoscopic procedures, the operators have to mentally transform the 2D images into the 3D images using motion parallax through the movement of the laparoscope, relative position of instruments, and shading of light and dark (Byrn et al. 2007).
When Does Blur Matter? A Narrative Review and Commentary
Published in Journal of Binocular Vision and Ocular Motility, 2022
Blur is traditionally thought to be the main stimulus to accommodation, while disparity drives vergence.5 Blur is a “sufficient” stimulus to accommodation, which means that when presented as an isolated cue it can drive a large proportion of the accommodation required to clear the image, although it is less efficient away from the very central visual field.6 Reduced blur detection in the periphery is a combination of intrinsic (neural and anatomical) factors such as large cortical receptive fields, and decreased blur sensitivity.7 Despite blur being “sufficient,” blur nearly always occurs at the same time as other cues to nearness such as disparity and monocular proximal cues (looming, motion parallax, overlay of contours, learned size etc.). Individually, each of these cues can drive a significant proportion of the total response required, and if added, would produce much more than 100% of the required response, so in practice they must be weighted.
Stereopsis: are we assessing it in enough depth?
Published in Clinical and Experimental Optometry, 2018
Anna R O'connor, Laurence P Tidbury
Depth from disparity is determined by detecting the horizontal offset between the edges of stimuli, when the point of fixation is a single percept. The disparity in a ‘real’ depth plane is created by the horizontal separation between each eye creating two slightly different views of a scene. This feature makes the tests more susceptible to monocular cues, especially where a comparison can be made between two viewpoints observed at different times, that is motion parallax, exacerbated by the presence of an aperture such as the frame around the shapes in the FD2. Slight movement of either the test or observer can introduce this unwanted cue to the test.