The Third Dimension
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Questions and Answers

What occurs to the perception of objects closer than the horopter?

  • They create crossed disparity. (correct)
  • They project to corresponding points on both retinas.
  • They do not have any disparity.
  • They create uncrossed disparity.

    • How does the brain address the correspondence problem?

  • By merging both eye images into a single image.
  • By projecting images onto the same retinal points.
  • By determining which points in the left eye correspond to those in the right eye. (correct)
  • By creating a random pattern of dots.

    • What defines cyclopean stimuli in the context of depth perception?

  • They rely on binocular disparity. (correct)
  • They are limited to visual cues from one eye.
  • They are defined solely by brightness differences.
  • They are defined by monocular disparity.

    • Which cue helps in determining the order of objects in relation to each other without providing quantitative depth information?

    <p>Partial occlusion</p> Signup and view all the answers

    What effect does atmospheric perspective have on the appearance of distant objects?

    <p>They appear indistinct and bluer</p> Signup and view all the answers

    When an object has uncrossed disparity, what is its relative position to the horopter?

    <p>It is farther away than the horopter.</p> Signup and view all the answers

    How does texture gradient serve as a depth cue?

    <p>Through the use of repeating patterns</p> Signup and view all the answers

    What role does V1 play in processing binocular disparity?

    <p>It is the earliest point where input from both eyes can be coded.</p> Signup and view all the answers

    In the Bayesian approach to understanding depth perception, what does P(Sc | I) represent?

    <p>The likelihood of the scene based on observed input.</p> Signup and view all the answers

    What is binocular disparity?

    <p>The difference in views from each eye</p> Signup and view all the answers

    How do texture gradients contribute to depth perception?

    <p>They provide information about the relative position of objects.</p> Signup and view all the answers

    Which of the following is a dynamic depth cue influenced by the movement of the observer?

    <p>Motion parallax</p> Signup and view all the answers

    Which type of depth cue can inform us about actual distances in space?

    <p>Absolute metrical cues</p> Signup and view all the answers

    What effect does motion parallax have on depth perception?

    <p>It allows closer objects to move faster relative to the background.</p> Signup and view all the answers

    What happens to the perceived size of objects in the Ames room?

    <p>Smaller images are interpreted as smaller objects due to assumptions.</p> Signup and view all the answers

    What occurs when an object becomes occluded in the process of deletion and accretion?

    <p>It fades out of view</p> Signup and view all the answers

    What is the result of changing the point of fixation with respect to binocular disparity?

    <p>It alters whether objects have crossed or uncrossed disparity.</p> Signup and view all the answers

    What happens to images falling on the horopter?

    <p>They provide zero disparity</p> Signup and view all the answers

    What effect does the relative size cue provide regarding the distance of similar objects?

    <p>Smaller objects must be nearer</p> Signup and view all the answers

    Which of the following factors contributes to a strong sense of depth perception?

    <p>Binocular disparity</p> Signup and view all the answers

    Which of the following cues require both eyes for depth perception?

    <p>Binocular cues</p> Signup and view all the answers

    Accommodation refers to how much we adjust our ciliary muscles to focus on a visual object.

    <p>True</p> Signup and view all the answers

    What term describes the depth cue arising from the difference in viewpoints between our two eyes?

    <p>binocular disparity</p> Signup and view all the answers

    As an object moves further away, it appears less distinct and ________ due to atmospheric perspective.

    <p>bluer</p> Signup and view all the answers

    Match each type of depth cue with its corresponding example:

    <p>Oculomotor cues = Accommodation and vergence Monocular cues = Relative size and texture gradient Binocular cues = Stereopsis and horopter Dynamic cues = Motion parallax and optic flow</p> Signup and view all the answers

    Which of the following describes the phenomenon where objects appear to expand from a central point as one moves forward?

    <p>Optic flow</p> Signup and view all the answers

    Relative height gives absolute depth information about objects in space.

    <p>False</p> Signup and view all the answers

    What is the meaning of 'vergence' in the context of oculomotor cues?

    <p>The positioning of the eyes to focus on an object in a scene, either converging or diverging.</p> Signup and view all the answers

    The ________ is an imaginary surface where objects appear to be at the same distance from both eyes.

    <p>horopter</p> Signup and view all the answers

    Which cue provides quantitative information about distances in depth?

    <p>Metrical cues</p> Signup and view all the answers

    What does crossed disparity indicate?

    <p>Objects are closer to the observer than the horopter.</p> Signup and view all the answers

    Uncrossed disparity occurs when an object is closer to the observer than the horopter.

    <p>False</p> Signup and view all the answers

    What is the primary challenge the brain faces in the correspondence problem?

    <p>Matching visual information from both eyes to create a unified perception of depth.</p> Signup and view all the answers

    In the Bayesian approach, P(I | Sc) refers to the probability of the __________ being produced by a particular scene.

    <p>image</p> Signup and view all the answers

    Match the type of disparity with its description:

    <p>Crossed disparity = Closer than the horopter Uncrossed disparity = Farther than the horopter Cyclopean stimuli = Defined by binocular disparity Binocular cells = Receive input from both eyes</p> Signup and view all the answers

    What effect does changing the point of fixation have on binocular disparity?

    <p>It changes the horopter.</p> Signup and view all the answers

    Binocular disparity is defined as the differences in images received by each eye due solely to their positions.

    <p>True</p> Signup and view all the answers

    Name a type of cue that helps to determine the three-dimensional structure of an object.

    <p>Depth cues</p> Signup and view all the answers

    The __________ states that our knowledge of the world helps interpret the visually observed input.

    <p>Bayesian approach</p> Signup and view all the answers

    What do random dot stereograms primarily illustrate?

    <p>Cyclopean stimuli defined by binocular disparity.</p> Signup and view all the answers

    Match the following depth cues to whether they are metrical or relative cues

    <p>Partial Occlusion = Relative cue Relative Height = Relative-metrical Relatize Sie = Relative-metrical Familiar size = Absolute metrical</p> Signup and view all the answers

    What happens to the lens when the ciliary muscles are contracted more?

    <p>The lens becomes thick</p> Signup and view all the answers

    Divergence is the process of turning our eyes inward to look at near objects.

    <p>False</p> Signup and view all the answers

    What does motion parallax allow us to infer about objects in our visual field?

    <p>The distances of the objects.</p> Signup and view all the answers

    The __________ perspective indicates that distant objects appear less distinct and bluer due to light scattering.

    <p>atmospheric</p> Signup and view all the answers

    Match each oculomotor cue with its definition:

    <p>Accommodation = Adjustment of the lens based on distance Convergence = Inward turning of the eyes for near objects Divergence = Outward turning of the eyes for far objects</p> Signup and view all the answers

    Which cue relies on light differences on a surface to provide information about depth?

    <p>Shading</p> Signup and view all the answers

    Binocular disparity provides a strong cue about depth, especially for distant objects.

    <p>False</p> Signup and view all the answers

    What process involves changes in occlusion as an object moves behind another?

    <p>Deletion and accretion.</p> Signup and view all the answers

    Relative size cues suggest that for similar objects, a smaller object is perceived as being __________.

    <p>farther away</p> Signup and view all the answers

    Which of these cues provides no absolute depth information?

    <p>Relative height</p> Signup and view all the answers

    What happens to the lens when there is more contraction of the ciliary muscles?

    <p>The lens becomes thick.</p> Signup and view all the answers

    What is the primary function of the horopter in depth perception?

    <p>To create a surface where objects have zero disparity.</p> Signup and view all the answers

    Which cue helps to determine the relative size of an object without knowing its actual size?

    <p>Relative size cue.</p> Signup and view all the answers

    What does convergence refer to in the context of oculomotor cues?

    <p>The inward turning of the eyes for near objects.</p> Signup and view all the answers

    Which of the following describes the phenomenon of motion parallax?

    <p>Different rates of motion across the visual field indicate distance.</p> Signup and view all the answers

    How does atmospheric perspective affect the appearance of distant objects?

    <p>They appear less distinct and take on a bluer hue.</p> Signup and view all the answers

    What is the result of deletion and accretion in depth perception?

    <p>Objects experience changes in visibility over time.</p> Signup and view all the answers

    Which cue provides information about depth through the use of textures?

    <p>Texture gradient.</p> Signup and view all the answers

    How does binocular disparity assist in depth perception?

    <p>It helps in determining distances for near to moderately distant objects.</p> Signup and view all the answers

    Which of the following is an example of a static depth cue?

    <p>Lighting variations.</p> Signup and view all the answers

    Match the following Bayesian approach formula components with what they represent:

    <p>P(Sc | I) = the probability of the Scene given the observed input P(Sc) = the probability of the scene occurring at all, based on our knowledge of the world P(I | Sc) = the probability of the Image being produced by a particular Scene P(Sc | I ) = P(Sc) x P (I | Sc) = the Bayesian formula</p> Signup and view all the answers

    Study Notes

    Depth Perception Categories

    • Three categories of visual cues provide depth information: oculomotor cues, monocular cues, and binocular cues.
    • Oculomotor cues: require eye movement and focus.
    • Monocular cues: require only one eye to perceive depth.
    • Binocular cues: require both eyes, and rely on the disparity between the images seen by each eye.
    • Depth cues can provide absolute or relative information about depth.
    • Metrical cues: provide quantitative information about distance.
    • Non-metrical cues: provide information about depth order (relative depth).

    Oculomotor Cues

    • Accommodation: the degree of contraction of the ciliary muscles to focus on a visual object.
      • More contraction: thicker lens, closer object.
      • Less contraction: thinner lens, farther object.
    • Vergence: the position of our eyes to look at a part of the scene.
      • Convergence: eyes turn inward, for near objects.
      • Divergence: eyes turn outward, for far objects.

    Monocular Depth Cues

    • Monocular depth cues: cues that can be perceived with just one eye.
    • Position-based cues:
      • Partial occlusion: if one object occludes another, the occluding object must be in front.
      • Relative height: objects higher in the visual field appear closer than objects lower in the visual field.
      • Relative height is a relative-metrical cue, can be used to infer relative depth, but not absolute depth.
    • Size-based cues:
      • Relative size: a comparison of the size of objects without knowing the true size. Smaller objects appear farther away.
      • Texture gradient: repeating patterns of relative size cues, provides depth information.
      • Familiar size: when object size is known, it can be used to judge depth based on its retinal size.
      • Linear perspective: parallel lines that appear to converge in the distance.
    • Lighting-based cues:
      • Atmospheric perspective: distant objects appear less distinct and bluer due to light scatter.
      • Shading: differences in shading on a surface provide clues about depth, assuming light is from above.
    • Dynamic cues:
      • Motion parallax: as we move, objects at different distances move at different rates across the visual field.
      • Optic flow: as we move towards objects, they expand from a central point in the direction of motion.
      • Deletion and accretion: changes in occlusion over time, as objects become occluded or are revealed from behind another.

    Binocular Depth Cues

    • Binocular disparity: the difference between the images seen by each eye.
    • Steropsis: sense of depth that arises from binocular disparity.
      • Convergence: the eyes turn inward to fixate on a point, and the images from each eye project to corresponding points on the retinas.
    • Horopter: an imaginary curve or surface in space where objects appear at the same distance from both eyes, meaning that light from those objects falls on corresponding points in both retinas.
      • Zero disparity: occurs when an object is located on the horopter. The brain interprets it as being at the same depth as the fixation point.
      • Crossed disparity: objects closer to the observer than the horopter project to non-corresponding points on the retinas, but they're closer to the nose (crossed), making the object appear closer than the fixation point.
      • Uncrossed disparity: objects farther away than the horopter project to non-corresponding points, but they're away from the nose (uncrossed), making the object appear farther than the fixation point.
    • Cyclopean stimuli: stimuli that are entirely defined by binocular disparity.
      • Random dot stereograms: cyclopean stimuli created from random dot patterns, with part of the pattern shifted for the left and right images, creating depth perception.
      • Free fusion: decoupling vergence and focus, which allows perception of a 3D image from two separate images.
      • Correspondence problem: matching visual information from the two eyes to create a unified perception of depth and 3D structure.
        • The brain must figure out which points in the left eye's image correspond to the same points in the right eye's image.
    • Neurophysiological basis for binocular disparity:
      • Binocular cells: neurons that receive input from both eyes.
      • Binocular cells are tuned to zero disparity (the horopter), and others respond best when similar images occupy slightly different positions on the retina.
      • These cells are found in V1 and at later stages of both the dorsal and ventral pathways.

    Combining Depth Cues

    • We combine depth cues to interpret a visual scene and consider the most likely interpretation given the constraints of the world.
    • The Bayesian approach: uses prior knowledge and experience to estimate the probability of a scene given visual input.

    Ames Room

    • Depth cues can affect our perception of an object's size.
    • The Ames room is an illusion that demonstrates this principle.
    • It is a distorted room that uses depth cues to create false perceptions of size.
    • People appear to change size as they move around the room.
    • Because of size perception, we assume that objects that are farther away are smaller.

    Depth Perception

    • Depth perception is the ability to perceive the distance of objects in space
    • Our visual system creates depth perception through a combination of visual cues.
    • Three categories of visual cues provide us with depth information:
      • Oculomotor cues: based on the movement and focusing of our eyes
      • Monocular cues: based on the image of a single eye, such as perspective
      • Binocular cues: based on the differences in the images of both eyes

    Oculomotor Cues

    • Depend on the movement and focusing of our eyes
    • Accommodation: the extent of the focusing of our eyes, based on contraction of the ciliary muscles
      • More contraction means a thicker lens, used for focusing on near objects
      • Less contraction means a thinner lens, used for focusing on far objects
    • Vergence: the angle of our eyes
      • Convergence: Eyes turned inward, used for looking close objects
      • Divergence: Eyes turned outward, used for looking at distant objects

    Monocular Depth Cues

    • Depth cues that can be perceived with one eye.

    Position Based Cues

    • Partial Occlusion: If one object obstructs part of another, the object in front is closer.
    • Relative Height: Objects higher in the visual field appear further away; this is relative to the viewer's eye level.

    Size Based Cues

    • Relative Size: Comparing the apparent size of objects helps infer the relative depth. Smaller apparent size usually means a further object.
    • Texture Gradient: When a repeating pattern or texture appears smaller as it gets further away.
    • Familiar Size: If we know the actual size of an object, we can judge its distance based on its apparent size.
    • Linear Perspective: Parallel lines appear to converge as they go further away.

    Lighting Based Cues

    • Atmospheric Perspective: As objects are further away, light scatters more in the air. This makes objects appear less distinct, bluer, and less detailed.
    • Shading: The way light falls on an object creates shading patterns, which provide information about its shape and depth.

    Dynamic Cues

    • Motion Parallax: As an observer moves, objects at different distances move at different speeds across their visual field. Closer objects appear to move faster, and further objects appear to move slower.
    • Optic Flow: As an observer moves forward, objects appear to expand from a point in the direction of motion.
    • Deletion and Accretion: Changes in occlusion over time can reveal depth clues. An object appearing behind another is deleted, and appearing from behind is accreted.

    Binocular Depth Cues

    • Rely on the difference between the images projected onto each retina
    • Binocular Disparity: The difference between the images from our two eyes creates a strong depth cue.
      • Stereopsis: The sense of depth created by binocular disparity.
      • Horopter: An imaginary curved surface where objects appear at the same distance from both eyes. Light from the objects on the horopter fall on corresponding points in the retinas of both eyes
      • Zero Disparity: Objects on the horopter project to corresponding points on both retinas, resulting in zero disparity.
      • Crossed Disparity: Objects between the observer and the horopter project to non-corresponding points on the retinas, displaced closer to the nose.
      • Uncrossed Disparity: Objects further than the horopter project non-corresponding points on the retinas, displaced away from the nose.
    • Cyclopean Stimuli: Stimuli which depend solely on binocular disparity, such as random dot stereograms.

    Combining Depth Cues

    • We use these cues in combination with our knowledge of the world to interpret visual scenes.
    • This can be explained through a Bayesian approach: We combine information from the visual scene with our knowledge of the world to generate the most likely interpretation.
    • Example : If a coin partially occludes another, we are likely to assume it is two coins, one behind the other.

    Ames Room

    • The Ames room illusion is a classic example of how depth cues can influence our perception of size.
    • An Ames room design creates an illusion that one person is much larger than another, despite their actual sizes being similar.
    • The room is built with distorted dimensions, and it relies on specific viewpoints and depth cues to create the illusion.

    Oculomotor Cues

    • Oculomotor cues are based on how we control our eyes when looking at an object.
    • Accommodation refers to the contraction of ciliary muscles to focus on an object:
      • More contraction leads to a thicker lens, used for near objects.
      • Less contraction leads to a thinner lens, used for far objects.
    • Vergence refers to the positioning of our eyes to look at a specific part of a scene:
      • Convergence involves turning eyes inwards for near objects.
      • Divergence involves turning eyes outwards for far objects.

    Position-Based Cues

    • Partial occlusion: When one object partially hides another, the occluding object is perceived as being in front.
    • Relative height: Objects further away from eye level appear closer, while objects at eye level appear further away.
      • Provides relative depth information, but not absolute depth.

    Size-Based Cues

    • Relative size: Comparing the sizes of objects without knowing their actual sizes. Smaller objects are perceived as further away.
      • A relative-metrical cue.
    • Texture gradient: Repeating patterns of relative size cues provide depth information.
    • Familiar size: Knowing the actual size of an object allows us to infer distance based on its size on the retina.
      • An absolute metrical cue.
    • Linear perspective: Parallel lines that converge in the distance provide a sense of depth.
      • A relative cue.

    Lighting-Based Cues

    • Atmospheric perspective: Distant objects appear less distinct and bluer due to light scattering in the air.
      • A relative cue.
    • Shading: Differences in shading on smooth surfaces provide depth cues.
      • We assume light is from above in the absence of explicit information.

    Dynamic Cues

    • Motion parallax: Objects parallel to our direction of movement appear to move at different rates depending on their distance when we move; further objects move slower.
    • Optic flow: Objects expand from a central point as we move forwards, providing a dynamic depth cue.
    • Deletion and accretion: Changes in occlusion over time provide depth information; objects becoming occluded are deleted, and objects emerging from behind another object are accreted.

    Binocular Disparity

    • Binocular disparity: The difference in viewpoints from each eye provides strong depth information for nearby objects.
    • Stereopsis: Our sense of depth arising from binocular disparity.
    • Horopter: An imaginary curve where objects appear at the same distance from both eyes.
      • Zero disparity: Occurs when an object is on the horopter, projecting to corresponding points on both retinas.
      • Objects not on the horopter will have crossed or uncrossed disparity, indicating their distance from the horopter.

    Neural Processing of Binocular Disparity

    • Binocular disparity requires input from both eyes, and neural processing begins in V1.
    • Binocular cells respond to specific disparities.
      • Some cells are tuned to zero disparity (the horopter), while others respond to slightly different image positions on the retina.
    • Binocular cells are found in V1 and later stages of both the dorsal and ventral pathways.

    Oculomotor Cues

    • Oculomotor cues are provided by how we control our eyes when we look at an object
    • Accommodation is the degree of contraction of the ciliary muscles to focus on an object
      • More contraction leads to a thicker lens for closer objects.
      • Less contraction leads to a thinner lens for farther objects.
    • Vergence is how we position our eyes to look at part of a scene.
      • Convergence is turning our eyes inward to look at near objects.
      • Divergence is turning our eyes outward to look at far objects.

    Position-Based Cues

    • Partial occlusion: If one object occludes another, the occluding object is in front.

      • Provides relative depth information (non-metrical).

    • Relative height: The vertical position of an object within the field of view relative to eye level.

      • Objects further away from eye level appear closer, while objects at eye level appear further away.
      • Relative-Metrical: Can be used to infer relative depth, but does not provide absolute depth information.

    Size-Based Cues

    • Relative size: Comparing the size of objects without knowing their true size.

      • For alike objects, smaller means farther away.
      • Relative-Metrical cue.

    • Texture gradient: Repeating patterns of relative size cues.

    • Familiar size: If we know the size of the object, we know its size on the retina at different depths.

      • Absolute metrical cue.

    • Linear perspective: Parallel lines that get farther away appear to converge.

      • Relative cue.

    Lighting-Based Cues

    • Atmospheric perspective: The farther an object is, the more light is scattered by the air.

      • Distant objects appear less distinct and bluer than near objects.
      • Relative cue.

    • Shading: Light falling on a smooth surface leads to shading differences, providing depth information.

      • In the absence of explicit information about the light source, we assume it is from above.

    Dynamic Cues

    • Motion parallax: A dynamic depth cue caused by motion of the observer.

      • As we move, objects parallel to our direction of movement move at different rates across our visual field depending on their distance.
      • Further objects move slower than closer objects.
      • This relative motion allows us to infer the distances of the objects.

    • Optic flow: A dynamic depth cue caused by motion of the observer.

      • As we move forward, objects expand from a central point in the direction of motion.

    • Deletion and accretion: Changes in occlusion over time.

      • An object moving behind another becomes occluded, and then accreded as it comes back out.

    Binocular Disparity

    • Binocular disparity: The difference between the 2 viewpoints from each eye provides a strong cue about the depth of an object, for near to moderately distant objects.

    • Stereopsis: Our sense of depth that arises from binocular disparity.

    • Horopter: Imaginary curve or surface in space where objects appear at the same distance from both eyes.

      • Light from these objects falls on corresponding points in both retinas.
      • Zero disparity occurs when an object is located on the horopter. Since it projects to corresponding points on both retinas, the brain interprets it as being at the same depth as the fixation point.
      • Other points will have a certain disparity (crossed/uncrossed) depending on their distance from the horopter.

    • For a neuron to code for binocular disparity, it must receive input from both eyes.

    • Binocular cells tuned to zero disparity (the horopter) while others respond best when similar images occupy slightly different positions on the retina.

      • Found in V1 and at later stages of both the dorsal and ventral pathways.
      • Requires the object to be at a particular depth for cells to fire.

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    The Third Dimension PDF

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    Explore the different categories of depth perception, including oculomotor, monocular, and binocular cues. Understand how each type of cue provides information about distance and depth order. This quiz will help you grasp the nuances of visual perception.

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