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Questions and Answers
What occurs to the perception of objects closer than the horopter?
How does the brain address the correspondence problem?
What defines cyclopean stimuli in the context of depth perception?
Which cue helps in determining the order of objects in relation to each other without providing quantitative depth information?
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When an object has uncrossed disparity, what is its relative position to the horopter?
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What effect does atmospheric perspective have on the appearance of distant objects?
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How does texture gradient serve as a depth cue?
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What role does V1 play in processing binocular disparity?
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In the Bayesian approach to understanding depth perception, what does P(Sc | I) represent?
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What is binocular disparity?
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How do texture gradients contribute to depth perception?
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Which of the following is a dynamic depth cue influenced by the movement of the observer?
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Which type of depth cue can inform us about actual distances in space?
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What effect does motion parallax have on depth perception?
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What occurs when an object becomes occluded in the process of deletion and accretion?
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What happens to the perceived size of objects in the Ames room?
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What happens to images falling on the horopter?
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What is the result of changing the point of fixation with respect to binocular disparity?
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What effect does the relative size cue provide regarding the distance of similar objects?
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Which of the following factors contributes to a strong sense of depth perception?
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Which of the following cues require both eyes for depth perception?
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Accommodation refers to how much we adjust our ciliary muscles to focus on a visual object.
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What term describes the depth cue arising from the difference in viewpoints between our two eyes?
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As an object moves further away, it appears less distinct and ________ due to atmospheric perspective.
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Match each type of depth cue with its corresponding example:
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Which of the following describes the phenomenon where objects appear to expand from a central point as one moves forward?
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Relative height gives absolute depth information about objects in space.
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What is the meaning of 'vergence' in the context of oculomotor cues?
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The ________ is an imaginary surface where objects appear to be at the same distance from both eyes.
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Which cue provides quantitative information about distances in depth?
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What does crossed disparity indicate?
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Uncrossed disparity occurs when an object is closer to the observer than the horopter.
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What is the primary challenge the brain faces in the correspondence problem?
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In the Bayesian approach, P(I | Sc) refers to the probability of the __________ being produced by a particular scene.
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Match the type of disparity with its description:
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What effect does changing the point of fixation have on binocular disparity?
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Binocular disparity is defined as the differences in images received by each eye due solely to their positions.
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Name a type of cue that helps to determine the three-dimensional structure of an object.
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The __________ states that our knowledge of the world helps interpret the visually observed input.
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What do random dot stereograms primarily illustrate?
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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.
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Description
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.
