Depth Perception Flashcards
Name the Binocular Depth Cues
- Retinal disparity
- Convergence
Name the Monocular Depth Cues
- Motion Parallax
- Accommodation
- Pictorial
- Angular Declination below the Horizon
- Kinetic Depth
Name the Pictorial Depth Cues
- Relative Size
- Familiar Size
- Linear Perspective
- Texture
- Interposition
- Clairy
- Lighting & Shadow
Describe the Relative Size as a depth cue with an example
- Objects that produce the smaller retinal image size is perceived as farther away
- Relative size is an important depth cue when viewing a scene that includes objects whose sizes can be compared to each other
- Not useful for determining the plane’s distance
- There are no objects to which it can be compared (against the blue sky)
Because we have no reference, we assume that the 2 balloons are of the same size
Describe the Familiar Size (Size Constancy) as a depth cue with an example
- Used when viewing objects of known size
- In judging its distance, we would probably assume it is the size of a typical plane (size constancy)
- If it produces a small retinal image, the plane would be seen as far away
Describe the Linear Perspective as a depth cue with an example
- Related to relative size
- Can be experienced by looking down a long corridor or railroad track
- The retinal image size of the rail separation in the background, however, is smaller than the foreground, creating an illusion of depth
- Although all aspects of photograph are physically the same distance from the eyes
Describe the Texture Gradient as a depth cue with an example
- Densely packed objects that produce smaller retinal image sizes are perceived as more distant
- i.e., distance objects are seen as smaller and densely packed
- Bricks in the background appears more densely packed than those in the foreground
Describe the Ariel Perspective (Clarity) as a depth cue with an example
- A form of interposition/clarity
- Unobstructed objects in photographs are perceived as closer than those that are obscured by Haze
- Example:
- Fog, rain, smoke, and smog may act as interposing elements-causing them to appear more distant and contributes to the sense of depth
Describe the Interposition as a depth cue with an example
- Occurs when the view of scene is partially obstructed
- A nearer object occludes the distant object creating a sense of depth
- Church is interposed between the viewer and the mountains (perceived as lying distant to it)
Describe the Lighting and Shadow as a depth cue with an example
- When light falls on an object -> casts a shadow
- Shadow is interpreted as falling behind the object, consequently, a sense of depth is created
Name the nonpictorial depth cues
- Kinetic Depth Effect
- Angular Declination below the horizon
- Motion parallax
- Accommodation
Describe the Kinetic depth effect
- Shape from motion
- Kinetic depth effect is stimulated by matlab graphics
- Two random “wires” of 7 angles are in the movie
- Rotating wire (2D)-(differential motion) gives rise to 3D percept
- Looming: rapid expansion (or shrinking) in the size of any given image
Describe the Angular declination below the horizon with an example
- Monocular observer standing upright in an empty room viewing an object at 10 feet
- Despite the absence of pictorial depth cues, the observer can correctly judge the object’s distance
- The object makes and angle with the horizon referred to as angular declination below the horizon
- The visual system uses this angle to determine object distance
Describe Emmert’s Law
- The principle that the perceived size of an afterimage is proportional to the distance of the surface on which it is projected
- The larger the afterimage, the farther away it is
- Afterimage illusions
Describe Motion Parallax with an example
- A kinetic monocular depth cue that results when a moving observer fixates on an object while noticing the relative motion of surrounding objects
- Relative motion provides information regarding relative distance
- Demonstration:
- Place 2 index fingers directly in line with each other in front of the right eye
- One at 15 cm, another at 30 cm
- Close your left eye
- Fixate on distant finger while moving your head sideways
- Near finger appears to move opposite to the direction of your head (against motion)
- Fixate on near finger while moving your head sideways
- Distance finger appears to move in the same direction of your head (with motion)
- Place 2 index fingers directly in line with each other in front of the right eye
Describe how motion parallax is useful depth cue in clinical examination
- Has useful clinical application when viewing ocular structures with a monocular instrument
- Consider a small dot like opacity that is observed during monocular ophthalmoscopy
- If the clinician fixates on the iris and moves her head sideways:
- The opacity will show against motion when located ANTERIOR TO THE IRIS
- With motion when the opacity is located POSTERIOR TO THE IRIS
- If the clinician fixates on the iris and moves her head sideways:
Describe how accommodation is a monocular depth cue
- During accommodation = power of the lens increases
- Although the signal for accommodation contains information that could be used to determine the distance of viewed objects, the extent to which this information is utilized is not known
- Hypothesis: level of innervation of accommodation could provide distance information
- Studies have shown accommodation is not utilized much to judge distances
- Accommodation seems to be a weak cue to depth perception
What are the binocular depth cues?
- Stereopsis
- Convergence
How does stereopsis provide depth information to the visual system?
- The perception of depth that is produced by retinal disparity is referred to as stereopsis
- It’s an important contributor to depth perception at near distances
- Less important when viewing far objects because the threshold for retinal disparity requires such objects to be separated by great distances
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Retinal disparity
- Produces stereopsis only if it is sufficiently small to allow fusion
- A binocular cue to the visual system
- If the disparity is large, the images fall on retinal positions that signal grossly different directions resulting in double vision or physiological diplopia
- Uncrossed disparity – images form nasal to the foveas (signaling that the ball is farther than fixation)
- Crossed disparity – images form temporal to the foveas (signaling that the ball is closer)
- You can experience physiological diplopia by holding (& fixating) at one index finger at 15cm from your nose and your other index finger directly behind it at arm’s length
- Certain binocular cortical neurons are maximally responsive when a stimulus is located at a specific distance from the eyes
- The same stimulus, when positioned at other distances, elicits a less vigorous neural response
- By encoding disparity, these neurons may contribute to the physiological basis for stereopsis
How does convergence contribute to depth perception?
- The eyes converge when we view near objects and diverge when we view distant objects
- The degree of convergence can potentially provide information regarding distance
- The way this information is incorporated into the conscious perception of depth, however, is unresolved
Describe Perceptual Constancy
- The tendency to see familiar objects as having standard shape, size, color, or location regardless of changes in the angle of perspective, distance, or lighting
- As it is assumed to be, rather than to the actual stimulus presented to the eye
- I.e., stability in perception despite gross instability in stimulation
Size Constancy
When people’s perception of a particular object’s size does not change regardless of changes in distance from the object, even though distance affects the size of the object as it is projected onto the retina
Shape Constancy
When people’s perception of the shape of an object does not change regardless of changes to the object’s orientation
Distance Constancy
Refers to the relationship between apparent distance and physical distance: it can cause us to perceive things as closer or farther away than they actually are