Lecture 6 - Space Perception and Binocular Vision PDF

Lecture 6 Space Perception and Binocular Vision © 2024 Oxford University Press  2 Chapter 6 Space Perception and Binocular Vision 2 6.1 Monocular Cues to Three-Dimensional...

Lecture 6 Space Perception and Binocular Vision © 2024 Oxford University Press  2 Chapter 6 Space Perception and Binocular Vision 2 6.1 Monocular Cues to Three-Dimensional Space 6.2 Triangulation Cues to Three-Dimensional Space 6.3 Binocular Vision and Stereopsis 6.4 Combining Depth Cues 6.5 Development of Binocular Vision and Stereopsis © 2024 Oxford University Press  3 6.0 Introduction 3 Realism: The external world exists. Positivists: The world depends on the evidence of the senses; it could be a hallucination! This is an interesting philosophical position, but for the purposes of this course, let’s just assume the world exists. © 2024 Oxford University Press  4 6.0 Introduction 4 Euclidian geometry: Parallel lines remain parallel as they are extended in space. – Objects maintain the same size and shape as they move around in space. – Internal angles of a triangle always add up to 180 degrees, etc. © 2024 Oxford University Press  5 6.0 Introduction 5 Notice that images projected onto the retina are non- Euclidean! – Therefore, our brains work with non-Euclidean geometry all the time, even though we are not aware of it. © 2024 Oxford University Press FIGURE 6.2 Geometries of visual space © 2024 Oxford University Press  7 6.0 Introduction 7 Probability summation: The increased probability of detecting a stimulus from having two or more samples. – One of the advantages of having two eyes that face forward. © 2024 Oxford University Press  8 6.0 Introduction 8 Binocular summation: The combination (or “summation”) of signals from each eye in ways that make performance on many tasks better with both eyes than with either eye alone. The two retinal images of a three-dimensional world are not the same! © 2024 Oxford University Press FIGURE 6.3 The two retinal images of a three-dimensional world are not the same © 2024 Oxford University Press  10 6.0 Introduction 10 Binocular disparity: The differences between the two retinal images of the same scene. – Disparity is the basis for stereopsis, a vivid perception of the three- dimensionality of the world that is not available with monocular vision. © 2024 Oxford University Press  11 6.0 Introduction 11 Depth cue: Information about the third dimension (depth) of visual space. Monocular depth cue: A depth cue that is available even when the world is viewed with one eye alone. Binocular depth cue: A depth cue that relies on information from both eyes. © 2024 Oxford University Press FIGURE 6.4 Comparing rabbit and human visual fields © 2024 Oxford University Press FIGURE 6.5 M. C. Escher, Relativity, 1953 © 2024 Oxford University Press  14 6.1 Monocular Cues to Three-Dimensional Space 14 Occlusion: A cue to relative depth order in which, for example, one object partially obstructs the view of another object. © 2024 Oxford University Press FIGURE 6.6 Accidental versus generic views © 2024 Oxford University Press  16 6.1 Monocular Cues to Three-Dimensional Space 16 Metrical depth cue: A depth cue that provides quantitative information about distance in the third dimension. Nonmetrical depth cue: A depth cue that provides information about the depth order (relative depth) but not depth magnitude. © 2024 Oxford University Press  17 6.1 Monocular Cues to Three-Dimensional Space 17 Relative size: A comparison of size between items without knowing the absolute size of either one. – All things being equal, we assume that smaller objects are farther away from us than larger objects. © 2024 Oxford University Press FIGURE 6.7 Depth from size © 2024 Oxford University Press  19 6.1 Monocular Cues to Three-Dimensional Space 19 Relative height: For objects touching the ground, those higher in the visual field appear to be farther away. In the sky above the horizon, objects lower in the visual field appear to be farther away. © 2024 Oxford University Press  20 6.1 Monocular Cues to Three-Dimensional Space 20 Texture gradient: A depth cue based on the geometric fact that items of the same size form smaller, closer spaced images the farther away they get. – Texture gradients result from a combination of the cues of relative size and relative height. © 2024 Oxford University Press FIGURE 6.8 Texture gradient © 2024 Oxford University Press FIGURE 6.9 Texture gradients, continued © 2024 Oxford University Press FIGURE 6.11 Apparent size is changed by apparent depth © 2024 Oxford University Press  24 6.1 Monocular Cues to Three-Dimensional Space 24 Familiar size: A cue based on knowledge of the typical size of objects. – When you know the typical size of an object, you can guess how far away it is based on how small or large it appears. – The cue of familiar size often works in conjunction with the cue of relative size. © 2024 Oxford University Press FIGURE 6.12 The cue of familiar size © 2024 Oxford University Press  26 6.1 Monocular Cues to Three-Dimensional Space 26 Relative size and relative height both provide some metrical information. – Relative metrical depth cue: A depth cue that could specify, for example, that object A is twice as far away as object B without providing information about the absolute distance to either A or B. © 2024 Oxford University Press  27 6.1 Monocular Cues to Three-Dimensional Space 27 Familiar size can provide precise metrical information if your visual system knows the actual size of the object and the visual angle it takes up on the retina. – Absolute metrical depth cue: A depth cue that provides quantifiable information about distance in the third dimension. © 2024 Oxford University Press  28 6.1 Monocular Cues to Three-Dimensional Space 29 Aerial perspective: A depth cue based on the implicit understanding that light is scattered by the atmosphere. – More light is scattered when we look through more atmosphere. – Thus, more distant objects appear fainter, bluer, and less distinct. © 2024 Oxford University Press FIGURE 6.14 A real-world example of aerial perspective © 2024 Oxford University Press  30 6.1 Monocular Cues to Three-Dimensional Space 31 Linear perspective: Lines that are parallel in the three- dimensional world will appear to converge in a two- dimensional image as they extend into the distance. Vanishing point: The apparent point at which parallel lines receding in depth converge. © 2024 Oxford University Press FIGURE 6.15 Linear perspective © 2024 Oxford University Press FIGURE 6.16 Linear perspective in art © 2024 Oxford University Press FIGURE 6.17 Two-point perspective © 2024 Oxford University Press  34 6.1 Monocular Cues to Three-Dimensional Space 35 Pictorial depth cue: A cue to distance or depth used by artists to depict three-dimensional depth in two-dimensional pictures. Anamorphosis (or anamorphic projection): Use of the rules of linear perspective to create a two-dimensional image so distorted that it looks correct only when viewed from a special angle or with a mirror that counters the distortion. © 2024 Oxford University Press FIGURE 6.20 Modern-day anamorphic art © 2024 Oxford University Press  36 6.2 Triangulation Cues to Three-Dimensional Space 38 Motion parallax: Images closer to the observer move faster across the visual field than images farther away. – The brain uses this information to calculate the distances of objects in the environment. – Head movements and any other relative movements between observers and objects reveal motion parallax cues. © 2024 Oxford University Press FIGURE 6.21 Motion parallax © 2024 Oxford University Press  38 6.2 Triangulation Cues to Three-Dimensional Space 40 Accommodation: The process by which the eye changes its focus (in which the lens gets fatter as gaze is directed toward nearer objects). Convergence: The ability of the two eyes to turn inward, often used to focus on nearer objects. Divergence: The ability of the two eyes to turn outward, often used to focus on farther objects. © 2024 Oxford University Press FIGURE 6.22 Vergence © 2024 Oxford University Press  40 6.3 Binocular Vision and Stereopsis 42 Corresponding retinal points: A geometric concept stating that points on the retina of each eye where the monocular retinal images of a single object are formed are at the same distance from the fovea in each eye. © 2024 Oxford University Press FIGURE 6.25 Binocular disparity © 2024 Oxford University Press FIGURE 6.27 What’s on Bob’s retinas? © 2024 Oxford University Press  43 6.3 Binocular Vision and Stereopsis 45 Horopter: The location of objects whose images lie on the corresponding points. The surface of zero disparity. Vieth–Müller circle: The location of objects whose images fall on geometrically corresponding points in the two retinas. – The Vieth–Müller circle and the horopter are technically different, but for our purposes you may consider them the same. © 2024 Oxford University Press FIGURE 6.28 Vieth-Müller circle © 2024 Oxford University Press  45 6.3 Binocular Vision and Stereopsis 47 Objects on the horopter are seen as single images when viewed with both eyes. – Panum’s fusional area: The region of space, in front of and behind the horopter, within which binocular single vision is possible. © 2024 Oxford University Press  46 6.3 Binocular Vision and Stereopsis 48 Objects significantly closer to or farther away from the horopter fall on noncorresponding points in the two eyes and are seen as two images. – Diplopia: Double vision. If visible in both eyes, stimuli falling outside of Panum’s fusional area will appear diplopic. © 2024 Oxford University Press FIGURE 6.30 Superposition of Bob’s retinal images © 2024 Oxford University Press  48 6.3 Binocular Vision and Stereopsis 53 Stereoscope: A device for presenting one image to one eye and another image to the other eye. – Stereoscopes were a popular item in the 1900s. – Many children in modern days had a ViewMaster, which is also a stereoscope. – The Oculus Rift headset is a more modern example of a stereoscope. © 2024 Oxford University Press FIGURE 6.33 Wheatstone’s stereoscope © 2024 Oxford University Press FIGURE 6.34 Stereopsis for the masses © 2024 Oxford University Press  51 6.3 Binocular Vision and Stereopsis 56 Free fusion: The technique of converging (crossing) or diverging (uncrossing) the eyes in order to view a stereogram without a stereoscope. – “Magic Eye” pictures rely on free fusion. © 2024 Oxford University Press  52 6.3 Binocular Vision and Stereopsis 57 Stereoblindness: An inability to make use of binocular disparity as a depth cue. – Can result from a childhood visual disorder, such as strabismus, in which the two eyes are misaligned. – Most people who are stereoblind do not even realize it. © 2024 Oxford University Press FIGURE 6.35 Free fusion © 2024 Oxford University Press  54 6.3 Binocular Vision and Stereopsis 59 Recovering stereo vision – Susan Berry had strabismus as an infant and never developed stereo vision. – At age 48, she began visual therapy to improve coordination between her two eyes. – One day she suddenly developed stereo vision! – Suggests that binocular vision might be developed outside of the normally accepted “critical period.” © 2024 Oxford University Press  55 6.3 Binocular Vision and Stereopsis 60 Random dot stereogram (RDS): A stereogram made of a large number of randomly placed dots. – RDSs contain no monocular cues to depth. – Stimuli visible stereoscopically in RDSs are cyclopean stimuli. – Cyclopean: Referring to stimuli that are defined by binocular disparity alone. © 2024 Oxford University Press FIGURE 6.37 A random dot stereogram © 2024 Oxford University Press  57 6.3 Binocular Vision and Stereopsis 62 For movies to appear 3D, each eye must receive a slightly different view of the scene (just like in real life). – Early methods for seeing movies in 3D involved “anaglyphic” glasses with a red lens on one eye and a blue lens on the other. – Current methods use polarized light and polarizing glasses to ensure that each eye sees a slightly different image. © 2024 Oxford University Press  58 6.3 Binocular Vision and Stereopsis 63 Correspondence problem: In binocular vision, the problem of figuring out which bit of the image in the left eye should be matched with which bit in the right eye. – The problem is particularly vexing in images like random dot stereograms. © 2024 Oxford University Press FIGURE 6.40 Three purple dots © 2024 Oxford University Press FIGURE 6.41 The problem with three dots © 2024 Oxford University Press  61 6.3 Binocular Vision and Stereopsis 66 There are several ways to solve the correspondence problem: – Blurring the image: Leaving only the low-spatial frequency information helps. © 2024 Oxford University Press  62 6.3 Binocular Vision and Stereopsis 67 – Uniqueness constraint: The observation that a feature in the world is represented exactly once in each retinal image. – Continuity constraint: The observation that, except at the edges of objects, neighboring points in the world lie at similar distances from the viewer. © 2024 Oxford University Press FIGURE 6.42 Matching blobs © 2024 Oxford University Press  64 6.3 Binocular Vision and Stereopsis 69 How is stereopsis implemented in the human brain? – Input from two eyes must converge onto the same cell. © 2024 Oxford University Press  65 6.3 Binocular Vision and Stereopsis 70 – Many binocular neurons respond best when the retinal images are on corresponding points in the two retinas: Neural basis for the horopter. – However, many other binocular neurons respond best when similar images occupy slightly different positions on the retinas of the two eyes (tuned to particular binocular disparity). © 2024 Oxford University Press FIGURE 6.43 Receptive fields sensitive to disparity © 2024 Oxford University Press  67 6.3 Binocular Vision and Stereopsis 72 Stereopsis can be used as both a metrical and nonmetrical depth cue. – Some cells just code whether a feature lies in front of or behind the plane of fixation (nonmetrical depth cue). – Other cells code the precise distance of a feature from the plane of fixation (metrical depth cue). © 2024 Oxford University Press  68 6.3 Binocular Vision and Stereopsis 73 Stereopsis in a Hunting Insect Question: How can you tell if a praying mantis has stereopsis? Hypothesis: Praying mantises catch bugs using stereoscopic depth perception. Test: Researchers equipped mantises with small anaglyphic glasses, showed them 3D movies of bugs at various distances, and recorded if the mantises struck when the bugs were at the critical 2 cm distance. © 2024 Oxford University Press  69 6.3 Binocular Vision and Stereopsis 74 Results: Mantises didn’t react to 2D movies of simulated bugs but did react to 3D movies when the bugs were at the apparently correct striking distance. Conclusions: The praying mantis has stereoscopic vision and will respond to depth defined by disparity. © 2024 Oxford University Press FIGURE 6.46 Stereopsis in praying mantis © 2024 Oxford University Press Cuttlefish have stereoscopic vision Feord et al. (2020) © 2024 Oxford University Press  72 6.4 Combining Depth Cues 76 Like object recognition, depth perception results from the combination of many different cues, including the likelihood of events © 2024 Oxford University Press  73 6.4 Combining Depth Cues 80 Illusions and the construction of space – Our visual systems take into account depth cues when interpreting the size of objects. © 2024 Oxford University Press FIGURE 6.50 The Ponzo illusion © 2024 Oxford University Press FIGURE 6.51 A real-world Ponzo illusion © 2024 Oxford University Press FIGURE 6.52 Explaining the Ponzo illusions © 2024 Oxford University Press FIGURE 6.53 Zollner and Hering illusions © 2024 Oxford University Press  78 6.4 Combining Depth Cues 85 Binocular rivalry: The competition between the two eyes for control of visual perception, which is evident when completely different stimuli are presented to the two eyes. © 2024 Oxford University Press FIGURE 6.55 Binocular rivalry © 2024 Oxford University Press FIGURE 6.56 The dynamics of rivalry © 2024 Oxford University Press  81 6.5 Development of Binocular Vision and Stereopsis 88 Stereoacuity: A measure of the smallest binocular disparity that can generate a sensation of depth. Dichoptic: Referring to the presentation of two stimuli, one to each eye. Different from binocular presentation, which could involve both eyes looking at a single stimulus. – Stereoacuity is often tested using dichoptic stimuli. © 2024 Oxford University Press FIGURE 6.58 The onset of stereopsis © 2024 Oxford University Press FIGURE 6.59 The development of stereoacuity © 2024 Oxford University Press  84 6.5 Development of Binocular Vision and Stereopsis 91 Abnormal visual experience can disrupt binocular vision: – Critical period: In the study of development, a period of time when the organism is particularly susceptible to developmental change. © 2024 Oxford University Press  85 6.5 Development of Binocular Vision and Stereopsis 92 Strabismus: A misalignment of the two eyes such that a single object in space is imaged on the fovea of one eye, and on a nonfoveal area of the other (turned) eye. Suppression: In vision, the inhibition of an unwanted image. © 2024 Oxford University Press FIGURE 6.62 Left esotropia © 2024 Oxford University Press  87 6.5 Development of Binocular Vision and Stereopsis 94 Esotropia: Strabismus in which one eye deviates inward. Exotropia: Strabismus in which one eye deviates outward. © 2024 Oxford University Press FIGURE 6.63 Development of stereopsis © 2024 Oxford University Press Outlook Many cells in V1 respond to binocular disparity almost immediately after birth, so why does stereopsis take longer? Perception of stereopsis likely relies on processing beyond V1, which is probably also why it can sometimes be recovered later in life © 2024 Oxford University Press Outlook Could visual therapy be used to develop stereoscopic vision later in life? After never having stereo vision his whole life, Bruce Bridgeman acquired stereopsis while watching the 3D movie Hugo © 2024 Oxford University Press Guest lecture – Mel Goodale Prof. Mel Goodale guest lecture, Jan 28th at 1pm “What single-case studies can tell us about the functional organization of the visual brain” Accolades West 005 © 2024 Oxford University Press